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Using a network of meteor radar observations, observational evidence of polar-to-tropical mesospheric coupling during the 2018 major sudden stratosphere warming (SSW) event in the northern hemisphere is presented. In the tropical lower mesosphere, a maximum zonal wind reversal (−24 m/s) is noted and compared with that identified in the extra-tropical regions. Moreover, a time delay in the wind reversal between the tropical/polar stations and the mid-latitudes is detected. A wide spectrum of waves with periods of 2 to 16 days and 30–60 days were observed. The wind reversal in the mesosphere is due to the propagation of dominant intra-seasonal oscillations (ISOs) of 30–60 days and the presence and superposition of 8-day period planetary waves (PWs). The ISO phase propagation is observed from high to low latitudes (60° N to 20° N) in contrast to the 8-day PW phase propagation, indicating the change in the meridional propagation of winds during SSW, hence the change in the meridional circulation. The superposition of dominant ISOs and weak 8-day PWs could be responsible for the delay of the wind reversal in the tropical mesosphere. Therefore, this study has strong implications for understanding the reversed (polar to tropical) mesospheric meridional circulation by considering the ISOs during SSW.

Using the ERA5 reanalysis and subseasonal to seasonal (S2S) real-time forecasts, this study explores the prediction of stratospheric disturbances in the 2022/23 winter, with a particular focus on the February 2023 major sudden stratospheric warming (SSW). Diagnostics of the annular mode index in the Northern Hemisphere (NAM) and the circulation anomalies reveals that stratosphere-troposphere coupling was enhanced in three periods and drove surface climate extremes. The February 2023 SSW was primarily driven by enhanced wave activities originating in the lower stratosphere. In the enhanced stratosphere-troposphere coupling periods, cold anomalies prevailed over Asian or/and North American midlatitudes, and compound wet-cold anomalies were evident in Northeastern Asia or/and North Atlantic. Snowstorm frequency increased along the midlatitude edge of the stratospheric and especially tropospheric polar vortices. Forecasts initialized around two lead time groups capture one SSW, one within the medium range time limit (1–2 weeks, true alarm), and the other (4–6 weeks, earlier alarm) far beyond the typical prediction skill of SSWs. During periods with strong stratosphere-troposphere coupling, the prediction skill of precipitation and snowstorms was higher with a more realistic spatial pattern than the weak coupling periods. Consistent with the reanalysis, the snowstorms were more active where the tropospheric polar vortex extended equatorward in models. However, models also tend to exaggerate the tropospheric impact of the SSW and forecast more snowstorms along the midlatitude vortex edge. Forecasts with a better SSW representation usually capture the cold over the North American continent during SSW occurrence and post-SSW periods.

This study investigates the day-to-day variability of equatorial plasma bubbles (EPBs) over the Atlantic–American region and their connections to atmospheric planetary waves during the sudden stratospheric warming (SSW) event of 2021. The investigation is conducted on the basis of the GOLD (Global Observations of the Limb and Disk) observations, the ICON (Ionospheric Connection Explorer) neutral wind dataset, ionosonde measurements, and simulations from the WACCM-X (Whole Atmosphere Community Climate Model with thermosphere–ionosphere eXtension). We found that the intensity of EPBs was notably reduced by 35% during the SSW compared with the non-SSW period. Furthermore, GOLD observations and ionosonde data show that significant quasi-6-day oscillation (Q6DO) was observed in both the intensity of EPBs and the localized growth rate of Rayleigh–Taylor (R-T) instability during the 2021 SSW event. The analysis of WACCM-X simulations and ICON neutral winds reveals that the Q6DO pattern coincided with an amplification of the quasi-6-day wave (Q6DW) in WACCM-X simulations and noticeable ∼6-day periodicity in ICON zonal winds. The combination of these multi-instrument observations and numerical simulations demonstrates that certain planetary waves like the Q6DW can significantly influence the day-to-day variability of EPBs, especially during the SSW period, through modulating the strength of prereversal enhancement and the growth rate of R-T instability via the wind-driven dynamo. These findings provide novel insights into the connection between atmospheric planetary waves and ionospheric EPBs.

