scholarly journals The Structure and Dynamics of the Stratospheric Northern Annular Mode in CMIP5 Simulations

2014 ◽  
Vol 28 (1) ◽  
pp. 86-107 ◽  
Author(s):  
Yun-Young Lee ◽  
Robert X. Black
Keyword(s):  
Rossby Wave ◽  
Planetary Wave ◽  
Regional Analysis ◽  
Storm Track ◽  
Polar Vortex ◽  
Wave Activity ◽  
Flux Analysis ◽  
Annular Mode ◽  
Northern Annular Mode ◽  
Structure And Dynamics

Abstract The structure and dynamics of stratospheric northern annular mode (SNAM) events in CMIP5 simulations are studied, emphasizing (i) stratosphere–troposphere coupling and (ii) disparities between high-top (HT) and low-top (LT) models. Compared to HT models, LT models generally underrepresent SNAM amplitude in stratosphere, consistent with weaker polar vortex variability, as demonstrated by Charlton-Perez et al. Interestingly, however, this difference does not carry over to the associated zonal-mean SNAM signature in troposphere, which closely resembles observations in both HT and LT models. Nonetheless, a regional analysis illustrates that both HT and LT models exhibit anomalously weak and eastward shifted (compared to observations) storm track and sea level pressure anomaly patterns in association with SNAM events. Dynamical analyses of stratosphere–troposphere coupling are performed to further examine the distinction between HT and LT models. Variability in stratospheric planetary wave activity is reduced in LT models despite robust concomitant tropospheric variability. A meridional heat flux analysis indicates relatively weak vertical Rossby wave coupling in LT models consistent with the excessive damping events discussed by Shaw et al. Eliassen–Palm flux cross sections reveal that Rossby wave propagation is anomalously weak above the tropopause in LT models, suggesting that weak polar vortex variability in LT models is due, at least in part, to the inability of tropospheric planetary wave activity to enter the stratosphere. Although the results are consistent with anomalously weak vertical dynamical coupling in LT models during SNAM events, there is little impact upon attendant tropospheric variability. The physical reason behind this apparent paradox represents an important topic for future study.

scholarly journals Tropospheric forcing of the boreal polar vortex splitting in January 2003

2010 ◽  
Vol 28 (11) ◽  
pp. 2133-2148 ◽  
Author(s):  
D. H. W. Peters ◽  
P. Vargin ◽  
A. Gabriel ◽  
N. Tsvetkova ◽  
V. Yushkov
Keyword(s):  
Rossby Wave ◽  
Planetary Wave ◽  
Winter Season ◽  
Polar Vortex ◽  
Wave Activity ◽  
The Arctic ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Stratospheric Polar Vortex ◽  
Wave Trains

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.

Final Sudden Stratospheric Warmings and the memory of the stratosphere

2021 ◽  
Author(s):  
Alain Hauchecorne ◽  
Chantal Claud ◽  
Philippe Keckhut
Keyword(s):  
Zonal Wind ◽  
Planetary Wave ◽  
Middle Atmosphere ◽  
Temperature Anomaly ◽  
Polar Vortex ◽  
Wave Activity ◽  
Late Winter ◽  
Easterly Wind ◽  
Weather Forecasts ◽  
Stratospheric Circulation

<p>Sudden Stratospheric Warming (SSW) is the most spectacular dynamic event occurring in the middle atmosphere. It can lead to a warming of the winter polar stratosphere by a few tens of K in one to two weeks and a reversal of the stratospheric circulation from wintertime prevailing westerly winds to easterly winds similar to summer conditions. This strong modification of the stratospheric circulation has consequences for several applications, including the modification of the stratospheric infrasound guide. Depending on the date of the SSW, the westerly circulation can be re-established if the SSW occurs in mid-winter or the summer easterly circulation can be definitively established if the SSW occurs in late winter. In the latter case it is called Final Warming (FW). Each year, it is possible to define the date of the FW as the date of the final inversion of the zonal wind at 60°N - 10 hPa . If the FW is associated with a strong peak of planetary wave activity and a rapid increase in polar temperature, it is classified as dynamic FW. If the transition to the easterly wind is smooth without planetary wave activity, the FW is classified as radiative.</p><p>The analysis of the ERA5 database, which has recently been extended to 1950 (71 years of data), allowed a statistical analysis of the evolution of the stratosphere in winter. The main conclusions of this study will be presented :</p><p>- the state of the polar vortex in a given month is anticorrelated with its state 2 to 3 months earlier. The beginning of winter is anticorrelated with mid-winter and mid-winter is anticorrelated with the end of winter;</p><p>- dynamic FWs occur early in the season (March - early April) and are associated with a strong positive polar temperature anomaly, while radiative FWs occur later (late April - early May) without a polar temperature anomaly;</p><p>- the summer stratosphere (polar temperature and zonal wind) keeps the memory of its state in April-May at the time of FW at least until July .</p><p>These results could help to improve medium-range weather forecasts in the Northern Hemisphere due to the strong dynamic coupling between the troposphere and stratosphere during SSW events.</p>

