The Experts below are selected from a list of 2004 Experts worldwide ranked by ideXlab platform
Hassan Bencherif - One of the best experts on this subject based on the ideXlab platform.
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evaluation of inter hemispheric characteristics of the tropopause Stratopause mesopause over sub tropical regions
Pure and Applied Geophysics, 2018Co-Authors: Som Sharma, Prashant Kumar, Rajesh Vaishnav, Chintan Jethva, Hassan BencherifAbstract:The transition regions in thermal structure viz. Tropopause, Stratopause and mesopause play a vital role in the vertical coupling of the Earth’s atmosphere. For the first time, interhemispheric characteristics of the transition regions over two subtropical regions are studied using temperature observations from the SABER onboard TIMED satellite and the ERA Interim reanalysis during year 2002 to 2015. Results show that tropopause height is higher over Reunion Island (21.11S, 55.53E) in the Southern Hemisphere (SH) as compared to Mt. Abu region (24.59°N, 72.70°E) in the Northern Hemisphere (NH). Temporal variation of tropopause temperature reveals a decreasing (* 4 K) trend from year 2002 to 2008 and beyond this, an increasing (* 1.5 K) trend is found in tropopause temperature. These features are reinforcing for Mesopause as compared to tropopause temperature. The SH shows stronger variations in Mesopause temperature (* 7 K) compared to NH during year 2002 to 2008. The occurrence frequency of mesopause and Stratopause height shows that the maximum occurrence frequency (* 60%) of mesopause at * 100 km in NH, while frequency is found to be * 55% in the SH. Results show that Stratopause (mesopause) is cooler (warmer) in NH as compared SH. Moreover, Lomb Scargle Periodogram and wavelet transform techniques are used to investigate the periodicity of mesopause, Stratopause and tropopause temperatures and heights. Investigations revealed prominent annual oscillations in the tropopause and Stratopause temperatures in both hemispheres. These findings will be of immense use for the vertical and inter-hemispheric atmospheric coupling studies.
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Evaluation of Inter-Hemispheric Characteristics of the Tropopause–Stratopause–Mesopause Over Sub-Tropical Regions
Pure and Applied Geophysics, 2017Co-Authors: Som Sharma, Prashant Kumar, Rajesh Vaishnav, Chintan Jethva, Hassan BencherifAbstract:The transition regions in thermal structure viz. Tropopause, Stratopause and mesopause play a vital role in the vertical coupling of the Earth’s atmosphere. For the first time, interhemispheric characteristics of the transition regions over two subtropical regions are studied using temperature observations from the SABER onboard TIMED satellite and the ERA Interim reanalysis during year 2002 to 2015. Results show that tropopause height is higher over Reunion Island (21.11S, 55.53E) in the Southern Hemisphere (SH) as compared to Mt. Abu region (24.59°N, 72.70°E) in the Northern Hemisphere (NH). Temporal variation of tropopause temperature reveals a decreasing (* 4 K) trend from year 2002 to 2008 and beyond this, an increasing (* 1.5 K) trend is found in tropopause temperature. These features are reinforcing for Mesopause as compared to tropopause temperature. The SH shows stronger variations in Mesopause temperature (* 7 K) compared to NH during year 2002 to 2008. The occurrence frequency of mesopause and Stratopause height shows that the maximum occurrence frequency (* 60%) of mesopause at * 100 km in NH, while frequency is found to be * 55% in the SH. Results show that Stratopause (mesopause) is cooler (warmer) in NH as compared SH. Moreover, Lomb Scargle Periodogram and wavelet transform techniques are used to investigate the periodicity of mesopause, Stratopause and tropopause temperatures and heights. Investigations revealed prominent annual oscillations in the tropopause and Stratopause temperatures in both hemispheres. These findings will be of immense use for the vertical and inter-hemispheric atmospheric coupling studies.
