Major Sudden Stratospheric Warming Events Research Articles

Equatorial 150 km echoes and daytime F region vertical plasma drifts in the Brazilian longitude sector

Abstract. Previous studies showed that conventional coherent backscatter radar measurements of the Doppler velocity of the so-called 150 km echoes can provide an alternative way of estimating ionospheric vertical plasma drifts during daytime hours (Kudeki and Fawcett, 1993; Chau and Woodman, 2004). Using observations made by a small, low-power 30 MHz coherent backscatter radar located in the equatorial site of São Luís (2.59° S, 44.21° W; −2.35° dip lat), we were able to detect and monitor the occurrence of 150 km echoes in the Brazilian sector. Using these measurements we estimated the local time variation of daytime vertical ionospheric drifts in the eastern American sector. Here, we present a few interesting cases of 150 km-echoes observations made by the São Luís radar and estimates of the diurnal variation of vertical drifts. These cases exemplify the variability of the vertical drifts in the Brazilian sector. Using same-day 150 km-echoes measurements made at the Jicamarca Radio Observatory in Peru, we also demonstrate the variability of the equatorial vertical drifts across the American sector. In addition to first estimates of the absolute vertical plasma drifts in the eastern American (Brazilian) sector, we also present observations of abnormal drifts detected by the São Luís radar associated with the 2009 major sudden stratospheric warming event.

The influence of major sudden stratospheric warming and elevated stratopause events on the effects of energetic particle precipitation in WACCM

We investigate the influence of major sudden stratospheric warming (SSW) and elevated stratopause (ES) events in the Northern Hemisphere winter on the transport of NOx produced by energetic particle precipitation (EPP) from the mesosphere–lower thermosphere to the stratosphere using the Whole Atmosphere Community Climate Model (WACCM). Increases in NOx following a major SSW and/or ES event are in excess of 100% compared to winters when no major SSW or ES event occurred. The increase in NOx is attributed to an increase in the descending branch of the residual circulation () following the event. The timing of the event strongly affects the amount of NOx that descends to the stratosphere: the earlier the event occurs, the more NOx descends to the stratosphere. We also quantify the amount of NOx produced by EPP descending to the stratosphere in each winter and find that the largest increases in NOx are in years that have a major SSW followed by an ES event early in the season (December or early January). The strength of following an event shows a very strong seasonal dependence and explains why the timing of the event affects the transport of NOx.

On the lack of stratospheric dynamical variability in low‐top versions of the CMIP5 models

We describe the main differences in simulations of stratospheric climate and variability by models within the fifth Coupled Model Intercomparison Project (CMIP5) that have a model top above the stratopause and relatively fine stratospheric vertical resolution (high‐top), and those that have a model top below the stratopause (low‐top). Although the simulation of mean stratospheric climate by the two model ensembles is similar, the low‐top model ensemble has very weak stratospheric variability on daily and interannual time scales. The frequency of major sudden stratospheric warming events is strongly underestimated by the low‐top models with less than half the frequency of events observed in the reanalysis data and high‐top models. The lack of stratospheric variability in the low‐top models affects their stratosphere‐troposphere coupling, resulting in short‐lived anomalies in the Northern Annular Mode, which do not produce long‐lasting tropospheric impacts, as seen in observations. The lack of stratospheric variability, however, does not appear to have any impact on the ability of the low‐top models to reproduce past stratospheric temperature trends. We find little improvement in the simulation of decadal variability for the high‐top models compared to the low‐top, which is likely related to the fact that neither ensemble produces a realistic dynamical response to volcanic eruptions.

