Etude des caractéristiques globales des ondes de gravité atmosphérique à l'aide des mesures de vent du satellite de l'ESA Aeolus

Understanding and predicting the evolution of global climate strongly relies on the knowledge of dynamical processes in the middle atmosphere such as atmospheric waves. Since the global atmospheric circulation is largely driven by middle atmosphere dynamics, it is essential that the climate models take a proper account for the dynamical processes, which has not been fully understood yet. Small-scale atmospheric waves, called internal gravity waves (IGWs) pose a particular challenge for models, whereas inaccurate parameterization of IGWs can dramatically bias the predictions of future atmospheric circulation changes. This issue is aggravated by insufficient understanding of IGW sources, propagation and dissipation, but above all by the lack of observations of wind in the stratosphere. Indeed, spatially-sparse radiosoundings are essentially the only source of data on stratospheric wind profiles. With that, they only provide a snapshot of the local atmospheric conditions therefore missing important IGW parameters. European Space Agency's Aeolus satellite mission is designed to provide global information on the wind speed from the ground up to 30 km, which is highly demanded for weather forecasting. Aeolus satellite has been set into orbit in August 2018 and its payload consists of a sophisticated ALADIN lidar instrument measuring wind velocity by sensing Doppler spectral shift of the laser echo scattered by the different layers of the atmosphere. Aeolus global-scale wind measurements are expected to be of great value for studying the dynamical processes in the stratosphere.The primary objective of this doctoral project is to explore and quantify the capacities of Aeolus observations in capturing and resolving dynamical processes such as IGWs at various spatial and temporal scales. The work will consist first of all in geophysical analysis of Aeolus wind profiles for deriving IGW parameters such as horizontal and vertical wavelengths, energy and momentum flux. The retrieved parameters and their variability in time and space will be compared with those derived from global temperature profiling data of GPS radio occultation missions such as GRAS onboard MetOp satellites. Another task will be to validate the quality of Aeolus wind measurements using the two French ground-based Doppler lidars operating at a mid-latitude site (Observatoire de Haute-Provence) and at a south tropical site (Maïdo Observatory à la Réunion). The time-resolved wind measurements by ground-based lidars will also be used for IGW analysis. An important outcome of this doctoral project will be the first ever climatology of IGW parameters based on a combination of global-coverage wind and temperature profilingLa compréhension et la prédiction de l'évolution du climat global dépendent fortement de la connaissance des processus dynamiques dans l'atmosphère moyenne, comme les ondes atmosphériques. Étant donné que la circulation atmosphérique globale est largement influencée par la dynamique de l'atmosphère moyenne, il est essentiel que les modèles climatiques tiennent compte des processus dynamiques qui n'ont pas encore été complètement compris. Les ondes atmosphériques à petite échelle, appelées ondes de gravité internes (IGWs), posent un défi particulier pour les modèles, alors que la paramétrisation inexacte des IGWs peut biaiser de façon spectaculaire les prédictions des changements futurs de la circulation atmosphérique. Cette question est aggravée par une compréhension insuffisante de la génération des IGWs, de leur propagation et de leur dissipation, mais surtout par le manque d'observations du vent dans la stratosphère. En effet, les radiosondages dont la répartition est spatialement inhomogène sont pratiquement la seule source de données sur les profils de vent stratosphériques. Avec cela, ils ne fournissent qu'un «instantané» des conditions atmosphériques locales, ne permettant pas d'en déduire certains paramètres importants des IGWs. La mission satellitaire d'Aeolus de l'Agence Spatiale Européenne est conçue pour fournir des informations globales sur la vitesse du vent du sol à 30 km, variable essentielle pour les prévisions météorologiques. Le satellite Aeolus a été mis en orbite en aout 2018 et sa charge utile consiste en un lidar sophistiqué ALADIN mesurant la vitesse du vent par détection du décalage spectral Doppler de l'écho laser rétrodiffusé par les différentes couches atmosphériquesLes mesures de vent à l'échelle globale d'Aeolus seront d'une grande valeur pour l'étude des processus dynamiques dans la stratosphère. L'objectif principal de ce projet de thèse est d'explorer et de quantifier les capacités des observations d'Aeolus à capturer et à résoudre les processus dynamiques tels que les IGWs à différentes échelles spatiales ets temporelles. Le travail consistera tout d'abord dans l'analyse géophysique des profils de vent d'Aeolus pour dériver les paramètres des IGWs tels que les longueurs d'ondes horizontales et verticales, l'énergie et le flux de quantité de mouvement. Les paramètres obtenus et leur variabilité spatiale et temporelle seront comparés à ceux déduits des données globales de température des missions de radio occultation GPS telles que GRAS sur les satellite MetOp. Une autre tâche consistera à valider la qualité des mesures de vent d'Aeolus à l'aide des deux lidars français Doppler fonctionnant au sol sur un site de moyenne latitude (Observatoire de Haute-Provence) et sur un site tropical sud (Observatoire du Maïdo à la Réunion). Les mesures de vent résolues dans le temps des lidars au sol seront également utilisées pour l'analyse des IGWs. Un résultat important de ce projet de thèse sera la première climatologie des paramètres des IGWs s'appuyant sur une combinaison de profils de vent et de température à couverture globale

