scholarly journals Stratosphere–Troposphere Coupling in the Southern Hemisphere

2005 ◽  
Vol 62 (3) ◽  
pp. 708-715 ◽  
Author(s):  
David W. J. Thompson ◽  
Mark P. Baldwin ◽  
Susan Solomon
Keyword(s):  
Climate Variability ◽  
Southern Hemisphere ◽  
Large Scale ◽  
Temporal Evolution ◽  
Polar Vortex ◽  
Climate Impacts ◽  
Sudden Stratospheric Warming ◽  
Stratospheric Polar Vortex ◽  
Tropospheric Circulation ◽  
Stratospheric Variability

Abstract This study examines the temporal evolution of the tropospheric circulation following large-amplitude variations in the strength of the Southern Hemisphere (SH) stratospheric polar vortex in data from 1979 to 2001 and following the SH sudden stratospheric warming of 2002. In both cases, anomalies in the strength of the SH stratospheric polar vortex precede similarly signed anomalies in the tropospheric circulation that persist for more than 2 months. The SH tropospheric circulation anomalies reflect a bias in the polarity of the SH annular mode (SAM), a large-scale pattern of climate variability characterized by fluctuations in the strength of the SH circumpolar flow. Consistent with the climate impacts of the SAM, variations in the stratospheric polar vortex are also followed by coherent changes in surface temperatures throughout much of Antarctica. The results add to a growing body of evidence that suggests that stratospheric variability plays an important role in driving climate variability at Earth’s surface on a range of time scales.

scholarly journals Nonstationarity in Southern Hemisphere Climate Variability Associated with the Seasonal Breakdown of the Stratospheric Polar Vortex

2017 ◽  
Vol 30 (18) ◽  
pp. 7125-7139 ◽  
Author(s):  
Nicholas J. Byrne ◽  
Theodore G. Shepherd ◽  
Tim Woollings ◽  
R. Alan Plumb
Keyword(s):  
Climate Variability ◽  
Southern Hemisphere ◽  
Seasonal Cycle ◽  
Vortex Breakdown ◽  
Polar Vortex ◽  
Reanalysis Data ◽  
Early Summer ◽  
Stratospheric Polar Vortex ◽  
Time Symmetry

Abstract Statistical models of climate generally regard climate variability as anomalies about a climatological seasonal cycle, which are treated as a stationary stochastic process plus a long-term seasonally dependent trend. However, the climate system has deterministic aspects apart from the climatological seasonal cycle and long-term trends, and the assumption of stationary statistics is only an approximation. The variability of the Southern Hemisphere zonal-mean circulation in the period encompassing late spring and summer is an important climate phenomenon and has been the subject of numerous studies. It is shown here, using reanalysis data, that this variability is rendered highly nonstationary by the organizing influence of the seasonal breakdown of the stratospheric polar vortex, which breaks time symmetry. It is argued that the zonal-mean tropospheric circulation variability during this period is best viewed as interannual variability in the transition between the springtime and summertime regimes induced by variability in the vortex breakdown. In particular, the apparent long-term poleward jet shift during the early-summer season can be more simply understood as a delay in the equatorward shift associated with this regime transition. The implications of such a perspective for various open questions are discussed.

The Combined Influence of the Stratospheric Polar Vortex and ENSO on Zonal Asymmetries in the Southern Hemisphere Upper Tropospheric Circulation during Austral Spring and Summer

2021 ◽  
Author(s):  
Marisol Osman ◽  
Theodore Shepherd ◽  
Carolina Vera
Keyword(s):  
Southern Hemisphere ◽  
Southern Oscillation ◽  
Polar Vortex ◽  
Austral Spring ◽  
Stratospheric Polar Vortex ◽  
Wave Source ◽  
Weather Forecasts ◽  
Rossby Wave Source ◽  
Enso Teleconnections ◽  
Tropospheric Circulation

