Evolution and persistence of Arctic and Antarctic stratospheric polar vortex over the 1979 - 2021 period

Ce travail de thèse porte sur l'étude de l’évolution de l'intensité et de la position de la bordure du vortex en fonction de la latitude équivalente sur la période 1979 - 2021 sur 3 niveaux isentropes (675 K, 550 K et 475 K) issus des réanalyses ECMWF ERA-Interim. Une analyse des dates de formation et de rupture des vortex polaires est incluse. Le cycle solaire et dans une moindre mesure, l'oscillation quasi-biennale, l'oscillation australe El Niño et l'oscillation arctique modulent l'évolution interannuelle de l’intensité de la bordure et des dates de rupture du vortex. Dans l’HS, une augmentation à long terme de l'intensité de la bordure du vortex et des dates de rupture est observée sur la période 1979 - 1999, liée à l'augmentation du trou d'ozone en Antarctique. Après des ruptures précoces entre 1981 et 1987, des vortex plus persistants sont apparus dans l’HN au cours des années 1990. Pour les deux hémisphères, on observe une bordure du vortex plus intense et une persistance lors des années de minimum solaire (minSC). Pour l’HS, la bordure du vortex est plus intense et dure plus longtemps pour les années maxSC/wQBO que pour les années maxSC/eQBO, et est un peu plus intense durant la phase ENSO froide (cENSO). Pour l’HN, l’intensité de la bordure est plus prononcée que dans l’HS durant la phase wQBO, et il est plus intense durant les années minSC/wQBO.This PhD study focuses on the study of the evolution of the stratospheric polar vortices over the last forty years. The intensity and position of the Southern and Northern stratospheric polar vortex edge are evaluated as a function of equivalent latitude over the 1979 - 2021 period on 3 isentropic levels in the lower and middle stratosphere (675 K, 550 K and 475 K) from ECMWF ERA-Interim reanalysis. An analysis of the onset and breakup dates of the polar vortices is included. The solar cycle and to a lower extent the quasi-biennal oscillation, El Niño Southern Oscillation and the Arctic Oscillation modulate the interannual evolution of the strength of the vortex edge and the vortex breakup dates. In the SH, long-term increase of the vortex edge intensity and breakup dates is observed over the 1979 - 1999 period, linked to the increase of the Antarctic ozone hole. After early break-ups between 1981 and 1987, more persistent vortex occured in the NH during the 1990s. For both hemispheres stronger vortex edge and longer vortex duration is observed in solar minimum (minSC) years. For the SH, the vortex edge is stronger and lasts longer for maxSC/wQBO years than for maxSC/eQBO years, and is somewhat stronger during cold ENSO phase (cENSO). For the NH, the stronger vortex edge is more pronounced than in SH during the wQBO phase, and it is stronger during minSC/wQBO years

Évolution et persistance des vortex stratosphériques polaires Arctique et Antarctique sur la période 1979 - 2021