Gravity Waves in the Tropical UTLS: New Insights from Aeolus Wind Profiling Data

The European Space Agency's Aeolus satellite mission, launched in 2018, provides global wind profiling using a Doppler lidar instrument ALADIN. In this study, we examined ALADIN’s ability to capture and resolve internal gravity waves (IGWs) in the upper troposphere and lower stratosphere (UTLS). To derive the IGW-induced perturbations in the vertical profiles of ALADIN’s horizontal line-of-sight (HLOS) quasi-zonal wind velocity at ~1 km vertical resolution, we subtract the Aeolus-derived "background" wind profiles from the individual measurements. Through a spectral analysis of these data, we then derive the IGW kinetic energy and dominant vertical wavelength in the UTLS over the entire Aeolus mission lifespan. This study represents the first attempt to reconstruct the global distribution of IGW activity using the global wind information exclusively provided by the Aeolus mission. The analysis reveals the well-known IGW sources such as orography, polar vortex dynamics and tropical convection. Here we focus on the tropical UTLS region, where ALADIN has an extended stratospheric coverage. The analysis reveals a previously undocumented spot of enhanced IGW activity in the UTLS, recurring above the Indian Ocean during Boreal Summer. The IGW activity spot is shown to slowly migrate from eastern Africa to the Pacific maritime continent during the June-December period. The Aeolus-derived distribution and seasonal variation of IGW activity were cross-validated using the global temperature profiling by EUMETSAT radio-occultation (RO) satellites. The RO data were resampled to ALADIN resolution and spectrally analyzed in the same way as it was done for ALADIN wind data. The derived IGW potential energy data confirm the seasonal/zonal variation of IGW activity observed by ALADIN, in particular the eastward migration of the IGW activity hotspot, presumably linked to convection within the MJO (Madden-Julian Oscillation). The results suggest that the interannual variation of the IGW kinetic and potential energies in the UTLS is modulated by the Quasi-Biennial Oscillation, whereas the MJO-related waves can be characterized by shorter vertical wavelengths. Another important finding enabled by the joint analysis of the Aeolus wind and RO temperature data is the evidence for a strong IGW generation by the Smoke-Charged Vortex (SCV) produced by the 2019/20 Australian megafires. Overall, with this study we point out the potential of Aeolus wind profiling to improve our understanding of atmospheric dynamics, particularly in the UTLS region

Co‐Located Wind and Temperature Observations at Mid‐Latitudes During Mesospheric Inversion Layer Events

International audienceThe mesosphere (50-90 km) is a substantial layer of the atmosphere where large and small-scale perturbations occur. These perturbations are caused by the propagation and breaking of atmospheric tides and waves from sources above and below, inducing deviations from its natural thermal structure. The so-called Mesospheric Inversion Layer (MIL) phenomenon is an especially significant perturbation that is now recognized to be responsible for a large part of the mesospheric variability. Moreover, MILs have garnered interest among researchers, since mesospheric perturbations are significant issues for applications in aeronautics, in particular the safe reentry of space shuttles and missiles (Wing et al., 2020). Indeed, since the first MIL phenomenon's signatures observed by rockets (e.g., Schmidlin, 1976; Stroud et al., 1960; Theon et al., 1967) that reported a non-expected positive lapse rate in the mesosphere, researchers have carried out numerous studies of MIL events (e.g.

New observations showing temperature-wind interconnection during mesospheric inversion layer events

International audienceIt is known that propagation of atmospheric waves and their dissipation are responsible for the small and large disturbances governing the variability observed in the mesosphere (50-90 km). One of the main phenomena caused by these waves is the so-called mesospheric inversion layer (MIL) referring to a vertical layer of ~10 km where there is an enhanced temperature (15-50 K) lasting many days over thousands of kilometers in the mesosphere. Additionally, as perturbations in the mesosphere are crucial issues in aeronautics for the safe reentry of space shuttles or missiles, the study of MILs have aroused a large interest. However, the understanding of MIL’s formation mechanisms is still not fully complete as MILs’ impact on wind behavior has never been observed accurately in the middle atmosphere preventing to determine the shear profile or study how gravity waves propagate from the stratosphere to the thermosphere. Though numerous studies have suggested the important role of gravity waves in the MIL’s apparition. For instance, Hauchecorne and Maillard (1990) have simulated MIL’s formation by the breaking of gravity waves inside and above the MIL making decrease wind above the mesospheric jet, generating turbulence.In this context, we report here, for the first time, an investigation of co-located temperature-wind observations in the altitude range 30-90 km during MIL events. According to these observations, the temperature inversion within the MIL is associated with a wind deceleration occurring in the same altitude range, confirming an inter-connection and arguing in favor of the role of gravity wave in the occurrence of MIL phenomenon

Self-lofting and dynamical confinement of the Raikoke volcanic plume.

