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Utilizing multistatic specular meteor radar (MSMR) observations, this study delves into global aspects of wind perturbations in the mesosphere and lower thermosphere (MLT) from the unprecedented 2022 eruption of the Hunga Tonga‐Hunga Ha'apai (HTHH) submarine volcano. The combination of MSMR observations from different viewing angles over South America and Europe, and the decomposition of the horizontal wind in components along and transversal to the HTHH eruption's epicenter direction allow an unambiguous detection and identification of MLT perturbations related to the eruption. The performance of this decomposition is evaluated using Whole Atmosphere Community Climate Model with thermosphere/ionosphere extension (WACCM‐X) simulations of the event. The approach shows that indeed the HTHH eruption signals are clearly identified, and other signals can be easily discarded. The winds in this decomposition display dominant Eastward soliton‐like perturbations observed as far as 25,000 km from HTHH, and propagating at 242 m/s. A weaker perturbation observed only over Europe propagates faster (but slower than 300 m/s) in the Westward direction. These results suggest that we might be observing the so‐called Pekeris mode, also consistent with the L1 pseudomode, reproduced by WACCM‐X simulations at MLT altitudes. They also rule out the previous hypothesis connecting the observations in South America to the Tsunami associated with the eruption because these perturbations are observed over Europe as well. Despite the progress, the L0 pseudomode in the MLT reproduced by WACCM‐X remains elusive to observations. Key Points: A decomposition of the horizontal wind in longitudinal and transverse components, allows clear identification of Hunga Tonga‐Hunga Ha'apai eruption signaturesEastward soliton‐like mesosphere and lower thermosphere horizontal wind perturbations are observed propagating at 242 m/s, up to at least 25,500 km from the epicenterWeaker westward propagating perturbations are observed at phase speeds in between the expected L0 and L1 speeds, but up to 17,000 km [ABSTRACT FROM AUTHOR]

An exceptionally strong westward propagating quasi‐6‐day wave (Q6DW) with zonal wavenumber 1 in connection with the rare 2019 Southern Hemispheric Sudden Stratospheric Warming (SSW) is observed by two meteor radars at 30°S and is found to modulate and interact with the diurnal tide and gravity waves (GWs). The diurnal tide is amplified every 6 days and a prominent 21 hr child wave attributed to Q6DW‐diurnal tide nonlinear interaction occurs. Q6DW modulation on GWs is confirmed as the 4–5 day periodicity in GW variances. Simultaneously, the Q6DW appears to shift its period toward the periodicity of the modulated GW variances. Enhancement is also observed in the first results of meteor radar observed Q6DW Eliassen‐Palm flux, which may facilitate the global perturbation and persistence of this Q6DW. We conclude that the observed SSW triggered Q6DW‐tide and Q6DW‐GW interactions play an important role in coupling the lower atmospheric forcings to ionospheric variabilities. Plain Language Summary: Our work provides observational evidence for the 6‐day planetary wave‐tide and 6‐day planetary wave‐gravity wave interactions at the Earth's mesosphere and lower thermosphere. The results strongly support the theory that wave‐wave interactions are the primary mechanism coupling planetary waves to ionospheric variability and provide an additional mechanism as the 6‐day wave modulation on the gravity waves. We utilize measurements from two meteor radars to diagnose planetary wave characteristics and identify wave‐wave interactions, and compute the first‐time meteor radar observed Eliassen‐Palm flux. Enhancement is observed in the Eliassen‐Palm flux of 6‐day wave following the SSW maximum phase, which demonstrates that energy of the 6‐day wave is enhanced and therefore, facilitates the global perturbation and persistence of the 6‐day wave for an extended time period. While meteor radar observations are widely used to investigate planetary waves and tides, high meteor detection rate is required for further studying temperature perturbations and small scale waves (e.g., gravity waves). Thus, this work also highlights the capability of a modern multi‐static meteor radar system, Chilean Observation Network De meteOr Radars, in resolving oscillations of small spatial scales over a broad range of periods, and for calculating Eliassen‐Palm flux of planetary waves. Key Points: A dominating W1 Q6DW is observed at 30°S and its Eliassen‐Palm flux is enhanced during the 2019 SH SSWQ6DW amplifies the diurnal tide every 6 days and a strong 21 hr child wave is observedQ6DW modulates the gravity wave variances and its frequency appears to shift accordingly [ABSTRACT FROM AUTHOR]