The Dynamical Response to Snow Cover Perturbations in a Large Ensemble of Atmospheric GCM Integrations

2009 ◽  
Vol 22 (5) ◽  
pp. 1208-1222 ◽  
Author(s):  
Christopher G. Fletcher ◽  
Steven C. Hardiman ◽  
Paul J. Kushner ◽  
Judah Cohen
Keyword(s):  
Snow Cover ◽  
General Circulation ◽  
Circulation Model ◽  
Wave Activity ◽  
Dynamical Response ◽  
Mean Flow ◽  
Surface Cooling ◽  
Fall Season ◽  
Annular Mode ◽  
Northern Annular Mode

Abstract Variability in the extent of fall season snow cover over the Eurasian sector has been linked in observations to a teleconnection with the winter northern annular mode pattern. Here, the dynamics of this teleconnection are investigated using a 100-member ensemble of transient integrations of the GFDL atmospheric general circulation model (AM2). The model is perturbed with a simple persisted snow anomaly over Siberia and is integrated from October through December. Strong surface cooling occurs above the anomalous Siberian snow cover, which produces a tropospheric form stress anomaly associated with the vertical propagation of wave activity. This wave activity response drives wave–mean flow interaction in the lower stratosphere and subsequent downward propagation of a negative-phase northern annular mode response back into the troposphere. A wintertime coupled stratosphere–troposphere response to fall season snow forcing is also found to occur even when the snow forcing itself does not persist into winter. Finally, the response to snow forcing is compared in versions of the same model with and without a well-resolved stratosphere. The version with the well-resolved stratosphere exhibits a faster and weaker response to snow forcing, and this difference is tied to the unrealistic representation of the unforced lower-stratospheric circulation in that model.

The Role of Linear Interference in the Annular Mode Response to Extratropical Surface Forcing

2010 ◽  
Vol 23 (22) ◽  
pp. 6036-6050 ◽  
Author(s):  
Karen L. Smith ◽  
Christopher G. Fletcher ◽  
Paul J. Kushner
Keyword(s):  
Rossby Wave ◽  
General Circulation ◽  
Classical Problem ◽  
Circulation Model ◽  
Wave Activity ◽  
Surface Cooling ◽  
Annular Mode ◽  
Positive Tendency ◽  
Phase Wave ◽  
Wave Response

Abstract The classical problem of predicting the atmospheric circulation response to extratropical surface forcing is revisited in the context of the observed connection between autumnal snow cover anomalies over Siberia and wintertime anomalies of the northern annular mode (NAM). Previous work has shown that in general circulation model (GCM) simulations in which autumnal Siberian snow forcing is prescribed, a vertically propagating Rossby wave train is generated that propagates into the stratosphere, drives dynamical stratospheric warming, and induces a negative NAM response that couples to the troposphere. Important questions remain regarding the dynamics of the response to this surface cooling. It is shown that previously unexplained aspects of the evolution of the response in a comprehensive GCM can be explained by examining the time evolution of the phasing, and hence the linear interference, between the Rossby wave response and the background climatological stationary wave. When the wave response and background wave are in phase, wave activity into the stratosphere is amplified and the zonal-mean stratosphere–troposphere NAM response displays a negative tendency; when they are out of phase, wave activity into the stratosphere is reduced and the NAM response displays a positive tendency. The effects of linear interference are probed further in a simplified GCM, where an imposed lower tropospheric cooling is varied in position, strength, and sign. As in the comprehensive GCM, linear interference strongly influences the response over a realistic range of forcing strengths. The transition from linear to nonlinear behavior is shown to depend simply on forcing strength.

Case studies of the relation between upper-tropospheric wave propagation and the Red Sea trough

2021 ◽  
Author(s):  
Zakieh Alizadeh ◽  
Alireza Mohebalhojeh ◽  
Farhang Ahmadi-Givi ◽  
Mohammad Mirzaei ◽  
Sakineh Khansalari
Keyword(s):  
Saudi Arabia ◽  
Red Sea ◽  
Rossby Wave ◽  
Meridional Circulation ◽  
Eastern Mediterranean ◽  
Storm Track ◽  
Wave Activity ◽  
The North ◽  
Wave Activity Flux ◽  
Precipitation Events