This PhD study focuses on the study of the evolution of the stratospheric polar vortices over the last forty years. The intensity and position of the Southern and Northern stratospheric polar vortex edge are evaluated as a function of equivalent latitude over the 1979 - 2021 period on 3 isentropic levels in the lower and middle stratosphere (675 K, 550 K and 475 K) from ECMWF ERA-Interim reanalysis. An analysis of the onset and breakup dates of the polar vortices is included. The solar cycle and to a lower extent the quasi-biennal oscillation, El Niño Southern Oscillation and the Arctic Oscillation modulate the interannual evolution of the strength of the vortex edge and the vortex breakup dates. In the SH, long-term increase of the vortex edge intensity and breakup dates is observed over the 1979 - 1999 period, linked to the increase of the Antarctic ozone hole. After early break-ups between 1981 and 1987, more persistent vortex occured in the NH during the 1990s. For both hemispheres stronger vortex edge and longer vortex duration is observed in solar minimum (minSC) years. For the SH, the vortex edge is stronger and lasts longer for maxSC/wQBO years than for maxSC/eQBO years, and is somewhat stronger during cold ENSO phase (cENSO). For the NH, the stronger vortex edge is more pronounced than in SH during the wQBO phase, and it is stronger during minSC/wQBO years.Ce travail de thèse porte sur l'étude de l’évolution de l'intensité et de la position de la bordure du vortex en fonction de la latitude équivalente sur la période 1979 - 2021 sur 3 niveaux isentropes (675 K, 550 K et 475 K) issus des réanalyses ECMWF ERA-Interim. Une analyse des dates de formation et de rupture des vortex polaires est incluse. Le cycle solaire et dans une moindre mesure, l'oscillation quasi-biennale, l'oscillation australe El Niño et l'oscillation arctique modulent l'évolution interannuelle de l’intensité de la bordure et des dates de rupture du vortex. Dans l’HS, une augmentation à long terme de l'intensité de la bordure du vortex et des dates de rupture est observée sur la période 1979 - 1999, liée à l'augmentation du trou d'ozone en Antarctique. Après des ruptures précoces entre 1981 et 1987, des vortex plus persistants sont apparus dans l’HN au cours des années 1990. Pour les deux hémisphères, on observe une bordure du vortex plus intense et une persistance lors des années de minimum solaire (minSC). Pour l’HS, la bordure du vortex est plus intense et dure plus longtemps pour les années maxSC/wQBO que pour les années maxSC/eQBO, et est un peu plus intense durant la phase ENSO froide (cENSO). Pour l’HN, l’intensité de la bordure est plus prononcée que dans l’HS durant la phase wQBO, et il est plus intense durant les années minSC/wQBO

Évolution et persistance des vortex stratosphériques polaires Arctique et Antarctique sur la période 1979 - 2021

This PhD study focuses on the study of the evolution of the stratospheric polar vortices over the last forty years. The intensity and position of the Southern and Northern stratospheric polar vortex edge are evaluated as a function of equivalent latitude over the 1979 - 2021 period on 3 isentropic levels in the lower and middle stratosphere (675 K, 550 K and 475 K) from ECMWF ERA-Interim reanalysis. An analysis of the onset and breakup dates of the polar vortices is included. The solar cycle and to a lower extent the quasi-biennal oscillation, El Niño Southern Oscillation and the Arctic Oscillation modulate the interannual evolution of the strength of the vortex edge and the vortex breakup dates. In the SH, long-term increase of the vortex edge intensity and breakup dates is observed over the 1979 - 1999 period, linked to the increase of the Antarctic ozone hole. After early break-ups between 1981 and 1987, more persistent vortex occured in the NH during the 1990s. For both hemispheres stronger vortex edge and longer vortex duration is observed in solar minimum (minSC) years. For the SH, the vortex edge is stronger and lasts longer for maxSC/wQBO years than for maxSC/eQBO years, and is somewhat stronger during cold ENSO phase (cENSO). For the NH, the stronger vortex edge is more pronounced than in SH during the wQBO phase, and it is stronger during minSC/wQBO years.Ce travail de thèse porte sur l'étude de l’évolution de l'intensité et de la position de la bordure du vortex en fonction de la latitude équivalente sur la période 1979 - 2021 sur 3 niveaux isentropes (675 K, 550 K et 475 K) issus des réanalyses ECMWF ERA-Interim. Une analyse des dates de formation et de rupture des vortex polaires est incluse. Le cycle solaire et dans une moindre mesure, l'oscillation quasi-biennale, l'oscillation australe El Niño et l'oscillation arctique modulent l'évolution interannuelle de l’intensité de la bordure et des dates de rupture du vortex. Dans l’HS, une augmentation à long terme de l'intensité de la bordure du vortex et des dates de rupture est observée sur la période 1979 - 1999, liée à l'augmentation du trou d'ozone en Antarctique. Après des ruptures précoces entre 1981 et 1987, des vortex plus persistants sont apparus dans l’HN au cours des années 1990. Pour les deux hémisphères, on observe une bordure du vortex plus intense et une persistance lors des années de minimum solaire (minSC). Pour l’HS, la bordure du vortex est plus intense et dure plus longtemps pour les années maxSC/wQBO que pour les années maxSC/eQBO, et est un peu plus intense durant la phase ENSO froide (cENSO). Pour l’HN, l’intensité de la bordure est plus prononcée que dans l’HS durant la phase wQBO, et il est plus intense durant les années minSC/wQBO

