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We present the first continuous observations of three‐dimensional spatially resolved wind fields and atmospheric motions in the mesosphere and lower thermosphere in the mid‐latitudes of the Northern Hemisphere. Our observations were performed during a 19‐month campaign from January 2022 to July 2023 and exploited the composite data from the first multistatic meteor radar system in China and an adjacent monostatic meteor radar. To retrieve the atmospheric kinetic properties, we introduce an improved volume velocity processing method including coordinate transformations and non‐linear constraints to minimize errors. The vertical winds are estimated separately from the iteration of the horizontal divergence to avoid potential biases or contamination from the horizontal winds. The winds and air motions show annual/semiannual variation characteristics within certain altitudes, usually more variable around the equinoxes. The vertical winds are basically within the magnitude of 1 m/s and are upward as expected at the mesopause during the summer, which corresponds to the adiabatic cooling. Plain Language Summary: The mesosphere and lower thermosphere (MLT) is a coupling region between the upper and lower atmosphere and contains various dynamic and chemical processes. Meteor is a convenient and reliable tool for MLT mean horizontal wind observations. Multistatic meteor radars can investigate the more sophisticated dynamic properties of the MLT winds from different viewing angles. In this work, for the first time, we reported 3‐dimensional spatially resolved MLT winds and atmospheric motions in the mid‐latitudes of the Northern Hemisphere. To minimize errors in the retrieved winds, we proposed improvements to the volume velocity processing method by performing coordinate transformations and adding non‐linear constraints. The mean winds and air motions show annual/semiannual variations and are more variable near the equinoxes. Due to the small value of the vertical wind, we estimated it from the integration of the horizontal divergence and obtained a reasonable range of less than 1 m/s. The upwelling in the summer mesopause corresponds to the adiabatic cooling. Key Points: The first continuous observations of 3‐D spatially resolved winds and air motions in the Northern Hemisphere mid‐latitudes are reportedA newly developed volume velocity processing method including coordinate transformations and non‐linear constraints is introducedThe vertical wind is basically less than 1 m/s and is upward at the mesopause during summer, corresponding to the adiabatic cooling [ABSTRACT FROM AUTHOR]

Wind shear has important implications for Kelvin–Helmholtz instability (KHI) and gravity waves (GWs) in the mesosphere–lower thermosphere (MLT) region where its momentum transport process is dominated by short-period (<1 h) GWs. However, the sub-hourly variation in wind shear is still not well quantified. This study aims to improve current understanding of vertical wind shear by analyzing multi-year meteor radar measurements at the Mohe (MH, 53.5°N, 122.3°E), Beijing (BJ, 40.3 ° N , 116.2 ° E ), Wuhan (WH, 30.5 ° N , 114.6 ° E ), and Fuke (FK, 19.5°N, 109.1°E) stations in China. The wind field is estimated by a new algorithm, e.g., the damped least squares fitting. Taking the wind shear estimated by normal products as a criterion, the shear produced by the new algorithm has more statistical convergence as compared to the traditional algorithm, e.g., the least squares fitting. Therefore, we argue that the 10 min DLSA wind probably produces a more reasonable vertical shear. Both intensive wind shears and GW kinetic energy can be simultaneously captured during the 0600–1600 UTs of May at MH and during the 1300–2400 UTs of March at FK, possibly implying that the up-propagation of GWs could contribute to the production of large wind shears. The sub-hourly variation in wind shears is potentially valuable for understanding the interrelationship between shear (or KHI) and GWs. [ABSTRACT FROM AUTHOR]

