Stratospheric Warming Research Articles

Unexpected Global Structure of Quasi‐4‐Day Wave With Westward Zonal Wavenumber 2 During the February 2023 Unusual Major Sudden Stratospheric Warming With Elevated Stratopause

AbstractDuring February 2023, the quasi‐4‐day wave (Q4DW) with westward zonal wavenumber 2 (W2) reached its largest amplitude of ∼400 m in the Southern Hemisphere (SH) geopotential height observations since 2004, which occurred simultaneously with an Arctic major sudden stratospheric warming (SSW) with an elevated stratopause (ES). However, the Q4DW‐W2 perturbations in the Northern Hemisphere (NH) were unexpectedly suppressed despite the unstable Arctic stratosphere and mesosphere during the 2023 ES‐SSW. Diagnostic analysis shows that the westward winds at ∼54°N–70°N in the upper stratosphere of ∼‐79 m/s during the 2023 ES‐SSW were the strongest during boreal winters over the past two decades, which benefited from the onset of a preceding minor SSW at the end of January. The strongest westward wind generated a wave geometry configuration of full reflection for Q4DW‐W2 in the NH, while the Q4DW‐W2 enhancement in the SH was induced by the in‐situ amplification of the surviving seeding perturbations.

Cyclone‐Like Features Within the Stratospheric Polar‐Night Vortex

AbstractDistinctive synoptic‐scale (∼1,500 km) flow features are identified within the core of the stratospheric polar‐night vortex at stratopause altitudes (∼50 km). Typically they comprise a train or a complex pattern of transient vortices, each characterized by enhanced values of potential vorticity (PV) and relative vorticity but with a weaker thermal signal. In the MERRA‐2 (and two other) reanalysis fields these cyclone‐like features persist for several days, occur episodically, and form essentially within the core of the polar‐night vortex itself. Their origin is plausibly linked to a form of barotropic instability associated with a radiatively‐induced annular ring of enhanced PV. Moreover, their ubiquity and dynamics carries possible implications for: ‐ the structure of the larger‐scale polar vortex and its preconditioning ahead of a Sudden Stratospheric Warming event; the distribution of trace‐constituents within the core; and the features representation in extended range/seasonal prediction and climate models.

Investigation of wave processes during complex sudden stratospheric warmings

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Characterizing the Spatial Distribution of Mixing and Transport in the Northern Middle Atmosphere During Winter

AbstractA three‐dimensional winter (DJF) climatology of Lagrangian diffusivity characterizing eddy mixing and transport in the northern middle atmosphere is presented. To emphasize aspects other than zonal averages, we use the theory of Lagrangian diffusivity (κyy) hitherto not applied in stratospheric contexts to our knowledge. Our formulation of Lagrangian diffusivity requires the calculation of parcel trajectories, which is made on isentropic surfaces. A Lagrangian descriptor is used to estimate the boundary of the stratospheric polar vortex (SPV). To characterize quasi‐geostrophic motions and their influence on the SPV we apply the wave activity flux (W) and Local Wave Activity . Our data set is the ERA5 reanalysis for the period 1979–2013. Results for κyy show important zonal asymmetries. In the lower and middle stratosphere, κyy is highest at midlatitudes, particularly around the prime meridian. This location is surrounded by manifolds associated with hyperbolic trajectories emanating from the outer SPV boundary. κyy is also high within the SPV, and near the locations where the SPV boundary is open. Zonal asymmetries are also clear in W at midlatitudes. The larger values of are at high latitudes and upstream of the opening of the vortex boundary. The role of quasi‐geostrophic waves on the south‐north shift of the midlatitude westerlies is highlighted. In particular, the waves contribute to open the SPV boundary at around 90W. The interannual variability of κyy is explored by contrasting winters with positive‐negative Northern Annular Mode index, and Sudden Stratospheric Warmings of displacement‐split type.

