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Different meteor radars at low latitudes observed abnormally strong westward mesospheric winds around the March Equinox of 2023, that is, during the first phase of the Mesospheric Semiannual Oscillation. This event was the strongest of at least the last decade (2014–2023). The westward winds reached −80 m/s at 82 km of altitude in late March, and decreased with increasing altitude and latitude. A considerable increase in the diurnal tide amplitude was also observed. The Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension constrained to meteorological reanalysis up to ∼50 km does not capture the observed low‐latitude behavior. Additionally, these strong mesospheric winds developed during the westerly phase of the Quasi‐Biennial Oscillation, in accordance with the filtering mechanism of gravity waves in the stratosphere proposed in previous works. Finally, analysis of SABER temperatures strongly suggests that the breaking of the migrating diurnal tide may be the main driver of these strong winds. Plain Language Summary: Around the March Equinox of 2023, abnormally strong westward winds were observed in the low latitude region at altitudes between 80 and 100 km. This event was the strongest in at least the last decade. The westward winds reached a maximum amplitude of 80 m/s at 82 km of altitude during late March, and decreased with increasing altitude and latitude. A considerable increase in the amplitude of the diurnal tide was also observed. Simulations based on a whole atmosphere global circulation model constrained to meteorological reanalysis up to ∼50 km do not capture the observed behavior. Results based on specular meteor radar and satellite measurements suggest that the strong westward winds were driven by two main factors: the filtering mechanism of eastward‐propagating gravity waves in the stratosphere and the breaking of the diurnal tide at about 85 km of altitude. Key Points: Strong mesospheric westward winds during March equinox 2023 are observed globally at low latitudesThe westward winds reached a peak of −80 m/s at 82 km, the largest in the last ten years, accompanied by an enhancement of the diurnal tideThe breaking of the DW1 plays a role in generating these strong winds, in addition to the filtering of gravity waves in the stratosphere [ABSTRACT FROM AUTHOR]

The OI 630.0 nm airglow emission variability provides salient information on the dynamical changes taking place in the upper atmosphere at around 250 km. The emission rates vary with the changes in the ambient electron densities and the neutral constituents that are associated with these emissions. On several occasions, enhancements in these emissions are observed during post‐sunset hours, around 21 local time (LT), as measured from Mt. Abu (24.6°N, 72.7°E, 19°N Mag), a low‐latitude location at Indian longitudes. These enhancements occur following the typical monotonic decrease in emission intensity after sunset. The presence of poleward meridional wind preceded by cessation and reversal of equatorward wind at the post‐sunset hours was shown to be the cause for such observed emission enhancements in an earlier study. In this study, the cause of such reversal in meridional winds during post‐sunset hours has been investigated using the variation in electron densities and meridional winds simulated by the Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCM‐X), which also shows enhancements in electron densities similar to those observed in the post‐sunset OI 630.0 nm nightglow emissions, and simultaneous reversal in meridional winds as well. The amplitudes and phases of different components of tides obtained from WACCM‐X meridional winds reveal a significant contribution of higher‐order tides, especially, quarter‐diurnal tides, to the observed reversal in the meridional winds during post‐sunset hours. Plain Language Summary: Airglow emissions occur when atoms and molecules are deexcited after being excited by the solar energetic photons. OI 630.0 nm emissions (redline), which peak around 250 km and have a width of emissions around 100 km, act as tracers of that altitudinal region. Typically, the redline emissions decrease monotonically with time after sunset in the absence of solar radiation. However, on several occasions, an enhancement in redline emissions has been measured during post‐sunset hours over a low‐latitude location in the Indian longitudes. A previous study attributed this enhancement to the increase in electron density at the emission altitudes in the presence of poleward meridional winds, despite usually being equatorward during such times. The cause of such reversal in the equatorward winds and simultaneous increase in electron density at post‐sunset hours has been examined in this study using the variation in electron densities and winds simulated by the Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCM‐X). Remarkably, the simulation results also show enhancements in electron density similar to those observed in redline emissions. A strong tidal contribution, especially quarter‐diurnal component, has been found to be the cause behind the poleward reversal of meridional winds after sunset that causes an enhancement in redline emissions. Key Points: OI 630.0 nm post‐sunset emission enhancement over low‐latitudes is consistent with the presence of poleward meridional windsOn some days, WACCM‐X simulated meridional winds show a poleward wind reversal during post‐sunset hoursQuarter‐diurnal tides seem to play a significant role in reversing the meridional winds after sunset [ABSTRACT FROM AUTHOR]

