Landmasses cover a large portion of the northern hemisphere, and nearly one-half of Eurasia and N... more Landmasses cover a large portion of the northern hemisphere, and nearly one-half of Eurasia and North America are extensively covered with snow in the cold season (Dery and Brown, 2007). Snowcovered land plays a key role in the climate system, owing to the snow radiative and thermodynamical properties, such as high albedo, high emissivity and low thermal conductivity, and its effect on surface fluxes of moisture and heat. Snow covered land can hence impact climate in a variety of ways. The snow-albedo feedback plays an important role in the spring (e.g. Schlosser and Mocko, 2003) when an early seasonal retreat of the snow cover acts as a positive feedback on spring temperatures. However, the climate response to high-latitude snow cover could also involve thermodynamical feedbacks in the surface energy balance, as well as large-scale dynamical feedbacks. Eastern Eurasia for example, is a region where the Asian jet establishes a near-zonal waveguide for propagating Rossby waves arisin...
Eastward-propagating planetary waves (EPWs) were investigated prior to the boreal January 2009 ma... more Eastward-propagating planetary waves (EPWs) were investigated prior to the boreal January 2009 major sudden stratospheric warming (SSW) event simulated by the National Center for Atmospheric Research's Whole Atmosphere Community Climate Model with specified dynamics. About 22 days before SSW onset, a background flow with jet maxima around the upper polar stratosphere and subtropical mesosphere developed due to the net forcing by gravity and planetary waves. The mesospheric wind structure was largely unstable and supported a wave geometry conducive to overreflection. With a zonal phase speed of ∼10 m s−1, EPWs appeared near their turning and critical layers as wavenumber-2 perturbations in the stratosphere and mesosphere. Accompanied by upward EPW activity from the lower stratosphere, EPW growth exhibited characteristics of wave instability and overreflection
Journal of Geophysical Research: Atmospheres, 2019
Using meteor wind data from the Super Dual Auroral Radar Network (SuperDARN) in the Northern Hemi... more Using meteor wind data from the Super Dual Auroral Radar Network (SuperDARN) in the Northern Hemisphere, we (1) demonstrate that the migrating (Sun‐synchronous) tides can be separated from the nonmigrating components in the mesosphere and lower thermosphere (MLT) region and (2) use this to determine the response of the different components of the semidiurnal tide (SDT) to sudden stratospheric warming (SSW) conditions. The radars span a limited range of latitudes around 60°N and are located over nearly 180° of longitude. The migrating tide is extracted from the nonmigrating components observed in the meridional wind recorded from meteor ablation drift velocities around 95‐km altitude, and a 20‐year climatology of the different components is presented. The well‐documented late summer and wintertime maxima in the semidiurnal winds are shown to be due primarily to the migrating SDT, whereas during late autumn and spring the nonmigrating components are at least as strong as the migrating...
Atmospheric Chemistry and Physics Discussions, 2016
A Sudden Stratospheric Warming (SSW) affects the chemistry and dynamics of the middle atmosphere.... more A Sudden Stratospheric Warming (SSW) affects the chemistry and dynamics of the middle atmosphere. The major warmings occur roughly every second year in the Northern Hemispheric (NH) winter, but has only been observed once in the Southern Hemisphere (SH), during the Antarctic winter of 2002. Using the National Center for Atmospheric Research's (NCAR) Whole Atmosphere Community Climate Model with specified dynamics (WACCM-SD), this study investigates the effects of this rare warming event on the ozone layer located around the SH mesopause. This secondary ozone layer changes with respect to hydrogen, oxygen, temperature, and the altered SH polar circulation during the major SSW. The 2002 SH winter was characterized by three zonal-mean zonal wind reductions in the upper stratosphere before a fourth wind reversal reaches the lower stratosphere, marking the onset of the major SSW. At the time of these four wind reversals, a corresponding episodic increase can be seen in the modeled ni...
ABSTRACT The primary modes of wintertime variability, such as the North Atlantic Oscillation (NAO... more ABSTRACT The primary modes of wintertime variability, such as the North Atlantic Oscillation (NAO) have a marked signature on the ozone layer. The recent realisation that the NAO is part of a more global pattern, termed the Arctic Oscillation (AO), which extends from the surface upwards into the stratosphere, highlighted the coupling of the NAO with the stratosphere and the ozone layer. We examine nearly 20 years of global TOMS observations, and diagnose the signatures of the leading patterns of climatic variability upon total ozone. Our main emphasis is on the E uropean and Atlantic sector. These signatures are twofold. We seek for influences on both the seasonal-mean (quasi-stationary) ozone, and else on the fast transient (eddy) ozone variability linked to passing weather systems. We hence systematically examine how leading climate patterns influence seasonal-mean ozone in winter and spring, through a statistical analysis using empirical orthogonal functions. In addition, we carried out an analysis of ozone synoptic variability. Satellite column ozone observations indicate a strong signature of storm tracks in ozone, with marked asymm etries between the Pacific and Atlantic storm tracks. Of particular interest are the large amplitude ozone "mini-hole" events that frequently develop over the Atlantic in winter. We examine the relationship between the occurrences of such ozone minihole events and the NAO or other climate patterns.