The ionospheric response during the 2013 stratospheric sudden warming over the East Asia region

During the 2013 SSW, ionospheric disturbances were observed at eighteen stations on three meridional chains of 100°E, 110°E and 120°E ranging from 19.03°N to 49.21°N at latitudes over the East Asia region. The total electron content (TEC) response showed evident semidiurnal disturbances with TEC enhancement in the morning and depletion in the afternoon. The maximum TEC increased by more than 220 % along the 120°E longitude. In addition, the semidiurnal disturbance of the TEC was enhanced and indicated evident latitudinal and longitudinal dependence. The wavelet spectra of semidiurnal disturbance in TEC presented quasi-16-day planetary wave-like oscillations at middle latitudes and quasi-10-day planetary wave-like oscillations near Sanya at low latitudes. Moreover, the zonal winds and meridional winds at altitudes of 92 km and 96 km showed quasi-16-day planetary waves at the Mohe station located at middle latitudes and quasi-10-day planetary waves at the Sanya station located at low latitudes, which maybe relate to the semidiurnal disturbance of the TEC. In particular, the 12hrs oscillation of the TEC showed a quasi-16-day periodic component at middle latitudes and a quasi-10-day periodic component at low latitudes, indicating that the modulated semidiurnal tides may transmit these 10-day and 16-day planetary wave-like oscillations to the ionosphere. The coupling between the atmosphere and ionosphere may be strengthened by quasi-16-day waves at middle latitudes and quasi-10-day waves at low latitudes (near Sanya). This finding can further confirm the PW-tide interaction theory during the 2013 SSW event, and it is of significance in the middle and low latitude ionospheric response to SSW.

Regression Forest Approaches to Gravity Wave Parameterization for Climate Projection

AbstractWe train random and boosted forests, two machine learning architectures based on regression trees, to emulate a physics‐based parameterization of atmospheric gravity wave momentum transport. We compare the forests to a neural network benchmark, evaluating both offline errors and online performance when coupled to an atmospheric model under the present day climate and in 800 and 1,200 ppm CO2 global warming scenarios. Offline, the boosted forest exhibits similar skill to the neural network, while the random forest scores significantly lower. Both forest models couple stably to the atmospheric model, and control climate integrations with the boosted forest exhibit lower biases than those with the neural network. Integrations with all three data‐driven emulators successfully capture the Quasi‐Biennial Oscillation (QBO) and sudden stratospheric warmings, key modes of stratospheric variability, with the boosted forest more accurate than the random forest in replicating their statistics across our range of carbon dioxide perturbations. The boosted forest and neural network capture the sign of the QBO period response to increased CO2, though both struggle with the magnitude of this response under the more extreme 1,200 ppm scenario. To investigate the connection between performance in the control climate and the ability to generalize, we use techniques from interpretable machine learning to understand how the data‐driven methods use physical information. We leverage this understanding to develop a retraining procedure that improves the coupled performance of the boosted forest in the control climate and under the 800 ppm CO2 scenario.

Large-scale dynamic processes during the minor and major sudden stratospheric warming events in January–February 2023

Using data from reanalyses of meteorological information, this study examines peculiarities of the thermodynamic regime of the Arctic stratosphere in the winter season of 2022–2023. For this purpose, components of the global meridional circulation, wave activity fluxes, volume of polar stratospheric clouds type I (PSC NAT) are analyzed, as well as changes in these indicators during sudden stratospheric warming (SSW) events formed in January–February. The main features of the 2022–2023 winter season were the following: (1) a persistent cold stratospheric polar vortex was observed until mid-January, which caused the PSC NAT volume growth to its maximum values since 1980; (2) enhanced wave activity from mid-January led to the formation of a minor SSW at the end of January, an increase in the temperature of the lower stratosphere and a sharp reduction in PSC NAT; (3) a week of intensification of the polar vortex was then observed, followed by a weakening due to the next burst of wave activity propagation during the second SSW event in mid-February. This second SSW event was major, accompanied by a reversal of the mean zonal wind, which lasted until early March; (4) meridional heat flux in January–February 2023 was the highest since 1948, resulting in unprecedented warming of the lower Arctic stratosphere and preventing ozone depletion in March; (5) the minor SSW at the end of January was accompanied by a more intense change in the meridional circulation than the major SSW in mid-February. Formation of ozone mini-hole over Northern and Central Europe in February 2023 was associated with the strengthening of the anticyclone, leading to a stratopause elevation and northward transport of ozone-poor air masses from the subtropics along the western periphery of the anticyclone additionally to related to the major SSW temperature changes affected the ozone concentration in the lower stratosphere.

