Sudden Stratospheric Warming Research Articles

Signature of Sudden Stratospheric Warming in the Pole and Its Antipode

AbstractIn this study, the boreal sudden stratospheric warming (SSW) event of 2013 and the austral SSW event of 2019 are considered to investigate the influence of the SSW events on the polar and antipodal upper mesosphere and lower thermosphere (UMLT) regions using ground‐based, space‐borne, reanalysis and model data sets. During the SSW events, the solar semi‐diurnal tidal (SDT) amplitudes are much larger than the lunar amplitudes in both UMLT regions. Besides, the solar SDT shows an increase in its amplitude in both the polar UMLT heights during the SSW events. However, the lunar tides show enhancement in its amplitude in the boreal polar UMLT region during both the SSW events. In the antipodal UMLT region, a peak enhancement in solar SDT amplitude is observed a few days after the onset of the boreal SSW and near to the onset time of the austral SSW. No concurrent stratospheric ozone volume mixing ratio (vmr) increase is observed which indicates that the SDT peak can be unlikely due to the underlying stratospheric ozone vmr changes. However, similar periodicity in the UMLT zonal winds of both poles indicates the possibility of cross equatorial propagation of planetary wave (PW). As the SDT amplitude also reveal similar planetary wave periodicity as observed in zonal wind, it is suggested that the PW modulation of the SDT could be the reason for the enhancement of SDT in the opposite polar UMLT region.

Stratospheric influence on the winter North Atlantic storm track in subseasonal reforecasts

Abstract. Extreme stratospheric polar vortex events, such as sudden stratospheric warmings (SSWs) or extremely strong polar vortex events, can have a significant impact on surface weather in winter. SSWs are most often associated with negative North Atlantic Oscillation (NAO) conditions, cold air outbreaks in the Arctic and a southward-shifted midlatitude storm track in the North Atlantic, while strong polar vortex events tend to be followed by a positive phase of the NAO, relatively warm conditions in the extratropics and a poleward-shifted storm track. Such changes in the storm track position and associated extratropical cyclone frequency over the North Atlantic and Europe can increase the risk of extreme windstorm, flooding or heavy snowfall over populated regions. Skillful predictions of the downward impact of stratospheric polar vortex extremes can therefore improve the predictability of extratropical winter storms on subseasonal timescales. However, there exists a strong inter-event variability in these downward impacts on the tropospheric storm track. Using ECMWF reanalysis data and reforecasts from the Subseasonal to Seasonal (S2S) Prediction Project database, we investigate the stratospheric influence on extratropical cyclones, identified with a cyclone detection algorithm. Following SSWs, there is an equatorward shift in cyclone frequency over the North Atlantic and Europe in reforecasts, and the opposite response is observed after strong polar vortex events, consistent with the response in reanalysis. However, although the response of cyclone frequency following SSWs with a canonical surface impact is typically captured well during weeks 1–4, less than 25 % of the reforecasts manage to capture the response following SSWs with a “non-canonical” impact. This suggests a possible overconfidence in the reforecasts with respect to reanalysis in predicting the canonical response after SSWs, although it only occurs in about two-thirds of the events. The cyclone forecasts following strong polar vortex events are generally more successful. Understanding the role of the stratosphere in subseasonal variability and predictability of storm tracks during winter can provide a key for reliable forecasts of midlatitude storms and their surface impacts.

Technical note: Multi-year changes in the Brewer–Dobson circulation from Halogen Occultation Experiment (HALOE) methane