Évolution et persistance des vortex stratosphériques polaires Arctique et Antarctique sur la période 1979 - 2021

This PhD study focuses on the study of the evolution of the stratospheric polar vortices over the last forty years. The intensity and position of the Southern and Northern stratospheric polar vortex edge are evaluated as a function of equivalent latitude over the 1979 - 2021 period on 3 isentropic levels in the lower and middle stratosphere (675 K, 550 K and 475 K) from ECMWF ERA-Interim reanalysis. An analysis of the onset and breakup dates of the polar vortices is included. The solar cycle and to a lower extent the quasi-biennal oscillation, El Niño Southern Oscillation and the Arctic Oscillation modulate the interannual evolution of the strength of the vortex edge and the vortex breakup dates. In the SH, long-term increase of the vortex edge intensity and breakup dates is observed over the 1979 - 1999 period, linked to the increase of the Antarctic ozone hole. After early break-ups between 1981 and 1987, more persistent vortex occured in the NH during the 1990s. For both hemispheres stronger vortex edge and longer vortex duration is observed in solar minimum (minSC) years. For the SH, the vortex edge is stronger and lasts longer for maxSC/wQBO years than for maxSC/eQBO years, and is somewhat stronger during cold ENSO phase (cENSO). For the NH, the stronger vortex edge is more pronounced than in SH during the wQBO phase, and it is stronger during minSC/wQBO years.Ce travail de thèse porte sur l'étude de l’évolution de l'intensité et de la position de la bordure du vortex en fonction de la latitude équivalente sur la période 1979 - 2021 sur 3 niveaux isentropes (675 K, 550 K et 475 K) issus des réanalyses ECMWF ERA-Interim. Une analyse des dates de formation et de rupture des vortex polaires est incluse. Le cycle solaire et dans une moindre mesure, l'oscillation quasi-biennale, l'oscillation australe El Niño et l'oscillation arctique modulent l'évolution interannuelle de l’intensité de la bordure et des dates de rupture du vortex. Dans l’HS, une augmentation à long terme de l'intensité de la bordure du vortex et des dates de rupture est observée sur la période 1979 - 1999, liée à l'augmentation du trou d'ozone en Antarctique. Après des ruptures précoces entre 1981 et 1987, des vortex plus persistants sont apparus dans l’HN au cours des années 1990. Pour les deux hémisphères, on observe une bordure du vortex plus intense et une persistance lors des années de minimum solaire (minSC). Pour l’HS, la bordure du vortex est plus intense et dure plus longtemps pour les années maxSC/wQBO que pour les années maxSC/eQBO, et est un peu plus intense durant la phase ENSO froide (cENSO). Pour l’HN, l’intensité de la bordure est plus prononcée que dans l’HS durant la phase wQBO, et il est plus intense durant les années minSC/wQBO

Evolution of the stratospheric polar vortex in the Southern and Northern Hemispheres over the period 1979-2020