Quiet time variability of the GPS TEC and EEJ strength over Indian region associated with major sudden stratospheric warming events during 2005/2006

This paper describes the quiet time variabilities of the ionospheric total electron content (TEC) derived from the signals from Global Positioning Satellite System (GPS) recorded at several stations in India along with simultaneous observations of equatorial electrojet (EEJ) strength obtained from geomagnetic field variations during January–March 2006 when sudden stratospheric warming (SSW) events occurred. Analysis of the observations presented here confirms that strong correlation exists among the variabilities in EEJ strength and GPS TEC observations. Investigations suggest that there exist large‐scale wave like structures with periodicity of quasi 16‐day wave in the TEC observations near the equatorial ionization anomaly (EIA) crest quite similar to that of EEJ strength. Our observations also indicate the existence of morning enhancement and evening reduction of TEC and EEJ strength and vice versa during SSW events similar to that reported elsewhere. Using these observations, it is suggested that the quiet time variabilities seen in the GPS TEC over EIA could be caused due to the nonlinear interaction of upward propagating planetary waves (PWs) with atmospheric tides. Presence of similar periods in the EEJ strength and TEC observations near the EIA crest region, supports the view that the large‐scale wave like structures seen in TEC near the EIA crest are associated with PWs that are modifying the primary eastward electric field in the equatorial E region and hence the EEJ strength through non linear interactions with atmospheric tides.

The February 2010 Arctic Oscillation Index and its stratospheric connection

AbstractThe atmospheric dynamics during the occurrence of the extreme negative value of the Arctic Oscillation Index in February 2010 are investigated using meteorological fields from ERA‐Interim and ERA‐40 reanalysis data. The study focuses on the possible causes of this anomalous value, finding that it was forced by a geopotential anomaly that propagated downward from the stratosphere to the troposphere in association with a major sudden stratospheric warming event which occurred at the end of January. An analysis of the dynamics of this warming is also developed, together with a comparison with past similar events. Synoptic and spectral properties of the geopotential fields are analyzed, and the time series of the ‘Baroclinic Activity Index’ are computed, finding an abrupt increase of the middle latitude baroclinic activity immediately after the central date of the warming event. A possible interpretation of this feature is proposed. Copyright © 2012 Royal Meteorological Society

Observational evidence of deep convection over Indonesian sector in relation with major stratospheric warming events of 2003–04 and 2005–06

The major sudden stratospheric warming (SSW) events of 2003–04 and 2005–06 are considered to investigate changes in equatorial convection due to circulation changes associated with the SSW events. It is observed that the SSW events are accompanied by a considerable decrease in Outgoing Longwave Radiation (OLR), a proxy for tropical convection, over equatorial latitudes (15°N–15°S) in the Indonesian sector (90°E–150°E). However, unlike noted by earlier observations, the zonal mean OLR does not show any notable relationship with the SSW events. It can be explained from the latitude–longitude map of potential vorticity (PV) at 100 hPa, which shows a tongue of high PV emanating from high latitudes towards equator and converges in the longitude band of 90°E–150°E on the day of peak warming at 1 hPa in the case of 2003–04 and 10 hPa in the case of 2005–06. The latitude-height map of Eliassen–Palm (EP) vector and its divergence show convergence of EP flux in the upper troposphere at latitudes even lower than 20°N on these days. Further, vertical winds computed from the convergence of momentum flux are upward indicating convective activity at low-latitudes and downward at mid-latitudes.

C/NOFS observations of the equatorial ionospheric electric field response to the 2009 major sudden stratospheric warming event

[1] We present new observations made by the Coupled Ion Neutral Dynamics Investigation (CINDI) Ion Velocity Meter (IVM) instrument onboard the Communication/Navigation Outage Forecasting System (C/NOFS) satellite that show the effects of the January 2009 sudden stratospheric warming (SSW) event on equatorial electric fields. We have used IVM observations to construct composite curves of mean equatorial vertical plasma drifts as a function of local time and longitude sector. These curves show large upward vertical drifts during morning hours and downward drifts during afternoon. Our analysis indicates that this pattern could be observed over the range of longitudes where adequate IVM measurements were available, from approximately 165°E to about 315°E longitude. A clear day-to-day, quasi-deterministic variability in the drifts is also observed, with the transition from upward to downward drifts occurring at increasing local times from 25 to 30 January 2009. The analysis also suggests some level of longitudinal variability in the magnitude of the drifts. These in-situ observations are in good agreement with previous ground-based measurements of the response of equatorial electric fields to SSW events. In particular, we found that IVM drift measurements centered around 285°E depart significantly from climatological values but agree exceptionally well with ground-based measurements of vertical drifts made by the Jicamarca incoherent backscatter radar. Overall, the results agree well with previous studies of SSW events, demonstrate the usefulness of the IVM observations and motivate further studies of the variability of the equatorial ionosphere using C/NOFS.