<p>The influence of El Niño Southern Oscillation (ENSO) and the Stratospheric Polar Vortex (SPV) on the zonal asymmetries in the Southern Hemisphere atmospheric circulation during spring and summer is examined. The main objective is to explore if the SPV can modulate the ENSO teleconnections in the extratropics. We use a large ensemble of seasonal hindcasts from the European Centre for Medium-Range Weather Forecasts Integrated Forecast System to provide a much larger sample size than is possible from the observations alone.</p><p>We find a small but statistically significant relationship between ENSO and the SPV, with El Niño events occurring with weak SPV and La Niña events occurring with strong SPV more often than expected by chance, in agreement with previous works. We show that the zonally asymmetric response to ENSO and SPV can be mainly explained by a linear combination of the response to both forcings, and that they can combine constructively or destructively. From this perspective, we find that the tropospheric asymmetries in response to ENSO are more intense when El Niño events occur with weak SPV and La Niña events occur with strong SPV, at least from September through December. In the stratosphere, the ENSO teleconnections are mostly confounded by the SPV signal. The analysis of Rossby Wave Source and of wave activity shows that both are stronger when El Niño events occur together with weak SPV, and when La Niña events occur together with strong SPV.</p>

scholarly journals Arctic Oscillation impact on thermal regime in the Eastern part of the Baltic region

2016 ◽  
Vol 2 (1) ◽  
pp. 89-96
Author(s):  
Индре Гечайте ◽  
Indre Gecaite ◽  
Александр Погорельцев ◽  
Aleksandr Pogoreltsev ◽  
Александр Угрюмов ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
Geomagnetic Activity ◽  
Large Scale ◽  
Arctic Oscillation ◽  
Polar Vortex ◽  
Baltic Region ◽  
Stratospheric Polar Vortex ◽  
Weather Forecasts ◽  
Tropospheric Circulation ◽  
The Baltic

The paper presents statistical estimations of Arctic Oscillation (AO) impact on air temperature regime in the eastern part of the Baltic region. The region is characterized by high inter-annual and inter-seasonal variability. It is important to note that in the region of global warming extremely low winter temperatures can be observed on the European territory of Russia. AO is one of the large-scale global patterns of atmospheric circulation closely associated with weather variability in northern Europe. AО anomalies occur in the upper atmosphere (stratosphere) and only then are transferred to tropospheric lower layers. The anomalies can persist over a long period of time (up to two months); so they can serve as precursors in long-range weather forecasts. In turn, changes in stratospheric polar vortex and sudden stratospheric warmings can be related to geomagnetic activity. Perhaps geomagnetic activity influences the meridional temperature gradient and then changes the structure of the stratospheric zonal wind. These changes have an effect on the tropospheric circulation. The stratosphere–troposphere coupling takes place during winter months. Therefore, the paper deals with extremely cold winter anomalies in the eastern part of the Baltic Sea region. At the same time, we examine atmospheric circulation peculiarities associated with AO phase change. We analyze data for 1951–2014.

Exploring the Tropospheric Response to Stratospheric Variability Using Lagged Quantile Regression

2021 ◽  
Author(s):  
Kathrin Finke ◽  
Abdel Hannachi
Keyword(s):  
Quantile Regression ◽  
Conditional Distribution ◽  
Polar Vortex ◽  
Supplementary Information ◽  
Reanalysis Dataset ◽  
Stratospheric Polar Vortex ◽  
Response Variable ◽  
Tropospheric Circulation ◽  
The Impact ◽  
Stratospheric Variability

<p>Stratospheric variability has become increasingly popular due to its potential impact on the tropospheric circulation. Extreme states of the stratospheric polar vortex have been associated with reoccurring tropospheric weather patterns more than 2-3 weeks after the initial stratospheric signal. Standard linear regression methods used to assess the statistical stratosphere-troposphere connection estimate the distribution's mean effect of a stratospheric variable as a predictor on a tropospheric response variable. However,  supplementary information of the impact of extreme stratospheric behavior is hidden in the tails of the distribution, revealing a different behavior than the mean. Therefore, we use quantile regression, a method that enables us to model the complete conditional distribution of the response variable. This presentation explores various quantiles of the conditional distribution to investigate the impact of stratospheric variability on the tropospheric circulation using the ERA5 reanalysis dataset. Comparison between (lagged) linear and (lagged) quantile regression reveals significant differences making the latter method a neat tool that offers valuable information about the statistical connection between the stratosphere and the troposphere.</p>

scholarly journals The Splitting of the Stratospheric Polar Vortex in the Southern Hemisphere, September 2002: Dynamical Evolution

2005 ◽  
Vol 62 (3) ◽  
pp. 590-602 ◽  
Author(s):  
Andrew J. Charlton ◽  
Alan O’Neill ◽  
William A. Lahoz ◽  
Paul Berrisford
Keyword(s):  
High Resolution ◽  
Southern Hemisphere ◽  
Large Scale ◽  
Dynamical Evolution ◽  
Polar Vortex ◽  
Dynamical Analysis ◽  
Stratospheric Polar Vortex ◽  
Upper Troposphere ◽  
Dynamical Features ◽  
Stratospheric Circulation

