Contribution of stratospheric warmings to temperature trends in the middle atmosphere from the lidar series obtained at Haute-Provence Observatory (44°N)

International audienceThis study describes a method to calculate long-term temperature trends, as an alternative to the ones based on monthly mean temperatures, which are highly impacted by the high winter variability partially due to wave-mean flow interactions like Sudden Stratospheric Warmings (SSW). This method avoids the strong influence of SSWs and provides "background" temperature trend estimates which are in better agreement with expected direct radiative effects. The data set used results from lidar measurements - performed above southern France continuously since late 1978 - combined with radiosonde profiles. With this new methodology, the long-term trends during winter at 40 km shows a larger cooling per decade (−2 ± 0.4 K) than when the mean temperature is used (−0.4 ± 0.4 K). The background temperature trend is closer to the summer trend estimates which are similar whatever the temperature proxy used, due to the absence of SSWs (−2.9 ± 0.3 K per decade with the mean-based method and −3.4 ± 0.3 K per decade with the background-based calculation). Based on this background temperature, composite evolutions of winter anomalies for both vortex-displacement and vortex-splitting major SSWs have been displayed: in both cases the largest warming occurs at the time of the SSW in the upper stratosphere, with mean amplitudes of more than 10 K. A warm signal in the upper mesosphere could suggest a potential precursory role of gravity waves. Displacement-type events present an 18-day periodicity, which is a clear sign of the wave number one Rossby wave. Colder tropospheric temperatures are noticed before and during the SSW, and warmer ones after the event, with a stronger signal for split-type events

Temperature climatology with Rayleigh lidar above Observatory of Haute-provence : dynamical feedback

International audienceRayleigh lidar in synergy with satellite observations (SSU and AMSU) allow insuring an efficient monitoring and showing that cooling has continued. New approach for trend detection has been developed allowing a better estimate of changes due to radiative forcing. Stratospheric Warmings and gravity waves contribute to insure a dynamical feedback of the long-term changes

Contribution des échauffements stratosphériques à la variabilité et à l'évolution à long terme de la moyenne atmosphère : observations et modélisations numériques

The influence of stratospheric conditions on the climate has recently become widely accepted. Coupling in the stratosphere-troposphere system causes large amplitude dynamical activity occurring in the middle atmosphere to have significant consequences on the troposphere's equilibrium and flow. Sudden stratospheric warmings are the clearest and strongest manifestation of such activity. This study focuses on the impact of these events on the variability of the middle atmosphere and on estimations of temperature trends. Another objective of our work is to acquire a better understanding of the evolution of a stratospheric warming, from the state of the atmosphere that initiates such an event to its consequences on both the middle atmosphere and the troposphere from a few days to a couple of months after it. First, we describe a novel methodology to perform a statistical analysis of long series and we apply it on a lidar measurement from the Haute-Provence Observatory. The large dynamical activity and the so-called background component can be distinguished, which allows to explain the differences observed between summer and winter. Second, the methodology is validated and its results are extended to a global scope thanks to a dataset from the Canadian Middle Atmosphere Model. Spatial differences are also explained by variations in the dynamical activity. Third, sensitivity tests are performed using RACCORD model to investigate what state of the atmosphere leads to a major stratospheric warming. Meteorological nudging is essential to produce a major warming, especially for split-type events. Last, our results are applied and compared to a case-study of winter 2012-2013.Le rôle joué par la stratosphère sur le climat est aujourd'hui avéré. Le couplage du système troposphère-stratosphère implique que les processus dynamiques de grande amplitude de la moyenne atmosphère perturbent l'équilibre atmosphérique et l'écoulement dans les plus basses couches. Parmi ces phénomènes dynamiques, les échauffements stratosphériques soudains sont les plus emblématiques. Cette étude s'intéresse à l'impact de ces événements sur la variabilité de la moyenne atmosphère et sur l'estimation des tendances de température. Nous cherchons également à mieux caractériser l'évolution spatio-temporelle des échauffements stratosphériques, depuis leurs causes jusqu'à leurs conséquences. Tout d'abord, une méthodologie novatrice d'analyse statistique de séries temporelles est développée et testée sur des mesures lidar de l'Observatoire de Haute-Provence. L'impact des événements dynamiques les plus importants peut ainsi être efficacement isolé de la contribution radiative de fond, ce qui explique les différences observées entre l'été et l'hiver. Ensuite, une simulation du Canadian Middle Atmosphere Model nous permet de valider la méthodologie et d'étendre notre étude à l'ensemble du globe. On montre que les variations spatiales sont elles aussi majoritairement causées par l'activité dynamique. Les conditions de formation d'un échauffement stratosphérique sont également étudiées, à l'aide de tests de sensibilité du modèle RACCORD. On prouve l'importance du rappel vers la météorologie pour produire un échauffement majeur, particulièrement dans le cas d'une rupture du vortex. Enfin, la méthode et nos résultats sont mis à profit dans une analyse de l'hiver 2012-2013

Modes of variability of the vertical temperature profile of the middle atmosphere at mid-latitude: Similarities with solar forcing