Aura MLS observations of the westward-propagating <i>s</i>=1, 16-day planetary wave in the stratosphere, mesosphere and lower thermosphere

Abstract. The Microwave Limb Sounder (MLS) on the Aura satellite has been used to measure temperatures in the stratosphere, mesosphere and lower thermosphere. The data used here are from August 2004 to December 2010 and latitudes 75° N to 75° S. The temperature data reveal the regular presence of a westward-propagating 16-day planetary wave with zonal wavenumber 1. The wave amplitudes maximise in winter at middle to high latitudes, where monthly-mean amplitudes can be as large as ~8 K. Significant wave amplitudes are also observed in the summer-time mesosphere and lower thermosphere (MLT) and at lower stratospheric heights of up to ~20 km at middle to high latitudes. Wave amplitudes in the Northern Hemisphere approach values twice as large as those in the Southern Hemisphere. Wave amplitudes are also closely related to mean zonal winds and are largest in regions of strongest eastward flow. There is a reduction in wave amplitudes at the stratopause. No significant wave amplitudes are observed near the equator or in the strongly westward background winds of the atmosphere in summer. This behaviour is interpreted as a consequence of wave/mean-flow interactions. Perturbations in wave amplitude summer MLT are compared to those simultaneously observed in the winter stratosphere of the opposite hemisphere and found to have a correlation coefficient of +0.22, suggesting a small degrees of inter-hemispheric coupling. We interpret this to mean that some of the summer-time MLT wave may originate in the winter stratosphere of the opposite hemisphere and have been ducted across the equator. We do not observe a significant QBO modulation of the 16-day wave amplitude in the polar summer-time MLT. Wave amplitudes were also observed to be suppressed during the major sudden stratospheric warming events of the Northern Hemisphere winters of 2006 and 2009.

Variabilities of mesospheric tides during sudden stratospheric warming events of 2006 and 2009 and their relationship with ozone and water vapour

The present study demonstrates how the relationship between the high latitude northern hemispheric major sudden stratospheric warming (SSW) events of 2006 and 2009 and low-latitude mesospheric tidal variability in zonal winds observed by the MF radar at Tirunelveli (8.7°0N, 77.8°E) exists. It is found that the ozone mixing ratio increases at low latitudes during the SSW and it could probably be due to the SSW induced reversal of meridional circulation towards southward, which may aid the transport of ozone from high to low latitudes, but prevent the same from low to high latitudes. As semi-diurnal tide is produced due to solar insolation absorption of ozone and the increase in the ozone mixing ratio could be a reason for the increase in the semi-diurnal tidal amplitude. The variabilities of diurnal tide appear to be governed mostly by variation of specific humidity at 300hPa over equator and intraseasonal variability dominates the variabilities in both the parameters.

Sudden stratospheric warming effects on the mesospheric tides and 2-day wave dynamics at 7°S

The dynamics of the equatorial mesosphere have been investigated during austral summers of 2004–2005, 2005–2006 and 2006–2007 from meteor radar measurements obtained at São João do Cariri, Brazil (7.4°S, 36.5°W), together with stratospheric northern hemisphere polar parameters. Some recent studies have demonstrated coupling between high latitude northern hemisphere major Sudden Stratospheric Warming (SSW) events and mesospheric–ionospheric disturbances, including the equatorial region. Here we have analyzed the tides, quasi-two-day planetary wave and local mean zonal wind variability in the equatorial upper Mesosphere and Lower Thermosphere (MLT) region during three austral summers and found that upper mesospheric dynamics at 7°S has been affected when a remarkable major SSW event took place in January 2006. The more intense tides and quasi-two-day wave amplitudes during the major SSW event are suggestive of an association between them and high planetary wave activity in the northern stratospheric winter.

