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Produced by both nature and human activities, sulfur dioxide (SO2) is an important species in the earth's atmosphere. SO2 has also been found in the atmospheres of other planets and satellites in the solar system. The photoabsorption cross sections and photodissociation of SO2 have been studied for several decades. In this paper, we reported the experimental results for photodissociation dynamics of SO2 via the G ̃ 1B1 state. By analyzing the images from the time-sliced velocity map ion imaging method, the vibrational state population distributions and anisotropy parameters were obtained for the O(1D2) + SO(X3Σ−, a1Δ, b1Σ+) and O(1S0) + SO(X3Σ−) channels, and the branching ratios for the channels O(1D2) + SO(X3Σ−), O(1D2) + SO(a1Δ), and O(1D2) + SO(b1Σ+) were determined to be ∼0.3, ∼0.6, and ∼0.1, respectively. The SO products were dominant in electronically and rovibrationally excited states, which may have yet unrecognized roles in the upper planetary atmosphere. [ABSTRACT FROM AUTHOR]

We present a method by which the direct detection effect in superconducting hot-electron bolometer mixers can be analytically accounted for with sufficient practical accuracy. This is achieved by means of the advanced uniform, non-linear two-temperature model that considers the effective temperatures of electrons and phonons alongside established material parameters. We demonstrate the efficacy of this approach for the ex situ correction of the radiance of the emission line of atomic oxygen under conditions when the direct detection causes a 30% error in the line magnitude. The correction was applied to data collected by a balloon-borne heterodyne receiver operating in the upper atmosphere of Earth. The corrected line shape and magnitude are in reasonable agreement with the predictions of atmospheric radiation transfer models. [ABSTRACT FROM AUTHOR]

The density of the upper atmosphere can be determined by orbit and accelerometer data from low Earth orbit satellites as insitu measurements along the orbit. One main challenge therein is the estimation of physical accelerometer calibration parameters, meaning that these parameters should not absorb other effects and model deficiencies in the Precise Orbit Determination (POD) process. The accelerometers of all geodetic satellites like GRACE and GRACE-FO are affected by time dependent bias and scale factors. Therefore a calibration of the data is indispensable. A dynamic POD based physical accelerometer calibration is developed for the complete GRACE and GRACE-FO missions. We investigate different parametrization strategies and utilize different observation data, as the accurate inter-satellite ranging additionally to GPS orbit data. For the estimation parameters we distinguish between offset and scale, furthermore, cross-track and radial directions are significantly less sensitive than along-track and require a different evaluation. For the offset, constant and time dependent parameters are investigated. Furthermore, a continuous offset calibration over arc boundaries is implemented and tested. The sensitivity of the scale factor is lower, although, in contrast to the offset, it increases with higher total accelerations. This means that it needs to be estimated over longer time periods. We investigate periods between three hours and one month as well as results from Gravity Field Recovery (GFR). Monthly scale factors give valuable results, at least for x-axis and when the Solar activity is not very low. Nevertheless, we also estimate weighted constant scale factors from the monthly results and use these in a subsequent POD, giving more realistic offset results for most periods and cross-track and radial directions. From the used background models in the POD, Earth's gravitational model has a noticeable influence on the estimated calibration parameters, especially the scale factors. We utilized several different models. Results with monthly ITSG solutions are distinctly better than the ones with the time dependent GOCO06s model. We show that the validation with usual metrics, like post-fit POD residuals, is not able to reflect the quality of the different estimated calibration parameters. For a quantitative validation we introduce an approach based on the modeled non-gravitational accelerations. Therefore, the uncertainty of the models is evaluated first. The influence of main error sources in the models is assessed and propagated to the results. We compare our scale parameters to available references and the complete calibration to TU Delft's latest results. Finally we show the effect of different calibration options on the retrieved density. The estimated calibration parameters and non-gravitational accelerations for the whole GRACE and GRACE-FO missions are available on our data server www.zarm.uni-bremen.de/zarm_daten. [ABSTRACT FROM AUTHOR]

Nitric Oxide (NO) significantly impacts energy distribution and chemical processes in the mesosphere and lower thermosphere (MLT). During geomagnetic storms, a substantial influx of energy in the thermosphere leads to an increase in NO infrared emissions. Accurately predicting the radiative flux of Nitric Oxide is crucial for understanding the thermospheric energy budget, particularly during extreme space weather events. With advancements in computational techniques, machine learning (ML) has become a highly effective tool for space weather forecasting. This effort becomes even more worthwhile considering the availability of two decades of continuous NO infrared emissions measurement by TIMED/SABER along with several other key thermospheric variables. We present the scheme of development of an ML-based predictive model for Nitric Oxide Infrared Radiative Flux (NOIRF). Various ML algorithms have been tested for better predictive ability, and an optimized model (NOEMLM) has been developed for the study of NOIRF. This model is able to extract the underlying relationships between the input features and effectively predict the NOIRF. The NOEMLM predictions have very good agreements with SABER observation during quiet time as well as geomagnetic storms. In comparison with the existing TIEGCM model, NOEMLM has very good performance, especially during extreme space weather conditions. The results of this study suggest that utilizing geomagnetic and space weather indices with ML/AI can serve as superior parameters for studying the upper atmosphere, as compared to focusing on specific species having complex chemical processes and associated uncertainties in constituents. ML techniques can effectively carry out the analysis with greater ease than traditional chemical studies. [ABSTRACT FROM AUTHOR]

Alfvén waves are important carriers of solar wind energy into the Earth's magnetosphere and upper atmosphere. The observed distribution of Alfvénic power at low altitude exhibits significant dawn‐dusk asymmetry with different causes and impacts on the dayside and nighside. The nightside asymmetry has been shown to be controlled by the meridional gradient in the ionospheric Hall conductance. It is not clear what controls the dayside asymmetry. Both the ionospheric conductance gradient and orientation of the y‐component of the interplanetary magnetic field (IMF) are possible factors. We examined both possibilities using global magnetohydrodynamic (MHD) simulations. Our results show: (a) The dayside distribution of Alfvénic power is very sensitive to the orientation of IMF By, with enhanced power in the dawn (dusk) sector of the northern hemisphere for positive (negative) By (and opposite in the southern hemisphere); and (b) gradients in ionospheric conductance exert a weaker influence on the dayside asymmetry. Plain Language Summary: Alfvénic energy flux, which has an important impact on the low‐altitude space environment, is observed to be enhanced in the postnoon (prenoon) sector relative to prenoon (postnoon). In this study, we use global MHD simulations to determine the extent to which the dayside asymmetry in Alfvénic energy flux is controlled by the interplanetary magnetic field (IMF) and gradients in ionospheric conductance. Most of the dayside Alfvénic power is generated on open magnetic field lines, so we might expect the IMF By component to exert a significant influence on pre/postnoon flux distributions. The simulation experiments confirm this expectation and further show that the effects of gradients in ionospheric conductance are comparatively weaker. The results explain why some satellite observations on average exhibit a asymmetric enhancement in Alfvénic energy fluxes. Key Points: Dawn‐dusk asymmetry in dayside Alfvénic power is due to different magnetic field configurations associated with the direction of IMF ByIonospheric conductance contributes less to the asymmetric dayside Alfvénic Poynting flux distribution around noon [ABSTRACT FROM AUTHOR]

The continental United States is well instrumented with facilities for mid‐latitude upper atmosphere research that operate on a continuous basis. In addition, citizen scientists provide a wealth of information when unusual events occur. We combine ionospheric total electron content (TEC) data from distributed arrays of GNSS receivers, magnetometer chains, and auroral observations obtained by citizen scientists, to provide a detailed view of the intense auroral breakup and westward surge occurring at the peak of the 10–11 May 2024 extreme geomagnetic storm. Over a 20‐min interval, vertical TEC (vTEC) increased at unusually low latitude (∼45°) and rapidly expanded azimuthally across the continent. Individual receiver/satellite data sets indicate sharp bursts of greatly elevated of vTEC (∼50 TECu). Intense red aurora was co‐located with the leading edge of the equatorward and westward TEC enhancements, indicating that the large TEC enhancement was created by extremely intense low‐energy precipitation during the rapid substorm breakup. Plain Language Summary: For over 12 hr, the 10–11 May 2024 the extreme Gannon geomagnetic storm sent brilliant auroral displays into the night skies at mid and low latitudes around the world. Precipitating auroral electrons and protons ionize the upper atmosphere at 100–500 km altitude, increasing ionospheric total electron content (TEC). We use the perturbation of the signals received by the distributed array of navigation satellite receivers to map the intensification and spread of an extreme auroral event across the continental US. Photo and video observations of the auroral event contributed by citizen scientists indicate that the TEC enhancement closely matched the westward and equatorward expansion of strong red aurora. Coincident with the auroral breakup, sharp bursts of greatly elevated TEC were observed. Auroral breakup was accompanied by a bright red over green discrete auroral feature at the leading edge of the equatorward expansion of strong red aurora. Based on the direct auroral observations, we believe that the westward expansion of low‐energy electron precipitation is likely the driver of the large TEC enhancements observed during the event. Key Points: Total electron content (TEC) maps show the intensification and spread of the 11 May 2024 extreme auroral event across the continental US over a 20‐min intervalAll sky camera imagery indicates that the TEC enhancement closely matches the westward and equatorward expansion of strong red auroraCoincident with auroral breakup, individual receiver/satellite data sets show sharp bursts of greatly elevated TEC 50 TECu above background [ABSTRACT FROM AUTHOR]

Simulations with the Saturn Thermosphere‐Ionosphere General Circulation Model have revealed global‐scale gravity waves in Saturn's upper atmosphere that have not been observed or predicted before. They are forced by diurnally varying zonally non‐uniform distributions of Joule heating and ion drag at the high‐latitude auroral regions in both hemispheres and propagate outward from the source region. The supersonic zonal phase speed imposed by Saturn's rotation and the subsonic meridional phase velocity of about 800 m s−1 ${\mathrm{s}}^{-1}$ form a distinct spiral wave structure. They exhibit features of gravity waves: vertical phase progression opposite to the propagation of wave energy and long vertical wavelengths consistent with the dispersion relation for gravity waves. The amplitudes of the perturbations grow with height, reaching 6%–10% for relative temperature variations and up to 350 m s−1 ${\mathrm{s}}^{-1}$ for the meridional velocity perturbations. The main effect of these waves is to accelerate the retrograde westerly jets. Plain Language Summary: Gravity waves are common in all convectively stable atmospheres. They are caused by a variety of sources and have horizontal extents ranging from a few kilometers to scales comparable to the radius of the planet. In simulations of the Saturnian upper atmosphere, we found a new form of gravity wave that has not been observed or predicted before. The waves are excited at 900–1,000 km above the 1 bar pressure level near the auroral ovals in both hemispheres. They are caused by the changing heating and drag in the auroral regions as Saturn rotates throughout the day. Saturn's large size and fast rotation make the waves move around the planet faster than the speed of sound in Saturn's atmosphere. They spread out from their source, creating a spiral pattern that covers a large part of the planet. We studied these waves and how they affect the global circulation. Unlike gravity waves on Earth and similar planets, which mostly slow down the surrounding winds, these waves in Saturn's upper atmosphere mainly speed up the strong westward jets. Key Points: General circulation modeling reveals large‐scale gravity waves in the upper atmosphere of Saturn that have never been reported beforeWaves are forced by Joule heating and ion drag at high‐latitude auroral regions, propagate outward and form a global spiral structureThe net dynamical effect of these zonally supersonic and meridionally subsonic waves is to accelerate the westward retrograde jets [ABSTRACT FROM AUTHOR]