This paper investigates the ionospheric responses to the February and April 2023 geomagnetic storms using Total Electron Content (TEC) derived from the 10 Global Navigation Satellite System (GNSS) stations at the transition of low to mid-latitudes (Approx. 20 ∼ 30°N) across different longitudes in the American and Asian sectors. Significant variations in both sectors were recorded during the recovery phase and were mainly attributed to the Prompt Penetration Electric Field (PPEF), Disturbance Dynamo Electric Field (DDEF) and the thermospheric neutral composition changes as O/N 2 depletion. Similarly, the American and Asian sectors showed TEC enhancements, primarily attributed to the PPEF, during the main phase of the April storm. The negative TEC variations during the recovery phase were observed due to the DDEF and changes in O/N 2. In the Asian sector, positive and negative variations were recorded over Pakistan and China, respectively, during the main phase of the April storm. These variations resulted in high and low concentrations of the O/N 2 ratio due to Magnetosphere-Ionosphere-Thermosphere coupling. [ABSTRACT FROM AUTHOR]

Fabry Perot interferometer (FPI) is an essential ground‐based passive optical observation device to detect middle and upper atmospheric information. Three FPIs are located at Kunming (103.8°E, 25.6°N), Xinglong (117.4°E, 40.2°N), and Mohe (122.3°E, 53.5°N), China. The diurnal and annual variation of night wind at 87, 97, and 250 km are investigated from 2019 to 2021, compared to Horizontal Wind Model 14 (HWM14) to check the prediction accuracy for the local wind field. Our results are as follows: (a) At 87 km, the zonal winds are similar in Kunming and Xinglong, but the meridional winds are generally stronger in Kunming. The zonal and meridional winds in both locations are dominated by semidiurnal variations. (b) At 97 km, the duration of semidiurnal variation of zonal winds and diurnal variation of meridional winds in Kunming is long, which is opposite to that of Xinglong. (c) At 250 km, the wind speed increases with latitude for both zonal and meridional winds, which are both dominated by diurnal variations for all the three sites. Unlike 87 and 97 km, the entire wind field at 250 km is dominated by annual variation, except for a significant semiannual variation at midnight in Mohe. (d) Overall, the HWM14 predictions are stronger than the FPI measurements at peak wind speeds and similar at 87 and 97 km, which surpasses the performance at 250 km. Especially at 250 km, the model results are worse for the zonal winds of Kunming and the meridional winds of Mohe. These results will help to understand the wind field in the middle and upper atmosphere and improve the accuracy of the model. Key Points: Characteristics of mesospheric and thermospheric winds over the three stations are studied using three FPIs and compared with HWM14The winds over the three observatories showed latitudinal variation characteristicsOverall, HWM14 predicts stronger winds than FPI measurements [ABSTRACT FROM AUTHOR]

The Chinese Meridian Project (CMP) is devoted to establishing a comprehensive ground-based monitoring network for China's space weather research. CMP is a major national science and technology infrastructure project with the participation of more than 10 research institutions and universities led by the National Space Science Center of the Chinese Academy of Sciences. CMP is planned to be constructed in two phases: CMP phases I and II. The first phase (CMP-I) started construction in 2008 and completed in 2012, after which it entered the operation stage. The 10-year observation of CMP-I has made significant scientific discoveries and achievements in the research fields of the middle and upper atmospheric fluctuations, metal layers in the mesosphere and lower thermosphere, ionospheric disturbances and irregularities, geomagnetic disturbances, and influences of solar activity. The review summarizes the main observations and research achievements, space weather forecast modeling and methods based on CMP-I over the past 10 years, and presents a future extension perspective along with the construction of CMP-II. [ABSTRACT FROM AUTHOR]

