scholarly journals Mechanisms and predictability of sudden stratospheric warming in winter 2018

2020 ◽  
Vol 1 (2) ◽  
pp. 657-674
Author(s):  
Irina A. Statnaia ◽  
Alexey Y. Karpechko ◽  
Heikki J. Järvinen
Keyword(s):  
Wave Packets ◽  
Wave Activity ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Ural Mountains ◽  
Rossby Wave Breaking ◽  
The Pacific ◽  
Individual Wave ◽  
In The Beginning ◽  
Rapid Deceleration

Abstract. In the beginning of February 2018 a rapid deceleration of the westerly circulation in the polar Northern Hemisphere stratosphere took place, and on 12 February the zonal-mean zonal wind at 60∘ N and 10 hPa reversed to easterly in a sudden stratospheric warming (SSW) event. We investigate the role of the tropospheric forcing in the occurrence of the SSW, its predictability and teleconnection with the Madden–Julian oscillation (MJO) by analysing the European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble forecast. The SSW was preceded by significant synoptic wave activity over the Pacific and Atlantic basins, which led to the upward propagation of wave packets and resulted in the amplification of a stratospheric wavenumber 2 planetary wave. The dynamical and statistical analyses indicate that the main tropospheric forcing resulted from an anticyclonic Rossby wave breaking, subsequent blocking and upward wave propagation in the Ural Mountains region, in agreement with some previous studies. The ensemble members which predicted the wind reversal also reasonably reproduced this chain of events, from the horizontal propagation of individual wave packets to upward wave-activity fluxes and the amplification of wavenumber 2. On the other hand, the ensemble members which failed to predict the wind reversal also failed to properly capture the blocking event in the key region of the Urals and the associated intensification of upward-propagating wave activity. Finally, a composite analysis suggests that teleconnections associated with the record-breaking MJO phase 6 observed in late January 2018 likely played a role in triggering this SSW event.

scholarly journals Mechanisms and predictability of Sudden Stratospheric Warming in winter 2018

2020 ◽  
Author(s):  
Irina A. Statnaia ◽  
Alexey Y. Karpechko ◽  
Heikki J. Järvinen
Keyword(s):  
Wave Packets ◽  
Wave Activity ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Ural Mountains ◽  
Rossby Wave Breaking ◽  
The Pacific ◽  
Individual Wave ◽  
In The Beginning ◽  
Rapid Deceleration

Abstract. In the beginning of February 2018 a rapid deceleration of the westerly circulation in the polar Northern Hemisphere stratosphere took place and on 12 February the zonal mean zonal wind at 60° N and 10 hPa reversed to easterly in a Sudden Stratospheric Warming (SSW) event. We investigate the role of the tropospheric forcing in the occurrence of the SSW, its predictability and teleconnection with the Madden-Julian oscillation (MJO) by analysing the European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble forecast. The SSW was preceded by significant synoptic wave activity over the Pacific and Atlantic basins, which led to the upward propagation of wave packets and resulted in the amplification of a stratospheric wavenumber 2 planetary wave. The dynamical and statistical analyses indicate that the main tropospheric forcing resulted from an anticyclonic Rossby wave breaking, subsequent blocking and upward wave propagation in the Ural Mountains region, in agreement with some previous studies. The ensemble members which predicted the wind reversal, also reasonably reproduced this chain of events, from the horizontal propagation of individual wave packets to upward wave activity fluxes and the amplification of wavenumber 2. On the other hand, the ensemble members which failed to predict the wind reversal, also failed to properly capture the blocking event in the key region of the Urals and the associated intensification of upward propagating wave activity. Finally, a composite analysis suggests that teleconnections associated with the record-breaking MJO phase 6 observed in the late January 2018 likely played a role in triggering this SSW event.

scholarly journals Diagnosing the Horizontal Propagation of Rossby Wave Packets along the Midlatitude Waveguide