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Observations of a middle atmosphere thermal structure over Durban using a ground-based Rayleigh LIDAR and satellite data
South African Journal of Science, 2012Co-Authors: Nkanyiso Mbatha, Venkataraman Sivakumar, Hassan Bencherif, Sandile B. Malinga, Sadhasivan R. Pillay, Ashokabose Moorgawa, Max M. MichaelisAbstract:Studying the middle atmospheric thermal structure over southern Africa is an important activity to improve the understanding of atmospheric dynamics of this region. Observations of a middle atmosphere thermal structure over Durban, South Africa (29.9°S, 31.0°E) using the Durban Rayleigh Light Detection and Ranging (LIDAR) data collected over 277 nights from April 1999 to July 2004, including closest overpasses of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and Halogen Occultation Experiments (HALOE) satellites, are presented in this paper. There seems to be good agreement between the LIDAR and satellite observations. During autumn and winter, the temperatures measured by the LIDAR in the height region between 40 km and 55 km were 5 K to 12 K higher than those measured by the satellites. The data from the LIDAR instrument and the SABER and HALOE satellites exhibited the presence of an annual oscillation in the stratosphere, whereas in the mesosphere, semi-annual oscillations dominated the annual oscillation at some levels. The Stratopause was observed in the height range of ~40 km - 55 km by all the instruments, with the Stratopause temperatures measured as 260 K - 270 K by the LIDAR, 250 K - 260 K by the SABER and 250 K - 270 K by the HALOE. Data from the SABER and HALOE satellites indicated almost the same thermal structure for the middle atmosphere over Durban.
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20-year LiDAR observations of stratospheric sudden warming over a mid-latitude site, Observatoire de Haute Provence (OHP; 44° N, 6° E): case study and statistical characteristics
Atmospheric Chemistry and Physics Discussions, 2007Co-Authors: D. V. Charyulu, Venkataraman Sivakumar, Hassan Bencherif, Philippe Keckhut, Alain Hauchecorne, Guillaume Kirgis, D. Narayana RaoAbstract:The present study delineates the characteristics of Stratospheric Sudden Warming (SSW) events observed over the Observatoire de Haute Provence (OHP: 44° N, 6° E). The study uses 20 years of Rayleigh LiDAR temperature measurements for the period, 1982–2001, which corresponds to 2629 daily temperature profiles. Characteristics of warming events, such as type of warming (major and minor), magnitude of warming, height of occurrence and day period of occurrence are presented with emphasis on wave propagation and isentropic transport conditions. The major and minor warming events are classified with respect to temperature increase and reversal in the zonal wind direction in the polar region using reanalysis data from the National Centre for Environmental Prediction (NCEP). SSWs occur with a mean frequency of 2.15 events per winter season. The percentage of occurrence of major and minor warming events are found to be ~23% and ~77%, respectively. The observed major and minor SSW is associated with a descent of the Stratopause layer by -6 to 6 km range. The heights of occurrences of major SSWs are distributed between 38 km and 54 km with magnitudes in the 12.2–35.7 K temperature range, while minor SSW occurrences appear in the 42–54 km range, closer to the usual Stratopause layer (~47 km) and with a slightly larger range of temperature magnitude (10.2–32.8 K). The observed major and minor events are examined in connection with Quasi-Biennial Oscillation (QBO) phases.
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Rayleigh Lidar investigation of stratospheric sudden warming over a low latitude station, Gadanki (13.5ºN; 79.2ºE): a statistical study
Lidar Remote Sensing for Environmental Monitoring VIII, 2007Co-Authors: D. V. Charyulu, Venkataraman Sivakumar, Hassan Bencherif, D. Narayana RaoAbstract:In this paper, we report the statistical characteristics of Stratospheric Sudden Warming (SSW) events observed over a low latitude station, Gadanki; 13.5°N, 79.2°E. The study uses 7 years (1998 to 2004) of quasi-continuous nighttime LiDAR temperature measurements, which corresponds to 312 observations. The statistical characteristics are presented in terms of major or minor, magnitude of warming, height of occurrence and Stratopause descent with reference to the mean climatological profile. The warming events are classified into major or minor warming with respect to the observed warm temperature magnitude and reversal in the zonal wind direction in the polar region using National Centre for Environmental Prediction (NCEP) reanalysis data. In total, 14 SSW events observed and have been classified into 2 (14.3 %) major and 12 (85.7 %) minor warming events. The magnitudes of warm temperatures with respect to the mean winter temperature is in the range from 8.2 K to 18.1 K. Occurrence of SSWs are observed to accompany with the descent of Stratopause layer from 0 km to 6.3 km with respect to the calculated mean winter Stratopause height.
Ulrike Langematz - One of the best experts on this subject based on the ideXlab platform.