Abstract. This study makes use of Halogen Occultation Experiment (HALOE) methane (CH4) in a search for multi-year changes in the Brewer–Dobson circulation (BDC). Changes in CH4 are determined for three successive 5-year time spans from 1992 to 2005, and there are significant differences between them. There is a clear separation between the changes in the Northern Hemisphere near 30 hPa and at the transition of the shallow and deep branches of the BDC. The CH4 changes are positive and large in the shallow branch following the eruption of Pinatubo, but they then decrease and agree with tropospheric trends in the late 1990s and early 2000s. CH4 decreases in the upper part of the deep branch from 1992 to 1997 or following the eruption of Pinatubo. CH4 continues to decrease in the deep branch in the late 1990s but then increases in the early 2000s, although those changes are small compared with the seasonal and interannual variations of CH4. Multi-year changes are due, in part, to wave forcings during the El Niño–Southern Oscillation (ENSO) of 1997–1998 and beyond and to episodic, sudden stratospheric warming (SSW) events during both time spans. It is concluded that time series of HALOE CH4 provide effective tracer diagnostics for studies of the nature of the BDC from 1992 to 2005.

A CMIP6 Analysis of Past and Future Arctic Winter Stratospheric Temperature Trends

AbstractReanalysis data reveal a weak warming trend in the midwinter Arctic stratosphere, contrary to the cooling expectation based on the greenhouse gas effect. This trend is also influenced by the occurrence of sudden stratospheric warmings (SSWs). Using Phase 6 of the Coupled Model Intercomparison Project (CMIP6) we investigate temperature trends over a similar timescale as ERA5 and find that CMIP6 models can replicate the positive midwinter temperature trend in the mid‐lower stratosphere. However, when considering the multi‐model mean, this positive temperature trend is much weaker than ERA5. Extrapolating to the future, we find that the SSW‐driven positive temperature trend will likely not continue in the future based on the SSP2‐4.5 and SSP5‐8.5 climate scenarios. Instead, the models project there will be widespread cooling throughout the Arctic winter stratosphere regardless of the occurrence of SSWs. Using a subsample of CMIP6 models which replicate the seasonality of the Arctic winter stratosphere most similarly to that of ERA5, we also find that the zonal wind strength during SSWs correlates the most with the temperature trends found there. However, trends in the zonal wind strength alone cannot account for the observed temperature trends among the CMIP6 models.

The tropical influence on sub‐seasonal predictability of wintertime stratosphere and stratosphere–troposphere coupling

AbstractA unique set of relaxation experiments with a forecast model initialized during December–January 1999–2019 is used to explore tropical influence on the Northern Hemisphere polar stratosphere and stratosphere–troposphere coupling, to quantify predictability benefits due to the perfect knowledge of the tropical variability. On average, predictability of the polar stratosphere, as represented by the 50 hPa geopotential height anomalies north of 50°N (Z50), increases from 17 days in freely running (control) forecasts to 21 days in the tropical relaxation experiments. At sub‐seasonal time‐scales, a statistically significant improvement in weekly mean skill scores can be demonstrated in 14%–20% of individual forecast ensembles, mostly in cases when the skill of the corresponding control forecast is worse than average. In these forecasts, root‐mean‐square errors and forecast spread of Z50 during forecast weeks 3–5 are decreased by 10%–15%. Stratospheric improvements are detected during periods of both vortex strengthening and vortex weakening, including most major Sudden Stratospheric Warmings that occurred during the study period, via modulation of the upward wave activity fluxes. An active Madden–Julian Oscillation (MJO) is found in most of these events with MJO phase 5–7 preceding vortex weakening and MJO phase 3–4 preceding vortex strengthening. Forecasts with improved stratospheric circulation also have improved tropospheric circulation during and after the periods when improvements are detected in the stratosphere. We attribute these improvements to both stratosphere–troposphere coupling and tropospheric tropical teleconnections.

Characteristics and Mechanism of Interhemispheric Coupling in Austral Winter Revealed by Long‐Term Reanalysis Data for the Whole Middle Atmosphere

