scholarly journals Tropospheric eddy feedback to different stratospheric conditions in idealised baroclinic life cycles

2020 ◽  
Author(s):  
Philip Rupp ◽  
Thomas Birner
Keyword(s):  
Lower Stratosphere ◽  
Polar Vortex ◽  
Surface Friction ◽  
Life Cycles ◽  
Synoptic Scale ◽  
Sudden Stratospheric Warming ◽  
Final State ◽  
Northern Annular Mode ◽  
Wind Structure ◽  
Winter Time

Abstract. A pronounced signature of stratosphere-troposphere coupling is a robust negative anomaly in the surface northern annular mode (NAM) following major sudden stratospheric warming (SSW) events, consistent with an equatorward shift of the tropospheric jet. It has previously been pointed out that tropospheric eddy feedbacks, mainly induced by anomalies in the lowermost extratropical stratosphere, play an important role in creating this surface NAM-signal. We use the basic setup of idealised baroclinic life cycles to investigate the influence of stratospheric conditions on the behaviour of tropospheric synoptic-scale eddies. Particular focus is hereby given on the enhancement of the tropospheric eddy response by surface friction, as well as the sensitivity to wind anomalies in the lower stratosphere. We find systems that include a tropospheric jet only (modelling post-SSW conditions) to be characterised by an equatorward shift of the tropospheric jet in the final state of the life cycle, relative to systems that include a representation of the polar vortex (mimicking more undisturbed winter-time conditions), consistent with the observed NAM-response after SSWs. The corresponding surface NAM-signal is increased if the system includes surface friction, presumably associated with a direct coupling of the eddy field at tropopause level to the surface winds. We further show that the jet shift signal observed in our experiments is mainly caused by changes in the zonal wind structure of the lowermost stratosphere, while changes in the wind structure of the middle and upper stratosphere have almost no influence.

scholarly journals Tropospheric eddy feedback to different stratospheric conditions in idealised baroclinic life cycles

2021 ◽  
Vol 2 (1) ◽  
pp. 111-128
Author(s):  
Philip Rupp ◽  
Thomas Birner
Keyword(s):  
Lower Stratosphere ◽  
Polar Vortex ◽  
Surface Friction ◽  
Life Cycles ◽  
Synoptic Scale ◽  
Final State ◽  
Northern Annular Mode ◽  
Wind Structure ◽  
Basic Set ◽  
Set Up

Abstract. A pronounced signature of stratosphere–troposphere coupling is a robust negative anomaly in the surface northern annular mode (NAM) following sudden stratospheric warming (SSW) events, consistent with an equatorward shift in the tropospheric jet. It has previously been pointed out that tropospheric synoptic-scale eddy feedbacks, mainly induced by anomalies in the lowermost extratropical stratosphere, play an important role in creating this surface NAM signal. Here, we use the basic set-up of idealised baroclinic life cycles to investigate the influence of stratospheric conditions on the behaviour of tropospheric synoptic-scale eddies. Particular attention is given to the enhancement of the tropospheric eddy response by surface friction and the sensitivity to wind anomalies in the lower stratosphere. We find systems that include a tropospheric jet only (modelling post-SSW conditions) to be characterised by an equatorward shift in the tropospheric jet in the final state of the life cycle, relative to systems that include a representation of the polar vortex (mimicking more undisturbed stratospheric wintertime conditions), consistent with the observed NAM response after SSWs. The corresponding relative surface NAM signal is increased if the system includes surface friction, presumably due to a direct coupling of the eddy field at tropopause level to the surface winds. We further show that the jet shift signal observed in our experiments is mainly caused by changes in the zonal wind structure of the lowermost stratosphere, while changes in the wind structure of the middle and upper stratosphere have almost no influence.

scholarly journals Polar processing in a split vortex: early winter Arctic ozone loss in 2012/13