In this article, high spatiotemporal resolution data obtained by the atmospheric density detector carried by China's APOD satellite are used to study the hemispheric asymmetry of thermospheric density. A detailed analysis is first performed on the dual magnetic storm event that occurred near the autumnal equinox on 8 September 2017. The results show that the enhancement ratio of atmospheric density in the southern polar region (SPR) on the duskside was approximately 1.33–1.65 times that of the northern polar region (NPR), demonstrating a strong hemispheric asymmetry of thermospheric atmospheric density response during the magnetic storm. However, the asymmetry response was smaller on the dawnside, suggesting that the hemispheric density response asymmetry is related to local time (LT). The energy injection in high-latitude regions increases local atmospheric density and forms traveling atmospheric disturbances (TADs). TADs can propagate to low-latitude regions over several hours and affect the global distribution of thermospheric atmospheric density. Similarly, the geomagnetic index fitting slope of SPR relative density difference is greater than that of NPR. The SuperDARN convection pattern indicates that the plasma convection velocity of SPR is significantly greater than that of NPR, indicating that joule heating caused by neutral friction of ions in the Southern Hemisphere may be stronger. Subsequently, an analysis of annual solar activity and seasons was carried out on the thermospheric NPR, SPR atmospheric density, and their differences from December 2015 to December 2020. The results show that thermospheric atmospheric density decreases overall as the number of sunspots decreases. The differences between the NPR and SPR atmospheric densities in the thermosphere exhibits a noticeable annual periodicity. The NPR and SPR atmospheric densities appear to have different distribution characteristics in different seasons. The NPR density peak is mainly in March or April. In particular, the "double-peak" phenomenon occurred in 2017, with peaks in March and September, while the most obvious feature of SPR atmospheric density is that its minimum value occurs in the summer months of June and July. This paper reveals the annual, seasonal, and magnetic storm response characteristics of the hemispheric asymmetry of thermospheric atmospheric density, which has significant implications for the study of multilayer energy coupling of the magnetosphere–ionosphere–thermosphere. [ABSTRACT FROM AUTHOR]

The total electron content (TEC) derived from ground‐based BeiDou geostationary orbit (GEO) satellite receivers lying on both sides of the eclipse path is used to study the ionospheric variations in southern China, particularly targeting eclipse‐induced gravity waves in the ionosphere during the annular solar eclipse on 21 June 2020. Eclipse‐induced gravity waves (GWs) signatures with periods of about 70 min, from wavelet analysis, were identified on both sides of TEC observations, which are most likely to be induced in the thermosphere. However, there were significant differences in the intensity of the gravity waves on both sides of the eclipse path, gravity waves are stronger on the northern side of the eclipse path than on the southern side. Moreover, a postponement of TEC depletion shows on the northern side of the eclipse path which is caused by the convergence effect of the wind field. And at the same obstruction rate, GWs possibly can slightly adjust the postponement of TEC depletion on a small scale. Key Points: The eclipse‐induced thermospheric gravity waves are observed by BeiDou‐geostationary orbit total electron content (TEC) on both sides of the solar eclipse pathGravity waves are stronger on the northern side of the eclipse path than that on the southern side due to convergence effectsThe gravity waves on the northern side may slightly contribute to the postponement of the TEC depletion on a small scale [ABSTRACT FROM AUTHOR]

Gravity waves (GWs) strongly affect atmospheric dynamics and photochemistry and the coupling between the troposphere, stratosphere, mesosphere, and thermosphere. In addition, GWs generated by strong disturbances in the troposphere (e.g. thunderstorms and typhoons) can affect the atmosphere of Earth from the troposphere to the thermosphere. However, the fundamental process of GW propagation from the troposphere to the thermosphere is poorly understood because it is challenging to constrain this process using observations. Moreover, GWs tend to dissipate rapidly in the thermosphere because the molecular diffusion increases exponentially with height. In this study, a double-layer airglow network was used to capture concentric GWs (CGWs) over China that were excited by Typhoon Chaba (2016). We used ERA5 reanalysis data and Multi-functional Transport Satellite-1R observations to quantitatively describe the propagation processes of typhoon-generated CGWs from the troposphere, through the stratosphere and mesosphere, to the thermosphere. We found that the CGWs in the mesopause region were generated directly by the typhoon in the troposphere. However, the backward-ray-tracing analysis suggested that CGWs in the thermosphere originated from the secondary waves generated by the dissipation of the CGW and/or nonlinear processes in the mesopause region. [ABSTRACT FROM AUTHOR]