Gravity waves (GWs) and their associated multi‐scale dynamics are known to play fundamental roles in energy and momentum transport and deposition processes throughout the atmosphere. We describe an initial machine learning model—the Compressible Atmosphere Model Network (CAM‐Net). CAM‐Net is trained on high‐resolution simulations by the state‐of‐the‐art model Complex Geometry Compressible Atmosphere Model (CGCAM). Two initial applications to a Kelvin‐Helmholtz instability source and mountain wave generation, propagation, breaking, and Secondary GW (SGW) generation in two wind environments are described here. Results show that CAM‐Net can capture the key 2‐D dynamics modeled by CGCAM with high precision. Spectral characteristics of primary and SGWs estimated by CAM‐Net agree well with those from CGCAM. Our results show that CAM‐Net can achieve a several order‐of‐magnitude acceleration relative to CGCAM without sacrificing accuracy and suggests a potential for machine learning to enable efficient and accurate descriptions of primary and secondary GWs in global atmospheric models. Plain Language Summary: Atmospheric gravity waves (GWs) are well described by the Navier‐Stokes equations, but solving these equations including small scale remains daunting, limited by the very high computational cost of resolving the smallest spatial‐temporal features in a global context. To address this challenge, we developed a machine learning model called CAM‐Net. Our model demonstrates that neural networks can be trained on high‐resolution compressible atmospheric model data and then used to simulate GW evolution. Importantly, initial results show that using such trained model can achieve computational savings of >1,000 times compared to a physics‐based simulation while still achieve highly accurate results. These findings are exciting, as they suggest that CAM‐Net can overcome the limitations of current GW parameterizations and provide a promising avenue for studying the effects of sub‐grid‐scale processes in atmospheric science and properly incorporating them in global models. The development of CAM‐Net opens up major new opportunities for improving effective model resolution, accuracy, and efficiency. Key Points: A machine learning model (CAM‐Net) tailored for nonlinear Gravity wave (GW) simulations is developedCAM‐Net can achieve a several order‐of‐magnitude acceleration relative to physics‐based model without sacrificing accuracyCAM‐Net opens a new window to improve the parameterization of primary and secondary GWs in the global atmospheric models [ABSTRACT FROM AUTHOR]

On 15 January 2022, the Hunga volcano produced a massive explosion that generated perturbations in the entire atmosphere. Nonetheless, signatures in the mesosphere and lower thermosphere (MLT) have been challenging to identify. We report MLT horizontal wind perturbations using three multistatic specular meteor radars on the west side of South America (spanning more than 3,000 km). The most notorious signal is an exceptional solitary wave with a large vertical wavelength observed around 18 UT at all three sites, with an amplitude of ∼50 m/s mainly in the westward direction. Using a customized analysis, the wave is characterized as traveling at ∼200 m/s, with a period of ∼2 hr and a horizontal wavelength of ∼1,440 km in the longitudinal direction, away from the source. The perturbation is consistent with an L1 Lamb wave mode. The signal's timing coincides with the arrival time of the tsunami triggered by the eruption. Plain Language Summary: The eruption of the Hunga volcano in January 2022 had a widespread impact on the atmosphere, affecting various layers. We describe a perturbation in horizontal winds caused by the event, which was observed over the west coast of South America by three different meteor radar systems separated by more than 3,000 km between them. The perturbation behaved similarly in the altitude range of 80–100 km, and the wave parameters observed were consistent with high‐order Lamb wave solutions from simulations carried out using the Whole Atmosphere Community Climate Model with thermosphere/ionosphere extension. This finding complements other studies that have explored the impacts of the eruption on different atmospheric levels. Overall, this study provides valuable insights into the complex and far‐reaching effects of volcanic eruptions on the atmosphere. Key Points: Hunga eruption generated extreme horizontal wind perturbations at 80–100 km of altitude over South AmericaThe signal was detected almost simultaneously by three multistatic meteor radar systems spanning more than 3,000 kmThe perturbation had a period of ∼2 hr, a horizontal phase velocity of ∼200 m/s, and a horizontal wavelength of ∼1,440 km [ABSTRACT FROM AUTHOR]