AbstractGlobal characteristics of dynamical fields for the interhemispheric coupling (IHC) initiated with a sudden stratospheric warming (SSW) in the southern hemisphere in the austral winter were examined using the global reanalysis for the whole neutral atmosphere from a data assimilation with satellite observations over 15 years of 2005–2019. Even in the austral winter, a strong cold equatorial stratosphere associated with the SSW, which is essential for the IHC, occurs about once every two years. The mechanism of the IHC in the austral winter is basically similar to that in the boreal winter. However, there are two significant differences in the IHC characteristics between the austral and boreal winters. One is that the SSW in the austral winter occurs mainly at midlatitudes, whereas the SSW in the boreal winter occurs mainly at high latitudes. As a result, a warm temperature anomaly simultaneously appears in the southern polar mesosphere in the austral winter, which is not observed for the boreal winter. The other is related to the seasonal variation of the quasi‐two‐day wave activity and induced forcing and gravity wave forcing in the summer mesosphere. For the IHC events occurring in July, when these wave activities and forcings are high, the response in the summer mesosphere is similar to that of the boreal winter. In contrast, for late August and September, when these wave forcings are weak, the response in the summer mesosphere is small. This result indicates that the IHC characteristics are largely influenced by the seasonal variation of these waves.

Impact of sudden stratospheric warming on middle atmospheric circulation in the southern hemisphere: A comparative study

A comparative study on the impact of rare Southern Hemisphere (SH) Sudden Stratospheric Warmings (SSW) on the middle atmospheric circulation is investigated using a global reanalysis dataset. Since the SH SSW generally occur around spring equinox marking the seasonal transition, so an attempt has been made to isolate the seasonal transition effect from the actual data by carrying out deseasoning to delineate the effects mainly due to the warming. The deseasoned winds are able to extract relatively weak dynamical signatures of SSW at lower altitudes in terms of prominent zonal mean easterly forcing around the peak warming day (PWD) which are not evident from the actual winds. The influence of 2002 SSW seems to reach the troposphere in terms of easterly deseasoned forcing, which is not the case in 2019. Also the deseasoned winds in the stratosphere reveals earlier occurrence of easterly forcing in the extratropical latitudes, which progresses poleward around the PWD indicating a possible tropical precursor to the SH SSW. In general, the actual upper mesospheric wind is dominated by seasonal transition but the deseasoned winds reveal easterly and southerly forcing due to the SSW. Interestingly, the horizontal flow is found to be very different or even opposite in direction at different longitudes indicating uneven longitudinal response of the atmosphere to the warming events across the globe. Overall, the present study provides a detailed and comparative overview of the middle atmospheric circulation in terms of zonal mean flow and concomitant zonal variability during two rare major and minor SSW events in the SH.

Analysis of gravity wave activity during stratospheric sudden warmings in the northern hemisphere

Analysis of gravity wave activity during stratospheric sudden warmings in the northern hemisphere

Association of the 11-year solar cycle with correlation and teleconnection structures in tropospheric circulation

Analyzing spatial correlation structures and teleconnections in the 500 hPa heights of the Northern Hemisphere Extratropics in winter shows substantial differences between months with high and low solar activity. Patterns of spatial correlations of mid-tropospheric circulation differ between solar minima and maxima; the differences are geographically variable, particularly large and statistically significant in parts of the North Atlantic and North Pacific. Correlation structures of tropospheric circulation are significantly larger in solar maxima over parts of the North Atlantic. The geographical orientation of teleconnections is also associated with solar activity, the differences being most notable over the North Atlantic, North America, and the Arctic. The differences in teleconnections form a background for a response of modes of circulation variability and blocking anticyclones to solar activity, detected in previous studies. We detected no evidence of potential interference of responses to solar activity with quasi-biennial oscillation and volcanic eruptions; the interference with El Niño-Southern Oscillation is unlikely. The response to solar activity may be partly confused with the response to major sudden stratospheric warmings; however, sudden stratospheric warmings themselves may respond to the solar cycle.