Using the high-rate phase and amplitude scintillation data from FORMOSA7/COSMIC two mission and back-propagation method, we geolocate plasma irregularities that cause scintillations. The results of geolocation are compared with the NASA GOLD UV image data of plasma bubbles. The root mean square of the zonal difference between estimated locations of plasma irregularities and plasma bubbles are about 1.5° and for single intersection cases 0.5° in the magnetic longitude. The geolocation data provide more accurate scintillation location around the globe compared to assigning to the tangent point and is valuable space weather product, which will be routinely available for public use. [ABSTRACT FROM AUTHOR]

We provide observational evidence that the stability of the stratospheric Polar vortex (PV) is a significant driver of sub‐seasonal variability in the thermosphere during geomagnetically quiet times when the PV is anomalously strong or weak. We find strong positive correlations between the Northern Annular Mode (NAM) index and subseasonal (10–90 days) Global Observations of the Limb and Disk (GOLD) O/N2 perturbations at low to mid‐northern latitudes, with a largest value of +0.55 at ∼30.0°N when anomalously strong or weak (NAM >2.5 or < −2.1) vortex times are considered. Strong agreement for O/N2 variability and O/N2‐NAM correlations is found between GOLD observations and the Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCM‐X) simulations, which is then used to delineate the global distribution of O/N2‐NAM correlations. We find negative correlations between subseasonal variability in WACCM‐X O/N2 and NAM at high northern and southern latitudes (as large as −0.54 at ∼60.0°S during anomalous vortex times). These correlations suggest that PV driven upwelling at low latitudes is accompanied by corresponding downwelling at high latitudes in the lower thermosphere (∼80–120 km), which is confirmed using calculations of residual mean meridional circulation from WACCM‐X. Plain Language Summary: The stratospheric Polar vortex (PV) is a large‐scale circulation pattern that forms over the poles during the winter months, characterized by strong winds circulating in a counterclockwise direction in the Northern Hemisphere. It has previously been demonstrated that the breakup of the PV during sudden stratospheric warming (SSW) events has a large effect on the composition of the thermosphere. We demonstrate that the PV also influences thermospheric composition during non‐SSW times, including time periods in which the vortex is strong and times in which the vortex is inactive, by correlating observations of thermospheric O/N2 from the Global Observations of the Limb and Disk (GOLD) instrument with the Northern Annular Mode (NAM) index, which tracks the strength of the PV. We also find strong anti‐correlations between O/N2 and tidal amplitudes from model simulations, which suggests that the PV influences thermospheric composition via changes in mean circulation induced by the dissipation of enhanced waves. We use model simulations to confirm that the NAM‐O/N2 correlations reflect PV induced changes in global circulation patterns. We find that the PV causes enhanced upwelling at low latitudes and corresponding downwelling at high latitudes in both the northern and southern hemispheres. Key Points: Polar vortex (PV) activity is correlated with sub‐seasonal O/N2 variability during low Kp winter times at all latitudesWe observe enhanced O/N2 at high southern latitudes and reduced O/N2 at low latitudes in response to northern hemisphere PV activityPV‐O/N2 correlations are shown to reflect PV induced modulations of the residual mean meridional circulation (MMC) [ABSTRACT FROM AUTHOR]