Fritts, Wang, Lund, and Thorpe (2022, https://doi.org/10.1017/jfm.2021.1085) and Fritts, Wang, Thorpe, and Lund (2022, https://doi.org/10.1017/jfm.2021.1086) described a 3‐dimensional direct numerical simulation of interacting Kelvin‐Helmholtz instability (KHI) billows and resulting tube and knot (T&K) dynamics that arise at a stratified shear layer defined by an idealized, large‐amplitude inertia‐gravity wave. Using similar initial conditions, we performed a high‐resolution compressible simulation to explore the emission of GWs by these dynamics. The simulation confirms that such shear can induce strong KHI with large horizontal scales and billow depths that readily emit GWs having high frequencies, small horizontal wavelengths, and large vertical group velocities. The density‐weighted amplitudes of GWs reveal "fishbone" structures in vertical cross sections above and below the KHI source. Our results reveal that KHI, and their associated T&K dynamics, may be an important additional source of high‐frequency, small‐scale GWs at higher altitudes. Plain Language Summary: A high‐resolution compressible atmosphere model is applied to explore gravity wave emissions from a shear with Kelvin‐Helmholtz Instability initiated by a three‐dimensional, small‐amplitude initial noise field in velocity, such as must always occur in the atmosphere. Simulations reveal that a wind shear with an amplitude of 65 m/s and a half‐width of 0.8 km can induce strong Kelvin‐Helmholtz Instability dynamics, which can further emit gravity waves having periods of ∼10–20 min and horizontal wavelengths of ∼20 km. These gravity waves have high frequencies and small horizontal scales. The density‐weighted amplitudes of gravity waves created a "fishbone" structure in z‐t plots due to upward‐ and downward‐propagating gravity waves arising at the layer of Kelvin‐Helmholtz Instability. Our results demonstrate that Kelvin‐Helmholtz Instability and the resulting instability dynamics may be a prevalent source of gravity waves impacting higher altitudes. Key Points: Kelvin‐Helmholtz instabilities (KHI) generated by a stratified shear layer induce gravity waves (GWs) that penetrate to high altitudesKHI‐radiated GWs may be a major influence of near‐stationary shears at high altitudes to which they cannot readily propagate directlyGWs generated by KHI can account for "fishbone" structures seen in vertical profiling [ABSTRACT FROM AUTHOR]

Combining observations from three meteor radars in the Northern Hemisphere (NH) and a meteor radar in the Southern Hemisphere (SH) and reanalysis data, we present successive wavenumbers 3 and 4 (W3 and W4) quasi 2 day wave activities in austral summer. In the mesosphere and lower thermosphere, the wave exhibits two burst activities. The W3 dominates the first burst, while the W4 is the predominate mode in the second burst. The mode transition arises in the late January and is completed around the end of January. The W3 and W4 have the nearly same dominate period of about 46 hr and vertical wavelengths of 110 km in the SH and about 55–65 km in the NH, and the similar latitude and altitude distributions in the zonal and meridional winds and temperature, except stronger magnitude and farther extension in the NH for the W3. The analysis indicates that the unstable regions of the summer jets in the lower mesosphere and stratopause region have the boundaries which toward lower latitudes are largely consistent with the critical layers, and Eliassen‐Palm (EP) fluxes of the W3 and W4 increase rapidly near the unstable regions. This demonstrates that both the W3 and W4 originate from the jet instabilities. Nevertheless, the EP flux of the W3 shows a stronger transfer across the hemispheres than that of the W4. The W3 and W4 have the same period and vertical scale, which is different from previous reports. Key Points: W3 and W4 dominate the first and second bursts of quasi 2‐day wave respectively and transition from W3 to W4 is completed around the end of JanuaryW3 and W4 have nearly same dominant period and vertical wavelengths and similar latitude and altitude distributions in two hemispheresW3 and W4 originate from instabilities of summer easterly jets in the lower mesosphere and stratopause region [ABSTRACT FROM AUTHOR]