<p>In recent history, the eastern Mediterranean and Saudi Arabia have experienced extreme precipitation events involving significant financial and human losses. An important subset of these events is associated with the activation of the Red Sea trough (RST). In this study, the effect and role of Rossby wave propagation during three cases (Dec 1993, Jan 2011 and May 1982) of the active RST is investigated. Meanwhile, the synoptic and dynamic factors related to the tropical-extratropical interaction and the lower and upper levels of troposphere are discussed for each event. The data used were extracted from the Era-Interim subsection of the ECMWF database with a time step of 6 hours and a spatial step of 80 km in both latitude and longitude directions.</p><p>Despite differences in humidity sources and the amount of hot and humid air ascent in each event, a general pattern can be deduced in all three events. The results show that in all events from a few days before the maximum rainfall, fluxes of heat and humidity are directed to Saudi Arabia and the eastern Mediterranean and the RST is strengthened and extended to the east of the Mediterranean Sea. At the same time, a trough with varying intensity at the level of 500 hPa in the eastern Mediterranean exerts a southward influence, which is caused by the anticyclonic Rossby wave breaking. At the upper levels, associated with the wave activity flux divergence and convergence areas of the Mediterranean storm track, higher amounts of Rossby wave activity enter the northeast region of Africa. Also the meridional convergence of the wave activity flux strengthens the meridional circulation in the north of the Red Sea. Increased horizontal wave activity flux to the northeast Africa and the Red Sea is led to increased head and humidity flux to the region. On the other hand, the weakening of the extension of the Azores high pressure over Africa facilitates the tropical and extratropical interactions over the region. Also in the north or northeast of the Red Sea, a surface low pressure is formed. Having a different source in each case, the mid-level troughs exhibit a northwest-southeast title with respect to the surface lows which lead to baroclinic development and intensification of precipitation events in the eastern Mediterranean and Saudi Arabia.</p><p><strong>Keywords: </strong>Extreme precipitation, Rossby wave activity flux, Mediterranean storm track, upper level trough, meridional circulation, baroclinic development</p>

Influence of energetic particle precipitation on polar vortex mediated by planetary wave activity

2021 ◽  
Author(s):  
Timo Asikainen ◽  
Antti Salminen ◽  
Ville Maliniemi ◽  
Kalevi Mursula
Keyword(s):  
Planetary Wave ◽  
Energetic Electron ◽  
Polar Vortex ◽  
Analysis Data ◽  
Wave Activity ◽  
Necessary Condition ◽  
Atmospheric Conditions ◽  
Mean Flow ◽  
Ozone Loss ◽  
Near Earth Space

<p>The northern polar vortex experiences considerable inter-annual variability, which is also reflected to tropospheric weather. Recent research has established a link between polar vortex variations and energetic electron precipitation (EEP) from the near-Earth space into the polar atmosphere, which is mediated by EEP-induced chemical changes causing ozone loss in the mesosphere and stratosphere. However, the most dramatic changes in the polar vortex are due to strong enhancements of planetary wave activity, which typically result in a sudden stratospheric warming (SSW), a momentary breakdown of the polar vortex. Here we use the SSWs as an indicator of high planetary wave activity and consider their influence of SSWs on the atmospheric response to EEP in 1957-2017 using combined ERA-40 and ERA-Interim re-analysis data and geomagnetic activity as a proxy of EEP. We find that the EEP-related enhancement of the polar vortex and other associated dynamical responses are seen only during winters when a SSW occurs, and that the EEP-related changes take place slightly before the SSW onset. We show that the atmospheric conditions preceding SSWs favor enhanced wave-mean-flow interaction, which can dynamically amplify the initial polar vortex enhancement caused by ozone loss. These results highlight the importance of considering SSWs and sufficient level of planetary wave activity as a necessary condition for observing the effects of EEP on the polar vortex dynamics.</p>

scholarly journals Submonthly Polar Vortex Variability and Stratosphere–Troposphere Coupling in the Arctic

2009 ◽  
Vol 22 (22) ◽  
pp. 5886-5901 ◽  
Author(s):  
Robert X. Black ◽  
Brent A. McDaniel
Keyword(s):  
Intraseasonal Variability ◽  
Polar Vortex ◽  
Principal Component ◽  
The Arctic ◽  
Stratospheric Polar Vortex ◽  
Annular Mode ◽  
Northern Annular Mode ◽  
Second Mode ◽  
Latitudinal Position ◽  
Highly Correlated