2017 ◽  
Vol 145 (8) ◽  
pp. 3247-3264 ◽  
Author(s):  
Gabriel Wolf ◽  
Volkmar Wirth
Keyword(s):  
Wave Packet ◽  
Rossby Wave ◽  
Wave Breaking ◽  
Wave Packets ◽  
Wave Activity ◽  
Severe Weather ◽  
Robust Methods ◽  
Misleading Information ◽  
Individual Wave ◽  
Wave Activity Flux

It has been suggested that upper-tropospheric Rossby wave packets propagating along the midlatitude waveguide may play a role for triggering severe weather. This motivates the search for robust methods to detect and track Rossby wave packets and to diagnose their properties. In the framework of several observed cases, this paper compares different methods that have been proposed for these tasks, with an emphasis on horizontal propagation and on a particular formulation of a wave activity flux previously suggested by Takaya and Nakamura. The utility of this flux is compromised by the semigeostrophic nature of upper-tropospheric Rossby waves, but this problem can partly be overcome by a semigeostrophic coordinate transformation. The wave activity flux allows one to obtain information from a single snapshot about the meridional propagation, in particular propagation from or into polar and subtropical latitudes, as well as about the onset of wave breaking. This helps to clarify the dynamics of individual wave packets in cases where other, more conventional methods provide ambiguous or even misleading information. In some cases, the “true dynamics” of the Rossby wave packet turns out to be more complex than apparent from the more conventional diagnostics, and this may have important implications for the predictability of the wave packet.

scholarly journals Tropospheric and Stratospheric Precursors to the January 2013 Sudden Stratospheric Warming

2016 ◽  
Vol 144 (4) ◽  
pp. 1321-1339 ◽  
Author(s):  
Hannah E. Attard ◽  
Rosimar Rios-Berrios ◽  
Corey T. Guastini ◽  
Andrea L. Lang
Keyword(s):  
Zonal Wind ◽  
Planetary Wave ◽  
Wave Activity ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Climate Forecast System ◽  
Reanalysis Dataset ◽  
Climate Forecast System Reanalysis ◽  
Eddy Heat Flux ◽  
Wave Resonance

Abstract This paper investigates the tropospheric and stratospheric precursors to a major sudden stratospheric warming (SSW) that began on 6 January 2013. Using the Climate Forecast System Reanalysis dataset, the analysis identified two distinct decelerations of the 10-hPa zonal mean zonal wind at 65°N in December in addition to the major SSW, which occurred on 6 January 2013 when the 10-hPa zonal mean zonal wind at 65°N reversed from westerly to easterly. The analysis shows that the two precursor events preconditioned the stratosphere for the SSW. Analysis of the tropospheric state in the days leading to the precursor events and the major SSW suggests that high-latitude tropospheric blocks occurred in the days prior to the two December deceleration events, but not in the days prior to the SSW. A detailed wave activity flux (WAF) analysis suggests that the tropospheric blocking prior to the two December deceleration events contributed to an anomalously positive 40-day-average 100-hPa zonal mean meridional eddy heat flux prior to the SSW. Analysis of the stratospheric structure in the days prior to the SSW reveals that the SSW was associated with enhanced WAF in the upper stratosphere, planetary wave breaking, and an upper-stratospheric/lower-mesospheric disturbance. These results suggest that preconditioning of the stratosphere occurred as a result of WAF initiated by tropospheric blocking associated with the two December deceleration events. The two December deceleration events occurred in the 40 days prior to the SSW and led to the amplification of wave activity in the upper stratosphere and wave resonance that caused the January 2013 SSW.

scholarly journals Tropospheric circulation response to sudden stratospheric warming observed in January 2013

2020 ◽  
pp. 241-254
Author(s):  
A.I. Pogoreltsev ◽  
O.G. Aniskina ◽  
A.Y. Kanukhina ◽  
T.S. Ermakova ◽  
A.I. Ugryumov ◽  
...  
Keyword(s):  
Winter Season ◽  
Wave Activity ◽  
Cold Weather ◽  
Synoptic Situation ◽  
Dynamical Regime ◽  
Stratospheric Warming ◽  
Mean Flow ◽  
Sudden Stratospheric Warming ◽  
Middle Latitudes ◽  
Tropospheric Circulation