We report a detailed analysis of atmospheric stabilities in the mesopause region (85–100 km) based on over 2,000 hr of high‐resolution temperature and horizontal wind measurements made with a Na lidar at the Andes Lidar Observatory, located in Cerro Pachón, Chile (30.25°S, 70.74°W). The square of Brunt–Väisälä frequency and the Richardson number are calculated, and occurrence probabilities of convective and dynamic instabilities are derived. An approach to assess the biases due to measurement uncertainties is used to obtain more accurate occurrence probabilities. The overall occurrence probabilities of convective and dynamic instabilities are 2.7% and 6.7%, respectively. High‐, medium‐, and low‐ frequency gravity wave (GW) contributions to these probabilities are isolated, which show that the high‐frequency GWs contribute most but simultaneous presence of high‐ and medium frequency GWs is much more effective in increasing the probabilities. Convective and dynamic instabilities are mainly generated because of the joint effect of different‐scale GWs. Isolated parts of GWs have much less contribution to the generation of both convective and dynamic instabilities. The dynamic instability is mainly contributed from less stable stratification and large wind shear together. Either factor can lead to about 15% of dynamic instability. Key Points: Contributions from buoyancy frequency and wind shear to Richardson number are presentedBiases of the instability probabilities due to photon noise have been analyzedGravity waves with different frequency effects the generation of dynamical and convective instabilities [ABSTRACT FROM AUTHOR]

A compressible numerical model is applied for three‐dimensional (3‐D) gravity wave (GW) packets undergoing momentum deposition, self‐acceleration (SA), breaking, and secondary GW (SGW) generation in the presence of highly‐structured environments enabling thermal and/or Doppler ducts, such as a mesospheric inversion layer (MIL), tidal wind (TW), or combination of MIL and TW. Simulations reveal that ducts can strongly modulate GW dynamics. Responses modeled here include reflection, trapping, suppressed transmission, strong local instabilities, reduced SGW generations, higher altitude SGW responses, and induced large‐scale flows. Instabilities that arise in ducts experience strong dissipation after they emerge, while trapped smaller‐amplitude and smaller‐scale GWs can survive in ducts to much later times. Additionally, GW breaking and its associated dynamics enhance the local wind along the GW propagation direction in the ducts, and yield layering in the wind field. However, these dynamics do not yield significant heat transport in the ducts. The failure of GW breaking to induce stratified layers in the temperature field suggests that such heat transport might not be as strong as previously assumed or inferred from observations and theoretical assessments. The present numerical simulations confirm previous finding that MIL generation may not be caused by the breaking of a transient high‐frequency GW packet alone. Key Points: 3‐D gravity wave (GW) packets exhibit complex dynamics in the presence of highly structured wind and temperature environmentsResponses include reflection, trapping, transmission, reduced secondary GWs, and induced strong local flow accelerationsBreaking of a transient high‐frequency GW packet may not provide sufficient heating rates for the generation of mesospheric inversion layers [ABSTRACT FROM AUTHOR]