Long-term variation of Arctic Sudden Stratospheric Warmings (SSW) and potential causes

Long-term variation of Arctic Sudden Stratospheric Warmings (SSW) and potential causes

Identifying Perturbations That Tipped the Stratosphere Into a Sudden Warming During January 2013

AbstractWe present a new methodology demonstrating that specific small‐magnitude regional perturbations can cause large systematic responses in subseasonal predictions. We show this with ensemble forecasts of the January 2013 Sudden Stratospheric Warming (SSW) from an operational long‐range global prediction system. In forecast members which predict the SSW, tropospheric ridging over the North Atlantic is strengthened 10 days prior to the event. This subsequently enhances planetary wave forcing and weakens the stratospheric polar vortex. Transplanting tropospheric conditions in this region from “correct” to “incorrect” forecasts (and vice versa) significantly alters the SSW forecast probability. The occurrence of this SSW is therefore strongly controlled by the troposphere several days prior. Tipping more members into a sudden warming also significantly affects surface predictions the following month. Despite chaotic behavior of the climate system, small‐magnitude synoptic‐scale perturbations can drive different dynamical states and systematically impact medium and long‐range predictions.

A Data-Driven Study of the Drivers of Stratospheric Circulation via Reduced Order Modeling and Data Assimilation

Stratospheric dynamics are strongly affected by the absorption/emission of radiation in the Earth’s atmosphere and Rossby waves that propagate upward from the troposphere, perturbing the zonal flow. Reduced order models of stratospheric wave–zonal interactions, which parameterize these effects, have been used to study interannual variability in stratospheric zonal winds and sudden stratospheric warming (SSW) events. These models are most sensitive to two main parameters: Λ, forcing the mean radiative zonal wind gradient, and h, a perturbation parameter representing the effect of Rossby waves. We take one such reduced order model with 20 years of ECMWF atmospheric reanalysis data and estimate Λ and h using both a particle filter and an ensemble smoother to investigate if the highly-simplified model can accurately reproduce the averaged reanalysis data and which parameter properties may be required to do so. We find that by allowing additional complexity via an unparameterized Λ(t), the model output can closely match the reanalysis data while maintaining behavior consistent with the dynamical properties of the reduced-order model. Furthermore, our analysis shows physical signatures in the parameter estimates around known SSW events. This work provides a data-driven examination of these important parameters representing fundamental stratospheric processes through the lens and tractability of a reduced order model, shown to be physically representative of the relevant atmospheric dynamics.

Conjugate hemispheric response of Earth’s ionosphere due to 2019 Antarctic minor Sudden Stratospheric Warming (SSW): Comparison with 2013 Arctic major SSW

In this paper, we attempt to compare the Antarctic SSW of 2019 with the Arctic SSW of 2013. Despite being a minor SSW, the rare Antarctic event of September 2019 caused a significant enhancement of stratospheric temperature at high latitudes with more temperature deviation than the Arctic major SSW of 2013. On the basis of the duration and extent of stratospheric zonal mean zonal wind, the 2019 SSW is comparable to major SSWs. An exceptionally strong wave 1 planetary wave was observed during the 2019 SSW. We have investigated the response of the ionospheric total electron content (TEC) during both the SSWs over two low mid-latitude locations Okinawa and Darwin, which form magnetic conjugate pair. The extent of maximum ionospheric deviations during the 2019 SSW is almost comparable to the 2013 SSW in their respective hemispheres. We have observed mostly night time enhancement in TEC during the Arctic SSW, while daytime enhancement is noted during the Antarctic SSW. Hemispheric asymmetry is observed during both the SSWs. Minor geomagnetic storm has been noticed coinciding with each SSW during different phases of the warming. The SSW, solar flux, and storm contribution on the TEC have been calculated during both the SSWs, which shows clear contribution of SSW on the total TEC despite the presence of storm and during moderately high solar activity. We have also investigated the foF2 variations from ionosonde and IRI-16 at the same two locations. The peak electron density from ionosonde responds to the warming in a manner similar to TEC. The foF2 of IRI-16 exhibits overestimation during daytime and underestimation during nighttime on quiet days during low solar activity (2019), while during moderate solar activity (2013), it overestimates during morning hours. However, it can not predict the enhancements of foF2 during SSWs.