International audienceA long and continuous temperature data set from ground to mesopause was obtained in merging lidar and radiosonde data at mid-latitude over south of France (44°N). The analyses using Empirical Orthogonal Functions has been applied on vertical temperature profiles to investigated the variability differently than it has been done in previous investigations. This study reveals as the first mode in winter, a strong anti-correlation between upper stratosphere and mesosphere that is most probably link with planetary waves propagation and associated stratospheric warmings. While in summer the variability is located in the mesosphere and associated with mesospheric inversions that are probably generated by gravity waves breaking. This study shows that even if the daily temperature variability appears to be complex, a large part (30%) can be modeled, each season, using the first EOF. These vertical patterns exhibit some similarities with solar atmospheric responses, suggesting a potential feedback of the dynamic. This is already observed for winter response, but during summer the contribution of gravity waves on the mesospheric solar response suggest future investigations to explore the role of this potential mechanism in solar-atmospheric connections

Refroidissement de la stratosphère : Détection réussie mais quantification encore incertaine,

International audienceLa stratosphère se refroidit sous l'effet de la diminution d'ozone et de l'augmentation de l'effet de serre. Même si les observations disponibles, qui n'ont pas été prévues initialement pour des études climatiques, présentent toutes de fortes discontinuités temporelles, on identifie clairement ce refroidissement, avec des variations en fonction de l'altitude et de la latitude. Cependant, les incertitudes concernant la quantification de ces tendances varient d'un facteur 2. Dans le futur, la synergie entre les mesures spatiales et celles depuis le sol devra se renforcer afin d'assurer notamment une meilleure continuité entre les instruments SSU et AMSU

Temperature trends in the middle atmosphere and the role of the dynamics

International audienceThe continuous temperature measurements since 1979 using Rayleigh scattering have been used to derive the variability, long-term trends and to insure satellite adjustment. Some discrepancies remain due to tides, under-sampling, and dynamic feedbacks. A new analysis method has been developed based on background temperatures instead of mean temperatures. The winter trend estimates was smaller than summer estimates before and is in better agreement with the new method. Stratospheric warmings play a critical role in trend estimates. Sudden stratospheric warmings seem to be associated with a cooling at ground level

Recent dynamic studies on the middle atmosphere at mid- and low-latitudes using Rayleigh Lidar and other technologies

International audienc

Temperature Climatology with Rayleigh Lidar Above Observatory of Haute-Provence: Dynamical Feedback

Rayleigh lidar in synergy with satellite observations (SSU and AMSU) allow insuring an efficient monitoring and showing that cooling has continued. New approach for trend detection has been developed allowing a better estimate of changes due to radiative forcing. Stratospheric Warmings and gravity waves contribute to insure a dynamical feedback of the long-term changes

Update of stratospheric temperature interannual variability and trends from space sounders and ground-based lidars observations

International audiencethe stratosphere is expected to cool, in conjunction with the global warming at the surface and in the troposphere, due to the increase of greenhouse gas concentration in the atmosphere, and also to stratospheric ozone loss. this is already observed but the rate of cooling is not constant and there is still a debate on its amplitude. several other factors may influence the evolution of the stratospheric temperature. external forcings, like the solar variability that modulate the UV solar flux and strong volcanic eruptions injecting aerosols in the stratosphere, participate to its decadal variability. the variability of the stratospheric dynamics is also adding some complexity to the system. For instance global climate models predicts an increase of the occurrence frequency of sudden stratospheric warming (SSW) events not yet confirmed by the observations. A monitoring of the stratospheric temperature evolution is crucially needed to better understand the complexity of the processes playing a role in the coupling between the stratosphere, the troposphere and the climate.the stratospheric temperature is measured at a global scale by satellite instruments; mainly microwave sounders aMsU (advanced Microwave sounding Unit) on board meteorological satellites. these sounders are very useful to provide the global overview but may suffer from biases and orbital drifts and have a poor vertical resolution in the upper stratosphere. since 2000 radio-occultation sensors, among them the Us-taiwan COsMiC constellation, provide well-resolved and accurate temperature profiles but limited to the upper troposphere-lower stratosphere. rayleigh lidars implemented within the nDaCC (network for the Detection of atmospheric Composition Change) international network measure accurately the temperature profile from the middle stratosphere to the upper mesosphere but in a very few locations. they are used climate change monitoring, dynamics studies and satellite validation.in this presentation we will present an update of the interannual variability and trends in the stratospheric temperature from aMsU, rayleigh lidar and radio- occultation measurements. similarities and differences in the temperature evolution captured by these various sensors will be evaluated. the contribution of anthropogenic and natural forcings to the observed changes will be discussed. a particular focus will be given to the role of SSW events to the stratospheric temperature evolution as a function of latitude and season

Les nouveaux satires et exercices gaillards d'Angot l'Éperonnière.

"Vie de Robert Angot, par Guillaume Colletet": p. [xi]-xix.With reproduction of t.-p. of original edition, Rouen, 1637."Bibliographie": p. [xxix]-xxxii.Mode of access: Internet