Hindcasting the January 2009 Arctic Sudden Stratospheric Warming and Its Influence on the Arctic Oscillation with Unified Parameterization of Orographic Drag in NOGAPS. Part I: Extended-Range Stand-Alone Forecast

Abstract A very strong Arctic major sudden stratospheric warming (SSW) event occurred in late January 2009. The stratospheric temperature climbed abruptly and the zonal winds reversed direction, completely splitting the polar stratospheric vortex. A hindcast of this event is attempted by using the Navy Operational Global Atmospheric Prediction System (NOGAPS), which includes the full stratosphere with its top at around 65 km. As Part I of this study, extended-range (3 week) forecast experiments are performed using NOGAPS without the aid of data assimilation. A unified parameterization of orographic drag is designed by combining two parameterization schemes; one by Webster et al., and the other by Kim and Arakawa and Kim and Doyle. With the new unified orographic drag scheme implemented, NOGAPS is able to reproduce the salient features of this Arctic SSW event owing to enhanced planetary wave activity induced by more comprehensive subgrid-scale orographic drag processes. The impact of the SSW on the tropospheric circulation is also investigated in view of the Arctic Oscillation (AO) index, which calculated using 1000-hPa geopotential height. The NOGAPS with upgraded orographic drag physics better simulates the trend of the AO index as verified by the Met Office analysis, demonstrating its improved stratosphere–troposphere coupling. It is argued that the new model is more suitable for forecasting SSW events in the future and can serve as a tool for studying various stratospheric phenomena.

Tropospheric forcing of the boreal polar vortex splitting in January 2003

Abstract. The dynamical evolution of the relatively warm stratospheric winter season 2002–2003 in the Northern Hemisphere was studied and compared with the cold winter 2004–2005 based on NCEP-Reanalyses. Record low temperatures were observed in the lower and middle stratosphere over the Arctic region only at the beginning of the 2002–2003 winter. Six sudden stratospheric warming events, including the major warming event with a splitting of the polar vortex in mid-January 2003, have been identified. This led to a very high vacillation of the zonal mean circulation and a weakening of the stratospheric polar vortex over the whole winter season. An estimate of the mean chemical ozone destruction inside the polar vortex showed a total ozone loss of about 45 DU in winter 2002–2003; that is about 2.5 times smaller than in winter 2004–2005. Embedded in a winter with high wave activity, we found two subtropical Rossby wave trains in the troposphere before the major sudden stratospheric warming event in January 2003. These Rossby waves propagated north-eastwards and maintained two upper tropospheric anticyclones. At the same time, the amplification of an upward propagating planetary wave 2 in the upper troposphere and lower stratosphere was observed, which could be caused primarily by those two wave trains. Furthermore, two extratropical Rossby wave trains over the North Pacific Ocean and North America were identified a couple of days later, which contribute mainly to the vertical planetary wave activity flux just before and during the major warming event. It is shown that these different tropospheric forcing processes caused the major warming event and contributed to the splitting of the polar vortex.

Mie lidar and radiosonde observations at Gadanki (13.5°N, 79.2°E) during sudden stratospheric warming of 2009

During a major sudden stratospheric warming event (21–27 January 2009), Mie-lidar observations at Gadanki (13.5°N, 79.2°E) show persistent occurrence of cirrus clouds. Outgoing long-wave radiation averaged for 70°E–90°E, decreases to a low value (170W/m2) on 27 January 2009 over equator indicating deep convection. The zonal mean ERA-Interim data reveal large northward and upward circulation over equatorial upper troposphere. The latitude–longitude map of ERA-Interim zonal mean potential vorticity (PV) indicates two tongues of high PV emanating from polar latitudes and extending further down to equator. Radiosonde observations at Gadanki show the presence of ∼40% relative humidity at 11–13km and lower tropopause temperature. It is inferred that the tropical circulation change due to PV intrusion leads to deep convection, which along with high humidity and low tropopause temperature leading to the formation of persistent cirrus clouds, the occurrence frequency of which is normally less during winter season over Gadanki.