Symmetric and Antisymmetric Solar Migrating Semidiurnal Tides in the Mesosphere and Lower Thermosphere

AbstractUpward‐propagating solar tides are responsible for a large part of atmospheric variability in the mesosphere and lower thermosphere (MLT) region, and they are also an important source of ionospheric variability. Tides can be divided into the parts that are symmetric and antisymmetric about the equator. Their distinction is important, as the electrodynamic responses of the ionosphere to symmetric and antisymmetric tides are different. This study examines symmetric and antisymmetric tides using 21 years of temperature measurements by the Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry. The main focus is on the solar migrating semidiurnal tide (SW2), which is one of the dominant tides in the MLT region. It is shown that symmetric and antisymmetric parts of SW2 are comparable in amplitude. However, their spatiotemporal characteristics are different. That is, the symmetric part is strongest during March–June at 30–35° latitude, while the antisymmetric part is most prominent during May–September with the largest amplitude at 15–20° latitude. The symmetric and antisymmetric parts can be well described by the first two symmetric and antisymmetric Hough modes, respectively. Amplification is observed in the antisymmetric part during the major sudden stratospheric warmings (SSWs) in January 2006, 2009, 2013 and 2019. Atmospheric model simulations for the 2009 and 2019 SSWs confirm the amplification in the antisymmetric part of SW2. The enhanced antisymmetric tidal forcing explains the previously‐reported asymmetric response of the ionospheric solar‐quiet current system to SSWs.

Response of the low latitude mesosphere and lower thermosphere to the recent sudden stratospheric warming events of 2017–18 and 2019

Upper mesospheric wind data acquired by the medium frequency radar at Kolhapur (16.7oN, 74.2oE) and Modern–Era Retrospective analysis for Research and Application version 2 (MERRA-2) temperature and wind reanalysis datasets are used to investigate the dynamical response of the low-latitude middle atmosphere to the sudden stratospheric warming (SSW) events that occurred during the 2017–18 and 2018–19 winters. When the amplitude of the high-latitude stratospheric planetary wave (PW) of zonal wavenumber one reduces considerably with the onset of the SSW event, the low-latitude mesospheric PW over Kolhapur also shows a considerable reduction in the PW activity. It is noteworthy that the upper mesospheric winds are eastward for approximately 3 weeks after the onset of SSW. The reduced PW activity is associated with the enhanced gravity wave activity in the meridional wind during the SSW 2018–19 event. The plane of propagation of gravity waves obtained from the perturbation ellipse method suggests that their predominant plane of propagation is in the north–south direction. The persistence of the eastward winds is suggested to be due to the interaction of the northward propagating gravity waves with the mean flow, leading to the eastward acceleration due to the Coriolis force.

Roles of Gravity Waves in Preconditioning of a Stratospheric Sudden Warming

AbstractAs well as strong upward propagation of planetary waves from the troposphere, the state of the stratospheric mean flow has been recognized as a key factor for the occurrence of stratospheric sudden warmings (SSWs). The modification of the mean flow to a suitable state for an SSW occurrence is called “vortex preconditioning.” Recently, increasing attention has been paid to the role of gravity waves (GWs) in the preconditioning mechanism. However, because of the limited availability of data sets covering the whole neutral atmosphere, much uncertainty still exists in the role of GWs in the preconditioning. The aim of this study is to investigate the mechanism of modification of the mean flow in the stratosphere and mesosphere before SSWs from a climatological viewpoint and elucidate the role of GWs in it. We use two state‐of‐the‐art data sets covering the whole neutral atmosphere: a 17‐year medium‐resolution reanalysis data set and the output data from hindcast simulations performed with a GW‐permitting general circulation model. It is shown that the second principal component of the zonal‐mean zonal wind in the stratosphere and mesosphere tends to show a maximum prior to an SSW, characterizing preconditioning. GW forcing alters the structure of the upper part of the jet and contributes to the preconditioning along with planetary waves. Comparison of GW forcing between the reanalysis and GW‐permitting model suggests that the magnitude of parameterized GW forcing is approximately half that of the GW forcing in the polar upper stratosphere where the forcing is responsible for the preconditioning.