Sudden Stratospheric Warmings (SSWs) are extreme polar atmospheric disturbances that significantly impact mid-latitude cold surges, but their early prediction remains a challenge for conventional numerical models. In this study, we propose a video prediction framework for SSW forecasting and introduce a Decoupled Spatiotemporal Memory Flow Network (DSMF-Net) to more effectively capture the dynamic evolution of stratospheric polar vortices. DSMF-Net separates spatial and temporal dependencies using specialized memory flow modules, enabling fine-grained modeling of vortex morphology and dynamic transitions. Experiments on representative SSW events from 2018 to 2021 show that DSMF-Net can reliably predict SSW occurrences up to 20 days in advance while accurately replicating the evolution of polar vortex structures. Compared to baseline models such as the Predictive Recurrent Neural Network (PredRNN) and Motion Recurrent Neural Network (MotionRNN), our method achieves consistent improvements across various metrics, with average gains of 10.5% in Mean Squared Error (MSE) and 6.4% in Mean Absolute Error (MAE) and a 0.7% increase in the Structural Similarity Index Measure (SSIM). These findings underscore the potential of deep video prediction frameworks to improve medium-range stratospheric forecasts and bridge the gap between data-driven models and atmospheric dynamics.

The semi-annual oscillation (SAO) dominates seasonal variability in the equatorial stratosphere and mesosphere. However, the seasonally dependent modulation of the SAO in the stratosphere (SSAO) and mesosphere (MSAO) by sudden stratospheric warmings (SSWs) in the Arctic has not been investigated in detail. In this study, we examine the seasonal evolution of the SAO during 16 major SSW events spanning 2004 to 2024 using the Japanese Atmospheric General Circulation Model for Upper Atmosphere Research Data Assimilation System Whole Neutral Atmosphere Re-analysis (JAWARA). Basic features of the SAO are well captured by JAWARA, as evidenced by the SSAO and MSAO appearing at around 50 km and 85 km, respectively. The different responses of the SAO to early and late winter SSWs are particularly strong during the Northern Hemisphere winter of 2023/24. Early winter SSWs tend to significantly intensify the westward SSAO, while late winter SSWs tend to weaken the eastward SSAO. Similarly, the eastward MSAO is amplified during early winter SSWs, whereas the westward MSAO is slightly weakened during late winter SSWs. The weak MSAO response is probably due to its smaller climatological magnitude. Modulation of the SAO by SSWs is related to meridional temperature changes during SSWs through the thermal wind balance. Our findings contribute to the understanding of coupling between the tropics and high latitudes, as well as interhemispheric coupling.

In this investigation, a comparison is presented between variations in temperature and ozone concentration at different altitude levels in the stratosphere for the Northern Hemisphere in the conditions of Sudden Stratospheric Warming (SSW) for the period January–March 2023. Spatial and altitude distribution of atmospheric characteristics derived from MERRA-2 are represented by their Fourier decomposition. A cross-correlation analysis between temperature and Total Ozone Column (TOC) is used. The longitudinal inhomogeneities in temperature, caused by stationary Planetary Waves with wavenumber 1 (SPW1), are found to be significant at altitudes around the maximum of the maximum of the ozone number density vertical distribution. As a result, it is established that the latitudinal and longitudinal distribution of TOC has a noticeable similarity with that of the temperature at altitudes close to the ozone concentration maximum. The results of correlation between temperature at individual stratospheric levels and ozone concentration show that (i) in the region around the ozone concentration maximum, the correlation is high and positive, (ii) at higher altitudes the sign of the correlation changes to negative (~37 km). The examination shows that the anomalous increases in TOC during SSW are due to an increase in ozone concentration in the altitudes between 10 km and 15 km.