The long‐term statistical characteristics of high‐frequency quasi‐monochromatic gravity waves are presented using multi‐year airglow images observed at Andes Lidar Observatory (ALO, 30.3°S, 70.7°W) in northern Chile. The distribution of primary gravity wave parameters including horizontal wavelength, vertical wavelength, intrinsic wave speed, and intrinsic wave period are obtained and are in the ranges of 20–30 km, 15–25 km, 50–100 m s−1, and 5–10 min, respectively. The duration of persistent gravity wave events captured by the imager approximately follows an exponential distribution with an average duration of 7–9 min. The waves tend to propagate against the local background winds and show evidence of seasonal variations. In austral winter (May–August), the observed wave occurrence frequency is higher, and preferential wave propagation is equator‐ward. In austral summer (November–February), the wave occurrence frequency is lower, and the waves mostly propagate pole‐ward. Critical‐layer filtering plays a moderate role in determining the preferential propagation direction in certain months, especially for waves with a smaller observed phase speed (less than typical background winds). The observed wave occurrence and preferential propagation direction are related to the locations of convection activities nearby and their relative distance to ALO. However, direct wave generations are less likely due to the large distance between the ALO and convective sources. Other mechanisms such as secondary wave generation and possible ducted propagation should be considered. The estimated mean momentum fluxes have typical values of a few m2 s−2. Plain Language Summary: The area around the Andes contains hot spots of gravity waves due to surrounding geographical conditions, such as oceans, rainforests, and mountains. This study presents a statistical analysis of gravity waves with a shorter period based on 6‐year airglow emissions observations in the mesosphere over the Andes. Wave information of many gravity waves was extracted from the airglow emission images. The preferential wave propagation direction and wave occurrence frequency are found to be highly correlated with the convection activities nearby, especially during solstice seasons. In austral summer, waves might originate from the Amazon Basin through a long‐range ducted propagation, resulting in a southwestward propagation tendency. These waves would alter the atmospheric winds when they dissipate and deposit the momentum into the atmosphere. This study expands the understanding of gravity waves hot spots over the Andes to the upper atmosphere. Key Points: High‐frequency gravity waves were observed near the mesopause over the Andes with duration following an exponential distributionPreferential propagation direction of the waves shows seasonal dependence, southwestward in austral summer and equator‐ward in winterThe observed waves are likely associated with convections, playing an important role in shaping the observed wave directionality [ABSTRACT FROM AUTHOR]

The middle atmosphere over South America, particularly above the Andes mountain range, is known as one of the most dynamically active regions in the world. Previous studies have investigated wave dynamics at mesosphere and lower thermosphere (MLT) altitudes within this region, but only a handful of them have made use of continuous measurements provided by specular meteor radars (SMRs). Furthermore, it was only until recently that MLT horizontal wind gradients were estimated for the first time using Spread Spectrum Interferometric Multistatic meteor radar Observing Network (SIMONe) Argentina, a multistatic SMR network located in southern Patagonia. By observing larger amounts of meteors from different viewing angles, multistatic SMRs allow, among others, for more reliable momentum flux estimates. In this work, we explore and compare the summer and winter MLT momentum flux dynamics at low and middle latitude sectors over the Andes mountain range. We also investigate the intermittency of the total momentum flux over these sectors. For this purpose, we analyze measurements provided by four multistatic SMR networks: SIMONe Peru (12°S), Chilean observation network de Meteor radars (30°S), SIMONe Argentina (49°S) and multi‐frequency Agile radar for investigations of the atmosphere‐southern Argentina agile meteor radar (54°S). We find that the momentum flux dynamics can change considerably over distances of only a few hundred km (e.g., southern Argentina). On the other hand, the contributions of large momentum fluxes to the total flux can be similar between regions separated by thousands of km (e.g., between Peru and southern Argentina). Key Points: First latitudinal comparison of mesosphere and lower thermosphere momentum fluxes along the Andes mountain range28‐day mean momentum flux dynamics vary depending on the latitude and the seasonTotal momentum flux distributions are well represented by log‐normal functions, with parameters varying on location and season [ABSTRACT FROM AUTHOR]