Mesosphere and lower thermosphere temperature anomalies during the 2002 Antarctic stratospheric warming event

Abstract. We present kinetic temperatures at ~87 km and ~94 km altitudes inferred from OH (6,2) and O2 At(0,1) airglow observations, respectively, at South Pole (90° S), Antarctica in the austral winter of 2002. These OH and O2 rotational temperatures measurements show mesosphere and lower thermosphere (MLT) temperature anomalies prior to the 2002 Southern Hemisphere Sudden Stratospheric Warming (SSW) . In this paper we focus on the first of the three minor stratospheric warmings which preceded the major SSW event. Temperature anomalies observed in the MLT region show sudden cooling (ΔT=~30 K) in OH temperatures accompanied by warming (ΔT=~15 K) in O2 temperatures preceding the onset of SSW event by about three to four weeks. This shallow vertical extent of mesospheric cooling is in agreement with the numerical simulation of Coy et al. (2005), however, the model cooling was centered well below the mesopause level. The other observed feature of the South Pole MLT temperature dataset is the intensification of planetary wave activity prior to the onset of SSW event. Fourier analyses of both OH and O2 temperatures show amplification of planetary wave activity in the 5–10 day range prior to the onset of SSW. The timing of wave amplification seen in the wave spectra coincides with the peak in OH and O2 temperature anomalies.

Variabilities of mesospheric tides and equatorial electrojet strength during major stratospheric warming events

Abstract. The present study demonstrates the relationship between the high latitude northern hemispheric major sudden stratospheric warming (SSW) events and the reversal in the afternoon equatorial electrojet (EEJ), often called the counter-electrojet (CEJ), during the winter months of 1998–1999, 2001–2002, 2003–2004 and 2005–2006. As the EEJ current system is driven by tidal winds, an investigation of tidal variabilities in the MF radar observed zonal winds during the winters of 1998–1999 and 2005–2006 at 88 km over Tirunelveli, a site close to the magnetic equator, shows that there is an enhancement of semi-diurnal tidal amplitude during the days of a major SSW event and a suppression of the same immediately after the event. The significance of the present results lies in demonstrating the latitudinal coupling between the high latitude SSW phenomenon and the equatorial ionospheric current system with clear evidence for major SSW events influencing the day-to-day variability of the CEJ.

Dynamical response of low-latitude middle atmosphere to major sudden stratospheric warming events

The zonally averaged UK Meteorological Office (UKMO) zonal mean temperature and zonal winds for the latitudes 8.75°N and 60°N are used to investigate the low-latitude dynamical response to the high latitude sudden stratospheric warming (SSW) events that occurred during winter of the years 1998–1999, 2003–2004 and 2005–2006. The UKMO zonal mean zonal winds at 60°N show a short-term reversal to westward winds in the entire upper stratosphere and lower mesosphere and the low-latitude winds (8.75°N) show enhanced eastward flow in the upper stratosphere and strong westward flow in the lower mesosphere during the major SSW events at high latitudes. The mesosphere and lower thermosphere (MLT) zonal winds acquired by medium frequency (MF) radar at Tirunelveli (8.7°N, 77.8°E) show a change of wind direction from eastward to westward several days before the onset of SSW events and these winds decelerate and weak positive (eastward) winds prevail during the SSW events. The time variation of zonal winds over Tirunelveli is nearly similar to the one reported from high latitudes, except that the latter shows intense eastward winds during the SSW events. Besides, the comparison of daily mean meridional winds over Tirunelveli with those over Collm (52°N, 15°E) show that large equatorial winds are observed over Tirunelveli during the 2005–2006 event and over Collm during the 1998–1999 events. The variable response of MLT dynamics to different SSW events may be explained by the variability of gravity waves.