2015 ◽  
Vol 15 (4) ◽  
pp. 4973-5029 ◽  
Author(s):  
G. L. Manney ◽  
Z. D. Lawrence ◽  
M. L. Santee ◽  
N. J. Livesey ◽  
A. Lambert ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Lower Stratosphere ◽  
Polar Vortex ◽  
The Arctic ◽  
Early Winter ◽  
Sudden Stratospheric Warming ◽  
Ozone Loss ◽  
Chlorine Monoxide ◽  
Polar Stratospheric Cloud ◽  
Vortex Split

Abstract. A sudden stratospheric warming (SSW) in early January 2013 caused the polar vortex to split. After the lower stratospheric vortex split on 8 January, the two offspring vortices – one over Canada and the other over Siberia – remained intact, well-confined, and largely at latitudes that received sunlight until they reunited at the end of January. As the SSW began, temperatures abruptly rose above chlorine activation thresholds throughout the lower stratosphere. The vortex was very disturbed prior to the SSW, and was exposed to much more sunlight than usual in December 2012 and January 2013. Aura Microwave Limb Sounder (MLS) nitric acid (HNO3) data and observations from CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) indicate extensive polar stratospheric cloud (PSC) activity, with evidence of PSCs containing solid nitric acid trihydrate particles during much of December 2012. Consistent with the sunlight exposure and PSC activity, MLS observations show that chlorine monoxide (ClO) became enhanced early in December. Despite the cessation of PSC activity with the onset of the SSW, enhanced vortex ClO persisted until mid-February, indicating lingering chlorine activation. The smaller Canadian offspring vortex had lower temperatures, lower HNO3, lower hydrogen chloride (HCl), and higher ClO in late January than the Siberian vortex. Chlorine deactivation began later in the Canadian than in the Siberian vortex. HNO3 remained depressed within the vortices after temperatures rose above the PSC existence threshold, and passive transport calculations indicate vortex-averaged denitrification of about 4 ppbv; the resulting low HNO3 values persisted until the vortex dissipated in mid-February. Consistent with the strong chlorine activation and exposure to sunlight, MLS measurements show rapid ozone loss commencing in mid-December and continuing through January. Lagrangian transport estimates suggest ~ 0.7–0.8 ppmv (parts per million by volume) vortex-averaged chemical ozone loss by late January near 500 K (~ 21 km), with substantial loss occurring from ~ 450 to 550 K. The surface area of PSCs in December 2012 was larger than that in any other December observed by CALIPSO. As a result of denitrification, HNO3 abundances in 2012/13 were among the lowest in the MLS record for the Arctic. ClO enhancement was much greater in December 2012 through mid-January 2013 than that at the corresponding time in any other Arctic winter observed by MLS. Furthermore, reformation of HCl appeared to play a greater role in chlorine deactivation than in more typical Arctic winters. Ozone loss in December 2012 and January 2013 was larger than any previously observed in those months. This pattern of exceptional early winter polar processing and ozone loss resulted from the unique combination of dynamical conditions associated with the early January 2013 SSW, namely unusually low temperatures in December 2012 and offspring vortices that remained well-confined and largely in sunlit regions for about a month after the vortex split.

scholarly journals The Effect of Lower Stratospheric Shear on Baroclinic Instability

2007 ◽  
Vol 64 (2) ◽  
pp. 479-496 ◽  
Author(s):  
Matthew A. H. Wittman ◽  
Andrew J. Charlton ◽  
Lorenzo M. Polvani
Keyword(s):  
Growth Rate ◽  
Lower Stratosphere ◽  
Baroclinic Instability ◽  
Phase Speed ◽  
Finite Amplitude ◽  
Reanalysis Data ◽  
Life Cycles ◽  
Vertical Shear ◽  
Northern Annular Mode ◽  
Jet Structure