Neutral thermospheric density is a crucial parameter for orbital tracking and upper atmosphere research. Here, we present a method to monitor global neutral thermospheric density testing simulations in various space environments with various satellite configurations and altitudes. The simulation results at 1° × 1° pixel resolution show that (1) within the range of 300–600 km orbital altitudes, the monitoring accuracy improves with the increase of the number of satellites, but this gain is significantly attenuated when the number of satellites increases to approximately 1,000; (2) the monitoring accuracy decreases with the increase of the altitude; and (3) the method presented in this study exhibits robustness under different space weather conditions. Furthermore, a differentiated satellite usage strategy (High Tightness and Low Looseness, HTLL) is developed to reduce the number of satellites used. Preliminary results indicate that the use of the HTLL method can reduce the number of satellites used from 2,592 to 1,044, whereas the maximum average relative deviation (ARD) does not exceed 1 %. The methods presented in this study have potential for future applications in the development of thermosphere research and satellite tracking. [ABSTRACT FROM AUTHOR]

In Lammer et al. (2024), we defined Earth-like habitats (EHs) as rocky exoplanets within the habitable zone of complex life (HZCL) on which Earth-like N2-O2-dominated atmospheres with minor amounts of CO2 can exist, and derived a formulation for estimating the maximum number of EHs in the galaxy given realistic probabilistic requirements that have to be met for an EH to evolve. In this study, we apply this formulation to the galactic disk by considering only requirements that are already scientifically quantifiable. By implementing literature models for star formation rate, initial mass function, and the mass distribution of the Milky Way, we calculate the spatial distribution of disk stars as functions of stellar mass and birth age. For the stellar part of our formulation, we apply existing models for the galactic habitable zone and evaluate the thermal stability of nitrogen-dominated atmospheres with different CO2 mixing ratios inside the HZCL by implementing the newest stellar evolution and upper atmosphere models. For the planetary part, we include the frequency of rocky exoplanets, the availability of surface water and subaerial land, and the potential requirement of hosting a large moon by evaluating their importance and implementing these criteria from minima to maxima values as found in the scientific literature. We also discuss further factors that are not yet scientifically quantifiable but may be requirements for EHs to evolve. Based on such an approach, we find that EHs are relatively rare by obtaining plausible maximum numbers of 2.5 − 2.4 + 71.6 × 10 5 and 0.6 − 0.59 + 27.1 × 10 5 planets that can potentially host N2-O2-dominated atmospheres with maximum CO2 mixing ratios of 10% and 1%, respectively, implying that, on average, a minimum of ∼ 10 3 − 10 6 rocky exoplanets in the HZCL are needed for 1 EH to evolve. The actual number of EHs, however, may be substantially lower than our maximum ranges since several requirements with unknown occurrence rates are not included in our model (e.g., the origin of life, working carbon–silicate and nitrogen cycles); this also implies extraterrestrial intelligence (ETI) to be significantly rarer still. Our results illustrate that not every star can host EHs nor can each rocky exoplanet within the HZCL evolve such that it might be able to host complex animal-like life or even ETIs. The Copernican Principle of Mediocrity therefore cannot be applied to infer that such life will be common in the galaxy. [ABSTRACT FROM AUTHOR]

Long-term trends of the three-dimensional Plumb wave activity flux are studied using data from the JRA-55 global atmospheric reanalysis. The vertical component of the Plumb flux characterizes the propagation of atmospheric planetary waves generated in the troposphere to the upper atmosphere and is used for the analysis of the stratosphere–troposphere dynamic interaction. The study of the wave activity flux covers three latitudinal sectors of the Northern Hemisphere from December to March for a 64-year period since 1958. It is shown that in January and March over the Russian Far East there is a statistically significant trend for an increase in the wave activity flux from the troposphere to the stratosphere, which can contribute to an increase in the frequency of cold wave formation in the mid-latitude troposphere. The study of the stratosphere–troposphere dynamic interaction in general and wave activity fluxes in particular is necessary for solving problems related to both global and regional climatic changes and mixing of long-lived atmospheric components. [ABSTRACT FROM AUTHOR]

A dual-wavelength spaceborne Martian polarized wind imaging Michelson interferometer based on liquid crystal tunable filters (LCTF-MPWIMI) has been proposed for the remote sensing detection of dynamic parameters such as wind speed and temperature in the middle and upper atmosphere of Mars. Using the detected Martian oxygen atom emission lines at 557.7 nm and 630.0 nm as observation spectral lines, this technology extends the detection altitude range for Martian atmospheric wind speed and temperature to 60–180 km. By leveraging the different spectral line visibility of the interferograms at the two wavelengths, a novel method for measuring Martian atmospheric temperature is proposed: the dual-wavelength spectral line visibility product method. This new approach reduces the uncertainty of temperature detection compared to traditional single spectral line visibility methods, while maintaining the precision of wind speed measurements. The feasibility of the LCTF-MPWIMI for measuring wind and temperature fields in the Martian middle and upper atmosphere has been validated through theoretical modeling and computer simulations. The interferometer, as a key component of the system, has been designed and analyzed. The proposed LCTF-MPWIMI instrument is free of mechanical moving parts, offering flexible wavelength selection and facilitating miniaturization. The dual-wavelength temperature measurement method introduced in this work provides superior temperature measurement precision compared to any single spectral line when the signal-to-noise ratio (SNR) of the interferograms is comparable. Moreover, this method does not impose specific requirements on the atomic state of the spectral lines, making it broadly applicable to similar interferometric wind measurement instruments. These innovations offer advanced tools and methodologies for measuring wind speeds and temperatures in the atmospheres of Mars and other planets. [ABSTRACT FROM AUTHOR]

The technological advancements in the current era have highlighted the increasing significance of satellite-based positioning, navigation, and timing services in a wide range of dynamic and critical applications. This has led to significant efforts towards enhancing the performance of global navigation satellite systems (GNSS) operating under challenging ionospheric conditions. The Sri Lankan ionosphere region is a focal point of equatorial aeronomy scientists, being situated in the southernmost landmass of the Indian longitude sector within the vicinity of the magnetic equator where a combination of electric, wind, and temperature dynamics exerts a substantial influence on the ionosphere but was relatively unexplored in the past. In the present work, we employed a Kriging interpolation technique on the total electron content (TEC) variables from ten GNSS receivers operating under the Continuously Operating Reference Stations (CORS) network in Sri Lanka first ever of its kind to deliver two-dimensional regional ionospheric TEC maps at hourly intervals, both during quiet and disturbed ionospheric conditions in the equinoctial March and April months of 2022. The latitudinal variation patterns are discernable from the hourly TEC maps. Furthermore, a comparative analysis of the performance of GNSS-derived TEC with that of the routinely published Global Ionospheric Maps (GIMs) confirms overestimation characteristics of the latter irrespective of the local time of observation. The generated regional ionospheric maps are fairly responsive to the onset of the storm and the recovery phase thereafter. The extent of nighttime ionospheric irregularity is also probed through the rate of TEC index (ROTI) variations, demonstrating that the irregularities were insignificant during the selected storm event. [ABSTRACT FROM AUTHOR]

A solar eclipse is a fascinating event that gives a unique opportunity to study the ionospheric characteristics in a controlled blockage of solar radiation. We present the upper atmosphere's response, mostly F-layer, during the annular eclipse on October 14, 2023. This eclipse was mostly visible from the North and South American regions with a maximum obscuration of around 91%. We study the response of the ionospheric Total Electron Content (TEC) and the critical frequency of the F2 layer (f 0 F 2) for three consecutive days (October 13 to 15, 2023) using ground and space-based techniques. We present the ionospheric response for a large area that covers the path of the solar eclipse of latitude and longitude range from 50 ° N to 10 ° S and 30 ° W to 150 ° W. For the ground-based observation, we use fifty-five International GNSS Service (IGS) stations and eleven Global Ionospheric Radio Observatory (GIRO) Digisonde stations that cover the annular and partial solar eclipse and are in the close vicinity of the annularity belt. We compute the vertical TEC (VTEC) and f 0 F 2 from this database and check their temporal and spatial variations. It is found that the VTEC, as computed from the IGS stations, mostly shows decrements during the partial blockage of the sun by the lunar disc. The VTEC, as computed from the GIRO database, also shows a decreasing trend but with comparatively more oscillating in nature. The f 0 F 2 shows a similar decreasing trend due to the solar eclipse. For space-based observation, we use the Swarm satellite data for the tracks that have gone through the annularity belt. Also, a spatiotemporal study is executed using the Global Ionospheric Map (GIM) database. For both cases, the VTEC shows a prominent depletion. We investigate the variation in the percentage change in VTEC as a function of obscuration and observe a positive correlation between them. We also compute the time difference between the maximum eclipse and the maximum TEC modulation to investigate the response time profiles of the ionosphere at different receiving stations. All the methods give satisfactory and consistent outcomes that corroborate the physical mechanism of ionospheric variabilities due to the effect of the solar eclipse. We check the geomagnetic condition to eliminate the scope of contamination and observe that their values are normal during the study. [ABSTRACT FROM AUTHOR]