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Future changes in Elevated Stratopause Events
2014Co-Authors: Janice Scheffler, Yvan Orsolini, Ulrike Langematz, Blanca AyarzagüenaAbstract:The polar winter stratosphere is not only coupled to the troposphere by Sudden Stratospheric Warmings (SSW) but it is also coupled to the mesosphere. The strength and height of the polar winter Stratopause is determined by the poleward downward branch of the mesospheric residual circulation. During SSWs the propagation of the waves driving this residual circulation is changed and thus also height and strength of the Stratopause. Several observational and modelling studies have shown that the Stratopause height can increase strongly after some SSWs leading to a Stratopause that lies well above the winter mean. The Stratopause then descends back to its winter mean height. During the descent of the stratosphere mesospheric air can intrude into the stratosphere and thus influence the chemical composition of stratospheric air. Several studies have shown that the development of a strong Planetary wave 1 amplitude in the mesosphere is a common feature during the onset of Elevated Stratopause events (ESE). With a changing climate it is to be questioned if and how the development and strength of ESEs changes. In this study the possible change in ESE characteristica in the future is investigated using time slice simulations of the chemistry-climate model ECHAM/MESSy (EMAC). Changes in stratospheric winds are always accompanied by changes in wave propagation and thus by changes in wave driving for the residual circulation and Stratopause height and strength. Only those changes in daily Stratopause height are declared as ESE that exceed the 99.5% percentile of daily change in Stratopause height and have a newbuilt Stratopause that lies above its respective winter mean height. The dynamic threshold for ESE detection allows to compare data sets with different climatologies. Composite analyses are performed on the ESE simulated in recent past and the future. The robustness of the composites is tested using the Monte Carlo Method. We show that the number of ESE increases in the future. ESE with higher changes in Stratopause height can be found in the simulation of the future. The ESE simulated in past and future will be examined concerning their differences during onset and decay, also considering the type of SSW they follow. In both simulations the majority of ESE follow displacement SSWs.
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On the occurrence and evolution of extremely high temperatures at the polar winter Stratopause — A GCM study
Geophysical Research Letters, 2000Co-Authors: Peter Braesicke, Ulrike LangematzAbstract:Sudden warmings in the Stratopause region are a well known phenomenon in middle atmosphere dynamics. In this study, these Stratopause warmings are analyzed using a ten year integration of the Berlin Climate Middle Atmosphere Model. The good spatial and temporal resolution of the model allows to investigate the main properties on a statistical basis. It turns out that strong Stratopause warmings occur in almost each northern hemisphere winter. The associated temperature maximums and the descent of the Stratopause agree very well with observed events. Two selected warrnings are compared in terms of EP flux diagnostics and planetary wave amplitudes to study the links between Stratopause events and (major) warmings in the lower/middle stratosphere. Only with supply of upward propagating wave energy from the troposphere and lowest stratosphere, Stratopause warmings develop to lower stratospheric warmings.
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on the occurrence and evolution of extremely high temperatures at the polar winter Stratopause a gcm study
Geophysical Research Letters, 2000Co-Authors: Peter Braesicke, Ulrike LangematzAbstract:Sudden warmings in the Stratopause region are a well known phenomenon in middle atmosphere dynamics. In this study, these Stratopause warmings are analyzed using a ten year integration of the Berlin Climate Middle Atmosphere Model. The good spatial and temporal resolution of the model allows to investigate the main properties on a statistical basis. It turns out that strong Stratopause warmings occur in almost each northern hemisphere winter. The associated temperature maximums and the descent of the Stratopause agree very well with observed events. Two selected warrnings are compared in terms of EP flux diagnostics and planetary wave amplitudes to study the links between Stratopause events and (major) warmings in the lower/middle stratosphere. Only with supply of upward propagating wave energy from the troposphere and lowest stratosphere, Stratopause warmings develop to lower stratospheric warmings.
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A note on record‐high temperatures at the northern polar Stratopause in winter 1997/98
Geophysical Research Letters, 1998Co-Authors: U. Von Zahn, Ulrike Langematz, J. Fiedler, B. Naujokat, Kirstin KrugerAbstract:A series of lidar temperature soundings from the ALOMAR observatory in northern Norway indicated an extreme warming of a descending Stratopause in February 1998. The maximum temperature recorded during this event was +49°C at 40 km altitude. This stratospheric warming is described by means of SSU satellite radiance data and of stratospheric analyses from the Free University Berlin. Comparisons are made to a number of historical events with similar temperature observations from rocket soundings and to results from the Berlin general circulation model. It turns out that in all cases the highest Stratopause temperatures occur close to the 40 km altitude level.
