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.

Temperature Variation over East Asia during the Lifecycle of Weak Stratospheric Polar Vortex

2015 ◽  
Vol 28 (14) ◽  
pp. 5857-5872 ◽  
Author(s):  
Sung-Ho Woo ◽  
Baek-Min Kim ◽  
Jong-Seong Kug
Keyword(s):  
East Asia ◽  
Temperature Variation ◽  
Large Scale ◽  
East Asian ◽  
Polar Vortex ◽  
Tropospheric Temperature ◽  
Stratospheric Polar Vortex ◽  
The North ◽  
Stratospheric Circulation ◽  
Upper Level

Abstract The authors investigate the circulation change during the life cycle of a weak stratospheric polar vortex (WSV) event and its impact on temperature variation over East Asia. The lower-tropospheric temperature over East Asia strongly fluctuates despite the slow decay of stratospheric circulation and the continuously negative Arctic Oscillation (AO) pattern during the WSV event. The temperature fluctuation is critically influenced by the variation of the East Asian upper-level coastal trough (EAT), which may be coupled to the stratospheric circulation during the WSV events. The EAT is deepened anomalously during the Peak phase (from lag −5 to lag 5 day) of the WSV, and East Asian temperature is lowest during this phase. During the next period (Decay-1 phase: from lag 6 to lag 16 day), in spite of the slowly decaying WSV condition, the cold temperature anomaly over East Asia is suddenly weakened; this change is caused by a westward-propagating signal of an anticyclonic anomaly from the North Pacific to East Asia. After about two weeks (Decay-2 phase: from lag 17 to lag 27 day), the cold conditions over East Asia are restrengthened by an intensification of EAT, which is related to the eastward propagation of a large-scale wave packet originating from a negative North Atlantic Oscillation (NAO)-type structure in the Decay-1 phase and its delayed influence on the East Asia region.

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.

Analysis of interaction between parameterized orographic gravity wave drag and resolved dynamics in CMAM.

2021 ◽  
Author(s):  
Petr Šácha ◽  
Aleš Kuchař ◽  
Christoph Jacobi ◽  
Petr Pišoft ◽  
Roland Eichinger ◽  
...  
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Rossby Waves ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Dynamical Analysis ◽  
Future Research ◽  
Stratospheric Polar Vortex

<div class="page" title="Page 1"> <div class="layoutArea"> <div class="column"> <p>In the extratropical atmosphere, Rossby waves (RWs) and internal gravity waves (GWs) propagating from the troposphere mediate a coupling with the middle atmosphere by influencing the dynamics herein. In current generation chemistry-climate models (CCMs), GWs are usually smaller than the model resolution and the majority of their spectrum therefore must be parameterized. From observations, we know that GWs are intermittent and asymmetrically distributed around the globe, which holds to some extent also for the parameterized GW drag (GWD) (in particular for orographic GWD (oGWD)). The GW parameterizations in CCMs are usually tuned to mitigate biases in the zonal mean climatology of particular quantities, but the complex interaction of parameterized GWs with the large- scale circulation and resolved waves in the models remains to date poorly understood.</p> <p>This presentation will combine observational evidence, idealized modeling and dynamical analysis of a CCM output to study both the short-term and long-term model response to the oGWD. Our results demonstrate that the oGW-resolved dynamics interaction is a complex two-way process, with the most prominent oGWD impact being the alteration of propagation of planetary-scale Rossby waves on a time-scale of a few days. The conclusions give a novel perspective on the importance of oGWD for the stratospheric polar vortex and atmospheric transport studies outlining potential foci of future research.</p> </div> </div> </div>

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.

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.

scholarly journals Stratosphere–Troposphere Exchange and O3 Decline in the Lower Stratosphere over Irene SHADOZ Site, South Africa

2020 ◽  
Author(s):  
Thumeka Mkololo ◽  
Nkanyiso Mbatha ◽  
Sivakumar Venkataraman ◽  
Nelson Begue ◽  
Gerrie Coetzee ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Potential Vorticity ◽  
Lower Stratosphere ◽  
Polar Vortex ◽  
Air Masses ◽  
Upper Troposphere ◽  
Average Decrease ◽  
Ozone Trends ◽  
K 12 ◽  
Troposphere Ozone