The upper atmosphere of polar regions exhibits two distinct patterns of energetic particle precipitation that can lead to ozone destruction by ionizing the atmosphere: one is the energetic proton precipitation in the polar cap region during solar proton events (SPEs), and the other is the energetic electron precipitations (EEPs) in the auroral oval region from the radiation belt. In this study, we conduct case studies and statistical analyses of ozone observations from the Aura satellite to present the quantitative difference in the impact patterns of SPEs and EEPs on polar mesospheric ozone. According to our statistical analysis of 13 SPEs and 19 EEPs during the MLS time frame, the magnitude of ozone depletion during SPEs is greater than during EEPs. The ozone depletion during SPEs is more pronounced at higher geomagnetic latitudes and negatively correlates with the proton flux, while during EEPs the ozone depletion is more in favor of the geomagnetic latitude band of 60–70° but independent of the electron count rates. In addition, hydroxyl enhancement also exhibits different patterns during SPEs and EEPs, similar to that of ozone depletion. This study further validates the physical link between the magnetosphere and atmosphere and promotes our understanding of the solar influence on Earth's climate. Plain Language Summary: The Earth's middle and upper atmosphere is continuously impacted by charged energetic particles from space. During periods of intense space weather, substantial amounts of protons and electrons are injected into different latitudes of the polar regions, leading to solar proton events (SPEs) and energetic electron precipitations (EEPs). These energetic particles can substantially affect atmospheric components, including hydroxyl and ozone. While previous research has demonstrated the influence of energetic particles on atmospheric components, the different impacts of SPEs and EEPs on ozone depletion and the latitudinal effects have not been thoroughly investigated in a quantitative approach. This study uses ozone measurements from the Aura satellite to conduct case studies and statistical analyses. Our findings indicate that the peak ozone depletion aligns with the precipitation latitudes of protons and electrons during both SPEs and EEPs. In addition, more energetic protons are associated with more severe ozone depletion. Our results suggest that during the selected events, SPEs exert a more significant influence on ozone than EEPs. This research validates the correlation between energetic particles and ozone and enhances our understanding of the solar influence on climate. Key Points: SPEs and EEPs exert distinct latitudinal effects on ozone depletionOzone depletion during SPEs negatively correlates with proton flux, while no significant correlation is found between ozone and ECRsHydroxyl enhancement during SPEs and EEPs presents similar differences in latitudinal distribution [ABSTRACT FROM AUTHOR]

Effects of Hurricane Grace in August 2021 are studied in the thermosphere and ionosphere, using data from the COSMIC‐2, ICON, and GOLD satellites. Significant impacts on electron density, thermospheric winds, and temperature are observed after the onset of the hurricane, compared to the pre‐hurricane phase. Comparison of the observations during the hurricane with the ones during a non‐hurricane year clearly provides further evidence for substantial hurricane‐induced thermospheric and ionospheric changes. We reveal an enhancement in electron density during the hurricane's rapid intensification and pronounced changes in thermospheric winds. Additionally, the low‐latitude thermosphere exhibits considerable warming of up to 70 K around 150 km during this period. These changes highlight the long‐range vertical coupling mechanisms between hurricanes and the upper atmosphere, and provide valuable insights into the profound influence of meteorological events on upper atmospheric dynamics, emphasizing the need for further exploration. Plain Language Summary: Our research investigates how hurricanes, specifically Hurricane Grace in 2021, affect Earth's upper atmosphere. The hurricane was able to influence layers of the atmosphere that are critical for satellite communication and GPS. We used data from different satellites to study changes in the number of free electrons per unit volume of air (electron density), neutral winds, and temperature. We found that during the intensification of the hurricane, electron density increased in the ionosphere, which is the layer of Earth's atmosphere containing a high concentration of ions and free electrons. We also observed substantial changes in the winds high up in the atmosphere and found that a region of the upper atmosphere around 150 km warmed significantly. This research helps us understand how weather events on the Earth's surface can impact conditions hundreds of kilometers above the surface in Earth's atmosphere. Key Points: 2021 Hurricane Grace's impact on electron density, thermospheric winds, and temperature are analyzed using COSMIC‐2, ICON, and GOLDIonospheric electron density showed notable variations, predominantly increasing with the hurricane's intensificationSignificant thermospheric warming and circulation changes are observed [ABSTRACT FROM AUTHOR]

The response of the thermosphere ionosphere system to an X1.3 class solar flare is studied using observations of the total electron content (TEC) and the Global Ionosphere Thermosphere Model (GITM) simulations. The solar flare erupted from the active region AR12975 on 30 March 2022. Owing to the absence of accompanying severe geomagnetic activity, it was possible to isolate the effects of the flare on the upper atmosphere. TEC data are processed for Continental USA (CONUS), employing filtering and binning techniques to create 2D variation maps. The spectral content of the TEC variations is analyzed using a wavelet coherence method. The immediate response of the solar flare exhibited broad similarities, while notable differences were observed during the recovery period between the East and West sides of the CONUS. GITM is used to explore the East–West asymmetry of the key T‐I parameters. Simulation results reveal that the coinciding interplanetary magnetic field southward turning had a greater influence on these parameters compared to the solar flare, while their nonlinear interaction introduced complex variations. Additional investigation reveals gravity wave damping also contributes to the asymmetric solar flare response. Plain Language Summary: This study examines how a solar flare, which erupted on 30 March 2022, affected the Earth's upper atmosphere. We used satellite data to measure changes in the amount of charged particles in the atmosphere above the United States (specifically the area known as CONUS) and ran computer simulations to better understand these changes. We found that while the immediate reaction of the atmosphere to the flare was similar across the CONUS, differences emerged between the East and West during the recovery phase. The simulations showed that these differences were influenced by local time differences between the East and West, as well as by variations in the Earth's magnetic field geometry above these regions. Additionally, the study identified that the damping of gravity waves also played a role in these regional differences. Overall, the research highlights how complex interactions between various factors can lead to different responses to solar events in different parts of the CONUS. Key Points: Spectral content and temporal variation of total electron content perturbations associated with an X1.3 Solar Flare are analyzedThe thermosphere‐ionosphere exhibits a longitudinal flare response during the recovery phaseThe nonlinear interaction of the solar flare with the southward turning of the interplanetary magnetic field Bz ${\mathrm{B}}_{z}$ introduces significant variability [ABSTRACT FROM AUTHOR]

Using a nonlinear model of the general circulation of the middle and upper atmosphere (MUAM), spatio-temporal structures of planetary waves (PWs) during boreal winter were studied. Modeling of global atmospheric circulation was performed for January–February. Despite the tropospheric PW sources shaped in the model, the phenomenon of 16-day PW excitation arise out of internal atmospheric sources in the southern lower thermosphere was discovered. To explain the observed phenomenon, a number of numerical experiments were carried out according to different scenarios with a selective turning (on/off) tropospheric sources of PW individual modes (having periods of 4–16 days) in the model. Also, the evolution of perturbed potential enstrophy for a 16-day PW, as well as the contribution of nonlinear interactions between individual PW to it, was studied. This made it possible for the first time to demonstrate explicitly the process of generation a secondary 16-day PW as a result of the nonlinear interconnection of 4-day and 5-day PWs. [ABSTRACT FROM AUTHOR]

Context. Solar jets are an important field of study, as they may contribute to the mass and energy transfer from the lower to the upper atmosphere. Aims. We use the Interface Region Imaging Spectrograph (IRIS) and Solar Dynamic Observatory (SDO) observations to study two small-scale jets (jet 1 and jet 2) originating in the same on-disk coronal hole observed in October 2013. Methods. We combine dopplergrams, intensity maps, and line width maps derived from IRIS Si IV 1393.755 Å spectra along with images from the Atmospheric Imaging Assembly (AIA) on SDO to describe the dynamics of the jets. Images from AIA, with the use of the emission measure loci technique and rectangular differential emission measure (DEM) distributions, provide estimations of the plasma temperatures. We used the O IV 1399.77 Å, 1401.16 Å spectral lines from IRIS to derive electron densities. Results. For jet 1, the SDO images show a small mini-filament 2 minutes before the jet eruption, while jet 2 originates at a pre-existing coronal bright point. The analysis of asymmetric spectral profiles of the Si IV 1393.755 Å and 1402.770 Å lines reveals the existence of two spectral components at both regions. One of the components can be related to the background plasma emission originating outside the jet, while the secondary component represents higher-energy plasma flows associated with the jets. Both jets exhibit high densities of the order of 1011 cm−3 at their base and 1010 cm−3 at the spire, respectively, as well as similar average nonthermal velocities of ∼50–60 km/s. However, the two jets show differences in their length, duration, and plane-of-sky velocity. Finally, the DEM analysis reveals that both jets exhibit multithermal distributions. Conclusions. This work presents a comprehensive description of the thermal parameters and the dynamic evolution of two jets. The locations of the asymmetric profiles possibly indicate the areas of energy release triggering the jets. [ABSTRACT FROM AUTHOR]

The global energy budget is pivotal to understanding planetary evolution and climate behaviors. Assessing the energy budget of giant planets, particularly those with large seasonal cycles, however, remains a challenge without long-term observations. Evolution models of Saturn cannot explain its estimated Bond albedo and internal heat flux, mainly because previous estimates were based on limited observations. Here, we analyze the long-term observations recorded by the Cassini spacecraft and find notably higher Bond albedo (0.41 ± 0.02) and internal heat flux (2.84 ± 0.20 Wm−2) values than previous estimates. Furthermore, Saturn's global energy budget is not in a steady state and exhibits significant dynamical imbalances. The global radiant energy deficit at the top of the atmosphere, indicative of the planetary cooling of Saturn, reveals remarkable seasonal fluctuations with a magnitude of 16.0 ± 4.2%. Further analysis of the energy budget of the upper atmosphere including the internal heat suggests seasonal energy imbalances at both global and hemispheric scales, contributing to the development of giant convective storms on Saturn. Similar seasonal variabilities of planetary cooling and energy imbalance exist in other giant planets within and beyond the Solar System, a prospect currently overlooked in existing evolutional and atmospheric models. Global energy budgets of planets are important to understand their climate system. Here, the authors show long-term multi-instrument observations from Cassini spacecraft, which reveals dynamical imbalances of Saturn's global energy budget. [ABSTRACT FROM AUTHOR]

For satellites in Very Low Earth Orbit (VLEO) or the upper atmosphere, Air-Breathing Electric Propulsion (ABEP) can be used to counteract the drag effects of the atmosphere or provide attitude control without the need for onboard propellant storage. The Dense Plasma Focus (DPF) inspired the design of an ABEP Pulsed Plasma Thruster (TAMU PPT) which takes advantage of the simplicity, scalability, and high energy density of the DPF. This work details the design and testing of a PPT for use on satellites in the upper atmosphere. Testing was conducted at a variety of pressures and pulsing energies to determine which conditions provide maximum thrust and thrust to power ratios (TPR). It was found through single pulse experiments that a pressure of 6.3 hPa (corresponding to an altitude of about 35 km) and an energy per pulse of 9 J yield a TPR of 21 mN/kW. High frequency operation at 20 Hz in similar conditions showed a TPR of up to 28 mN/kW with a corresponding thrust of 4.8 mN. High speed imaging of the plasma plume found plasma velocities in excess of 2 km/s and identified metal ejecta with velocities up to 350 m/s. The pinching phenomenon associated with a DPF was also observed and a plasma jet velocity up to 50 km/s was recorded. The TPR of the TAMU PPT demonstrated in this work is comparable to that of other ABEP thrusters, however the TAMU PPT has an advantage when comparing thrust density. The TAMU PPT has a thrust density between 4.8 and 19 mN/cm2 while other ABEP thrusters have thrust densities between 0.019 and 0.36 mN/cm2. [ABSTRACT FROM AUTHOR]