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a note on record high temperatures at the northern polar Stratopause in winter 1997 98
Geophysical Research Letters, 1998Co-Authors: U. Von Zahn, Ulrike Langematz, J. Fiedler, B. Naujokat, Kirstin KrugerAbstract:A series of lidar temperature soundings from the ALOMAR observatory in northern Norway indicated an extreme warming of a descending Stratopause in February 1998. The maximum temperature recorded during this event was +49°C at 40 km altitude. This stratospheric warming is described by means of SSU satellite radiance data and of stratospheric analyses from the Free University Berlin. Comparisons are made to a number of historical events with similar temperature observations from rocket soundings and to results from the Berlin general circulation model. It turns out that in all cases the highest Stratopause temperatures occur close to the 40 km altitude level.
V. L. Harvey - One of the best experts on this subject based on the ideXlab platform.
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stratosphere mesosphere coupling during stratospheric sudden warming events
Advances in Space Research, 2014Co-Authors: A Chandran, R L Collins, V. L. HarveyAbstract:Abstract In this review article we summarize recent results in the coupling of the stratosphere–mesosphere during stratospheric sudden warming (SSW) events. We focus on the role of planetary and gravity waves in driving the middle atmosphere circulation and illustrate the stratosphere–mesosphere coupling during undisturbed wintertime circulation, during an SSW event, and after an SSW event during the formation of an elevated Stratopause using simulations of past Arctic and Antarctic winters from the Specified Dynamics version of the Whole Atmosphere Community Climate Model (SD-WACCM). We illustrate the transition of the polar Stratopause from being a gravity wave driven phenomena to a planetary wave driven phenomena during SSW events and its subsequent reestablishment and control by gravity waves. We also examine the synoptic structure of the stratosphere, mesosphere, and lower thermosphere using SD-WACCM data fields that show the structure of the vortex during specific dynamical events in both hemispheres. We illustrate the longitudinal asymmetry in the thermal structure in the stratosphere and mesosphere driven by differences in circulation over the polar cap regions during an SSW event. We complement this analysis of the middle atmosphere circulation with a classification of both the Arctic and Antarctic winters since 1979 into major, minor, elevated Stratopause or quiet winters based on the level of disturbance using the Modern Era-Retrospective Analysis for Research and Applications (MERRA) reanalysis data. From the MERRA data we find that the combined occurrences of both major and minor warmings in the Arctic have remained constant over the past three decades while we find a minor increase in their occurrences in the Antarctic.
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A climatology of the Stratopause in WACCM and the zonally asymmetric elevated Stratopause
Journal of Geophysical Research: Atmospheres, 2013Co-Authors: V. L. HarveyAbstract:[1] A climatology of the Stratopause is produced using a 40 year simulation of the Whole Atmosphere Community Climate Model (WACCM). Anomalies in polar winter Stratopause temperature and height are interpreted with respect to the location of the polar vortices and anticyclones. The WACCM climatology is compared to an 8 year climatology based on Microwave Limb Sounder (MLS) observations and data from the Goddard Earth Observing System (GEOS) version 5 from August 2004 to July 2012. The WACCM climatology is in excellent agreement with observations, except in the Antarctic vortex where the WACCM Stratopause is ~10K warmer and ~5 km higher than observations. WACCM diabatic heating rates support the hypothesis that ageostrophic vertical motions associated with baroclinic planetary waves are responsible for producing Arctic winter temperature anomalies. The area of the winter polar vortices in WACCM at the Stratopause is 30% smaller in the NH and 45% smaller in the SH compared to GEOS. The long WACCM record allows us to explore the geographical distribution and temporal evolution of a composite of 15 elevated Stratopause (ES) events. This composite is in good agreement with the 2012 ES event observed by MLS, though December ES events in WACCM are not observed by MLS. This is the first work to show that ES events are not zonally symmetric. In the 30 days following ES events, the ES composite shows that the Stratopause altitude is highest over the Canadian Arctic, and the highest Stratopause temperatures occur 90° to the east over the Norwegian Sea.