The Influence of Sudden Stratospheric Warming on the Development of Ionospheric Storms: The Alma-Ata Ground-Based Ionosonde Observations

This paper examines the response of the ionosphere to the impact of two moderate geomagnetic storms observed on January 17 and 26–27, 2013, under conditions of strong sudden stratospheric warming. The study uses data from ground-based ionosonde measurements at the Alma-Ata ionospheric station (43.25 N, 76.92 E) combined with optical observation data (The Spectral Airglow Temperature Imager (SATI)). Ionosonde data showed that the geomagnetic storms under consideration do not generate ionospheric storms but demonstrate some unusual types of diurnal foF2 variations with large (up to 60%) deviations in foF2 from median values observed during the night/morning periods on 13–15 and 20–23 January, which do not have any relation to solar or geomagnetic activity. Wave-like disturbances in foF2, h’F, and daily averaged foF2 values with a quasi-period of 5–8 days and peak-to-peak amplitude from about 1 MHz to 2 MHz (from 20% to 40%) and ~40 km are observed during the period 9–28 January, after registration of the occurrence of the major SSW event on 6–7 January. The observed variations in the OH emission rate are found to be quite similar to those observed in the ionospheric parameters that assume a community of processes in the stratosphere/mesosphere/ionosphere system. The study shows that the F region of the ionosphere is influenced by processes in the lower ionosphere, in this case by processes associated with sudden stratospheric warming SSW-2013, which led to modification of the structure of the ionosphere and compensation of processes associated with the development of the ionospheric storms.

Influences of sudden stratospheric warmings on the ionosphere above Okinawa

Abstract. We analyzed the ionosonde observations from Okinawa (26.7° N, 128.1° E; magnetic latitude: 17.0° N) for the years from 1972 to 2023. Okinawa is in the northern low-latitude ionosphere, where the influences of sudden stratospheric warmings (SSWs) on the ionosphere are expected to be stronger than in the mid- and high-latitude ionospheres. We divided the dataset into winters with major SSWs in the Northern Hemisphere (SSW years) and winters without major SSWs (no-SSW years). During the SSW years, the daily cycle of the F2-region electron density maximum (NmF2) is stronger than in the no-SSW years. The relative NmF2 amplitudes of solar and lunar tidal components (S2, O1, M2, MK3) are stronger by 3 % to 8 % in the SSW years than in the no-SSW years. The semidiurnal amplitude, averaged across 29 SSW events, has a significant peak at the central date of the SSW (epoch time 0 of the composite analysis). The SSW influence is not strong: the semidiurnal amplitude is about 38.2 % in the SSW years and about 34.0 % in the no-SSW years (relative to the NmF2 of the background ionosphere). However, there is a sharp decrease in the amplitude of about 10 % after the SSW peak is reached. The amplitude of the diurnal component does not show a single peak at the central date of the SSW. We present the maximal semidiurnal amplitudes of the SSWs since 1972. The SSW of 31 December 1984 has the strongest amplitude (162 %) in the ionosphere above Okinawa (with a high geomagnetic activity, Ap, of 37 nT). The most surprising finding of the study is the strong lunar tides with relative amplitudes of about 10 % and the discovery of a terdiurnal lunar tide (5 %) in the NmF2 during the SSW years. The periods of the ionospheric lunar tides align with the periods of ocean tides and lunisolar variations in the atmosphere.