In recent decades, theoretical studies and numerical models of thermal tides have gained attention. It has been recognized that tides have a significant influence on the dynamics of the middle and upper atmosphere; as they grow in amplitude and propagate upward, they transport energy and momentum from the lower to the upper atmosphere, contributing to the vertical coupling between atmospheric layers. The superposition of tides with other atmospheric waves leads to non-linear wave–wave interactions. However, direct measurements of thermal tides in the middle atmosphere are challenging and are often limited to satellite measurements in the tropics and at low latitudes. Due to orbit geometry, such observations provide only a reduced insight into the short-term variability in atmospheric tides. In this paper, we present tidal analysis from 5 years of continuous observations of middle-atmospheric temperatures. The measurements were performed with the ground-based temperature radiometer TEMPERA (TEMPErature RAdiometer), which was developed at the University of Bern in 2013 and was located in Bern (46.95° N, 7.45° E) and Payerne (46.82° N, 6.94° E). TEMPERA achieves a temporal resolution of 1–3 h and covers the altitude range between 25–50 km. Using an adaptive spectral filter with a vertical regularization (ASF2D) for the tidal analysis, we found maximum amplitudes for the diurnal tide of approximately 2.4 K, accompanied by seasonal variability. The maximum amplitude was reached on average at an altitude of 43 km, which also reflected some seasonal characteristics. We demonstrate that TEMPERA is suitable for providing continuous temperature soundings in the stratosphere and lower mesosphere with a sufficient cadence to infer tidal amplitudes and phases for the dominating tidal modes. Furthermore, our measurements exhibit a dominating diurnal tide and smaller amplitudes for the semidiurnal and terdiurnal tides in the stratosphere. [ABSTRACT FROM AUTHOR]

The numerical simulation of the HD 63433 system is performed with the aim to study upper atmospheres of two mini-Neptunes, planets b and c, interacting with the stellar wind of the parent star. The obtained results demonstrate that both exoplanets form the extended envelopes with strong supersonic outflows. The synthetic absorption profiles in the Ly α line show that under moderate stellar wind conditions, similar to those of the normal solar wind, the energetic neutral atoms contribute to the absorption in the high-velocity blue wing of the line at a level of tens per cent. The absorption in metastable helium He  i (23S) line appears rather weak and below the detection limit by current instruments. An important feature revealed by the simulations is that the tail of escaping atmospheric material of the inner planet disturbs the stellar wind at orbital location of the outer planet and might, therefore, affect its observation in Ly α line. [ABSTRACT FROM AUTHOR]

Extensive research efforts have revealed that the Martian dust storms can perturb the upper atmospheric condition and as a consequence, enhance plasma density and photoelectron flux in the ionosphere. However, previous observational studies of the Martian dust storm impacts have been restricted to regions below 400 km, which limits our understanding of the Martian dust storm effects in the upper ionosphere and magnetosphere. Here, based on the suprathermal electron measurements made by the Solar Wind Electron Analyzer onboard the Mars Atmosphere and Volatile Evolution, we identify with an automatic procedure the occurrences of all photoelectron boundary (PEB) crossings at solar zenith angle below 120° (with a dust-free median altitude of about 600 km). Using the dayside PEB as a proxy of the upper ionospheric and magnetospheric condition, we analyze the variations of the PEB altitude during the 2018 global dust storm (GDS) of Mars Year 34 (MY34) and compare them with the period in MY33 when there was no global dust storm. We conclude that the column dust optical depth (CDOD) emerges as one of the main driving factors for PEB altitude variations during the GDS. Our analysis implies that the GDS can affect the Martian upper atmosphere and ionosphere over considerable distances and extended time scales. [ABSTRACT FROM AUTHOR]

We performed a series of numerical experiments to study the changes in atmospheric and ionospheric parameters caused by the propagation and dissipation of atmospheric waves from the meteorological source in the troposphere under various geomagnetic conditions. The simulation was carried out using the high-resolution regional atmospheric model AtmoSym and the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP). Acoustic and internal gravity waves from a meteorological source were included in the large-scale model by additional source to the heat balance equation without using parameterization. A multi-model investigation showed that the propagation of waves from the troposphere leads to: a local heating of the thermosphere and a decrease in n[O]/n[N 2 ] ratio over the wave generation region; the formation of a dipole-like spatial structure of TEC disturbances with positive and negative values in the vicinity of the source of atmospheric waves. It is shown that the most important mechanism determining the dipole-like spatial structure of TEC disturbances under the influence of atmospheric waves is disturbances of the meridional component of the thermospheric wind. Thermospheric disturbances associated with geomagnetic activity have insignificant effect on the TEC response to the propagation and dissipation of atmospheric waves from the meteorological source in the troposphere. [ABSTRACT FROM AUTHOR]

The current study explores the dynamic interaction between Interplanetary coronal mass ejections (ICMEs) and the induced magnetosphere of Venus, utilizing measurements from the Venus Express (VEX) mission. We have investigated 16 ICME events during the period 2006–2013. The altitude of the inbound bow shock and ionopause at Venus are comprehensively studied during the passage of these ICMEs. The ionosphere is found to be highly magnetized due to the very high magnetic pressure of the induced magnetosphere. Remarkably, the altitude of the ionopause is found to be significantly changed as compared to the previous quiet day due to the increased solar wind dynamic pressure Pdyn $\left({P}_{\mathit{dyn}}\right)$. The ratio of the altitude of ionopause and magnitude of the magnetic field (∣B∣) $(\vert B\vert)$ at ionopause on the event days to the quiet days shows a strong anti‐correlation which indicates the ionopause height is inversely related to the magnetic field. Intriguingly, the position of the bow shock exhibited minimal deviations compared to typical quiet days, underscoring that, during ICME events, the ionopause location is more responsive to solar wind pressure fluctuations than the bow shock location. Additionally, the heavy‐ion density near and above the ionopause is found to be significantly higher than that observed on previous quiet days. This substantial increase implies that ICMEs can induce atmospheric loss in Venus's atmosphere and also cause a significant reduction in the ionopause location. Key Points: The ionopause is found to be significantly changed during the passage of ICMEs compared to the quiet time valuesThe bow shock position exhibited minimal deviations during the event compared to typical quiet daysThe heavy‐ion density near and above the ionopause is significantly higher during ICMEs compared to previous quiet days [ABSTRACT FROM AUTHOR]

This work presents an algorithm for automatic detection of anomalous electron heating (AEH) events in the auroral E‐region ionosphere using data from the Poker Flat Incoherent Scatter Radar (PFISR). The algorithm considers both E‐region electron temperature and magnetically conjugate electric field measurements. Application of this algorithm to 14 years of PFISR data spanning 2010 through 2023 detected 505 AEH events. Measured electron temperatures increase linearly with plasma drift speeds. Statistical trends of AEH occurrence as a function of space weather indices (AE and F10.7) demonstrate correlations with the solar cycle and geomagnetic activity levels. The magnetic local time occurrence rates show preferences for dusk and dawn with most events in the dusk sector. Observed AEH events tend to appear in regions of relatively low electron density and do not appear inside intense auroral arcs with high electron density. Furthermore, AEH detection requires a higher electric field than predicted by the threshold for a positive growth rate of the Farley‐Buneman instability (FBI), according to linear fluid theory. The implications of these findings for kinetic theories of FBI and AEH are discussed. Plain Language Summary: The ionized portion of the upper atmosphere, known as the ionosphere, can conduct electrical currents. In cases where those currents are so large that the relative motion of the electrons and ions exceeds a critical threshold, the ionosphere becomes unstable. The resulting instability rapidly heats electrons in the lower ionosphere, producing what are known as anomalous electron heating (AEH) events. We use ionospheric data from a radar facility in Alaska to detect AEH events. Our detection algorithm identified 505 AEH events in 14 years of data (2010–2023). The occurrence rates of AEH are strongly correlated with the 11‐year solar cycle and indicators of auroral activity. Furthermore, AEH events preferentially occur at times near dawn and dusk, with the highest number of events in the dusk sector. The elevated electron temperatures increase linearly with the magnitude of the ionospheric electric field. Key Points: A novel detection algorithm for identifying anomalous electron heating events primarily based on plasma flow velocities is presentedAnalysis of Poker Flat Incoherent Scatter Radar data from 2010 to 2023 detected 505 eventsStatistical analysis of occurrence rates revealed a strong relationship with geomagnetic activity over the 11‐year solar cycle [ABSTRACT FROM AUTHOR]

Increasing carbon dioxide concentrations in the mesosphere and lower thermosphere are increasing radiative cooling in the upper atmosphere, leading to thermospheric contraction and decreased neutral mass densities at fixed altitudes. Previous studies of the historic neutral density trend have shown a dependence upon solar activity, with larger F10.7 values resulting in lower neutral density reductions. To investigate the impact on the future thermosphere, the Whole Atmosphere Community Climate Model with ionosphere and thermosphere extension has been used to simulate the thermosphere under increasing carbon dioxide concentrations and varying solar activity conditions. These neutral density reductions have then been mapped onto the Shared Socioeconomic Pathways published by the Intergovernmental Panel on Climate Change. The neutral density reductions can also be used as a scaling factor, allowing commonly used empirical models to account for CO2 trends. Under the "best case" SSP1‐2.6 scenario, neutral densities reductions at 400 km altitude peak (when CO2 = 474 ppm) at a reduction of 13%–30% (under high and low solar activity respectively) compared to the year 2000. Higher CO2 concentrations lead to greater density reductions, with the largest modeled concentration of 890 ppm resulting in a 50%–77% reduction at 400 km, under high and low solar activity respectively. Plain Language Summary: Carbon dioxide (CO2) concentrations are increasing throughout the atmosphere, not just at ground level. While this results in global warming in the lower atmosphere, the much less dense upper atmosphere does not trap the radiated heat, resulting in cooling of the upper atmosphere. As the upper atmosphere cools, it contracts, reducing the atmospheric density at a fixed altitude. Satellites traveling in low Earth orbit, such as the International Space Station at 400 km altitude, experience atmospheric drag, slowly reducing their altitude until they "re‐enter" and burn up in the lower, denser atmosphere. Reducing neutral densities will increase satellite orbital lifetimes as they experience less drag. The upper atmosphere has been simulated under increasing CO2 concentrations and solar activity conditions. This has also been linked to potential future CO2 concentration scenarios. Scaling factors have been created allowing simpler, faster models to account for CO2 density reductions. Under a best‐case scenario (SSP1‐2.6) where CO2 concentrations peak in around the year 2065 and then decline, densities at 400 km are 13%–30% lower compared to the year 2000 at the CO2 peak concentration, and then recover as CO2 reduces. However, densities continue to reduce if CO2 concentrations keep rising. Key Points: Whole Atmosphere Community Climate Model with ionosphere and thermosphere extension has been used to model future thermospheric density reductions under increasing carbon dioxide concentrations and solar activityThe reductions in density have been mapped onto the Shared Socioeconomic Pathways to show future scenarios while accounting for solar cyclesDensities at 400 km are 13%–30% lower under high and low solar activity respectively in the SSP1‐2.6 scenario when CO2 peaks at 474 ppm [ABSTRACT FROM AUTHOR]