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High Resolution Dynamics Limb Sounder observations of the gravity wave-driven elevated Stratopause in 2006
Journal of Geophysical Research: Atmospheres, 2012Co-Authors: V. L. Harvey, Cora E. Randall, M. J. Alexander, John C. GilleAbstract:[1] Temperature observations during January and February 2006 from the High Resolution Dynamics Limb Sounder (HIRDLS), the Microwave Limb Sounder (MLS), and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instruments are compared to illustrate the vertical range over which version 6 HIRDLS temperatures are scientifically useful. In order to determine the quality of HIRDLS temperatures in the middle atmosphere, we compare the height and temperature of the HIRDLS Stratopause with MLS and SABER before, during, and after the 2006 major stratospheric sudden warming. Results show that HIRDLS observes the elevated Stratopause at 78 km two days later than MLS and five days after SABER. We compare the geographical temperature structure of these data sets at 0.01 hPa during this period. Though HIRDLS temperatures are consistently 5–10 K lower in the mesosphere, this is the first study to show that the horizontal temperature distribution is in good spatial and temporal agreement with MLS and SABER up to ∼80 km. Gravity wave momentum flux and planetary wave 1 amplitudes are derived from HIRDLS and shown to be in agreement with previous studies. We use HIRDLS to show a ∼30 K increase in Stratopause temperature following enhanced gravity wave momentum flux in the lower mesosphere.
Kirstin Kruger - One of the best experts on this subject based on the ideXlab platform.
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the evolution of the Stratopause during the 2006 major warming satellite data and assimilated meteorological analyses
Journal of Geophysical Research, 2008Co-Authors: M J Schwartz, G L Manney, Kirstin Kruger, Steven Pawson, Ken Minschwaner, W H Daffer, N J Livesey, Martin G Mlynczak, Ellis E RemsbergAbstract:Microwave Limb Sounder and Sounding of the Atmosphere with Broadband Emission Radiometry data provide the first opportunity to characterize the four-dimensional Stratopause evolution throughout the life-cycle of a major stratospheric sudden warming (SSW). The polar Stratopause, usually higher than that at midlatitudes, dropped by ∼30 km and warmed during development of a major “wave 1” SSW in January 2006, with accompanying mesospheric cooling. When the polar vortex broke down, the Stratopause cooled and became ill-defined, with a nearly isothermal stratosphere. After the polar vortex started to recover in the upper stratosphere/lower mesosphere (USLM), a cool Stratopause reformed above 75 km, then dropped and warmed; both the mesosphere above and the stratosphere below cooled at this time. The polar Stratopause remained separated from that at midlatitudes across the core of the polar night jet. In the early stages of the SSW, the strongly tilted (westward with increasing altitude) polar vortex extended into the mesosphere, and enclosed a secondary temperature maximum extending westward and slightly equatorward from the highest altitude part of the polar Stratopause over the cool Stratopause near the vortex edge. The temperature evolution in the USLM resulted in strongly enhanced radiative cooling in the mesosphere during the recovery from the SSW, but significantly reduced radiative cooling in the upper stratosphere. Assimilated meteorological analyses from the European Centre for Medium-Range weather Forecasts (ECMWF) and Goddard Earth Observing System Version 5.0.1 (GEOS-5), which are not constrained by data at polar Stratopause altitudes and have model tops near 80 km, could not capture the secondary temperature maximum or the high Stratopause after the SSW; they also misrepresent polar temperature structure during and after the Stratopause breakdown, leading to large biases in their radiative heating rates. ECMWF analyses represent the stratospheric temperature structure more accurately, suggesting a better representation of vertical motion; GEOS-5 analyses more faithfully describe Stratopause level wind and wave amplitudes. The high-quality satellite temperature data used here provide the first daily, global, multiannual data sets suitable for assessing and, eventually, improving representation of the USLM in models and assimilation systems.
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A note on record‐high temperatures at the northern polar Stratopause in winter 1997/98
Geophysical Research Letters, 1998Co-Authors: U. Von Zahn, Ulrike Langematz, J. Fiedler, B. Naujokat, Kirstin KrugerAbstract:A series of lidar temperature soundings from the ALOMAR observatory in northern Norway indicated an extreme warming of a descending Stratopause in February 1998. The maximum temperature recorded during this event was +49°C at 40 km altitude. This stratospheric warming is described by means of SSU satellite radiance data and of stratospheric analyses from the Free University Berlin. Comparisons are made to a number of historical events with similar temperature observations from rocket soundings and to results from the Berlin general circulation model. It turns out that in all cases the highest Stratopause temperatures occur close to the 40 km altitude level.