International audienceThe stratospheric polar vortex in the Southern Hemisphere plays an important role in the intensity of the stratospheric ozone destruction during austral spring, which started in the late 1970s. The so-called ozone hole has in turn influenced the evolution of weather patterns in the Southern Hemisphere in the last decades (WMO, 2018). The Northern Hemisphere polar vortex is less stable because of larger dynamical activity in winter. It is thus less cold and polar arctic ozone losses are less important. The seasonal and interannual evolution of the polar vortex in both hemispheres has been analyzed using meteorological fields from the European Center for Meteorology Weather Forecasts ERA-Interim reanalyses and the MIMOSA model (Modélisation Isentrope du transport Méso-échelle de l’Ozone Stratosphérique par Advection, Hauchecorne et al., 2002). This model provides high spatial resolution potential vorticity (PV) and equivalent latitude fields at several isentropic levels (675K, 550K and 475K) that are used to evaluate the temporal evolution of the polar vortex edge. The edge of the vortex is computed on isentropic surfaces from the wind and gradient of PV as a function of equivalent latitude (e.g. Nash et al, 1996; Godin et al., 2001). On an interannual scale, the signature of some typical forcings driving stratospheric natural variability such as the 11-year solar cycle, the quasi-biennial oscillation (QBO), and El Niño Southern Oscillation (ENSO) is evaluated. The study includes analysis of the onset and breakup dates of the polar vortex, which are determined from the wind field along the vortex edge. Several threshold values, such as 15.2m/s, 20m/s and 25m/s following Akiyoshi et al. (2009) are used. Results on the seasonal and interannual evolution of the intensity and position of the vortex edge, as well as the onset and breakup dates of the Southern and Northern polar vortex edge over the 1979 – 2020 period will be show

Evolution of the stratospheric polar vortex in the Southern Hemisphere over the period 1979 - 2016

International audienceThe stratospheric polar vortex in the Southern Hemisphere plays an important role in the intensity of the stratospheric ozone destruction during austral spring, which started in the late 1970s. The so-called ozone hole has in turn influenced the evolution of weather patterns in the Southern Hemisphere in the last decades (WMO, 2018) The seasonal and interannual evolution of the Southern polar vortex has been analyzed using meteorological fields from the European Center for Meteorology Weather Forecasts ERA-Interim reanalyses and the MIMOSA model (Modélisation Isentrope du transport Méso-échelle de l'Ozone Stratosphérique par Advection, Hauchecorne et al., 2002). This model provides potential vorticity (PV) fields at several isentropic levels (475 K, 550 K and 675 K) that are used to evaluate the edge and intensity of the polar vortex as a function of time from 1979 to 2016. The edge of the vortex is computed on isentropic surfaces from the wind and gradient of PV as a function of equivalent latitude (e.g. Nash et al, 1996; Godin et al., 2001). In order to remove the noise of PV gradient determination, tracers have been incorporated into the model, tracking air masses inside and outside the vortex as a function of time. Results on the statistical analysis of the seasonal and interannual evolution of the intensity and extension of the southern polar vortex over the last 3 decades will be presented

Evolution of the intensity and duration of the Southern Hemisphere stratospheric polar vortex edge for the period 1979–2020

International audienceThe intensity and position of the Southern Hemisphere stratospheric polar vortex edge is evaluated as a function of equivalent latitude over the 1979-2020 period on three isentropic levels (475K, 550K and 675K) from ECMWF ERA-Interim reanalysis. The study also includes an analysis of the onset and breakup dates of the polar vortex, which are determined from wind thresholds (e.g. 15.2 m.s −1 , 20 m.s −1 and 25 m.s −1) along the vortex edge. The vortex edge is stronger in late winter, over September-October-November with the period of strongest intensity occurring later at the lowermost level. A lower variability of the edge position is observed during the same period. Long-term increase of the vortex edge intensity and breakup date is observed over the 1979-1999 period, linked to the increase of the ozone hole. Long-term decrease of the vortex onset date related to the 25 m.s −1 wind threshold is also observed at 475K during this period. The solar cycle and to a lower extent the quasi-biennal oscillation (QBO) and El Niño Southern Oscillation (ENSO) modulate the inter-annual evolution of the strength of the vortex edge and the vortex breakup dates. Stronger vortex edge and longer vortex duration is observed in solar minimum (minSC) years, with the QBO and ENSO further modulating the solar cycle influence, especially at 475K and 550K: during West QBO (wQBO) phases, the difference between vortex edge intensity for minSC and maxSC years is smaller than during East QBO (eQBO) phases. The polar vortex edge is stronger and lasts longer for maxSC/wQBO years than for maxSC/eQBO years. ENSO has a weaker impact but the vortex edge is somewhat stronger during cold ENSO phases for both minSC and maxSC years