ABSTRACT Using the newly analyzed mesospheric water vapor and temperature observations from the S... more ABSTRACT Using the newly analyzed mesospheric water vapor and temperature observations from the SMR microwave instrument aboard the Odin research satellite, we present evidence for an anomalously strong descent of dry mesospheric air from the lower mesosphere into the upper stratosphere in the late winter of 2004, 2006, and 2009. In these cases, the descent follows the recovery of the upper stratospheric polar vortex from a mid-winter stratospheric sudden warming. This downward progression is also accompanied by the rapid formation of an anomalously warm polar mesospheric layer, giving rise to an elevated stratopause (near 75km) and its eventual return to pre-warming level (near 1 hPa) over 1.5-2 months. These three winters stand out in the record of Odin/SMR observations spanning the period July 2001 to June 2009.
ABSTRACT Three-hourly WACCM simulations are used to characterize a composite life cycle of the ma... more ABSTRACT Three-hourly WACCM simulations are used to characterize a composite life cycle of the major Stratospheric Sudden Warming (SSW) event from the surface up to 130 km. The life cycle reveals the intimate coupling between the stratosphere and mesosphere, in addition to the stratosphere-troposphere connection much studied in the past. During the SSW onset, the polar zonal-mean wind reversal occurs at nearly all model levels: eastward to westward direction below 80 km and vice versa above. Concurrent anomalous warming appears throughout the stratosphere and above 90 km with cooling in the intervening mesospheric layer, consistent with stratospheric and thermospheric downwelling as well as mesospheric upwelling. As SSW matures, these anomalous patterns migrate downward in time greatly affecting the distributions of polar NOx and local ozone maxima layers in ways observed by satellites. We further analyze the behavior of planetary waves and the variability in the secondary ozone maximum, associated with the abrupt reformation of a high-altitude stratopause in the polar mesosphere.
Landmasses cover a large portion of the northern hemisphere, and nearly one-half of Eurasia and N... more Landmasses cover a large portion of the northern hemisphere, and nearly one-half of Eurasia and North America are extensively covered with snow in the cold season (Dery and Brown, 2007). Snowcovered land plays a key role in the climate system, owing to the snow radiative and thermodynamical properties, such as high albedo, high emissivity and low thermal conductivity, and its effect on surface fluxes of moisture and heat. Snow covered land can hence impact climate in a variety of ways. The snow-albedo feedback plays an important role in the spring (e.g. Schlosser and Mocko, 2003) when an early seasonal retreat of the snow cover acts as a positive feedback on spring temperatures. However, the climate response to high-latitude snow cover could also involve thermodynamical feedbacks in the surface energy balance, as well as large-scale dynamical feedbacks. Eastern Eurasia for example, is a region where the Asian jet establishes a near-zonal waveguide for propagating Rossby waves arisin...
Eastward-propagating planetary waves (EPWs) were investigated prior to the boreal January 2009 ma... more Eastward-propagating planetary waves (EPWs) were investigated prior to the boreal January 2009 major sudden stratospheric warming (SSW) event simulated by the National Center for Atmospheric Research's Whole Atmosphere Community Climate Model with specified dynamics. About 22 days before SSW onset, a background flow with jet maxima around the upper polar stratosphere and subtropical mesosphere developed due to the net forcing by gravity and planetary waves. The mesospheric wind structure was largely unstable and supported a wave geometry conducive to overreflection. With a zonal phase speed of ∼10 m s−1, EPWs appeared near their turning and critical layers as wavenumber-2 perturbations in the stratosphere and mesosphere. Accompanied by upward EPW activity from the lower stratosphere, EPW growth exhibited characteristics of wave instability and overreflection
Journal of Geophysical Research: Atmospheres, 2019
Using meteor wind data from the Super Dual Auroral Radar Network (SuperDARN) in the Northern Hemi... more Using meteor wind data from the Super Dual Auroral Radar Network (SuperDARN) in the Northern Hemisphere, we (1) demonstrate that the migrating (Sun‐synchronous) tides can be separated from the nonmigrating components in the mesosphere and lower thermosphere (MLT) region and (2) use this to determine the response of the different components of the semidiurnal tide (SDT) to sudden stratospheric warming (SSW) conditions. The radars span a limited range of latitudes around 60°N and are located over nearly 180° of longitude. The migrating tide is extracted from the nonmigrating components observed in the meridional wind recorded from meteor ablation drift velocities around 95‐km altitude, and a 20‐year climatology of the different components is presented. The well‐documented late summer and wintertime maxima in the semidiurnal winds are shown to be due primarily to the migrating SDT, whereas during late autumn and spring the nonmigrating components are at least as strong as the migrating...