Abstract The polar vortex of the Southern Hemisphere (SH) split dramatically during September 2002. The large-scale dynamical effects were manifest throughout the stratosphere and upper troposphere, corresponding to two distinct cyclonic centers in the upper troposphere–stratosphere system. High-resolution (T511) ECMWF analyses, supplemented by analyses from the Met Office, are used to present a detailed dynamical analysis of the event. First, the anomalous evolution of the SH polar vortex is placed in the context of the evolution that is usually witnessed during spring. Then high-resolution fields of potential vorticity (PV) from ECMWF are used to reveal several dynamical features of the split. Vortex fragments are rapidly sheared out into sheets of high (modulus) PV, which subsequently roll up into distinct synoptic-scale vortices. It is proposed that the stratospheric circulation becomes hydrodynamically unstable through a significant depth of the troposphere–stratosphere system as the polar vortex elongates.

scholarly journals The wave geometry of final stratospheric warming events

2021 ◽  
Vol 2 (2) ◽  
pp. 453-474
Author(s):  
Amy H. Butler ◽  
Daniela I. V. Domeisen
Keyword(s):  
Southern Hemisphere ◽  
Polar Vortex ◽  
Stratospheric Warming ◽  
Stratospheric Polar Vortex ◽  
Total Column Ozone ◽  
Planetary Scale ◽  
Tropospheric Circulation ◽  
Column Ozone ◽  
Total Column

Abstract. Every spring, the stratospheric polar vortex transitions from its westerly wintertime state to its easterly summertime state due to seasonal changes in incoming solar radiation, an event known as the “final stratospheric warming” (FSW). While FSWs tend to be less abrupt than reversals of the boreal polar vortex in midwinter, known as sudden stratospheric warming (SSW) events, their timing and characteristics can be significantly modulated by atmospheric planetary-scale waves. While SSWs are commonly classified according to their wave geometry, either by how the vortex evolves (whether the vortex displaces off the pole or splits into two vortices) or by the dominant wavenumber of the vortex just prior to the SSW (wave-1 vs. wave-2), little is known about the wave geometry of FSW events. We here show that FSW events for both hemispheres in most cases exhibit a clear wave geometry. Most FSWs can be classified into wave-1 or wave-2 events, but wave-3 also plays a significant role in both hemispheres. The timing and classification of the FSW are sensitive to which pressure level the FSW central date is defined, particularly in the Southern Hemisphere (SH) where trends in the FSW dates associated with ozone depletion and recovery are more evident at 50 than 10 hPa. However, regardless of which FSW definition is selected, we find the wave geometry of the FSW affects total column ozone anomalies in both hemispheres and tropospheric circulation over North America. In the Southern Hemisphere, the timing of the FSW is strongly linked to both total column ozone before the event and the tropospheric circulation after the event.

scholarly journals A meridional structure of static stability and ozone vertical gradient around the tropopause in the Southern Hemisphere extratropics

2010 ◽  
Vol 10 (8) ◽  
pp. 19175-19194 ◽  
Author(s):  
Y. Tomikawa ◽  
T. Yamanouchi
Keyword(s):  
Southern Hemisphere ◽  
Seasonal Variations ◽  
Inversion Layer ◽  
Polar Vortex ◽  
Vertical Gradient ◽  
Static Stability ◽  
Radiative Heating ◽  
Stratospheric Polar Vortex ◽  
Close Relationship ◽  
The Antarctic

Abstract. An analysis of the static stability and ozone vertical gradient in the ozone tropopause based (OTB) coordinate is applied to the ozonesonde data at 10 stations in the Southern Hemisphere (SH) extratropics. The tropopause inversion layer (TIL) with a static stability maximum just above the tropopause shows similar seasonal variations at two Antarctic stations, which are latitudinally far from each other. Since the sunshine hour varies with time in a quite different way between these two stations, it implies that the radiative heating due to solar ultraviolet absorption of ozone does not contribute to the seasonal variation of the TIL. A meridional section of the static stability in the OTB coordinate shows that the static stability just above the tropopause has a large latitudinal gradient between 60° S and 70° S in austral winter because of the absence of the TIL over the Antarctic. It is accompanied by an increase of westerly shear with height above the tropopause, so that the polar-night jet is formed above this latitude region. This result suggests a close relationship between the absence of the TIL and the stratospheric polar vortex in the Antarctic winter. A vertical gradient of ozone mixing ratio, referred to as ozone vertical gradient, around the tropopause shows similar latitudinal and seasonal variations with the static stability in the SH extratropics. In a height region above the TIL, a small ozone vertical gradient in the midlatitudes associated with the Antarctic ozone hole is observed in a height region of the subvortex but not around the polar vortex. This is a clear evidence of active latitudinal mixing between the midlatitudes and subvortex.