Analysis of the dynamical regime changes in the stratosphere during different phases of the Sudden Stratospheric Warming (SSW) that has been observed in January 2013 is presented. The different mechanisms of SSW influence on the tropospheric circulation through the stationary planetary waves (SPWs) reflection and/or increase in SPWs activity due to nonlinear interaction with the mean flow and their subsequent propagation into the troposphere are discussed. Three-dimensional wave activity flux and its divergence are determined using the UK Met Office data; the synoptic situation and its changes during the SSW events are analyzed. The wave activity penetrates downward from stratosphere into the troposphere and can affect weather processes during the SSW and right afterwards. It is this time that polar anticyclones can be formed at high latitudes, which quickly go southward along meridional directions and then deviate to the East at middle latitudes. Interestingly, the locations of polar anticyclone formations and subsequent displacements correspond to the regions of maximal horizontal wave activity fluxes connected with stratospheric processes. The results obtained allow us to suggest that accounting of stratospheric processes and their influence on the troposphere in winter season can improve the middle-range forecast of anticyclone formation and cold weather events at middle latitudes.

Gravity wave activity during the southern hemispheric sudden stratospheric warming 2019

2020 ◽  
Author(s):  
Andreas Dörnbrack ◽  
Tyler Mixa ◽  
Bernd Kaifler ◽  
Markus Rapp
Keyword(s):  
Weather Prediction ◽  
Polar Vortex ◽  
Numerical Weather Prediction Model ◽  
Wave Activity ◽  
Meteorological Conditions ◽  
Background Information ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Airborne Measurements

<p>At the end of the austral winter 2019, a sudden stratospheric warming led to an early breakdown of the polar vortex. The meteorological conditions during this event are documented and analysed by means of operational analyses of the Intgrated Forecast System (IFS) of the ECMWF and ERA5 data. Especially, we focus on the decline of stratospheric wave activity over the southern tip of South America. For this region, ground-based and airborne measurements are employed to compare selected diagnostics with fields from the ECMWF's numerical weather prediction model IFS. Furthmore, the meteorological conditions for one selected research flight during the SOUTHTRAC campaign are presented. This part serves as background information for a case study presented by Tyler Mixa.</p>

scholarly journals A Study of False Alarms of a Major Sudden Stratospheric Warming by Real-Time Subseasonal-to-Seasonal Forecasts for the 2017/2018 Northern Winter

Atmosphere ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 875
Author(s):  
Masakazu Taguchi
Keyword(s):  
False Alarm ◽  
Real Time ◽  
Winter Season ◽  
Wave Activity ◽  
Wave Number ◽  
False Alarms ◽  
Stratospheric Warming ◽  
Seasonal Forecasts ◽  
Sudden Stratospheric Warming ◽  
First Case

This study investigates false alarms of a major sudden stratospheric warming (MSSW) by real-time subseasonal-to-seasonal forecast data of the European Centre for Medium-Range Weather Forecasts system for the 2017/2018 Northern Hemisphere winter season. The analysis reveals two false alarm cases in the season, one in early December and the other in early February. Each case is characterized by ensembles of which a considerable part of the members (MSSW members) show an MSSW, that is, reversal of the zonal mean zonal wind in the extratropical stratosphere on similar calendar dates. Ensemble forecasts that are initialized earlier or later basically lack an MSSW, demonstrating clear intraseasonal variability in the frequency of forecasted MSSWs. For each false alarm case, the MSSW member mean field shows equatorward displacement of the polar vortex around the onset date. For both cases, the MSSW members accompany stronger wave activity in the lower stratosphere than other non-MSSW members and reanalysis data. They are further associated with higher geopotential height than the non-MSSW members, in the upper troposphere over northeastern Canada and Greenland before the first case, and lower height over northeastern Eurasia before the second case. These are located over the ridge and trough, respectively, of the climatological planetary wave of zonal wave number one, and are consistent with the increased wave activity.