By analyzing data recorded at the Andes Lidar Observatory in Cerro Pachon, Chile (30.3°S, 70.7°W) from May 2014 to July 2019, we investigated the fundamental features of three‐dimensional wind and temperature spectra. The vertical wavenumber spectral amplitudes of horizontal winds show obvious seasonal variations that are closely related to the seasonal variations in the source and background winds. The wavenumber spectral slopes of the horizontal winds are systematically less negative than −3, with mean values of −1.96 and −2.18 for zonal and meridional winds, respectively. The zonal and meridional wind frequency spectra have mean slopes of −1.37 and −1.56, respectively; these values are slightly less negative than −5/3. Moreover, the frequency spectral amplitudes show different seasonal variations from those of the wavenumber spectra, possibly because they correspond to different GW spectral components. The vertical wind has obviously different spectral features than the horizontal winds. The vertical wind spectra are notably shallower than the horizontal wind spectra, with mean slopes of −0.82 and −0.91 for the wavenumber and frequency spectra, respectively, departing evidently from those expected under linear instability theory (LIT). Although the vertical wind spectrum is almost always separable, the horizontal wind spectra are separable only at high frequencies. As the frequency increased, the horizontal wind wavenumber spectra become shallower and depart from the spectral slope expected under LIT, likely because high‐frequency GWs are not completely saturated. In general, our results do not support LIT. Key Points: The vertical wavenumber and frequency spectra amplitudes have different seasonal variations, likely due to their spectral componentsVertical wind has much shallower wavenumber and frequency spectra than horizontal winds, inconsistent with the linear instability theoryVertical wind spectrum is nearly separable at all observed frequencies; horizontal wind spectra are separable only at high frequencies [ABSTRACT FROM AUTHOR]

Regeneration of skeletal muscle after volumetric injury is thought to be impaired by a dysregulated immune microenvironment that hinders endogenous repair mechanisms. Such defects result in fatty infiltration, tissue scarring, chronic inflammation, and debilitating functional deficits. Here, we evaluated the key cellular processes driving dysregulation in the injury niche through localized modulation of sphingosine‐1‐phosphate (S1P) receptor signaling. We employ dimensionality reduction and pseudotime analysis on single cell cytometry data to reveal heterogeneous immune cell subsets infiltrating preclinical muscle defects due to S1P receptor inhibition. We show that global knockout of S1P receptor 3 (S1PR3) is marked by an increase of muscle stem cells within injured tissue, a reduction in classically activated relative to alternatively activated macrophages, and increased bridging of regenerating myofibers across the defect. We found that local S1PR3 antagonism via nanofiber delivery of VPC01091 replicated key features of pseudotime immune cell recruitment dynamics and enhanced regeneration characteristic of global S1PR3 knockout. Our results indicate that local S1P receptor modulation may provide an effective immunotherapy for promoting a proreparative environment leading to improved regeneration following muscle injury. [ABSTRACT FROM AUTHOR]

Based on observations from lidar at Andes, we study the features of gravity wave activities and their spectra in the mesosphere and lower thermosphere (MLT). Case analysis shows that a quasimonochromatic inertia-gravity wave (IGW) dominates the perturbation fields, with clearly downward phase progression in the wind and temperature fields. Statistical investigation shows that the dominant waves in the MLT over Andes have the typical temporal and spatial scales of IGWs and show the preferential propagation in the meridional direction relative to in the zonal direction. The preferential propagation direction causes larger spectral peak and steeper spectral slope in the meridional wind as compared to the zonal counterpart. The 27-night observations indicate that the frequency (vertical wavenumber) spectrum has the slopes of about -1.4 (-1.5), -1.7 (-2.0), and -2.3 (-2.6) in the zonal wind, meridional wind, and relative temperature perturbations, more or less deviated from the universal spectral index of -5/3 (-3), respectively. The vertical wind has a steeper spectral tail in both the frequency and wavenumber spectra, which is different from the other three components. In the saturated spectrum region, the frequency and vertical wavenumber spectra have the slopes of -0.4 and -1.1 in the vertical wind, which are much shallower than those in the zonal and meridional winds, respectively. In the spectral tail region, the frequency and wavenumber spectrum slopes of -2.2 and -3.5 are far steeper relative to their saturated spectrum slopes. This suggests that the vertical wind should obey the different spectral laws from the horizontal winds. [ABSTRACT FROM AUTHOR]