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a note on record high temperatures at the northern polar Stratopause in winter 1997 98
Geophysical Research Letters, 1998Co-Authors: U. Von Zahn, Ulrike Langematz, J. Fiedler, B. Naujokat, Kirstin KrugerAbstract:A series of lidar temperature soundings from the ALOMAR observatory in northern Norway indicated an extreme warming of a descending Stratopause in February 1998. The maximum temperature recorded during this event was +49°C at 40 km altitude. This stratospheric warming is described by means of SSU satellite radiance data and of stratospheric analyses from the Free University Berlin. Comparisons are made to a number of historical events with similar temperature observations from rocket soundings and to results from the Berlin general circulation model. It turns out that in all cases the highest Stratopause temperatures occur close to the 40 km altitude level.
Yvan Orsolini - One of the best experts on this subject based on the ideXlab platform.
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Modelling the descent of nitric oxide during the elevated Stratopause event of January 2013
Journal of Atmospheric and Solar-Terrestrial Physics, 2017Co-Authors: Yvan Orsolini, Varavut Limpasuvan, Kristell Pérot, Patrick Espy, Robert Hibbins, Stefan Lossow, Katarina Raaholt Larsson, Donal P. MurtaghAbstract:Using simulations with a whole-atmosphere chemistry-climate model nudged by meteorological analyses, global satellite observations of nitrogen oxide (NO) and water vapour by the Sub-Millimetre Radiometer instrument (SMR), of temperature by the Microwave Limb Sounder (MLS), as well as local radar observations, this study examines the recent major stratospheric sudden warming accompanied by an elevated Stratopause event (ESE) that occurred in January 2013. We examine dynamical processes during the ESE, including the role of planetary wave, gravity wave and tidal forcing on the initiation of the descent in the mesosphere-lower thermosphere (MLT) and its continuation throughout the mesosphere and stratosphere, as well as the impact of model eddy diffusion. We analyse the transport of NO and find the model underestimates the large descent of NO compared to SMR observations. We demonstrate that the discrepancy arises abruptly in the MLT region at a time when the resolved wave forcing and the planetary wave activity increase, just before the elevated Stratopause reforms. The discrepancy persists despite doubling the model eddy diffusion. While the simulations reproduce an enhancement of the semi-diurnal tide following the onset of the 2013 SSW, corroborating new meteor radar observations at high northern latitudes over Trondheim (63.4°N), the modelled tidal contribution to the forcing of the mean meridional circulation and to the descent is a small portion of the resolved wave forcing, and lags it by about ten days.
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on the composite response of the mlt to major sudden stratospheric warming events with elevated Stratopause
Journal of Geophysical Research, 2016Co-Authors: Varavut Limpasuvan, Yvan Orsolini, Rolando R Garcia, A Chandran, Anne K. SmithAbstract:Based on a climate-chemistry model (constrained by reanalyses below ~50 km), the zonal-mean composite response of the mesosphere and lower thermosphere (MLT) to major sudden stratospheric warming events with elevated Stratopauses demonstrates the role of planetary waves (PWs) in driving the mean circulation in the presence of gravity waves (GWs), helping the polar vortex recover and communicating the sudden stratospheric warming (SSW) impact across the equator. With the SSW onset, strong westward PW drag appears above 80 km primarily from the dissipation of wave number 1 perturbations with westward period of 5–12 days, generated from below by the unstable westward polar stratospheric jet that develops as a result of the SSW. The filtering effect of this jet also allows eastward propagating GWs to saturate in the winter MLT, providing eastward drag that promotes winter polar mesospheric cooling. The dominant PW forcing translates to a net westward drag above the eastward mesospheric jet, which initiates downwelling over the winter pole. As the eastward polar stratospheric jet returns, this westward PW drag persists above 80 km and acts synergistically with the return of westward GW drag to drive a stronger polar downwelling that warms the pole adiabatically and helps reform the Stratopause at an elevated altitude. With the polar wind reversal during the SSW onset, the westward drag by the quasi-stationary PW in the winter stratosphere drives an anomalous equatorial upwelling and cooling that enhance tropical stratospheric ozone. Along with equatorial wind anomalies, this ozone enhancement subsequently amplifies the migrating semidiurnal tide amplitude in the winter midlatitudes.