In this study, we investigate the intricate electrodynamics of the Earth's horizontal component of the geomagnetic field (ΔH) in response to two significant solar flares (SF) occurring on 03 July and 28 October 2021. These flares are classified as X1.59 and X1.0, respectively. It is noted that the ΔH follows the X‐ray variation during the SF, but there is a time lag of a few minutes between the X‐ray and ΔH. A possible explanation for the time lag is the neutral atmosphere and ionosphere coupling, via ion drag. Plain Language Summary: The ionospheric electron density and Earth's magnetic field are strong disturbed during solar flares (SFs) X‐class. In this paper we show that horizontal component of the magnetic field (ΔH) follows the X‐ray variation during the SF, but there is a time lag of a few minutes, between the X‐ray and ΔH. The time lag between the X‐ray and ΔH peaks vary from 1 to 8 min, the ion drag force between the neutral atmosphere and ionosphere may explain. Key Points: The synchronization of ΔH peaks and valleys from equatorial‐low‐mid latitudes indicates that the X‐ray and ΔH variations are relatedA visible time lag exists between the X‐ray burst peak and ΔH peaks and valleysIt is proposed the coupling between the neutral upper atmosphere and the ionosphere as a possible explanatory framework for this time lag [ABSTRACT FROM AUTHOR]

Joule heating is a major energy sink in the solar wind‐magnetosphere‐ionosphere system and modeling it is key to understanding the impact of space weather on the neutral atmosphere. Ion drifts and neutral wind velocities are key parameters when modeling Joule heating, however there is limited validation of the modeled ion and neutral velocities at mid‐latitudes. We use the Blackstone Super Dual Auroral Radar Network radar and the Michigan North American Thermosphere Ionosphere Observing Network Fabry‐Perot interferometer to obtain the local nightside ion and neutral velocities at ∼40° geographic latitude during the nighttime of 16 July 2014. Despite being a geomagnetically quiet period, we observe significant sub‐auroral ion flows in excess of 200 ms−1. We calculate an enhancement to the local Joule heating rate due to these ion flows and find that the neutrals impart a significant increase or decrease to the total Joule heating rate of >75% depending on their direction. We compare our observations to outputs from the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM). At such a low geomagnetic activity however, TIEGCM was not able to model significant sub‐auroral ion flows and any resulting Joule heating enhancements equivalent to our observations. We found that the neutral winds were the primary contributor to the Joule heating rates modeled by TIEGCM rather than the ions as suggested by our observations. Plain Language Summary: Charged particle motion in Earth's upper atmosphere creates heating called Joule heating which causes the atmosphere to expand, increasing drag for objects and satellites. Charged particle velocities are typically greater at high‐latitudes than mid and lower latitudes. At mid and lower latitudes, Earth's neutral atmosphere can move faster than the charged particles and produce Joule heating. We can use ground based instruments to observe this particle motion and estimate the Joule heating. Physical models can estimate the Joule heating for different space weather conditions. These physical models show good estimations of the high‐latitude Joule heating compared to estimations, however there is limited validation of their performance at mid‐latitudes. We use ground based instruments to estimate the Joule heating over mid‐latitude North America for one night and compare to outputs from a physics model called the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM). Despite quiet driving conditions, we observe significant charged particle motion driving enhanced Joule heating rates. We find that TIEGCM was unable to model these strong charged particle motions nor any Joule heating enhancements equivalent to our observations. While the observed heating resulted from faster charged particle motion, the Joule heating rates in TIEGCM were produced by the greater neutral winds instead of ion drifts. Key Points: Observations from a Fabry‐Perot interferometer and Super Dual Auroral Radar Network radar were used to estimate quiet‐time mid‐latitude Joule heating rates during 16 July 2014The neutral winds accounted for between 24% and 43% of the total observed local Joule heating ratesJoule heating enhancements were observed approximately 8 times higher than modeled by the Thermosphere Ionosphere Electrodynamic General Circulation Model due to excitations in sub‐auroral ion motion [ABSTRACT FROM AUTHOR]

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Based on two meteor radars in mid‐latitudes of China, the mid‐latitude lower thermospheric neutral wind responses to the 2015 St. Patrick's Day great storm are investigated. The AE and PCN indices presented the similar quasi‐5‐hour oscillations during the storm. Interestingly, the analogous and close‐correlated storm‐time quasi‐5‐hour oscillations were also observed in both the meridional wind differences at 90–102 km derived from meteor radars. The meridional wind disturbances in the lower thermosphere also showed the extension toward the lower latitudes. It has been found that the enhanced equatorward wind disturbances at 250 km estimated by the Horizontal Wind Model‐14 and Fabry‐Perot Interferometer (FPI) emerged accordingly with the increases of AE and PCN with a time delay. And the enhancements of equatorward (poleward) wind disturbances at 250 km were accompanied by the increments of equatorward (poleward) wind disturbances at 94 km with a time lag of a few hours. It is thus suggested that the multiple intensified Joule heating events with quasi‐5‐hour time intervals were triggered by the successive substorm expansions during the storm. Then the Joule heating events led to the vertical wind and temperature disturbances in the mid‐latitude lower thermosphere via disturbing the thermospheric meridional circulation, which consequently induced the quasi‐5‐hour meridional wind disturbances therein. Plain Language Summary: The neutral temperature and global circulation in the middle and upper atmosphere can be strongly disturbed by the solar and geomagnetic activity. However, the effects of geomagnetic activity on the neutral winds in the mesosphere and lower thermosphere region at middle latitudes have not been fully understood. Using the neutral wind measurements from two meteor radars located at latitudes of 53.5°N and 40.3°N around 120°E meridian in China, we found that the meridional winds at different latitudes showed the prominent and similar disturbance patterns during the 2015 St. Patrick's Day geomagnetic storm. There exhibited the obvious quasi‐5‐hour oscillations in the meridional wind differences at 90–102 km derived from meteor radars. And such wind oscillations appeared to be analogous and close‐correlated to the quasi‐5‐hour oscillations in the AE and PCN indices. The possible contributors and physical processes responsible for such wind disturbances in the mid‐latitude lower thermosphere are discussed. This study is helpful to understand the influences of geomagnetic activity on the neutral winds in the mid‐latitude lower thermosphere region as well as the possible dynamic processes therein. Key Points: Storm‐time quasi‐5‐hour oscillations emerged in both the AE/PCN indices and the meridional winds in the mid‐latitude lower thermosphereThe increments of equatorward/poleward winds at 94 km exhibited the close correspondence and correlation to those at 250 km with a time lagThe successive Joule heating events led to the periodic meridional wind disturbances via disturbing thermospheric meridional circulation [ABSTRACT FROM AUTHOR]

Low latitude ionosphere experiences complex dynamical and electrodynamical processes, which make the spatiotemporal variations of the corresponding electron density complicated and therefore influence trans‐ionosphere radio communications. The monitoring of low latitude dynamical drivers, such as neutral wind and ionospheric electric field, is essential for both dynamic mechanism investigations and applications. The Sanya Incoherent Scatter Radar Tristatic System (SYISR‐TS) was proposed with the main objective of low latitude ionospheric monitoring and investigation and has been successfully developed over the past decade. The system consists of the Sanya (18.3°N, 109.6°E) trans‐receiving main station with key parameters of ∼1,600 m2 antenna aperture, >4 MW peak power, <120 K system noise temperature, and ∼46 dBi normal gain, and Danzhou (19.5°N, 109.1°E) and Wenchang (19.6°N, 110.8°E) receiving only stations with key parameters of ∼790 m2 antenna aperture, <130 K system noise temperature, and ∼43 dBi normal gain. Three stations form a quasi‐equilateral triangle at Hainan Island and use Global Navigation Satellite System satellite common view technique to achieve the time synchronization with the uncertainty of the timing and time synchronization less than 50 and 10 ns, respectively. Initial collaborative satellite tracking and ionospheric common volume experiments among three stations have confirmed the detection ability of SYISR‐TS and the feasibility of achieving its scientific goals in the future. Plain Language Summary: Ionosphere is the ionized part (electrons and ions) of upper atmosphere around 60–1,000 km altitude. In the ionosphere, the generation and movement of electrons and ions are jointly determined by the solar radiation, photo‐chemistry, winds and electric fields. Monitoring the density of electrons, and winds and electric fields as well, is important for understanding and predicting the status of ionosphere. Among numerous ionospheric detection methods, Incoherent Scatter Radar (ISR) plays an important role due to its profiling multiple parameters capability. In this paper, we will describe the technical details and initial experiments of the newly built Sanya Incoherent Scatter Radar Tristatic System. It is also the world first tristatic ISR system using phased array technology, which can switch the beam direction quickly therefore increase the time resolution of measurements significantly. Key Points: Sanya Incoherent Scatter Radar Tristatic System (SYISR‐TS) is the world first completed phased array based tristatic ISR systemSYISR‐TS includes 1 trans‐receiving and 2 remote receiving stations and uses Global Navigation Satellite System satellite common view technique to achieve synchronizationInitial collaborative experiments among three stations have confirmed the detection ability of SYISR‐TS [ABSTRACT FROM AUTHOR]

Prior to use in operational systems, it is essential to validate ionospheric models in a manner relevant to their intended application to ensure satisfactory performance. For Over‐the‐Horizon radars (OTHR) operating in the high‐frequency (HF) band (3–30 MHz), the problem of model validation is severe when used in Coordinate Registration (CR) and Frequency Management Systems (FMS). It is imperative that the full error characteristics of models is well understood in these applications due to the critical relationship they impose on system performance. To better understand model performance in the context of OTHR, we introduce an ionospheric model validation technique using the oblique ground backscatter measurements in soundings from the Super Dual Auroral Radar Network (SuperDARN). Analysis is performed in terms of the F‐region leading edge (LE) errors and assessment of range‐elevation distributions using calibrated interferometer data. This technique is demonstrated by validating the International Reference Ionosphere (IRI) 2016 for January and June in both 2014 and 2018. LE RMS errors of 100–400 km and 400–800 km are observed for winter and summer months, respectively. Evening errors regularly exceeding 1,000 km across all months are identified. Ionosonde driven corrections to the IRI‐2016 peak parameters provide improvements of 200–800 km to the LE, with the greatest improvements observed during the nighttime. Diagnostics of echo distributions indicate consistent underestimates in model NmF2 during the daytime hours of June 2014 due to offsets of −8° being observed in modeled elevation angles at 18:00 and 21:00 UT. Plain Language Summary: Models of the ionized upper atmosphere, a region known as the ionosphere, must be validated using appropriate techniques prior to their use in operational systems. This is of greatest importance for Over‐the‐Horizon radars (OTHR) that rely on the reflection of radio waves in the 3–30 MHz band from the ionosphere for their operation. The accuracy of OTHR is largely related to the performance of the model ionosphere used to establish target positions, and so it is essential to understand how models behave under different circumstances. We introduce a new technique for validating models using measurements from the Super Dual Auroral Radar Network (SuperDARN) of research radars. Using a dominant feature present within these radar echoes, we perform an example validation of the International Reference Ionosphere (IRI) 2016 by modeling the expected path of radio waves. The performance is seen to be best during winter and typically worse in the evening. Using further information present within the measurements, we diagnose the likely cause of errors to be due to underestimates in a key model parameter. This is confirmed when we offset model parameters using direct measurements of the ionosphere and observe a significant improvement in model performance. Key Points: We introduce an ionospheric model validation technique using SuperDARN ground backscatterPerformance of the IRI‐2016 is best during the daytime of January 2014 and 2018, whilst sporadic‐E in June causes significant degradationsIRI‐2016 range errors are seen to be most significant near the terminator and during the nighttime [ABSTRACT FROM AUTHOR]