High and Equatorial Mesospheric Dynamical Response to the Minor Stratospheric Warming of 2014/15: Comparison with major SSW Events 2005/06 and 2008/09

High and Equatorial Mesospheric Dynamical Response to the Minor Stratospheric Warming of 2014/15: Comparison with major SSW Events 2005/06 and 2008/09

Opposite spectral properties of Rossby waves during weak and strong stratospheric polar vortex events

Abstract. In this study we provide a systematic characterization of Rossby wave activity during the 25 sudden stratospheric warming (SSW) and 31 strong polar vortex (SPV) events that occurred in the period 1979–2021, identifying the specific tropospheric and stratospheric waves displaying anomalous behaviour during such events. Space–time spectral analysis is applied to ERA5 data for this purpose, so that both the wavenumber and the zonal phase speed of the waves can be assessed. We find that SSW events are associated with a reduction in the phase speed of Rossby waves, first in the stratosphere and then in the troposphere; SPV events are tied to a simultaneous increase of phase speed across vertical levels. Phase speed anomalies become significant around the event and persist for 2–3 weeks afterwards. Changes of Rossby wave properties in the stratosphere during SSW and SPV events are dominated by changes in the background flow, with a systematic reduction or increase, respectively, in eastward propagation of the waves across most wavenumbers. In the troposphere, on the other hand, the effect of the background flow is also complemented by changes in wave properties, with a shift towards higher wavenumbers during SSW events and towards lower wavenumbers for SPV events. The opposite response between SSW and SPV events is also visible in the meridional heat and momentum flux co-spectra, which highlight from a novel perspective the connection between stratospheric Rossby waves and upward propagation of waves.

Influence of temperature changes and vertically transported trace species on the structure of MLT region during major SSW events

Sudden stratospheric warming (SSW) events are large-scale dynamic phenomena which can significantly affect the circulation, temperature, and composition of different atmospheric layers. The circulation changes during these events induce variations in the atmospheric neutral and ion densities and cause the vertical transport of various trace species. The severity of effects induced by major SSW events in the mesosphere and lower thermosphere (MLT) region has received less attention than that in the lower atmosphere. The major influence of temperature and vertically transported trace species on the energetics, thermal and compositional structure of the MLT region has been investigated during two major SSW events with elevated stratopause. Variations in the nitric oxide volume emission rates (NO-VER), a measure of infrared radiative cooling by NO, are reported for the first time in the context of the dynamical changes during SSW events. This study investigates the role of temperature and NO variability on the energetics of the MLT region, particularly during the formation of elevated stratopause. The effects of supplemented NO density on the secondary ozone layer has also been investigated during these events, the anti-correlation between secondary ozone and NO does not conclude on the role of NO in the secondary ozone peak density variations. Notwithstanding the similarity in terms of defining characteristics, both SSW events impact the secondary ozone layer differently. In contrast to earlier studies, it is suggested that along with temperature, the availability of atomic oxygen is the major factor for the observed variation in secondary ozone during the SSW events.

Polar Vortex Disruptions by High Latitude Ocean Warming

AbstractMid‐latitude extreme cold outbreaks are associated with disruptions of the polar vortex, which often happen abruptly in connection to a sudden stratospheric warming. Understanding global warming (particularly Arctic amplification) impacts on forecasting such events is challenging for the scientific community. Here we apply clustering analysis on the Northern Annular Mode to identify surface precursors and the governing mechanisms causing polar vortex disruption events. Two clusters of vortex breakdown emerge; 65% of the events, mainly displacements, are associated with high‐latitude Ocean warming in the North Pacific and in Barents‐Kara Sea. Such warming may cause large scale modifications of the tropospheric flow that favors a slowdown of the stratospheric vortex. The persistence of Ocean surface temperature patterns favors polar vortex disruptions, potentially improving prediction skills at the sub‐seasonal to seasonal time scales.