This study aims to investigate the Stratosphere-Troposphere Exchange (STE) events and ozone trends over Irene (25.5°S, 28.1°E). Twelve years of ozonesondes data (2000–2007, 2012–2015) from Irene station operating in the framework of the Southern Hemisphere Additional Ozonesodes (SHADOZ) was used to study the troposphere (0–16 km) and stratosphere (17– 28 km) ozone (O3) vertical profiles. Ozone profiles were grouped into three categories (2000–2003, 2004–2007 and 2012–2015) and average composites were calculated for each category. Fifteen O3 enhancement events were identified over the study period. These events were observed in all seasons (one event in summer, four events in autumn, five events in winter and five events in spring), however, they predominantly occur in winter and spring. The STE events presented here are observed to be influenced by the Southern Hemisphere polar vortex. During the STE events, the advected potential vorticity maps assimilated using Modélisation Isentrope du transport Méso–échelle de l’Ozone Stratosphérique par Advection (MIMOSA) model for the 350 K (~12–13 km) isentropic level indicated a transport of high latitude air masses which seems to be responsible for the reduction of the O3 mole fractions at the lower stratosphere over Irene which takes place at the same time with the enhancement of ozone in the upper troposphere. In general, the stratosphere is dominated by higher Modern Retrospective Analysis for Research Application (MERRA-2) potential vorticity (PV) values compared to the troposphere. However, during the STE events, higher PV values from the stratosphere were observed to intrude the troposphere. Ozone decline was observed from 12 km to 24 km with highest decline occurring from 14 km to 18 km. An average decrease of 6.0 and 9.1% was calculated from 12 to 24 km in 2004–2007 and 2012–2015 respectively. The observed decline occurred in the upper troposphere and lower stratosphere with winter and spring showing more decline compared with summer and autumn.

scholarly journals Windows of Opportunity for Skillful Forecasts Subseasonal to Seasonal and Beyond

2020 ◽  
Vol 101 (5) ◽  
pp. E608-E625 ◽  
Author(s):  
Annarita Mariotti ◽  
Cory Baggett ◽  
Elizabeth A. Barnes ◽  
Emily Becker ◽  
Amy Butler ◽  
...  
Keyword(s):  
Land Surface ◽  
Large Scale ◽  
Polar Vortex ◽  
Prediction Skill ◽  
High Demand ◽  
Stratospheric Polar Vortex ◽  
Weather Forecasts ◽  
Windows Of Opportunity ◽  
Process Understanding ◽  
Persistent Anomalies

Abstract There is high demand and a growing expectation for predictions of environmental conditions that go beyond 0–14-day weather forecasts with outlooks extending to one or more seasons and beyond. This is driven by the needs of the energy, water management, and agriculture sectors, to name a few. There is an increasing realization that, unlike weather forecasts, prediction skill on longer time scales can leverage specific climate phenomena or conditions for a predictable signal above the weather noise. Currently, it is understood that these conditions are intermittent in time and have spatially heterogeneous impacts on skill, hence providing strategic windows of opportunity for skillful forecasts. Research points to such windows of opportunity, including El Niño or La Niña events, active periods of the Madden–Julian oscillation, disruptions of the stratospheric polar vortex, when certain large-scale atmospheric regimes are in place, or when persistent anomalies occur in the ocean or land surface. Gains could be obtained by increasingly developing prediction tools and metrics that strategically target these specific windows of opportunity. Across the globe, reevaluating forecasts in this manner could find value in forecasts previously discarded as not skillful. Users’ expectations for prediction skill could be more adequately met, as they are better aware of when and where to expect skill and if the prediction is actionable. Given that there is still untapped potential, in terms of process understanding and prediction methodologies, it is safe to expect that in the future forecast opportunities will expand. Process research and the development of innovative methodologies will aid such progress.

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

2017 ◽  
Author(s):  
Jonathan Conway ◽  
Greg Bodeker ◽  
Chris Cameron
Keyword(s):  
Southern Hemisphere ◽  
Potential Vorticity ◽  
Polar Vortex ◽  
Stratospheric Polar Vortex ◽  
Annual Variations ◽  
Distinct Structure ◽  
Barrier Region ◽  
Antarctic Continent ◽  
Winter Time ◽  
The Antarctic

Abstract. The winter-time 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 doubled-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 370 K and 850 K, bifurcation is strongest in winter and reduces dramatically during spring. From August onwards a distinct structure emerges, where elevated bifurcation remains between 475 K 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, inter-annual 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 characterized. 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.

Sign in / Sign up

Export Citation Format

Share Document