Burst of Unusual Quasi-10 day Wave During the 2019 Southern Sudden Stratospheric Warming

2021 ◽  
Author(s):  
Jack Wang ◽  
Scott Palo ◽  
Jeffrey Forbes ◽  
John Marino ◽  
Tracy Moffat-Griffin
Keyword(s):  
Southern Hemisphere ◽  
Planetary Wave ◽  
Wave Activity ◽  
Stratospheric Warming ◽  
Atmospheric Conditions ◽  
Meteor Radar ◽  
Sudden Stratospheric Warming ◽  
Zonal Wavenumber ◽  
Wind Measurements ◽  
Mlt Region

<div> <p>An unusual sudden stratospheric warming (SSW) occurred in the Southern hemisphere in September 2019. Ground-based and satellite observations show the presence of a transient westward-propagating quasi-10 day planetary wave with zonal wavenumber one during the SSW. The planetary wave activity maximizes in the MLT region approximately 10 days after the SSW onset. Analysis indicates the quasi-10 day planetary wave is symmetric about the equator which is contrary to theory for such planetary waves. </p> </div><div> <p>Observations from MLS and SABER provide a unique opportunity to study the global structure and evolution of the symmetric quasi-10 day wave with observations of both geopotential height and temperature during these unusual atmospheric conditions. The space-based measurements are combined with meteor radar wind measurements from Antarctica, providing a comprehensive view of the quasi-10 day wave activity in the southern hemisphere during this SSW. We will also present the results of our mesospheric and lower thermospheric analysis along with a preliminary analysis of the ionospheric response to these wave perturbations.</p> </div>

scholarly journals Analysis of the Arctic polar vortex dynamics during the sudden stratospheric warming in January 2009

2021 ◽  
Vol 67 (2) ◽  
pp. 134-146
Author(s):  
V. V. Zuev ◽  
E. S. Savelieva ◽  
A. V. Pavlinsky
Keyword(s):  
Wind Speed ◽  
Polar Vortex ◽  
Reanalysis Data ◽  
Wave Activity ◽  
The Arctic ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Mean Wind Speed ◽  
The Mean ◽  
Middle Stratosphere

The Arctic polar vortex is often affected by wave activity during its life cycle. The planetary Rossby waves propagating from the troposphere to the stratosphere occasionally lead to the displacement or splitting of the polar vortex, accompanied by sudden stratospheric warming (SSW). In January 2009, one of the largest SSWs was observed in the Arctic. In this work, the dynamics of the polar vortex during the 2009 SSW is considered using a new method that allows one to estimate the vortex area, the wind speed at the vortex edge, the mean temperature and ozone mass mixing ratio inside the vortex, based on the fact that the Arctic vortex edge at the 50 and 10 hPa pressure levels is determined by the geopotential values, respectively, 19.5. 104 and 29.5. 104 m2 /s2 , using the ERA5 reanalysis data. The application of this method is justified for the Arctic polar vortex, which is characterized by significant variability, especially during the period of its splitting. The splitting of the polar vortex in 2009 was observed on January 24 and 28, respectively, in the middle and lower stratosphere. About a week after the splitting, the vortices became closer in characteristics to small cyclones, which completely collapsed within 1–3 weeks. The influence of planetary wave activity on the polar vortex does not always lead to its breakdown. Short-term splitting of the polar vortex is sometimes observed for several days after which the polar vortex strengthens again and PSCs form inside the vortex. Such a recovery of the polar vortex is most likely to occur in the winter. Based on the analysis of the dynamics of the Arctic polar vortex for 1979–2020 and using the example of the 2009 SSW, we showed that when the vortex area decreases to less than 10 million km2 and the mean wind speed at the vortex edge decreases below 30 and 45 m/s, respectively, in the lower and middle stratosphere, the polar vortex becomes a small cyclone (with significantly higher temperatures within it), which usually collapses within 3 weeks.

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