This research proposes a new mathematical formulation of tornadoes based on the theory of tensor analysis and simulation in a non-inertial dynamics framework, both in two and three dimensions. This model may show the spherical upward movement of air in a tornado without taking into account vertical convection. A tornado requires several elements, including geocentric latitude, the Coriolis effect, increased airspeed in the upper atmosphere, and increased air pressure. Computing the three-dimensional location of the tornado or hurricane, as well as the mathematical models of airflow motion and the Earth's rotation in three-dimensional (3D) space, can determine a tornado's airflow characteristics. To show tornado patterns, we employed computer software that computed motion dynamics and did numerical computations. The results of 2-D modeling and simulation indicated that the greater the initial tornado angular speed, the larger the tornado area. Three-dimensional modeling and simulation also show that tornadoes are more powerful at higher geocentric latitude angles. The novelty of this study is that this model can be used to explain tornado patterns. In our research, we combine tensor analysis, computational modeling, as well as 2D and 3D simulations for simulating tornadoes for the first time. The scientific application of this finding is that researchers at the Meteorology, Climatology, and Geophysics Agency will be able to analyze a tornado and geophysical phenomena more readily with simulations and models. [ABSTRACT FROM AUTHOR]

After days of intense solar activity, active region AR3664 launched seven CMEs toward Earth producing an extreme G5 geomagnetic storm commencing at 17:05 UT on 10 May 2024. The storm impacted power grids, disrupted precision navigational systems used by farming equipment, and generated aurora seen around the globe. The storm produced remarkable effects on composition, temperature, and dynamics in the Earth's thermosphere that were observed by NASA's Global‐scale Observations of the Limb and Disk (GOLD) mission and are reported here for the first time. We use synoptic disk images of ΣO/N2 and neutral temperature (at ∼160 km) measured by GOLD to directly link dynamics resulting from the storm with dramatic changes in thermospheric composition and temperature. We observe a heretofore unseen spatial morphology simultaneously in ΣO/N2, neutral temperature, and total electron content. Equator‐to‐pole temperature differences reach 400 K with high latitude peak neutral temperatures near 160 km exceeding 1400 K. Plain Language Summary: On Saturday 10 May 2024, the sun launched a wave of energized plasma toward the Earth. A large disturbance in the Earth's magnetic field associated with the solar wind resulted in an extreme geomagnetic storm. The storm impacted power grids, disrupted navigational systems used by farming equipment, and produced aurora seen around the globe. The storm produced remarkable effects in the Earth's upper atmosphere that were observed by NASA's Global‐scale Observations of the Limb and Disk (GOLD) mission. In this letter, we use images measured by GOLD to directly link atmospheric dynamics resulting from the May 10–12 superstorm with dramatic changes in composition, temperature, and global circulation in the Earth's upper atmosphere. We observe previously unseen structure in the upper atmosphere associated with equator‐to‐pole temperature differences exceeding 400 K. Peak neutral temperatures near 160 km exceed 1400 K at high latitudes. Key Points: GOLD disk images of ΣO/N2 and neutral temperature link storm time dynamics with changes in thermospheric composition and temperatureWe observe a previously unseen spatial morphology in ΣO/N2, neutral temperature, and total electron contentPeak equator‐to‐pole temperature differences exceed 400 K but relax to pre‐storm conditions well before ΣO/N2 [ABSTRACT FROM AUTHOR]

Over the past decades, various experimental and numerical model studies have indicated cooling trend in the mesosphere and lower thermosphere (MLT), while the magnitude of the trend varies noticeably. Previous studies using the lidar observations derived the temperature trends and solar responses solely from the traditional nocturnal measurements. While these archived results are more or less in agreement with modeling studies, one of the main uncertainties in these studies is the potential biases induced by the trends of the diurnal tide forced in the lower atmosphere, and that of the in situ exothermal reactions involving the photolysis. In the MLT, the diurnal tide has significant seasonal variations, considerable amplitude and is one of the dominant dynamic sources. However, its potential effects in the trend studies have rarely been discussed. In this paper, we present and compare the long‐term temperature trends in the upper mesosphere utilizing the daily mean and nightly mean temperature profiles measured by a Sodium (Na) Doppler lidar at midlatitude. The system was operating routinely in full diurnal cycles between 2002 and 2017, obtaining a unique multi‐year temperature data set. A customized multi‐linear regression (MLR) model is applied to determine the linear trends and the other fitting parameters, such as ENSO and solar F10.7 responses in the upper mesosphere. This study indicates the daily mean cooling trend between 84 and 98 km is larger than that of nightly mean trend by ∼−1 K/decade, while differences in the solar response are within the fitting uncertainties. Plain Language Summary: The upper atmosphere is sensitive to both the climate change in the lower atmosphere and the solar activity. Studies have demonstrated this region has been experiencing long‐term cooling trend over the past several decades. Most of the previous ground‐based investigations utilized nighttime temperature observations to derive the long‐term changes in the mesosphere and lower thermosphere. However, these nighttime trend results can be biased due to the lack of daytime temperature measurements, leading to the uncertainty in these achieved results. In this study, the daily mean temperatures measured by a lidar at middle latitude between 2002 and 2017 are used to determine the trend and the upper atmosphere response to solar activity. The customized algorithm includes new and important climate parameters. This investigation eliminates such potential bias in the temperature, and the results demonstrated noticeably larger cooling trend in this atmospheric region when compared with those derived from the nightly temperature observations. In addition, the solar response derived from these daily mean lidar temperatures are positive but less than those based on nightly mean observations. The revealed differences will lead to future investigations on the underlying mechanisms and, thus, uncover new aspect of the long‐term studies. Key Points: The temperature in the mesosphere and lower thermosphere is coolingThe cooling trend derived from the daily mean temperatures is noticeably larger than that revealed by the nightly average temperaturesThe WACCM‐X simulations also indicate the differences between the daily mean trend and the nightly mean trend with less magnitude [ABSTRACT FROM AUTHOR]

Using NASA's Global‐scale Observations of the Limb and Disk (GOLD) imager, we report nightside ionospheric changes during the G5 super geomagnetic storm of 10 and 11 May 2024. Specifically, the nightside southern crest of the Equatorial Ionization Anomaly (EIA) was observed to merge with the aurora near the southern tip of South America. During the storm, the EIA southern crest was seen moving poleward as fast as 450 m/s. Furthermore, the aurora extended to mid‐latitudes reaching the southern tips of Africa and South America. The poleward shift of the equatorial ionospheric structure and equatorward motion of the aurora means there was no mid‐latitude ionosphere in this region. These observations offer unique insights into the ionospheric response to extreme geomagnetic disturbances, highlighting the complex interplay between solar activity and Earth's upper atmosphere. Plain Language Summary: On Earth's nightside during the super geomagnetic storm that occurred on 10 May 2024, NASA's GOLD imager saw something new: a part of Earth's ionosphere, the southern peak of what typically appears as a double‐peaked structure in the ionospheric density at equatorial and low latitudes, merged with the aurora near the southern tip of South America. This has never been reported before. Additionally, the boundary of the aurora expanded further equatorward than usual. These observations of what happened in the Earth's ionosphere during this super storm are reported for the first time in this study. Key Points: EIA crests between ∼70° and 35°W moved poleward, with northern and southern crest reaching ∼38°N and ∼35°S Mlat in the American sectorSouthern EIA crest moved poleward with a speed of ∼450 m/s near ∼55°W Glon during strong IMF Bz and d(Dst)/dtFirst observation of the merging of an EIA crest with the aurora indicating no mid‐latitude ionosphere [ABSTRACT FROM AUTHOR]

The paper describes a magnetoplasmodynamic accelerator and the laboratory facility based on it that have been developed at the Skobeltsyn Institute of Nuclear Physics of Moscow State University to simulate the impact of atomic oxygen in the Earth's upper atmosphere on materials of low-orbit satellites. The simulation methodology for accelerated ground-based testing of spacecraft materials is described in detail. Some results of laboratory research and numerical modelling of polymeric materials destruction by atomic oxygen are presented. [ABSTRACT FROM AUTHOR]

The spectacular visual displays from the aurora come from curtains of excited atoms and molecules, impacted by energetic charged particles. These particles are accelerated from great distances in Earth's magnetotail, causing them to precipitate into the ionosphere. Energetic particle precipitation is associated with currents that generate electric fields, and the end result is a dissipation of the hundreds of gigawatts to terrawatts of energy injected into Earth's atmosphere during geomagnetic storms. While much is known about how the aurora dissipates energy through Joule heating, little is known about how it does so via small‐scale plasma turbulence. Here we show the first set of combined radar and optical images that track the position of this turbulence, relative to particle precipitation, with high spatial precision. During two geomagnetic storms occurring in 2021, we unambiguously show that small‐scale turbulence (several meters) is preferentially created on the edges of auroral forms. We find that turbulence appears both poleward and equatorward of auroral forms, as well as being nestled between auroral forms in the north‐south direction. These measurements make it clear that small scale auroral plasma turbulence is an integral part of the electrical current system created by the aurora, in the sense that turbulent transport around auroral forms enhances ionospheric energy deposition through Joule heating while at the same time reducing the average strength of the electric field. Plain Language Summary: The aurora continuous to amaze the inhabitants and travelers of Earth's polar regions. Bright shifting folds of light extend down from the nightsky, appearing as green, red, or faint‐blue curtains. During geomagnetic storms the are particularly bright and dynamic, often visible in large parts of the inhabited globe. However, far from being simple displays of light, the aurora can wreak havoc on the thin gas of Earth's upper atmosphere. There, gigantic swirls of electric turbulence are excited in response to the energy that is being pumped into the atmosphere by the aurora. This plasma turbulence is detrimental to satellite communication, such as the principle operation of the GPS network, and future efforts are sorely needed to understand the when and how this turbulence appears. We present a series of photographical and radar‐based images of the aurora and its plasma turbulence, shedding light on the complex relationship between the two phenomena. The images and videos we present are accessible and interesting to a public readership. Key Points: Small‐scale auroral plasma turbulence is created preferably outside of but not far from optical auroral formsTurbulence appears both poleward and equatorward of auroral arcsStrong electric fields that trigger meter‐size E region turbulence are sometimes seen before the onset of optical aurora [ABSTRACT FROM AUTHOR]