Using the meteor radar data at the Mohe (53.5° N, 122.3° E) and Wuhan (30.5° N, 114.2° E) regions over China, this paper conducts a study on the diurnal and seasonal variation of high-frequency (within 2 h) gravity waves (GWs) activity in the mesosphere and the lower thermosphere (MLT). On the basis of the composite day analysis and Hocking's technique, the variance and momentum flux of the high-frequency GWs are derived from the radial velocities of individual meteor trails. Spectral results demonstrate that the high-frequency GWs activity shows 12 and 24 h periodicity, which may be due to the tidal modulation on the high-frequency GWs. The spectra of the variance and momentum flux also show 6 and 8 h periodicity. In addition to the diurnal variation, the high-frequency GWs activity shows the annual and semiannual oscillations. Additionally, the quasi-4-month oscillation is found at Mohe. [ABSTRACT FROM AUTHOR]

Using meteor radar measurements at Mohe (MH, 53.5°N, 122.3°E) and the reanalysis data from 2011 to 2020, the characteristics of intraseasonal oscillations (ISOs) in the mesosphere and lower thermosphere (MLT) region over MH are investigated for the first time. The radar observation shows a prominent ISO with periods of 40–60 days in the zonal wind during the 2015/2016 winter. The observed ISO is the strongest in the oscillation period of 30–60 days during nearly a decade of observation. The ISO amplitude reaches a maximum of 16 m/s at 90 km. The vertical structure indicates that intraseasonal variabilities in the lower mesosphere contribute to the ISO in the MLT region. By bandpassing the zonal wind obtained from the reanalysis data along 122.5°E at 52 km in the Northern Hemisphere with cutoff periods of 40 and 60 days, we show that ISOs in the tropical and mid‐latitude mesosphere are related to each other. Our results also indicate that the tropical mesospheric ISO and the tropospheric Madden‐Julian Oscillations (MJO) are highly correlated. Our analysis suggests that the MJO in the equatorial troposphere may contribute to the enhancement of the ISO in the MLT region over MH. Additionally, a very strong El Niño during the 2015/2016 winter was accompanied by the positive Indian Ocean Dipole, which confines the active MJO in phases 2‒4 for a long time. This may be the reason that in the oscillation period of 30–60 days, the ISO observed at MH is the strongest during almost a decade of observation. Key Points: A strong intraseasonal oscillation (ISO) with a period of 40–60 days is first observed in the mesosphere and lower thermosphere at MoheThe ISO observed at Mohe is likely associated with the equatorial Madden‐Julian Oscillations in the troposphereStrong El Niño and the positive Indian Ocean Dipole indices may contribute to the enhancement of the ISO at MH [ABSTRACT FROM AUTHOR]

We present an analysis of planetary‐scale oscillations during sudden stratospheric warming (SSW) events based on data obtained from a meteor radar located at Mohe (MH, 53.5°N, 122.3°E), the Aura satellite and Modern‐Era Retrospective analysis for Research and Applications, Version 2 data (MERRA2). The planetary‐scale oscillations in the mesosphere and lower thermosphere (MLT) region during eight SSW events from 2012 to 2019 have been statistically investigated. Our analysis reveals that the enhancement or the generation of westward propagating quasi 16‐day oscillation with wavenumber 1 (W1) is a common feature during SSWs over MH. A strong enhancement of the quasi 4‐day oscillation during the 2018/2019 SSW is captured by both radar and satellite observations. The amplified quasi 4‐day oscillation has a period of ~4.3 days in both meridional and zonal winds and with a wavenumber of W2 in the zonal component. Using the meteor radar and MERRA2 data, the vertical structure of the quasi 4‐day oscillation from the stratosphere to the lower thermosphere is derived. The upward propagating feature of the quasi 4‐day oscillation in the meridional component indicates that the oscillation is very likely generated in the lower mesosphere. The mesospheric zonal wind reversal after an elevated stratopause event is observed during the SSW, which results in a negative meridional gradient of the quasi‐geostrophic potential vorticity. Our results not only reveal that the amplified quasi 4‐day oscillation in the MLT region is associated with the 2018/2019 SSW but also suggest that the amplification is originally generated around 60 km due to barotropic/baroclinic instability and propagates upward to MLT region. Key Points: An enhancement of a quasi 4‐day oscillation is observed in the MLT region during the 2018/2019 SSW over MHThe enhanced quasi 4‐day oscillation during 2018/2019 SSW is originally generated from the lower mesosphereThe quasi 4‐day oscillation is likely generated by barotropic/baroclinic instability due to the large zonal wind reversal and the elevated stratopause during the SSW [ABSTRACT FROM AUTHOR]