Vertical energy transports due to dissipating gravity waves in the mesopause region (85–100 km) are analyzed using over 400 h of observational data obtained from a narrow‐band sodium wind‐temperature lidar located at Andes Lidar Observatory (ALO), Cerro Pachón (30.25°S, 70.73°W), Chile. Sensible heat flux is directly estimated using measured temperature and vertical wind; energy flux is estimated from the vertical wavenumber and frequency spectra of temperature perturbations; and enthalpy flux is derived based on its relationship with sensible heat and energy fluxes. Sensible heat flux is mostly downward throughout the region. Enthalpy flux exhibits an annual oscillation with maximum downward transport in July above 90 km. The dominant feature of energy flux is the exponential decrease from 10−2 to 10−4 W m−2 with the altitude increases from 85 to 100 km and is larger during austral winter. The annual mean thermal diffusivity inferred from enthalpy flux decreases from 303 m2 s−1 at 85 km to minimum 221 m2 s−1 at 90 km then increases to 350 m2 s−1 at 99 km. Results also show that shorter period gravity waves tend to dissipate at higher altitudes and generate more heat transport. The averaged vertical group velocities for high, medium, and low frequency waves are 4.15 m s−1, 1.15 m s−1, and 0.70 m s−1, respectively. Gravity wave heat transport brings significant cooling in the mesopause region at an average cooling rate of 6.7 ± 1.1 K per day. Key Points: Seasonal variation of gravity wave vertical fluxes are calculated with long‐term lidar dataEnergy flux is estimated through power spectra of temperature perturbationContributions of gravity waves with different periods to the vertical fluxes are investigated [ABSTRACT FROM AUTHOR]

The extension of the neutral sodium (Na) layer into the thermosphere (up to 170 km) has recently been observed at low and high latitudes using a Na lidar. However, the geophysical mechanisms and implications of its formation are currently unknown. In this study, we conduct an advanced two‐dimensional numerical simulation of the Na and Na+ variations in the E and F regions at low latitudes. The numerical simulations are used to investigate the contributions of the electromagnetic force, neutral wind, diffusion, and gravity. The simulations lead to three major findings. First, Na+ in the subtropical region of the geomagnetic equator acts as the major reservoir of the neutral sodium, and its distribution during nighttime is mostly below 200 km due to the combined effect of the vertical component of the E→×B→ drift and Coulomb‐induced drift. Second, we find that the fountain effect has little influence on the behavior of Na in the nighttime. Third, the probable explanation for the frequent generation of the thermospheric sodium layer during spring equinox at Cerro Pachón, Chile is attributed to the large vertical neutral transport generated by large vertical wind perturbations of unknown origin, with a magnitude exceeding 10 m/s that is closely associated with the semidiurnal tide. Key Points: Fountain effect does not have much influences on the structure of Na over subtropics region of geomagnetic equator during nightThe thermospheric Na layer observed over Cerro Pachón, Chile is probably formed due to the large vertical wind perturbationThe large vertical wind perturbation that may generate thermospheric Na layer is closely associated with semidiurnal tide [ABSTRACT FROM AUTHOR]