Abstract A principal component analysis is performed to characterize intraseasonal variability in the boreal stratospheric polar vortex. In contrast to previous studies, the current analysis examines daily zonal-mean variability within a limited spatial domain encompassing the stratospheric polar vortex. The leading EOFs are vertically coherent north–south dipoles in the zonal-mean zonal wind extending through the lower stratosphere. The first mode represents variability in polar vortex strength and is highly correlated with the stratospheric northern annular mode (SNAM). The second mode, the polar annular mode (PAM), represents variability in the latitudinal position of the polar vortex and possesses a poleward-retracted dipole anomaly structure. Composite analyses indicate that large-amplitude PAM events are relatively short lived (1–2 weeks) compared to SNAM events (1 month or longer). Trend analyses further reveal that recent decadal trends in the boreal polar vortex project more strongly onto PAM than SNAM. Composite analyses illustrate that the time evolution of sudden stratospheric warming events is dominated by SNAM, whereas SNAM and PAM play approximately equal roles in final warming events. Linear regression analyses reveal that SNAM and PAM result in circumpolar circulation and temperature anomalies of similar magnitudes within the high-latitude troposphere. It is concluded that PAM represents a previously unrecognized annular mode that strongly couples the stratosphere and troposphere on submonthly time scales at mid- to high latitudes. It is further suggested that the SNAM/PAM framework provides a means for isolating the proximate tropospheric response to respective variations in the strength and position of the stratospheric polar vortex.

The Role of Linear Interference in Northern Annular Mode Variability Associated with Eurasian Snow Cover Extent

2011 ◽  
Vol 24 (23) ◽  
pp. 6185-6202 ◽  
Author(s):  
Karen L. Smith ◽  
Paul J. Kushner ◽  
Judah Cohen
Keyword(s):  
Snow Cover ◽  
Rossby Wave ◽  
Wave Train ◽  
Stationary Wave ◽  
Wave Activity ◽  
Northern Annular Mode ◽  
Eurasian Snow Cover ◽  
Eurasian Snow ◽  
Rossby Wave Train ◽  
Wave Activity Flux

Abstract One of the outstanding questions regarding the observed relationship between October Eurasian snow cover anomalies and the boreal winter northern annular mode (NAM) is what causes the multiple-week lag between positive Eurasian snow cover anomalies in October and the associated peak in Rossby wave activity flux from the troposphere to the stratosphere in December. This study explores the following hypothesis about this lag: in order to achieve amplification of the wave activity, the vertically propagating Rossby wave train associated with the snow cover anomaly must reinforce the climatological stationary wave, which corresponds to constructive linear interference between the anomalous wave and the climatological wave. It is shown that the lag in peak wave activity flux arises because the Rossby wave train associated with the snow cover is in quadrature or out of phase with the climatological stationary wave from October to mid-November. Beginning in mid-November the associated wave anomaly migrates into a position that is in phase with the climatological wave, leading to constructive interference and anomalously positive upward wave activity fluxes until mid-January. Climate models from the Coupled Model Intercomparison Project 3 (CMIP3) do not capture this behavior. This linear interference effect is not only associated with stratospheric variability related to Eurasian snow cover anomalies but is a general feature of Northern Hemisphere troposphere–stratosphere interactions and, in particular, dominated the negative NAM events of the fall–winter of 2009/10.

scholarly journals A Numerical Sensitivity Study of the Influence of Siberian Snow on the Northern Annular Mode

2012 ◽  
Vol 25 (2) ◽  
pp. 592-607 ◽  
Author(s):  
Y. Peings ◽  
D. Saint-Martin ◽  
H. Douville
Keyword(s):  
General Circulation ◽  
Arctic Oscillation ◽  
Polar Vortex ◽  
Circulation Model ◽  
Sensitivity Study ◽  
The Arctic ◽  
Annular Mode ◽  
Northern Annular Mode ◽  
Model Free ◽  
The Arctic Oscillation

Abstract The climate version of the general circulation model Action de Recherche Petite Echelle Grande Echelle (ARPEGE-Climat) is used to explore the relationship between the autumn Siberian snow and the subsequent winter northern annular mode by imposing snow anomalies over Siberia. As the model presents some biases in the representation of the polar vortex, a nudging methodology is used to obtain a more realistic but still interactive extratropical stratosphere in the model. Free and nudged sensitivity experiments are compared to discuss the dependence of the results on the northern stratosphere climatology. For each experiment, a positive snow mass anomaly imposed from October to March over Siberia leads to significant impacts on the winter atmospheric circulation in the extratropics. In line with previous studies, the model response resembles the negative phase of the Arctic Oscillation. The well-documented stratospheric pathway between snow and the Arctic Oscillation operates in the nudged experiment, while a more zonal propagation of the signal is found in the free experiment. Thus, the study provides two main findings: it supports the influence of Siberian snow on the winter extratropical circulation and highlights the importance of the northern stratosphere representation in the models to capture this teleconnection. These findings could have important implications for seasonal forecasting, as most of the operational models present biases similar to those of the ARPEGE-Climat model.

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