Abstract Using a hierarchy of models, and observations, the effect of vertical shear in the lower stratosphere on baroclinic instability in the tropospheric midlatitude jet is examined. It is found that increasing stratospheric shear increases the phase speed of growing baroclinic waves, increases the growth rate of modes with low synoptic wavenumbers, and decreases the growth rate of modes with higher wavenumbers. The meridional structure of the linear modes, and their acceleration of the zonal mean jet, changes with increasing stratospheric shear, but in a way that apparently contradicts the observed stratosphere–troposphere northern annular mode (NAM) connection. This contradiction is resolved at finite amplitude. In nonlinear life cycle experiments it is found that increasing stratospheric shear, without changing the jet structure in the troposphere, produces a transition from anticyclonic (LC1) to cyclonic (LC2) behavior at wavenumber 7. All life cycles with wavenumbers lower than 7 are LC1, and all with wavenumber greater than 7 are LC2. For the LC1 life cycles, the effect of increasing stratospheric shear is to increase the poleward displacement of the zonal mean jet by the eddies, which is consistent with the observed stratosphere–troposphere NAM connection. Finally, it is found that the connection between high stratospheric shear and high-tropospheric NAM is present by NCEP–NCAR reanalysis data.

scholarly journals Middle atmospheric water vapor and ozone anomalies during the 2010 major sudden stratospheric warming

2011 ◽  
Vol 11 (12) ◽  
pp. 32391-32422 ◽  
Author(s):  
D. Scheiben ◽  
C. Straub ◽  
K. Hocke ◽  
P. Forkman ◽  
N. Kämpfer
Keyword(s):  
Water Vapor ◽  
Lower Stratosphere ◽  
Stratospheric Ozone ◽  
Polar Vortex ◽  
Atmospheric Water Vapor ◽  
High Latitudes ◽  
Stratospheric Warming ◽  
Atmospheric Water ◽  
Sudden Stratospheric Warming ◽  
Stratospheric Water Vapor

Abstract. A major sudden stratospheric warming (SSW) occurred in the Northern Hemisphere in January 2010. The warming started on 26 January 2010, was most pronounced by the end of January and was accompanied by a polar vortex shift towards Europe. After the warming, the polar vortex split into two weaker vortices. The zonal mean temperature in the polar upper stratosphere (35–45 km) increased by approximately 25 K in a few days, while there was a decrease in temperature in the lower stratosphere and mesosphere. Local temperature maxima were around 325 K in the upper stratosphere and minima around 175 and 155 K in the lower stratosphere and mesosphere, respectively. In this study, we present middle atmospheric water vapor and ozone measurements obtained by a meridional chain of European ground-based microwave radiometers in Bern (47° N), Onsala (57° N) and Sodankylä (67° N). The instruments in Bern and Onsala are part of the Network for the Detection of Atmospheric Composition Change (NDACC). Effects of the SSW were observed at all three locations and we perform a combined analysis in order to reveal transport processes in the middle atmosphere above Europe during the SSW event. Further we investigate the chemical and dynamical influences of the SSW event. We find that the anomalies during the warming in water vapor and ozone were different for each location. A few days before the beginning of the major SSW, we observed a decrease in mesospheric water vapor above Bern, which we attribute to movement of the mesospheric polar vortex towards Central Europe. The most prominent H2O anomaly observed in Bern was an increase in stratospheric water vapor during the warming. In Onsala and Sodankylä, mesospheric water vapor increased within a few days during the warming and slowly decreased afterwards. Upper stratospheric ozone decreased during the warming over Bern by approximately 30% and by approximately 20% over Onsala. Over Sodankylä, a decrease in ozone below 30 km altitude was observed. This decrease is assumed to be caused by heterogeneous chemistry on polar stratospheric clouds. After the SSW, stratospheric ozone increased to higher levels than before at all three locations. The observed anomalies are explained by a trajectory analysis with reanalysis data from the European Center for Medium-Range Weather Forecasts (ECMWF). Most of the observed anomalies in water vapor and ozone during the warming are attributed to the location of the polar vortex, depending on whether a measurement site was inside or outside the polar vortex. The observed increase in mesospheric water vapor at high latitudes is explained by advection of relatively moist air from lower latitudes, whereas the observed increase in stratospheric water vapor at midlatitudes is explained by advection from high latitudes, i.e. from the moist stratospheric polar vortex.