NmF2 and hmF2 outputted by the latest International Reference Ionosphere (IRI-2016) model are compared with COSMIC (Constellation Observing System for Meteorology Ionosphere and Climate) radio occultation (RO) measurements during 2008―2014 over China. For both NmF2 and hmF2, the correlations between IRI-2016 model outputs and COSMIC RO measurements are higher during high solar activity years (2011―2014) than low solar activity years (2008―2010). During LT(local time) 12:00―14:00 of equinox months in low solar activity years, IRI-2016 model generally underestimates NmF2 and overestimates hmF2 at 30°N - 55°N, while overestimates NmF2 and underestimates hmF2 at 15°N - 30°N. Outputs based on IRI_CCIR and IRI_URSI model options both overestimate NmF2 and the overestimation is more distinct during low solar activity years than high solar activity years. As for hmF2, during low solar activity years, both IRI_CCIR and IRI_AMTB model outputs are higher than COSMIC RO observations for all the three seasons and the deviations of IRI_AMTB model outputs from RO measurements are the largest, especially in winter. It is recommended that IRI_CCIR model and IRI_Shubin model should be used for calculating NmF2 and hmF2 over China respectively. [ABSTRACT FROM AUTHOR]

A scanning Fabry-Perot interferometer (SFPI) was first developed and deployed at the Langfang near Space Environment Field Scientific Observation Station (39.38°N, 116.65°E) of the National Space Science Center, CAS. The instrument is designed to measure the mesospheric and thermospheric wind velocities using the atomic oxygen 557.7-nm and 630.0-nm emissions. Data from February 28 to March 3 and February 28 to March 15 in 2011 were chosen for case study and mean value study, respectively. The errors of the meridional and zonal winds are 6.5 and 7.5 m/s at 557.7-nm and at 630.0-nm, they are 7.1 and 6.6 m/s, respectively. During the whole experiment, the instrument has performed in good condition and provided high-quality data. The mean neutral wind data were consistent with that predicted by HWM07. Good agreement has been found in between the SFPI and a neighbor Meridian Project Fabry-Perot interferometer (MP FPI), with a corresponding coefficient ( r) larger than 80 %. In general, the scanning FPI meets the design goal, and it is a useful ground-based instrument for measuring mesospheric and thermospheric winds at middle latitudes and is able to provide high-quality data for future scientific studies. [ABSTRACT FROM AUTHOR]

A compact and cost-effective all-sky Fabry-Perot interferometer, which is produced by Wuhan University and used for the observation of the thermospheric neutral wind, was installed at Chinese Yellow River Station in Ny-Ålesund, Svalbard in November 2010, and continuously operated in last two winter seasons. The 92-day all-sky interference data acquired from November 1, 2011 to February 26, 2012 were collected to get the velocity of thermospheric neutral wind, which was calculated from the Doppler shift caused by the movement of oxygen atom at the different layers. The database was divided into two periods: (1) The OI 557.7 nm emission was observed from November 1, 2011 to January 12, 2012. Observations showed that the velocity of horizontal wind is normally less than ∼40 m/s on the quiet condition, and exceeded 100 m/s on the disturbed condition; and (2) the OI 630.0 nm emission was observed from January 13, 2012 to February 26, 2012. Observations showed that the velocity of horizontal wind is normally less than ∼200 m/s, and enhanced to over 300 m/s on strong magnetic activities. It shows that the velocities of meridional and zonal wind are more consistent with the velocities calculated from the model HWM07 at the higher layer, especially for the zonal direction at nightside auroral regions. Ion drag and Joule heating were the two important processes considered in the analysis of the relationship between the wind pattern and aurora, suggesting that wind speed would be increased and accelerated in the direction perpendicular to the aurora arc when the aurora activity becomes strong. [ABSTRACT FROM AUTHOR]