Physical mechanism for the temporary intensification of wintertime sporadic E layers in 2009

This study provides a physical mechanism for the temporary intensification of wintertime sporadic E layers (EsLs) in 2009. It is widely accepted that vertical wind shears control EsL formations. EsL intensity is minimal in winter, partially because of the weakened vertical wind shears. Despite the wintertime minimum EsL intensity, temporary intensifications of EsLs occurred for 10–30 days in some winters, the cause of which remains unclear. In this study, we conducted month-long EsL simulations in 2009 and 2011, the years when both wintertime EsL (WiEsL) intensification and sudden stratospheric warming (SSW) occurred, and when neither did, respectively. The simulations aimed to reveal the physical mechanisms of the WiEsL intensification in 2009. We succeeded in reproducing the occurrence and non-occurrence of temporary WiEsL intensification in 2009 and 2011, respectively, observed by an ionosonde at Kokubunji, Japan, although day-to-day variations in WiEsL intensity were not reproduced well. Evidently, the temporary WiEsL intensification is attributed to vertical ion convergence (VIC) intensification at altitudes of 100–120 km between 4 and 8 local time (LT) and particularly after 15 LT. The VIC intensification is caused primarily by the vertical wind shears of SW2 tides, westward propagating semi-diurnal tides with wavenumber 2. The SW2 intensification is driven by the major SSW in January–February 2009. Additionally, 6–8-day planetary waves can also affect the WiEsL intensification superposed on the SW2 amplification effects.Graphical

Impacts of the Sudden Stratospheric Warming on Equatorial Plasma Bubbles: Suppression of EPBs and Quasi-6-Day Oscillations

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.

Exploiting a variational auto-encoder to represent the evolution of sudden stratospheric warmings

Sudden stratospheric warmings (SSWs) are the most dramatic events in the wintertime stratosphere. Such extreme events are characterized by substantial disruption to the stratospheric polar vortex, which can be categorized into displacement and splitting types depending on the morphology of the disrupted vortex. Moreover, SSWs are usually followed by anomalous tropospheric circulation regimes that are important for subseasonal-to-seasonal prediction. Thus, monitoring the genesis and evolution of SSWs is crucial and deserves further advancement. Despite several analysis methods that have been used to study the evolution of SSWs, the ability of deep learning methods has not yet been explored, mainly due to the relative scarcity of observed events. To overcome the limited observational sample size, we use data from historical simulations of the Whole Atmosphere Community Climate Model version 6 to identify thousands of simulated SSWs, and use their spatial patterns to train the deep learning model. We utilize a convolutional neural network combined with a variational auto-encoder (VAE)—a generative deep learning model—to construct a phase diagram that characterizes the SSW evolution. This approach not only allows us to create a latent space that encapsulates the essential features of the vortex structure during SSWs, but also offers new insights into its spatiotemporal evolution mapping onto the phase diagram. The constructed phase diagram depicts a continuous transition of the vortex pattern during SSWs. Notably, it provides a new perspective for discussing the evolutionary paths of SSWs: the VAE gives a better-reconstructed vortex morphology and more clearly organized vortex regimes for both displacement-type and split-type events than those obtained from principal component analysis. Our results provide an innovative phase diagram to portray the evolution of SSWs, in which particularly the splitting SSWs are better characterized. Our findings support the future use of deep learning techniques to study the underlying dynamics of extreme stratospheric vortex phenomena, and to establish a benchmark to evaluate model performance in simulating SSWs.

Observation of vertical coupling during a major sudden stratospheric warming by ICON and GOLD: a case study of the 2020/2021 warming event

The response of the thermospheric daytime longitudinally averaged zonal and meridional winds and neutral temperature to the 2020/2021 major sudden stratospheric warming (SSW) is studied at low-to middle latitudes (0◦ - 40◦N) using observations by NASA’s ICON and GOLD satellites. The major SSW commenced on 1 January 2021 and lasted for several days. Results are compared with the non-SSW winter of 2019/2020 and pre-SSW period of December 2020. Major changes in winds and temperature are observed during the SSW. The northward and westward winds are enhanced in the thermosphere especially above ∼140 km during the warming event, while temperature around 150 km drops up to 50 K compared to the pre-SSW phase. Changes in the zonal and meridional winds are likely caused by the SSW-induced changes in the propagation and dissipation conditions of internal atmospheric waves. Changes in the horizontal circulation during the SSW can generate upwelling at low-latitudes, which can contribute to the adiabatic cooling of the low-latitude thermosphere. The observed changes during the major SSW are a manifestation of long-range vertical coupling in the atmosphere.