Atmospheric Chemistry and Physics Discussions, 2016
A Sudden Stratospheric Warming (SSW) affects the chemistry and dynamics of the middle atmosphere.... more A Sudden Stratospheric Warming (SSW) affects the chemistry and dynamics of the middle atmosphere. The major warmings occur roughly every second year in the Northern Hemispheric (NH) winter, but has only been observed once in the Southern Hemisphere (SH), during the Antarctic winter of 2002. Using the National Center for Atmospheric Research's (NCAR) Whole Atmosphere Community Climate Model with specified dynamics (WACCM-SD), this study investigates the effects of this rare warming event on the ozone layer located around the SH mesopause. This secondary ozone layer changes with respect to hydrogen, oxygen, temperature, and the altered SH polar circulation during the major SSW. The 2002 SH winter was characterized by three zonal-mean zonal wind reductions in the upper stratosphere before a fourth wind reversal reaches the lower stratosphere, marking the onset of the major SSW. At the time of these four wind reversals, a corresponding episodic increase can be seen in the modeled ni...
ABSTRACT The primary modes of wintertime variability, such as the North Atlantic Oscillation (NAO... more ABSTRACT The primary modes of wintertime variability, such as the North Atlantic Oscillation (NAO) have a marked signature on the ozone layer. The recent realisation that the NAO is part of a more global pattern, termed the Arctic Oscillation (AO), which extends from the surface upwards into the stratosphere, highlighted the coupling of the NAO with the stratosphere and the ozone layer. We examine nearly 20 years of global TOMS observations, and diagnose the signatures of the leading patterns of climatic variability upon total ozone. Our main emphasis is on the E uropean and Atlantic sector. These signatures are twofold. We seek for influences on both the seasonal-mean (quasi-stationary) ozone, and else on the fast transient (eddy) ozone variability linked to passing weather systems. We hence systematically examine how leading climate patterns influence seasonal-mean ozone in winter and spring, through a statistical analysis using empirical orthogonal functions. In addition, we carried out an analysis of ozone synoptic variability. Satellite column ozone observations indicate a strong signature of storm tracks in ozone, with marked asymm etries between the Pacific and Atlantic storm tracks. Of particular interest are the large amplitude ozone "mini-hole" events that frequently develop over the Atlantic in winter. We examine the relationship between the occurrences of such ozone minihole events and the NAO or other climate patterns.
ABSTRACT Using the newly analyzed mesospheric water vapor and temperature observations from the S... more ABSTRACT Using the newly analyzed mesospheric water vapor and temperature observations from the SMR microwave instrument aboard the Odin research satellite, we present evidence for an anomalously strong descent of dry mesospheric air from the lower mesosphere into the upper stratosphere in the late winter of 2004, 2006, and 2009. In these cases, the descent follows the recovery of the upper stratospheric polar vortex from a mid-winter stratospheric sudden warming. This downward progression is also accompanied by the rapid formation of an anomalously warm polar mesospheric layer, giving rise to an elevated stratopause (near 75km) and its eventual return to pre-warming level (near 1 hPa) over 1.5-2 months. These three winters stand out in the record of Odin/SMR observations spanning the period July 2001 to June 2009.
ABSTRACT Three-hourly WACCM simulations are used to characterize a composite life cycle of the ma... more ABSTRACT Three-hourly WACCM simulations are used to characterize a composite life cycle of the major Stratospheric Sudden Warming (SSW) event from the surface up to 130 km. The life cycle reveals the intimate coupling between the stratosphere and mesosphere, in addition to the stratosphere-troposphere connection much studied in the past. During the SSW onset, the polar zonal-mean wind reversal occurs at nearly all model levels: eastward to westward direction below 80 km and vice versa above. Concurrent anomalous warming appears throughout the stratosphere and above 90 km with cooling in the intervening mesospheric layer, consistent with stratospheric and thermospheric downwelling as well as mesospheric upwelling. As SSW matures, these anomalous patterns migrate downward in time greatly affecting the distributions of polar NOx and local ozone maxima layers in ways observed by satellites. We further analyze the behavior of planetary waves and the variability in the secondary ozone maximum, associated with the abrupt reformation of a high-altitude stratopause in the polar mesosphere.
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Papers by Yvan Orsolini