How turbulent mountain stress influences sudden stratospheric warming ocurrence in WACCM

2020 ◽  
Author(s):  
Froila M. Palmeiro ◽  
Rolando R. Garcia ◽  
Natalia Calvo ◽  
David Barriopedro ◽  
Bernat Jiménez-Esteve
Keyword(s):  
Lower Stratosphere ◽  
Climate Model ◽  
Polar Vortex ◽  
Wave Drag ◽  
Late Winter ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Subtropical Jet ◽  
Vertical Propagation ◽  
Stress Influences

<p><span>The implementation of the Turbulent Mountain Stress (TMS) parametrization in the Whole Atmospheric Community Climate Model (WACCM) is found to be critical to obtain a realistic Sudden Stratospheric Warming (SSW) frequency in the Northern Hemisphere. Comparing two 50-year simluations, one with TMS (TMS-on) and one without (TMS-off) reveals lower than observed SSW frequency in TMS-off from December to February, while in March both simulations show SSW frequencies comparable to reanalysis. Meridional eddy heat fluxes in the lower stratosphere are stronger in TMS-on than in TMS-off, except in March. These differences are accompanied by increased orographic gravity wave drag (OGWD) in TMS-off that comes mainly from the Himalayas and the Rocky Mountains in response to stronger surface winds. Two different mechanisms of how planetary and GWs interact are identified in the simulations. In the lower stratosphere, enhanced dissipation of GWs in TMS-off modifies the subtropical jet and thus the conditions for refraction of planetary waves. </span><span>In early winter, w</span><span>ave</span><span> geometry diagnostics shows </span><span>waveguides </span><span>formation </span><span>from 55N to 75N </span><span>in TMS-on</span><span>, enhancing wave propagation to the polar vortex. On the contrary, vertical propagation </span><span>in TMS-off is </span><span>in inhibited above the lower stratosphere and confined to latitudes </span><span>s</span><span>outh of 50N. </span><span>C</span><span>ompensation between resolved and parametrized GWs </span><span>is also </span><span>observed</span><span>, </span><span>lead</span><span>ing</span><span> to weaker Eliassen-Palm flux divergence in response to stronger OGWD in TMS-off. </span><span>In late winter, conditions for </span><span>propagation are similar in both simulations by late winter, which </span><span>explain</span><span>s</span><span> the reduced TMS-off bias in the frequency of March SSWs. </span></p>

scholarly journals Long-range transport of volcanic aerosol from the 2010 Merapi tropical eruption to Antarctica

2018 ◽  
Author(s):  
Xue Wu ◽  
Sabine Griessbach ◽  
Lars Hoffmann
Keyword(s):  
Long Range ◽  
Lower Stratosphere ◽  
Polar Vortex ◽  
Volcanic Eruptions ◽  
Long Range Transport ◽  
Volcanic Plume ◽  
Volcanic Aerosol ◽  
The South ◽  
Range Transport ◽  
The Antarctic