Mesospheric Water Vapor From SABER as a Tracer for the Residual Mean Circulation During SSW Events

AbstractThe sparse wind observations and reanalysis winds in the mesosphere make it challenging to accurately determine the residual mean meridional circulation (MMC). As winds distribute tracers, an alternative approach is to utilize long‐lived trace species such as water vapor (H2O). The recently released H2O data from Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) version 2.07, combined with simulations by the Whole Atmosphere Community Climate Model eXtension with specified dynamics (SD‐WACCM‐X) and with the Data Assimilation Research Testbed (WACCMX + DART), provide an opportunity to assess the accuracy of using H2O isopleths to derive the vertical component of the residual MMC during the 2009 sudden stratospheric warming (SSW) event. In winter, the impact of photochemistry and diffusion on the distribution of mesospheric H2O is negligible compared to advective processes. H2O poleward of 70°N accurately captures the anomalous ascent that occurs a few days prior to the onset of the SSW and the subsequent descent. The derived vertical velocity in SD‐WACCM‐X and WACCMX + DART is qualitatively consistent with SABER observations. However, the derivation of vertical motion from isopleth analysis has limitations at the beginning of 2009 when the meridional transport is stronger than the vertical transport. While measuring winds in the mesosphere is challenging, satellite observations of mesospheric H2O prove to be an effective dynamical tracer during time periods characterized by strong vertical coupling.

Antarctic polar vortex dynamics in 2019 and 2020 under the influence of the subtropical stratosphere

The trend of strengthening of the Antarctic polar vortex in late spring and early summer (November–December) has been observed in recent decades. A good example of this trend is the dynamics of the Antarctic polar vortex in 2020 when it existed until the last week of December. In 2019, conversely, on the contrary, an unusually early breakup of the polar vortex occurred, a minor sudden stratospheric warming was recorded. Strengthening (or weakening) of the Antarctic polar vortex occurs as a result of an increase (or decrease) in the stratospheric meridional temperature gradient under conditions of growth (or decline) in the temperature of the lower subtropical stratosphere. We considered the temperature variations in the lower subtropical stratosphere in the spring of 2019 and 2020 and the corresponding response of the Antarctic polar vortex. The dynamics of the Antarctic polar vortex in September–October 2019 and November 2020 was largely synchronized with the temperature changes in the lower subtropical stratosphere relative to climatological means. Using correlation analysis, we show that the Antarctic polar vortex dynamics in December is largely due to the temperature changes in the lower subtropical stratosphere that occurred in the second half of November, which manifested itself in 2020.

Role of Southern Hemisphere sudden stratospheric warming in altering the intensity of Brewer-Dobson circulation and its impact on stratospheric ozone and water vapor

The changes in the intensity of Brewer-Dobson circulation (BDC) in the record-breaking Southern Hemisphere sudden stratospheric warming (SH SSW) event in 2019 are investigated in the present study. Wave driving was observed to be at its highest in 2019 SH SSW, despite the event being classified as a minor warming event. The Eliassen-Palm flux divergence, indicative of wave driving, was observed to be increasing before the SSW, and subsiding afterwards. The stratospheric circulation followed the wave driving and intensified along the warming episode. The resulting stratospheric distribution from Aura Microwave Limb Sounder showed a negative ozone anomaly (∼20%) in the tropical lower stratosphere and a downward propagating positive anomaly in the Southern Hemisphere polar stratosphere around the central dates. The water vapor mixing ratio showed an increase of more than 25% in the polar lower stratosphere and 10% in the tropical upper stratosphere. A cooling of about 5 K was observed in the tropical middle stratosphere. The results indicate that SH SSW can change the intensity of the stratospheric circulation which in turn affects the ozone and water vapor transport from the tropics to the pole.