An all-sky airglow imager (ASAI) was installed at Xinglong, in northern China (40.2° N, 117.4° E) in November 2009 to study the morphology of atmospheric gravity waves (AGWs) in the mesosphere and lower thermosphere (MLT) region. Using one year of OH airglow imager data from December 2009 to November 2010, the characteristics of short-period AGWs are investigated and a yearlong AGW climatology in northern China is first ever reported. AGW occurrence frequency in summer and winter is higher than that in equinoctial months. Observed bands mainly have horizontal wavelengths from 10 to 35 km, observed periods from 4 to 14 min and observed horizontal phase speeds in the range of 30 to 60ms-1. Most of the bands propagate in the meridional direction. The propagation directions of the bands show a strong southwestward preference in winter, while almost all bands propagate northeastward in summer. Although the wind filtering in the middle atmosphere may control AGW propagations in the zonal direction, the non-uniform distribution of wave sources in the lower atmosphere may contribute to the anisotropy in the meridional direction in different seasons. Additionally, as an indication of local instability, the characteristics of ripples are also analyzed. It also shows seasonal variations, occurring more often in summer and winter and mainly moving westward in summer and eastward in winter. [ABSTRACT FROM AUTHOR]

A Fabry-Perot interferometer, funded by the Meridian Project in China, was deployed at the Xinglong station (40.2°N,117.4°E) of the National Astronomical Observatories in Hebei Province, China. The instrument has been operating since April 2010, measuring mesospheric and thermospheric winds. The first observational data of winds at three heights in the mesosphere and thermosphere were analyzed, demonstrating the capacity of this instrument to aid basic scientific research. The wavelengths of three airglow emissions were OH892.0, OI 557.7, and OI 630.0 nm, which corresponded to heights of 87, 98, and 250 km, respectively. Three 38-day data sets of horizontal winds, from April 5, 2010 to May 12, 2010, show clear day-to-day variations at the same height. The minimum and maximum meridional winds at heights of 87, 98, and 250 km were -16.5 to 8.7 m/s, -24.4 to 15.9 m/s, and -43.6 to 1.5 m/s. Measurements of zonal winds were -5.4 to 7.6 m/s, 2.3 to 23.0 m/s, and -22.6 to 49.3 m/s. The average data from the observations was consistent with the data from HWM93. The wind data at heights of 87 and 98 km suggest a semi-diurnal oscillation, clearly consistent with HWM93 results. Conversely there was a clear discrepancy between the observations and the model at 250 km. In general, this Fabry-Perot interferometer is a useful ground-based instrument for measuring mesospheric and thermospheric winds at middle latitudes. [ABSTRACT FROM AUTHOR]

Fuke (19.5°N, 109.1°E) meteor radar is the first radar of the low latitudes of China, which is used to detect the wind in the mesosphere and lower thermosphere. In this paper, by using the wind data near three months (1 February20 April, 2009), we first present the variation of the atmospheric diurnal tide, semidiurnal tide and mean wind in the height range 80100 km over the low latitudes of China. The results from our analysis are summarized below. During spring months, there are quite strong tides in the mesopause region of Fuke. The diurnal tidal amplitude is significantly larger than the amplitude of semidiurnal tide, and the maximum amplitude (about 100 m/s) of diurnal tide appear in the meridional wind. The vertical phases of both diurnal tide and semidiurnal tide propagate downward. In addition, the observed tides are compared with the linear tide model (Global Scale Wave Model, GSWM02), and the results show that Fuke diurnal tide agrees well with the model, but there are many differences be- tween Fuke semidiurnal tide and the results from model. [ABSTRACT FROM AUTHOR]