Abstract. Volcanic sulfate aerosol is an important source of sulfur for Antarctica where other local sources of sulfur are rare. Mid- and high latitude volcanic eruptions can directly influence the aerosol budget of the polar stratosphere. However, tropical eruptions can also enhance polar aerosol load following long-range transport. In the present work, we analyze the volcanic plume of a tropical eruption, Mount Merapi in October 2010, using the Lagrangian particle dispersion model Massive-Parallel Trajectory Calculations (MPTRAC), Atmospheric Infrared Sounder (AIRS) SO2 observations and Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) aerosol observations. We investigate the pathway and transport efficiency of the volcanic aerosol from the tropical tropopause layer (TTL) to the lower stratosphere over Antarctica. We first estimated the time- and height-resolved SO2 injection time series over Mount Merapi during the explosive eruption using the AIRS SO2 observations and a backward trajectory approach. Then the SO2 injections were tracked for up to 6 months using the MPTRAC model. The Lagrangian transport simulation of the volcanic plume was compared to MIPAS aerosol observations and showed good agreement. Both of the simulation and the observations presented in this study suggest that a significant amount of aerosols of the volcanic plume from the Merapi eruption was transported from the tropics to the south of 60 °S within one month after the eruption and even further to Antarctica in the following two months. This relatively fast meridional transport of volcanic aerosol was mainly driven by quasi-horizontal mixing from the TTL to the extratropical lower stratosphere, which was facilitated by the weakening of the subtropical jet during the seasonal transition from austral spring to summer and linked to the westerly phase of the quasi-biennial oscillation (QBO). When the plume went to southern high latitudes, the polar vortex was displaced from the south pole, so the volcanic plume was carried to the south pole without penetrating the polar vortex. Based on the model results, the most efficient pathway for the quasi-horizontal mixing was in between the isentropic surfaces of 360 and 430 K. Although only 4 % of the initial SO2 load was transported into the lower stratosphere south of 60 °S, the Merapi eruption contributed about 8800 tons of sulfur to the Antarctic lower stratosphere. This indicates that the long-range transport under favorable meteorological conditions enables tropical volcanic eruptions to be an important remote source of sulfur for the Antarctic stratosphere.

scholarly journals Synoptic-Scale Variability and Its Relationship with Total Ozone and Antarctic Vortex Displacements

2005 ◽  
Vol 133 (8) ◽  
pp. 2374-2386 ◽  
Author(s):  
Paula K. Vigliarolo ◽  
Carolina S. Vera ◽  
Susana B. Díaz
Keyword(s):  
South America ◽  
Total Ozone ◽  
Lower Stratosphere ◽  
Meteorological Data ◽  
Atmospheric Model ◽  
Meridional Wind ◽  
Department Of Energy ◽  
Synoptic Scale ◽  
Austral Spring ◽  
Anomaly Pattern

Abstract The main synoptic-scale circulation anomaly pattern over extratropical South America during the austral spring (September–November) is identified by means of rotated extended empirical orthogonal function techniques, applied to the meridional wind perturbation time series at 300 hPa. The dataset is based on 15 spring seasons (1979–93) of meteorological data from the National Centers for Environmental Prediction–Department of Energy Atmospheric Model Intercomparison Project version-2 daily averaged reanalyses, given in 17 vertical levels from 1000 to 10 hPa. The total-ozone daily measurements for the same period are from the Total Ozone Mapping Spectrometer instrument (version 7). The principal synoptic-scale anomaly pattern is associated with an anticyclone–cyclone pair evolving eastward along subpolar latitudes (and hence it is termed the subpolar mode), with a typical length scale of 5000 km and a phase velocity of 8 m s−1. The subpolar-mode waves, which display the main characteristics of midlatitude baroclinic waves, typically maximize near or above the tropopause and propagate upward into the lower stratosphere, showing large amplitudes even at 50 hPa and above. Subpolar-mode-related circulation anomalies are found to be responsible for large total-ozone daily fluctuations near southern South America and nearby regions. In the positive phase of the subpolar mode, total-ozone fluctuations, which are negative, adopt a sigmoid structure, with a zonal scale as large as the anticyclone–cyclone pair. Moreover, it is herein shown that the associated anticyclone produces a local ozone-column decrease to the north and east of its center, due to adiabatic uplift of air parcels in the upper troposphere and lower stratosphere. At the same time, the downstream cyclonic disturbance is responsible for large negative total-ozone anomalies to the west and south of its center. As the cyclone develops in the lower stratosphere, it promotes the northward incursion of the Antarctic vortex up to about 55°S, along with air masses of highly depleted ozone levels.

scholarly journals Analyzing ozone variations and uncertainties at high latitudes during Sudden Stratospheric Warming events using MERRA-2

2021 ◽  
Author(s):  
Shima Bahramvash Shams ◽  
Von P. Walden ◽  
James W. Hannigan ◽  
William J. Randel ◽  
Irina V. Petropavlovskikh ◽  
...  
Keyword(s):  
Stratospheric Ozone ◽  
Polar Vortex ◽  
The Arctic ◽  
High Latitudes ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Total Column Ozone ◽  
Northern Latitudes ◽  
Stratospheric Dynamics ◽  
Zonal Average