scholarly journals Bifurcation of potential vorticity gradients across the Southern Hemisphere stratospheric polar vortex

2018 ◽  
Vol 18 (11) ◽  
pp. 8065-8077 ◽  
Author(s):  
Jonathan Conway ◽  
Greg Bodeker ◽  
Chris Cameron
Keyword(s):  
Southern Hemisphere ◽  
Potential Vorticity ◽  
Polar Vortex ◽  
Trace Gas ◽  
Stratospheric Polar Vortex ◽  
Distinct Structure ◽  
Barrier Region ◽  
Westerly Winds ◽  
Antarctic Continent ◽  
The Antarctic

Abstract. The wintertime stratospheric westerly winds circling the Antarctic continent, also known as the Southern Hemisphere polar vortex, create a barrier to mixing of air between middle and high latitudes. This dynamical isolation has important consequences for export of ozone-depleted air from the Antarctic stratosphere to lower latitudes. The prevailing view of this dynamical barrier has been an annulus compromising steep gradients of potential vorticity (PV) that create a single semi-permeable barrier to mixing. Analyses presented here show that this barrier often displays a bifurcated structure where a double-walled barrier exists. The bifurcated structure manifests as enhanced gradients of PV at two distinct latitudes – usually on the inside and outside flanks of the region of highest wind speed. Metrics that quantify the bifurcated nature of the vortex have been developed and their variation in space and time has been analysed. At most isentropic levels between 395 and 850 K, bifurcation is strongest in mid-winter and decreases dramatically during spring. From August onwards a distinct structure emerges, where elevated bifurcation remains between 475 and 600 K, and a mostly single-walled barrier occurs at other levels. While bifurcation at a given level evolves from month to month, and does not always persist through a season, interannual variations in the strength of bifurcation display coherence across multiple levels in any given month. Accounting for bifurcation allows the region of reduced mixing to be better characterised. These results suggest that improved understanding of cross-vortex mixing requires consideration of the polar vortex not as a single mixing barrier but as a barrier with internal structure that is likely to manifest as more complex gradients in trace gas concentrations across the vortex barrier region.

Stratospheric influence on idealised baroclinic life cycles

2020 ◽  
Author(s):  
Philip Rupp ◽  
Thomas Birner
Keyword(s):  
Life Cycle ◽  
Initial Conditions ◽  
Polar Vortex ◽  
Life Cycles ◽  
Stratospheric Polar Vortex ◽  
Shift Response ◽  
Tropospheric Circulation ◽  
Wave Development ◽  
Final Steady State ◽  
Numerical Model Experiments

<p>The importance of understanding the dynamical coupling of troposphere and stratosphere to make accurate weather and climate predictions is well-known. Over the past years and decades various signatures of such a<br>coupling have been discovered. A very robust result, for example, seems to be an equatorward shift of the tropospheric eddy driven jet following sudden stratospheric warming events, where the westerly winds of the stratospheric polar vortex weaken or even reverse. However, many aspects of this fundamental coupling are still not fully understood and research on how the state of the stratosphere can influence the tropospheric circulation and what dynamical processes are involved is still ongoing.</p><p><br>An important such process arises due to the interaction of a sharp, localised maximum in potential vorticity gradient near the tropopause with baroclinic eddies in the troposphere. Here, we analyse the sensitivity of baroclinic wave development and evolution to changes of various basic state characteristics, by performing a series of idealised baroclinic eddy life cycle experiments. Special attention is paid to sensitivities associated with the dynamical state of the stratosphere. We find that the final (steady) state of the life cycle simulations corresponds to an equatorward shift of the tropospheric jet in cases where the initial conditions do not include a stratospheric polar vortex (such as following sudden warming events) compared to those that do. These results further support the idea that the stratospheric state can strongly influence tropospheric dynamics and, in particular, highlight the robustness of the jet shift response following sudden warmings, that can be seen in a range of observations and numerical model experiments.</p>

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