Precursory Analysis Ensemble Spread Signals That Foreshadow Stratospheric Sudden Warmings

Abstract This study conducts a thorough investigation into the behaviors of analysis ensemble spreads linked to stratospheric sudden warming (SSW) events. A stratosphere-resolving ensemble data assimilation system is used here to document the evolution of analysis spread leading up to a pair of warming events. Precursory signals of the increased ensemble spreads were found a few days prior to two SSW events that occurred during December 2018 and August–September 2019 in the Northern and Southern Hemispheres, respectively. The signals appeared in the upper and middle stratosphere and did not appear at lower heights. When the signals appeared, it was found that both tendency by forecast and analysis increment in a forecast-analysis (data assimilation) cycle simultaneously became large. An empirical orthogonal function analysis showed that the dominant structures of the precursory signals were equivalent barotropic and were 90° out-of-phase with the analysis ensemble-mean field. Over the same period, the upper and middle stratosphere became more susceptible to barotropic instability than in their previous states. We conclude that the differing growth of barotropically unstable modes across ensemble members can amplify spread during the lead-up to SSW events. Significance Statement Winds in the winter stratospheric polar vortex are typically westerly. Occasionally, however, warming over the pole leads to a reversal of the flow through a process known as stratospheric sudden warming. These events are difficult to predict even in state-of-the-art analysis and forecasting systems. In this study, we identify a precursor signal in the form of increased ensemble spread that appears to originate from differing realizations of growing barotropic modes across the ensemble. This signal could serve as a useful forecasting tool by enhancing situational awareness in the lead-up to potential stratospheric sudden warming events.

The Evolution of Solar Tide‐Like Signatures in the Ionospheric Total Electron Content During Major Sudden Stratospheric Warming Events

AbstractBy using total electron content (TEC) from the global ionospheric maps, the solar tide‐like signatures in the ionosphere are explored. We further study how the main components evolve during the 2009 and 2018 major stratospheric sudden warming events (SSWs). The method of a least‐square fit is applied for extracting the solar tide‐like components. The three predominant components are SW2, D0, and SW1, amplitude of which increase in the equatorial ionization anomaly region after the onset of both SSW events, especially in the northern hemisphere. During the SSW events, the solar tide‐like components vary significantly with latitude and their evolutions show hemispherical asymmetries. Each same component presents similar evolutionary trend during both events. The characteristics of ionospheric tide‐like signatures and related mechanisms are discussed. The SW2 tide‐like responses in TEC closely follow the changes in the tidal wind fields in the lower thermosphere, which provide evidences of the atmosphere‐ionosphere coupling during SSW events. In addition, the latitudinal asymmetric distributing of stratospheric ozone and ionospheric TEC background during the SSW may be influence factors for the hemispherical asymmetries in tide‐like signatures responses in TEC.

Stratospheric Warming Events in the Period January–March 2023 and Their Impact on Stratospheric Ozone in the Northern Hemisphere

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.

Reasons for Low Fraction of Arctic Stratospheric Cloud in 2014/2015 Winter

AbstractPolar stratospheric clouds (PSCs) play a key role in Arctic amplification and stratospheric ozone destruction in polar regions. In this paper, we used the CALIPSO data to analyze the spatiotemporal distribution of Arctic PSCs from 2006 to 2021. We found that Arctic PSCs mainly appear in December, peak in late December and early January, disappearing in late February and early March. PSCs can extend from heights near the tropopause to over 25 km. However, there is the lowest fraction of PSCs in the 2014/2015 winter. This study found that the temperature in the 2014/2015 winter was warmer than the 15‐year average temperature, with the lowest temperature slightly below the PSCs formation temperature of about 5 K. The formation of the Ural blocking high accompanied by the poleward propagation of the planetary wave caused a sudden stratospheric warming (SSW) event on 3 January 2015, during which the warm air entered the polar vortex and divided it into two lobes. Additionally, a reduction in SO2 column mass density before the SSW event resulted PSCs occurring with a frequency of only 0.148 and dissipating rapidly in December. Moreover, the concentration of H2O and HNO3 in the gravitational settling process of PSCs decreased by 20–50%, the reduction of condensation nuclei made PSCs with the highest frequency of 0.074 in February appear briefly and then disappear. The chemical and dynamic analysis of PSCs formation is needed to further understand the spatiotemporal distribution of Arctic PSCs and to better predict future Arctic amplification and ozone destruction.