Abstract. Stratospheric circulation is a critical part of the Arctic ozone cycle. Sudden stratospheric warming events (SSWs) manifest the strongest alteration of stratospheric dynamics. Changes in planetary wave propagation vigorously influence zonal mean zonal wind, temperature, and tracer concentrations in the stratosphere over the high latitudes. In this study, we examine six major SSWs from 2004 to 2020 using the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). Using the unique density of observations around the Greenland sector at high latitudes, we perform comprehensive comparisons of high latitude observations with the MERRA-2 ozone dataset during the six major SSWs. Our results show that MERRA-2 captures the high variability of mid stratospheric ozone fluctuations during SSWs over high latitudes. However, larger uncertainties are observed in the lower stratosphere and troposphere. The zonally averaged stratospheric ozone shows a dramatic increase of 9–29 % in total column ozone (TCO) near the time of each SSW, which lasts up to two months. The SSWs exhibit a more significant impact on ozone over high northern latitudes when the polar vortex is mostly elongated as seen in 2009 and 2018 compared to the events in which the polar vortex is displaced towards Europe. The regional impact of SSWs over Greenland has a similar structure as the zonal average, however, exhibits more intense ozone anomalies which is reflected by 15–37 % increase in TCO. The influence of SSW on mid stratospheric ozone levels persists longer than their impact on temperature. This paper is focused on the increased (suppressed) wave activity before (after) the SSWs and their impact on ozone variability at high latitudes. This includes an investigation of the different terms of tracer continuity using MERRA-2 parameters, which emphasizes the key role of vertical advection on mid-stratospheric ozone during the SSWs.

scholarly journals Parallel Comparison of Major Sudden Stratospheric Warming Events in CESM1-WACCM and CESM2-WACCM

Atmosphere ◽  
2019 ◽  
Vol 10 (11) ◽  
pp. 679 ◽  
Author(s):  
Si-Ming Liu ◽  
Yuan-Hao Chen ◽  
Jian Rao ◽  
Can Cao ◽  
Si-Yu Li ◽  
...  
Keyword(s):  
North America ◽  
Climate Model ◽  
Polar Vortex ◽  
Statistical Characteristics ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Near Surface ◽  
Eddy Heat Flux ◽  
General Statistical ◽  
Vortex Split

After the recent release of the historical runs by community Earth system model version 2–the whole atmosphere community climate model (CESM2-WACCM), the major sudden stratospheric warming (SSW) events in this model and in its previous version (CESM1-WACCM) are compared based on a modern reanalysis (JRA55). Using the World Meteorological Organization (WMO) definition of SSWs and a threshold-based classification method that can describe the polar vortex morphology, SSWs in models and the reanalysis are further classified into two types, vortex displacement SSWs and vortex split SSWs. The general statistical characteristics of the two types of SSW events in the two model versions are evaluated. Both CESM1-WACCM and CESM2-WACCM models are shown to reproduce the SSW frequency successfully, although the circulations differences between vortex displacement SSWs and vortex split SSWs in CESM2-WACCM are smaller than in CESM1-WACCM. Composite polar temperature, geopotential height, wind, and eddy heat flux anomalies in both the two models and the reanalysis show similar evolutions. In addition, positive Pacific–North America and negative Western Pacific patterns in the troposphere preceding vortex displacement and split SSWs are observed in both observations and the models. The strong negative North Atlantic oscillation-like pattern, especially after vortex split SSW onset, is also identified in models. The near-surface cold Eurasia–warm North America pattern before both types of SSW onset, the warm Eurasia–cold North America pattern after displacement SSW onset, and the cold Eurasia–cold North America pattern after split SSW onset are consistently identified in JRA55, CESM1-WACCM, and CESM2-WACCM, although the temperature anomalies after the split SSW onset in CESM2-WACCM are somewhat underestimated.

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