International audienceRecent research has provided evidence of the self-lofting capacity of smoke aerosols in thestratosphere and their self-confinement by persistent anticyclones (Smoke-Charged Vortices, SCV),prolonging the atmospheric residence time and radiative effects of wildfire emissions. By contrast,the volcanic aerosols - composed mostly of non-absorptive sulphuric acid droplets – were neverreported to be subject of dynamical confinement. In this study, we use high-resolution satelliteobservations from various satellite instruments (TROPOMI, ALADIN, CALIPSO, OMPS-LP andEUMETSAT GNSS-RO) together with high-resolution ECMWF ERA5 reanalysis and meteorologicalradiosoundings to show that the eruption of Raikoke volcano in June 2019 produced a long-livedstratospheric anticyclone termed Vorticized Volcanic Plume (VVP). The primary VVP structurecontained 24% of the total erupted mass of sulphur dioxide, circumnavigated the globe threetimes, and ascended diabatically by more than 13 km in three months through radiative heating ofthe confined aerosol plume. We argue that persistent anticyclonic formations act to maintain thevolcanic plumes at high concentration thereby providing a high degree of radiative heating andupward thrust to volcanic plumes.The mechanism of dynamical confinement has important implications for the planetary-scaletransport of volcanic emissions, their stratospheric residence time, and atmospheric radiationbalance. It also provides a challenge or “out of sample test” for weather and climate models thatshould be capable of reproducing such dynamical structure

Towards a better constraining of UTLS dynamics using ESA Aeolus Wind Profiling

International audienceThe European Space Agency's Aeolus satellite mission is designed to provide global information on the wind speed from the ground up to 30 km, which is highly demanded for weather forecasting. Aeolus satellite has been set into orbit in August 2018 and its payload consists of a sophisticated ALADIN lidar instrument measuring wind velocity by sensing Doppler spectral shift of the laser echo scattered by the different layers of the atmosphere. Since the global atmospheric circulation is largely driven by middle atmosphere dynamics, it is essential that the climate models take a proper account for the dynamical processes. One type of small-scale atmospheric waves, called internal gravity waves (IGWs) pose a particular challenge for models, whereas inaccurate parameterization of IGWs can dramatically bias the predictions of future atmospheric circulation changes. In this paper, we explore the capacities of Aeolus wind observations in capturing and resolving dynamical processes in the upper troposphere and lower stratosphere (UTLS) such as IGWs at various temporal and spatial scales. This study also includes an overview of the various instrumental and retrieval issues affecting the ALADIN wind data quality. The perturbations in the vertical profiles of Rayleigh horizontal line-of-sight (HLOS) wind velocity, associated with IGW activity, are derived by subtracting the Aeolus-derived "background" wind profiles from the individual measurements. Then, the global distribution of the IGW kinetic energy in the UTLS and vertical wavelength is computed using Aeolus measurements over the entire mission lifespan. The derived variation of IGW activity over the Aeolus mission lifetime is analyzed in consideration of the time-varying performance of ALADIN instrument. The latter is quantified using two French ground-based Doppler wind lidars operating at a mid-latitude site (Observatoire de Haute-Provence) and at a southern tropical site (Maïdo Observatory at la Réunion island) as well as meteorological radiosoundings collocated with satellite overpasses. These comparisons helped identify recurring perturbations in the Aeolus wind profiles signal through their frequency analysis. Taking into account these perturbations and the evolution of the instrument's performance allows for the improvement of the IGW analysis. The global spatiotemporal distribution of IGW from Aeolus observations is compared with that derived from global high-resolution temperature profiling data provided by GPS radio occultation (RO) instruments operating onboard MetOp and COSMIC-2 satellite constellations. The comparison of Aeolus and RO-derived global IGW distribution allows concluding on the capacities and limitations of Aeolus wind profiling for studying UTLS dynamic