Upward propagating waves of lower atmospheric origin play an important role in coupling terrestrial weather with space weather on daily to inter‐annual timescales. Quantifying their short‐term (<30 days) variability is a difficult challenge because simultaneous observations at multiple local times are needed to sample diurnal cycles. This study demonstrates and validates a short‐term estimation method of the DE3 non‐migrating tide at the equator and then applies the technique to three independent data sets: MIGHTI, SABER, and TIDI. We find that daily DE3 estimates from SABER, MIGHTI, and TIDI at equator agree well with correlation coefficients ranging between 0.76 and 0.85. The daily DE3 amplitude variability is typically ∼7 m/s in zonal winds and ∼3 K in temperature. We also find that daily MLT variations and F‐region ionospheric DE3 from COSMIC‐2 Global Ionospheric Specification (GIS) show a correlation of 0.55–0.65, suggesting that not all ionospheric variability can be attributed to the E‐region dynamo; however, increasing correlation with increasing time‐scale suggests that lower atmospheric variability has pronounced impact on the ionosphere on intra‐seasonal scales. We find that the MLT and the F‐region ionosphere exhibit strong coherent intra‐seasonal oscillations (residual amplitudes upto 50%–60%); their coherency with the MJO in 2020 suggests a possible modulation of the upward propagating DE3 tide related to this major tropical tropospheric weather pattern. In addition, we find stratospheric QBO signatures in the MLT DE3 on inter‐annual scales. This study offers fresh observational insights into the pivotal role of tropospheric weather in shaping variability in the coupled thermosphere‐ionosphere system. Plain Language Summary: A growing body of research unequivocally demonstrates the important role upward propagating waves from the lower atmosphere play in shaping the meteorology of the mesosphere, thermosphere and ionosphere from daily to inter‐annual time scales. Understanding these variations is crucial for space weather studies and applications, including radio wave propagation, satellite communication, and space orbital debris. Among these oscillations, the diurnal eastward propagating tide with zonal wave number 3 (DE3) holds particular importance. This oscillation, driven by expansive tropospheric weather systems, can attain substantial amplitudes in the upper atmosphere. The primary objective of this study is to demonstrate and validate a methodology facilitating the short‐term estimation of DE3 to understand the tidal weather of the upper atmosphere. Our approach starts by using a physics‐based model of the upper atmosphere to test and validate this new daily DE3 retrieval method. Next, we apply our tidal estimation method to extensive satellite‐based measurements of winds, temperatures, and ionospheric electron density. Lastly, we analyze the results to provide fresh observational insights into the pivotal role of tropospheric weather on Earth's near space environment from daily to inter‐annual time scales. Key Points: Demonstrated and validated a short‐term DE3 tidal estimation technique at the equatorDaily DE3 tidal amplitude variability at the equator is typically ∼7 m/s in zonal winds and ∼3 K in temperatureStrong intra‐seasonal variations in MLT region DE3 and F‐region ionosphere electron densities possibly due to the MJO are observed [ABSTRACT FROM AUTHOR]

The Vertical Scale Height (VSH) is a crucial parameter that describes the shape of the ionospheric electron density profile. Evidence suggests a complex relationship between VSH and the thermal structure and dynamics of the ionosphere. A statistical study was conducted on the VSH at low altitudes (175 km) and high altitudes (300 km) in the Martian ionosphere, using data from the MAVEN observations from 2014 to 2023. The results suggest that the influence of the crustal magnetic field on VSH175 is more pronounced than on VSH300. VSH175 shows a minor peak around −20° latitudes, which is more than 7% higher than the average value, and an increasing trend with latitude in the northern hemisphere. VSH300 is higher in the southern hemisphere than in the northern hemisphere, especially in summer, by approximately 42.1%. Regarding the local time variation of VSH, we observed an increasing trend from midnight to morning and a decreasing trend from dusk to midnight in almost all conditions. The local time variation of VSH also exhibits seasonal and latitudinal dependence. These variations have different levels of consistency with the gradient of the electron temperature (Te) and the collision frequency between charged particles and neutrals. Specifically, the correlation coefficient between VSH175 and the collision frequency between charged particles and neutrals reaches as high as 0.93 in the northern hemisphere winter and southern hemisphere summer. The correlation coefficient between VSH300 and the gradient of the Te reaches up to 0.72 in the southern hemisphere equinox. Plain Language Summary: The ionosphere is produced by photo‐ionization of the Martian upper atmosphere. The Vertical Scale Height (VSH) is a parameter that describes how quickly the electron density in the ionosphere changes with height. It is closely linked to the thermal structure and dynamics of the ionosphere. Our research focuses on how the crustal magnetic field affects the VSH on Mars and looks at variations with latitude and local time at low altitudes (175 km) and high altitudes (300 km) using MAVEN observations. We find that high VSH values at 175 km align with areas of strong crustal magnetic fields on Mars. There are significant latitudinal and daily variations in the VSH of the Martian ionosphere. Latitudinal variation is mainly manifested as hemispherical asymmetry, which may be related to Martian topography. The daily variations are influenced by the temperature gradient and the collision frequency between charged particles and neutrals. These effects also have dependences on altitude and season. Key Points: The crustal magnetic field of Mars has a significant effect on Vertical Scale Height (VSH) at low altitudesOur analysis revealed evident diurnal and latitudinal variations in the VSH of the Martian ionosphereThe thermal structure and dynamics contribute differently to local time variation of the VSH at different heights [ABSTRACT FROM AUTHOR]

Low Earth orbit (LEO) radio occultation|radio occultations (RO) constellations can provide global electron density profiles (EDPs) to better specify and forecast the ionosphere‐thermosphere (I‐T) system. To inform future RO constellation design, this study uses comprehensive Observing System Simulation Experiments (OSSEs) to assess the ionospheric specification impact of assimilating synthetic EDPs into a coupled I‐T model. These OSSEs use 10 different sets of RO constellation configurations containing 6 or 12 LEO satellites with base orbit parameter combinations of 520 or 800 km altitude, and 24° or 72° inclination. The OSSEs are performed using the Ensemble Adjustment Kalman Filter implemented in the data assimilation (DA) Research Testbed and the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM). A different I‐T model is used for the nature run, the Whole Atmosphere Model‐Ionosphere Plasmasphere Electrodynamics (WAM‐IPE), to simulate the period of interest is the St. Patrick's Day storm on March 13–18, 2015. Errors from models and EDP retrieval are realistically accounted for in this study through distinct I‐T models and by retrieving synthetic EDPs through an extension Abel inversion algorithm. OSSE assessment, using multiple metrics, finds that greater EDP spatial coverage leading to improved specification at altitudes 300 km and above, with the 520 km altitude constellations performing best due to yielding the highest observation counts. A potential performance limit is suggested with two 6‐satellite constellations. Lastly, close examination of Abel inversion error impacts highlights major EDP limitations at altitudes below 200 km and dayside equatorial regions with large horizontal gradients and low electron density magnitudes. Plain Language Summary: The upper atmosphere, the region above 100 km altitude, is strongly influenced by space weather events that can negatively impact ground and space‐based technologies. These technologies include communication and navigation systems impacted by radio wave propagation through high altitudes plasma, a region called the ionosphere. Developing observing systems that provide global monitoring of the ionosphere is a critical need for understanding and forecasting space weather changes, such as radio occultations (RO) that provide plasma observations using global positioning radio signals. In this study, we evaluate these hypothetical RO observing systems in simulated experiments using data assimilation (DA), an approach that integrates synthetic observations into a physics‐based model. We find that increased observational coverage corresponds to better estimated plasma states, and that lower orbit altitude constellations yield higher observation counts. This study comprehensively incorporates model and observation errors to more realistically represent real‐world conditions. One limitation of RO data is highlighted in regions near the equator and at lower altitudes (below 250 km) where there is a breakdown in assumptions for observation retrieval. This study illustrates the clear operational benefits of these plasma observations, informing the future observing system design and aiding their use for space weather forecasting. Key Points: OSSE study assessing hypothetical radio occultation (RO) constellations, the first to comprehensively account for forecast model and Abel inversion errorsThe RO constellation with low‐ and high‐inclination orbits at 520 km altitude performs the best with the highest observation countsUncharacterized Abel inversion errors and poorly retrieved low plasma density limit assimilation impact on the equatorial ionosphere [ABSTRACT FROM AUTHOR]

Equatorial Plasma Bubbles (EPBs) can generate ionospheric scintillation at GHz frequencies used in the Global Navigation Satellite System (GNSS). Emerging at any longitude following sunset and typically moving eastward, monitoring the EPBs is essential for space weather services. Using three GNSS receivers positioned at the same latitude (∼0°N) but separated in longitudes (∼9°, ∼16°, and ∼25°) and the 47 MHz Equatorial Atmosphere Radar (EAR) in Indonesia, our study delineates the zonal extent of eastward‐traveling post‐sunset EPB inducing ionospheric GNSS scintillation. Typically, the scintillation occurrences detected by a ground receiver concentrate between 19 and 01 local time (LT), with a peak incidence observed at 21 LT. Furthermore, an experiment combining EAR observations with GNSS receiver data allowed for the determination of the linear change in the speed of eastward‐traveling EPB inducing scintillation during this time period. Interestingly, the longitudinal range of eastward‐traveling EPBs increased with higher solar flux (F10.7) levels. Our findings suggest that EPB can induce scintillation up to a longitudinal distance of approximately 25° from the onset location at sunset to the eastern midnight region, particularly in F10.7 ranging from 90 to 150 solar flux units. Moreover, experiments using longitudinally separated GNSS receivers indicated that scintillations during 19–01 LT originate from post‐sunset EPBs within a longitudinal range extending 25° to the west. In conclusion, our research provides valuable insight into the ability of eastward‐traveling EPB to induce GNSS scintillation within a longitudinal range of 25°, thereby enhancing EPB and scintillation monitoring and prediction in regional space weather services. Plain Language Summary: Many modern technologies rely on Global Navigation Satellite Systems (GNSS). GNSS refers to satellites constellations, including Global Positioning Systems, that send signals from space to the receivers on the ground, providing positioning and timing data. However, GNSS signals can be disrupted by natural phenomena in the Earth's ionosphere, a layer of charged particles in the upper atmosphere. One such phenomenon is the Equatorial Plasma Bubble (EPB) occurring at night, which can cause fluctuations or scintillations in GNSS signals, leading to errors in positioning and timing. Understanding how EPBs affect GNSS is essential for maintaining the reliability of navigation systems and ensuring the smooth operation of various technological applications that rely on GNSS data. EPBs usually move eastward and can cause scintillation in the longitude where they are generated and in other longitudes. Previous studies have not determined how far eastward‐traveling EPB can induce scintillation. Our recent discovery shows that EPBs can induce scintillation within a longitudinal range of up to 25°. This insight is essential for mitigating the adverse effects of EPBs on GNSS applications in regional or longitudinal sectors. Key Points: A ground GNSS receiver typically detects scintillations due to Equatorial Plasma Bubbles (EPBs) from 19 to 01 local time (LT) with the peak occurrence at 21 LTThe furthest longitudinal range of EPB inducing GNSS scintillation depends on solar flux (F10.7) levelEPBs can cause GNSS scintillation within a 25° longitudinal range at F10.7 levels of 90–150 solar flux units [ABSTRACT FROM AUTHOR]