Planetary and gravity waves in the mesosphere and lower thermosphere region over Tirunelveli (8.7°N, 77.8°E) during stratospheric warming events

An investigation of planetary wave (PW) activities in UKMO (UK Meteorological Office) winds during winter of the years 1998–99 and 2005–06, when major sudden stratospheric warming (SSW) events occurred, shows that the amplitude of PW of zonal wave number 1 is considerably reduced in zonal winds, when the warming event is onset and the reduced activity persists several days even after the end of the SSW event. Similar reduction of PW activity in zonal winds has been observed in the wavelet spectrum of MF radar zonal winds at altitudes 84–98 km over Tirunelveli (8.7°N, 77.8°E). During this period of reduced PW activity, enhancement in gravity wave activity is observed during 2005–06 and is not observed during 1998–99 and the mean meridional winds change to more equatorward during 2005–06 and remain poleward during 1998–99. In accordance with TIME‐GCM results, our observations show that the wind reversal occurred in the stratosphere during major warming events allows more eastward gravity waves to propagate into the mesosphere and lower thermosphere (MLT) region, which causes changes in the meridional circulation from poleward to equatorward.

Impact of the Stratosphere on the Winter Tropospheric Teleconnections between ENSO and the North Atlantic and European Region

Abstract The possible role of stratospheric variability on the tropospheric teleconnection between El Niño–Southern Oscillation (ENSO) and the North Atlantic and European (NAE) region is addressed by comparing results from two ensembles of simulations performed with an atmosphere general circulation model fully resolving the stratosphere (with the top at 0.01 hPa) and its low-top version (with the top at 10 hPa). Both ensembles of simulations consist of nine members, covering the 1980–99 period and are forced with prescribed observed sea surface temperatures. It is found that both models capture the sensitivity of the averaged polar winter lower stratosphere to ENSO in the Northern Hemisphere, although with a reduced amplitude for the low-top model. In late winter and spring, the ENSO response at the surface is instead different in the two models. A large-scale coherent pattern in sea level pressure, with high pressures over the Arctic and low pressures over western and central Europe and the North Pacific, is found in the February–March mean of the high-top model. In the low-top model, the Arctic high pressure and the western and central Europe low pressure are very much reduced. The high-top minus low-top model difference in the ENSO temperature and precipitation anomalies is that North Europe is colder and the Northern Atlantic storm track is shifted southward in the high-top model. In addition, it has been found that major sudden stratospheric warming events are virtually lacking in the low-top model, while their frequency of occurrence is broadly realistic in the high-top model. Given that this is a major difference in the dynamical behavior of the stratosphere of the two models and that these events are favored by ENSO, it is concluded that the occurrence of sudden stratospheric warming events affects the reported differences in the tropospheric ENSO–NAE teleconnection. Given that the essence of the high-top minus low-top model difference is a more annular (or zonal) pattern of the anomaly in sea level pressure, relatively larger over the Arctic and the NAE regions, this interpretation is consistent with the observational evidence that sudden stratospheric warmings play a role in giving rise to persistent Arctic Oscillation anomalies at the surface.

Sudden Stratospheric Warming and Anomalous U.S. Weather

Severe distortion of tropospheric circulation is associated with major sudden stratospheric warming (SSW) events. This distortion consisting primarily of weakening of smaller-scale synoptic mats and development of strong blocking activity, is reviewed in the context of associated weather anomalies over the United States. Temperature, precipitation and cyclone anomalies of 17 January and February months experiencing SSW are contrasted with months of no stratospheric warming. The SSW is marked by intense cold, dry anomalies centered in the Ohio Valley, with below average temperatures covering the entire United States. In January, slight wet anomalies occur in the lee of the Rockies, and in February the desert southwest becomes quite wet. Cyclone activity decreases by 25% throughout the United States during SSW, most strongly along the West Coast and in association with the disappearance of the Colorado low. Storm track anomalies are documented over the eastern Pacific, the Gulf and Atlantic seaboard, and northeastern Canada. Slight variations of the anomaly patterns in February over the western United States are linked to the temporal evolution of SSW.