The Microwave Limb Sounder (MLS) onboard the satellite Aura measures the temperature at 01:44 LST (after midnight) and at 13:44 LST after noon in the equatorial middle atmosphere. The signatures of the migrating solar diurnal tide (DW1) show up in the difference between the night-time and the daytime temperature profiles. We find a good agreement between the equatorial DW1 proxy of the Aura/MLS observations and the migrating diurnal tide estimated by the Global Scale Wave Model (GSWM) in March. The equatorial DW1 proxy is shown for the time interval from 2004 to 2021 reaching a temporal resolution of 1 day. The amplitude modulations of the DW1 proxy are correlated at several altitudes. There are indications of a semi-annual and annual oscillation (SAO and AO) of the DW1 proxy. The composite of 17 events of major sudden stratospheric warmings (SSWs) shows that the equatorial, mesospheric DW1 proxy is reduced by about 10% during the first week after the SSW event. The nodes and bellies of the equatorial DW1 proxy are shifted downward by about 1–2 km in the first week after the SSW. The 14 day-oscillation of the DW1 proxy in the equatorial mesosphere is enhanced from 25 days before the SSW onset to 5 days after the SSW onset.

The temporal variations in the sudden stratospheric warming (SSW) events in the winter stratosphere always coincide with the quasi-2-day wave (Q2DW) in the summer mesosphere, and the impact of SSW on Q2DW is interesting but still a mystery. Major SSWs occurred in both 2006 and 2009, while the Q2DW activity was quite different. The Second Modern Era-Retrospective Analysis for Research and Applications (MERRA-2) reanalysis dataset was used to comparatively analyze these two major SSW events and elucidate the reasons for the different Q2DW behaviors. We noticed that the summer easterly jet shows a large interannual variability. We conclude that the summer mesospheric Q2DWs are modulated by the winter SSW, whereas the modulation process is also affected by the interannual variability of the summer easterly flow itself. The effects of the SSW on the Q2DWs may differ from year to year due to the variability of the summer easterly flow itself, resulting in different anomalous Q2DW behavior. This conclusion may also be true for the interannual variability of other phenomena during the SSW period.

The total column ozone (TCO) at northern high latitudes is increased over a course of 1–2 months after a major sudden stratospheric warming as a consequence of enhanced ozone eddy transport and diffusive ozone fluxes. We analyzed ground-based measurements of TCO from Oslo, Andøya and Ny Ålesund from 2000 to 2020. During this time interval, 15 major sudden stratospheric warmings (SSWs) occurred. The observed TCO variations are in a good agreement with those of ECMWF Reanalysis v5 (ERA5), showing that TCO from ERA5 is reliable, even during dynamically active periods. ERA5 has the advantage that it has no data gaps during the polar night. We found that TCO was increased by up to 190 DU after the SSW of February 2010, over one month. The composite analysis of the 15 SSWs provided the result that TCO is increased on average by about 50 DU over one month after the central date of the SSW.

Processes behind Sudden Stratospheric Warming (SSW), which occurs more frequently in the northern hemispheric polar latitudes and its influence from the stratosphere to the upper atmosphere are well documented. However, physical processes associated with SSW, although it ensues rarely in the southern hemisphere (SH), have a strong influence on the background atmosphere from the stratosphere to the mesosphere and are poorly understood. Using a ground-based meteor radar, satellite-borne Microwave-Limb sounder, and Modern-Era Retrospective Analysis for Research and Applications observations, we identified cooling of Antarctic mesopause by 26 K in response to a 66 K warming in the polar stratosphere during the 2019 minor SSW in the SH. The observed cooling is attributed to the interplay between planetary waves, CO2 infrared cooling, and O3 depletion, rather than adiabatic cooling due to gravity waves alone during SSW. It is proposed that anthropogenic and other sources generating chemical tracers in the lower atmosphere have caused mesospheric cooling and could be transported from the lower atmosphere both vertically and meridionally through residual mean meridional circulation from the tropics. Therefore, our study for the first time demonstrates the effect of lower atmosphere chemistry on the polar mesosphere thermal structure during the 2019 SSW.