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Future changes in Elevated Stratopause Events
2014Co-Authors: Janice Scheffler, Yvan Orsolini, Ulrike Langematz, Blanca AyarzagüenaAbstract:The polar winter stratosphere is not only coupled to the troposphere by Sudden Stratospheric Warmings (SSW) but it is also coupled to the mesosphere. The strength and height of the polar winter Stratopause is determined by the poleward downward branch of the mesospheric residual circulation. During SSWs the propagation of the waves driving this residual circulation is changed and thus also height and strength of the Stratopause. Several observational and modelling studies have shown that the Stratopause height can increase strongly after some SSWs leading to a Stratopause that lies well above the winter mean. The Stratopause then descends back to its winter mean height. During the descent of the stratosphere mesospheric air can intrude into the stratosphere and thus influence the chemical composition of stratospheric air. Several studies have shown that the development of a strong Planetary wave 1 amplitude in the mesosphere is a common feature during the onset of Elevated Stratopause events (ESE). With a changing climate it is to be questioned if and how the development and strength of ESEs changes. In this study the possible change in ESE characteristica in the future is investigated using time slice simulations of the chemistry-climate model ECHAM/MESSy (EMAC). Changes in stratospheric winds are always accompanied by changes in wave propagation and thus by changes in wave driving for the residual circulation and Stratopause height and strength. Only those changes in daily Stratopause height are declared as ESE that exceed the 99.5% percentile of daily change in Stratopause height and have a newbuilt Stratopause that lies above its respective winter mean height. The dynamic threshold for ESE detection allows to compare data sets with different climatologies. Composite analyses are performed on the ESE simulated in recent past and the future. The robustness of the composites is tested using the Monte Carlo Method. We show that the number of ESE increases in the future. ESE with higher changes in Stratopause height can be found in the simulation of the future. The ESE simulated in past and future will be examined concerning their differences during onset and decay, also considering the type of SSW they follow. In both simulations the majority of ESE follow displacement SSWs.
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the roles of planetary and gravity waves during a major stratospheric sudden warming as characterized in waccm
Journal of Atmospheric and Solar-Terrestrial Physics, 2012Co-Authors: Varavut Limpasuvan, Yvan Orsolini, Jadwiga H Richter, Frode Stordal, Olekristian KvisselAbstract:Abstract The roles of planetary waves (PWs) and gravity waves (GWs) are examined during a realistic major stratospheric sudden warming (SSW), simulated in the National Center for Atmospheric Research Whole Atmosphere Community Climate Model (WACCM). This major SSW event is characterized by a well-separated polar Stratopause during a wind-reversal period. Formed by adiabatic warming induced by westward GW drag, the early-winter Stratopause layer appears at its climatological level. With the incipient wind reversal and SSW onset, this layer plunges ∼20 km in time, as the amplified PW interacts with the mean flow. The SSW recovery starts in the upper mesosphere as GW drag becomes eastward due to the filtering effects of the underlying wind. During this recovery, the Stratopause reforms at an elevated altitude due to adiabatic warming induced by strong upper mesospheric PW forcing. Intensified downward motion from the mesosphere then ensues as the Stratopause descends toward its climatological position.
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mesospheric intrusion and anomalous chemistry during and after a major stratospheric sudden warming
Journal of Atmospheric and Solar-Terrestrial Physics, 2012Co-Authors: Olekristian Kvissel, Varavut Limpasuvan, Yvan Orsolini, Jadwiga H Richter, Frode Stordal, D R MarshAbstract:Abstract Several major stratospheric sudden warmings (SSWs) characterized by a rapid vertical displacement of the winter polar Stratopause are simulated in the National Center for Atmospheric Research's Whole Atmosphere Community Climate Model. The Stratopause descends into the mid-stratosphere at the onset of the SSW, and then abruptly reforms near 70 km. The SSWs are accompanied by a strong equatorward and downward residual circulation between 40 and 60 km. The descent occurs mainly through the core of the highly displaced vortex, and is accompanied by an intrusion of air rich in carbon monoxide (CO) from the mesosphere into the mid-stratosphere. Around the periods when the Stratopause undergoes rapid vertical displacement, the simulation shows that the air of mesospheric origin is being cut off and remains distinct from surrounding stratospheric air masses for at least a month after SSW onset. Such mesospheric cut-off intrusion of CO-rich appears to be a defining signature of winters with major SSWs. Due to its strong temperature dependency, the secondary ozone maximum (between 90 and 110 km) abruptly decreases in amplitude at the time of the high-altitude Stratopause reformation that influences the thermal structure at these altitudes. The vertical location of the tertiary ozone maximum (between 70 and 75 km) shows significant variations in response to the changing vertical motion during SSW.