Altitude of smoke plumes observed by CALIPSOover the period 2008-2022

International audienceBiomass burning is one of the main sources of aerosols and many trace gases. It has significantradiative effects and alters air quality locally, but also sometimes on a hemispheric scale. In additionto the total amount of pollutants emitted, their altitude is key in estimating their impact: the higherthe injection height, the lower the local effect on air quality. However, higher wind speeds in the freetroposphere may induce a longer-range transport of the fire plumes injected above the planetaryboundary layer (PBL). In this work, we use the L2 CALIPSO observations of extinction and aerosolfeature mask (VFM) in order to analyse the altitude of the observed biomass burning plumes.First, a statistical comparison of the altitudes observed by CALIPSO with plume heights derivedfrom the Multi-angle Imaging SpectroRadiometer (MISR) onboard the Terra satellite is presented.Therefore, we use a database of fire plumes digitized with the MISR INteractive eXplore (MINX)software from observations during years 2008 to 2011, 2017 and 2018. This allows to analyse,depending on the region and the characteristic of the fire, the information provided by the CALIOPdata.The altitude of biomass combustion plumes is then analysed more generally using CALIOP day andnight observations, both in the vicinity of observed fires (based on MODIS fire data) and duringlong-range transport, with a particular focus on the Northern Hemisphere. In addition to the VFMproduct, observations from the IASI/METOP instrument (carbon monoxide as an indicator of acombustion plume) and MODIS/AQUA AOD are used to identify dense fire plumes in the NorthernHemisphere. These complementary observations are also used to differentiate local plumes fromplumes influenced by a potential inflow from another source region

Trends in polar ozone loss since 1989: potential sign of recovery in the Arctic ozone column

International audienceOzone depletion over the polar regions is monitored each year by satellite- and ground-based instru- ments. In this study, the vortex-averaged ozone loss over the last 3 decades is evaluated for both polar regions using the passive ozone tracer of the chemical transport model TOMCAT/SLIMCAT and total ozone observa- tions from Système d’Analyse par Observation Zénithale (SAOZ) ground-based instruments and Multi-Sensor Reanalysis (MSR2). The passive-tracer method allows us to determine the evolution of the daily rate of column ozone destruction and the magnitude of the cumulative column loss at the end of the winter. Three metrics are used in trend analyses that aim to assess the ozone recovery rate over both polar regions: (1) the maximum ozone loss at the end of the winter, (2) the onset day of ozone loss at a specific threshold, and (3) the ozone loss residuals computed from the differences between annual ozone loss and ozone loss values regressed with respect to sunlit volume of polar stratospheric clouds (VPSCs). This latter metric is based on linear and parabolic regressions for ozone loss in the Northern Hemisphere and Southern Hemisphere, respectively. In the Antarctic, metrics 1 and 3 yield trends of −2.3 % and −2.2 % per decade for the 2000–2021 period, significant at 1 and 2 standard deviations (σ ), respectively. For metric 2, various thresholds were considered at the total ozone loss values of 20%, 25%, 30%, 35%, and 40%, all of them showing a time delay as a function of year in terms of when the threshold is reached. The trends are significant at the 2σ level and vary from 3.5 to 4.2 d per decade between the various thresholds. In the Arctic, metric 1 exhibits large interannual variability, and no significant trend is detected; this result is highly influenced by the record ozone losses in 2011 and 2020. Metric 2 is not applied in the Northern Hemisphere due to the difficulty in finding a threshold value in enough of the winters. Metric 3 pro- vides a negative trend in Arctic ozone loss residuals with respect to the sunlit VPSC fit of −2.00 ± 0.97 (1σ ) % per decade, with limited significance at the 2σ level. With such a metric, a potential quantitative detection of ozone recovery in the Arctic springtime lower stratosphere can be made