Context. Gas in protoplanetary disks mostly cools via thermal accommodation with dust particles. Thermal relaxation is thus highly sensitive to the local dust size distributions and the spatial distribution of the grains. So far, the interplay between thermal relaxation and gas turbulence has not been dynamically modeled in hydrodynamic simulations of protoplanetary disks with dust. Aims. We aim to study the effects of the vertical shear instability (VSI) on the thermal relaxation times, and vice versa. We are particularly interested in the influence of the initial dust grain size on the VSI and whether the emerging turbulence is sustained over long timescales. Methods. We ran three axisymmetric hydrodynamic simulations of a protoplanetary disk including four dust fluids that initially resemble MRN size distributions of different initial grain sizes. From the local dust densities, we calculated the thermal accommodation timescale of dust and gas and used the result as the thermal relaxation time of the gas in our simulation. We included the effect of dust growth by applying the monodisperse dust growth rate and the typical growth limits. Results. We find that the emergence of the VSI is strongly dependent on the initial dust grain size. Coagulation also counteracts the emergence of hydrodynamic turbulence in our simulations, as shown by others before. Starting a simulation with larger grains (100 μm) generally leads to a less turbulent outcome. While the inner disk regions (within ∼70 au) develop turbulence in all three simulations, we find that the simulations with larger particles do not develop VSI in the outer disk. Conclusions. Our simulations with dynamically calculated thermal accommodation times based on the drifting and settling dust distribution show that the VSI, once developed in a disk, can be sustained over long timescales, even if grain growth is occurring. The VSI corrugates the dust layer and even diffuses the smaller grains into the upper atmosphere, where they can cool the gas. Whether the instability can emerge for a specific stratification depends on the initial dust grain sizes and the initial dust scale height. If the grains are initially ≳100 μm and if the level of turbulence is initially assumed to be low, we find no VSI turbulence in the outer disk regions. [ABSTRACT FROM AUTHOR]

Ground-based ionospheric, CHAMP/STAR, and GOCE satellite neutral density ρ observations under deep solar minimum conditions were used to find whether there is a dependence of longitudinal variations on polar vortex strength. Ionospheric stations at fixed-dipole geomagnetic Φ ≈ 38° and geographic φ ≈ 40°N latitudes located in 'near-pole' and 'far-from-pole' longitudinal sectors were used in the analysis. No significant longitudinal NmF2 (electron concentration in the F2-layer maximum) dependence on the polar vortex strength was revealed. Geomagnetic control was shown to be responsible for the observed longitudinal NmF2 variations. Satellite-observed longitudinal variations in neutral density did not show any visible reaction to the polar vortex strength. However, the impact of sudden stratospheric warming (SSW) on the upper atmosphere is strong enough to change the neutral density longitudinal distribution. The impact of SSW shows a global occurrence and 'works' within 3–5 days in geographic coordinates in the vicinity of the SSW peak. Atomic oxygen values retrieved under 'strong' and 'weak' polar vortex strengths confirm the results obtained on longitudinal variations in NmF2 and ρ. In conclusion, no visible effects related to 'strong' or 'weak' polar vortex strengths have been revealed in either NmF2 or satellite neutral density longitudinal variations. Alternatively, such effects may be very small and therefore cannot be confirmed experimentally. [ABSTRACT FROM AUTHOR]

Ozone pollution shows a trend of increasing, but the potential contribution of volatile organic compounds (VOCs) to ozone formation in the vertical direction is still unclear. The vertical distribution characteristics of VOCs and its impact on ozone formation were studied based the enhanced sounding data in the lower troposphere (0-1000 m) from October 17 to November 15, 2020 observed in the northern suburbs of Nanjing city, Jiangsu province. The results show that the volume fraction of VOCs ((73.4±26.1)×10-9 (50.4±20.3)×10-9) decreases with the increase of height, and alkanes account for the largest proportion (64.3%-71.6%) at each height, and the proportion of olefin (3.4%-9.9%) gradually decrease with the increase of height; there is no significant change in the proportion of aromatics, halohydrocarbons and acetylene; the VOCs accumulate in the lower layer in the morning and evening with a great gradient, and the proportion of alkane increases due to the traffic emissions and lower boundary layer; the VOCs profiles are uniform in the afternoon. Affected by atmospheric junction, the alkanes and olefin dominate the photochemical reactions in the mixing layer, with the loss rate of OH radicals (LOH) of 3.3 and 2.7s-1, accounting for 42.8% and 35.1%, respectively; alkanes and aromatics are the dominant species in the stable boundary layer and residual layer. The LOH and ozone formation potential (OFP) of VOCs in the afternoon mixing layer are positively correlated with the ozone volume fraction, which represent the relationship between local VOCs and ozone; however, there is no significant correlation between LOH, OFP and ozone in the stable boundary layer and residual layer in the morning; the contributions of VOCs components with high reaction activity to OFP are occurred in the low layer, and ethene and propene are the representative components; alkane makes greater contribution to the photochemical generation of ozone in the upper atmosphere, and the analysis result of X/E ratio reflects higher aging and the characteristics of regional atmospheric. Limiting chemical plant emissions, and improving vehicle emission standards and fuel quality, are the key to improve ozone pollution in Nanjing. [ABSTRACT FROM AUTHOR]

Earthquakes with moment magnitude (M w) ranging from 6.5 to 7.0 have been observed to generate sufficiently strong acoustic waves (AWs) in the upper atmosphere. These AWs are detectable in Global Navigation Satellite System satellite signals-based total electron content (TEC) observations in the ionosphere at altitudes ∼250–300 km. However, the specific earthquake source parameters that influence the detectability and characteristics of AWs are not comprehensively understood. Here, we extend our approach of coupled earthquake-atmosphere dynamics modelling by combing dynamic rupture and seismic wave propagation simulations with 2-D and 3-D atmospheric numerical models, to investigate how the characteristics of earthquakes impact the generation and propagation of AWs. We developed a set of idealized dynamic rupture models varying faulting types and fault sizes, hypocentral depths and stress drops. We focus on earthquakes of M w 6.0–6.5, which are considered the smallest detectable with TEC, and find that the resulting AWs undergo non-linear evolution and form acoustic shock N waves reaching thermosphere at ∼90–140 km. The results reveal that the magnitude of the earthquakes is not the sole or primary factor determining the amplitudes of AWs in the upper atmosphere. Instead, various earthquake source characteristics, including the direction of rupture propagation, the polarity of seismic wave imprints on the surface, earthquake mechanism, stress drop and radiated energy, significantly influence the amplitudes and periods of AWs. The simulation results are also compared with observed TEC fluctuations from AWs generated by the 2023 M w 6.2 Suzu (Japan) earthquake, finding preliminary agreement in terms of model-predicted signal periods and amplitudes. Understanding these nuanced relationships between earthquake source parameters and AW characteristics is essential for refining our ability to detect and interpret AW signals in the ionosphere. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of anomalies detected during the preparatory phase of the 9 November 2022 ML = 5.7 earthquake, occurring approximately 30 km off the coast of the Marche region in the Adriatic Sea (Italy). It was the largest earthquake in Italy in the last 5 years. According to lithosphere–atmosphere–ionosphere coupling (LAIC) models, such earthquake could induce anomalies in various observable variables, from the Earth's surface to the ionosphere. Therefore, a multiparametric and multilayer approach based on ground and satellite data collected in each geolayer was adopted. This included the revised accelerated moment release method, the identification of anomalies in atmospheric parameters, such as Skin Temperature and Outgoing Longwave Radiation, and ionospheric signals, such as Es and F2 layer parameters from ionosonde measurements, magnetic field from Swarm satellites, and energetic electron precipitations from NOAA satellites. Several anomalies were detected in the days preceding the earthquake, revealing that their cumulative occurrence follows an exponential trend from the ground, progressing towards the upper atmosphere and the ionosphere. This progression of anomalies through different geolayers cannot simply be attributed to chance and is likely associated with the preparation phase of this earthquake, supporting the LAIC approach. [ABSTRACT FROM AUTHOR]

The sporadic E‐layer (Es) exhibits unique opportunity for exploring the coupling from lower to upper atmosphere. It was found that the East Asia is with the highest intensity and occurrence probability of Es. By using the long‐term data of 21 ionosonde stations in China and Japan over the past 60 yrs, this paper explores the probable control on the Es layer from the lower layers. It is found that the intensity of the Es layer is strongly correlated with the surface atmospheric temperature, terrain, and land‐sea boundary. The correlation coefficient of the intensity of Es with surface temperature is as high as 0.8204, while that with the terrain and land‐sea boundary is up to 0.6668. Based on the coupling between the lower and upper atmosphere, this paper reveals the probable controls from lower layers on the intensity of the Es in East Asia. Plain Language Summary: As an occasional ionized layer of the ionosphere, the sporadic E‐layer (Es) exhibits unique opportunity for exploring the coupling from lower to upper atmosphere. Despite extensive research on both behavior and mechanism of the Es, none have adequately explained the strong inhomogeneous of its global morphology. It is found in fact that the East Asia is with the highest intensity and occurrence probability of Es. By using the long‐term data of 21 ionosondes in China and Japan over the past 60 yrs, this letter explores the formation mechanism of the strongest Es regions in the world. It is found that the intensity of the Es layer is strongly correlated with the surface atmospheric temperature, terrain, and land‐sea boundary. The correlation coefficient between the intensity of Es and surface temperature is highest, while that with the terrain and land‐sea boundary is also high. By analyzing the data as long as six decades, this letter reveals the probable controls from lower layers on the intensity of the Es in East Asia. Key Points: By analyzing the six‐decade data of 21 ionosondes in East Asia, it reveals probable controls on the strongest Es layer from lower layersFor the first time, it is found that the intensity of Es layer is highly correlated with the surface atmospheric temperatureAn interesting coupling from lower to upper atmosphere may be found by taking advantage of observations longer than half of a century [ABSTRACT FROM AUTHOR]