Dissipating waves contribute to vertical mixing of the atmosphere, alter molecular and eddy diffusion, and induce chemical transport of reactive species. These processes induce strong vertical transport of atmospheric constituents in regions where wave dissipation is significant. The effective wave diffusivity is proportional to the Stokes drift velocity imparted by the spectrum of vertically propagating waves, which is related to the vertical heat and wave energy fluxes. Because the heat flux cannot be derived from wave parameterization schemes employed in most atmospheric models, wave‐driven constituent transport has not been fully incorporated. However, we show in this paper that wave diffusivity can also be expressed in terms of the eddy diffusivity and variances of the temperature and lapse rate fluctuations, quantities that are readily derived from many wave parameterizations. The theory is in good agreement with lidar measurements of heat fluxes in the mesopause region. Total dynamical diffusivity associated with dissipating waves and turbulence can exceed 300 m2/s near the mesopause. Key Points: Dissipating waves induce strong vertical transport of atmospheric species, which has not been fully incorporated in global modelsWave‐driven constituent transport can be predicted in terms of quantities that are readily derived from many wave parameterization schemesTransport predictions compare favorably with observations of the mesopause region at midlatitudes [ABSTRACT FROM AUTHOR]

In order to understand the characteristics of long‐lasting "C‐type" structure in the Sodium (Na) lidargram, six cases from different observational locations have been analyzed. The Na lidargram, collected from low‐, middle‐, and high‐latitude sites, show long lifetime of the C‐type structures which is believed to be the manifestation of Kelvin‐Helmholtz (KH) billows in the Mesosphere and Lower Thermosphere (MLT) region. In order to explore the characteristics of the long‐lasting C‐type structures, the altitude profile of square of Brunt‐Väisälä frequency in the MLT region has been derived using the temperature profile collected from the Na lidar instruments and the SABER instrument onboard TIMED satellite. It is found to be positive in the C‐type structure region for all the six cases which indicates that the regions are convectively stable. Simultaneous wind measurements, which allowed us to calculate the Richardson numbers and Reynolds numbers for three cases, suggest that the regions where the C‐type structure appeared were dynamically stable and nonturbulent. This paper brings out a hypothesis wherein the low temperature can increase the magnitude of the Prandtl number and convectively stable atmospheric region can cause the magnitude of Reynolds number to decrease. As a consequence, the remnant of previously generated KH billows in nearly "frozen‐in" condition can be advected through this conducive region to a different location by the background wind where they can sustain for a long time without much deformation. These long‐lived KH billows in the MLT region will eventually manifest the long‐lasting C‐type structures in the Na lidargram. Key Points: The stability of KH billows in the MLT region on Reynold number and Prandtl number on long‐lasting "C‐type" structure in the Na lidargramLow temperature can increase magnitude of Prandtl number and convectively stable atmosphere can decrease the magnitude of Reynolds numberThis conducive atmosphere is responsible for the long lifetime of the remnant of previously generated KH billows in the MLT region [ABSTRACT FROM AUTHOR]

Objective: Emotional distress (ED) is an under-diagnosed problem in cancer patients and over the last decade a number of national guidelines have recommended an assessment and management model based on appropriate health professional response to a hierarchy of patient need. This study explores the views of cancer professionals regarding their current roles and responsibilities in the detection and management of ED, use of screening tools and access to expert psychological support. Methods: Interviews with 23 professionals were conducted [6 clinical nurse specialists (CNS), 8 oncologists, 4 surgeons and 5 ward sisters] from hospitals in Yorkshire, UK. Data were evaluated using framework analysis. Results: Detection of ED was seen to be the responsibility of the whole cancer team though nurses, particularly CNSs, are heavily depended upon to assess and manage distress. Experience of screening tools was limited and a number of reservations were expressed about routine implementation. A wide range of services are used to support distressed patients but a lack of referral guidance and access to specialist psychological care were reported to be a significant barrier to effective management. Conclusions: Cancer professionals describe working within the fundamental principles of the guidance frameworks; however, access to specialist support do not appear to meet recommendations, leaving the CNS with considerable responsibility for the detection and management of ED. Support for ED may be improved by the introduction of routine screening along with appropriate training and implementation of referral guidelines to assist professionals in accessing specialist psychology services. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]