Towards a better constraining of UTLS dynamics using ESA Aeolus Wind Profiling

International audienceThe European Space Agency's Aeolus satellite mission is designed to provide global information on the wind speed from the ground up to 30 km, which is highly demanded for weather forecasting. Aeolus satellite has been set into orbit in August 2018 and its payload consists of a sophisticated ALADIN lidar instrument measuring wind velocity by sensing Doppler spectral shift of the laser echo scattered by the different layers of the atmosphere. Since the global atmospheric circulation is largely driven by middle atmosphere dynamics, it is essential that the climate models take a proper account for the dynamical processes. One type of small-scale atmospheric waves, called internal gravity waves (IGWs) pose a particular challenge for models, whereas inaccurate parameterization of IGWs can dramatically bias the predictions of future atmospheric circulation changes. In this paper, we explore the capacities of Aeolus wind observations in capturing and resolving dynamical processes in the upper troposphere and lower stratosphere (UTLS) such as IGWs at various temporal and spatial scales. This study also includes an overview of the various instrumental and retrieval issues affecting the ALADIN wind data quality. The perturbations in the vertical profiles of Rayleigh horizontal line-of-sight (HLOS) wind velocity, associated with IGW activity, are derived by subtracting the Aeolus-derived "background" wind profiles from the individual measurements. Then, the global distribution of the IGW kinetic energy in the UTLS and vertical wavelength is computed using Aeolus measurements over the entire mission lifespan. The derived variation of IGW activity over the Aeolus mission lifetime is analyzed in consideration of the time-varying performance of ALADIN instrument. The latter is quantified using two French ground-based Doppler wind lidars operating at a mid-latitude site (Observatoire de Haute-Provence) and at a southern tropical site (Maïdo Observatory at la Réunion island) as well as meteorological radiosoundings collocated with satellite overpasses. These comparisons helped identify recurring perturbations in the Aeolus wind profiles signal through their frequency analysis. Taking into account these perturbations and the evolution of the instrument's performance allows for the improvement of the IGW analysis. The global spatiotemporal distribution of IGW from Aeolus observations is compared with that derived from global high-resolution temperature profiling data provided by GPS radio occultation (RO) instruments operating onboard MetOp and COSMIC-2 satellite constellations. The comparison of Aeolus and RO-derived global IGW distribution allows concluding on the capacities and limitations of Aeolus wind profiling for studying UTLS dynamic

Unexpected self-lofting and dynamical confinement of volcanic plumes: the Raikoke 2019 case

International audienceRecent research has provided evidence of the self-lofting capacity of smoke aerosols in the stratosphere and their self-confinement by persistent anticyclones, which prolongs their atmospheric residence time and radiative effects. By contrast, the volcanic aerosols—composed mostly of non-absorptive sulphuric acid droplets—were never reported to be subject of dynamical confinement. Here we use high-resolution satellite observations to show that the eruption of Raikoke volcano in June 2019 produced a long-lived stratospheric anticyclone containing 24% of the total erupted mass of sulphur dioxide. The anticyclone persisted for more than 3 months, circumnavigated the globe three times, and ascended diabatically to 27 km altitude through radiative heating of volcanic ash contained by the plume. The mechanism of dynamical confinement has important implications for the planetary-scale transport of volcanic emissions, their stratospheric residence time, and atmospheric radiation balance. It also provides a challenge or “out of sample test” for weather and climate models that should be capable of reproducing similar structures

Validation of Aeolus wind profiles using ground-based lidar and radiosonde observations at Réunion Island and the Observatoire de Haute Provence

International audienceThe European Space Agency's (ESA) Aeolus satellite mission is the first Doppler wind lidar in space, operating in orbit for more than three years since August 2018 and providing global wind profiling throughout the entire troposphere and the lower stratosphere. The Observatoire de Haute Provence (OHP) in southern France and the Observatoire de Physique de l'Atmosphère à La Réunion (OPAR) are equipped with ground-based Doppler Rayleigh-Mie lidars, which operate on similar principles to the Aeolus lidar, and are among essential instruments within ESA Aeolus Cal/Val program. This study presents the validation results of the L2B Rayleigh-clear HLOS winds from September 2018 to January 2022. The point-by-point validation exercise relies on a series of validation campaigns at both observatories: AboVE (Aeolus Validation Experiment) that were held in September 2019 and June 2021 at OPAR, and in January 2019 and December 2021 at OHP. The campaigns involved time-coordinated lidar acquisitions and radiosonde ascents collocated with the nearest Aeolus overpasses. During AboVE-2, Aeolus was operated in a campaign mode with an extended range bin setting allowing inter-comparisons up to 28.7 km. We show that this setting suffers from larger random error in the uppermost bins, exceeding the estimated error, due to lack of backscatter at high altitudes. To evaluate the long-term evolution in Aeolus wind product quality, twice-daily routine Météo-France radiosondes and regular lidar observations were used at both sites. This study evaluates the long-term evolution of the satellite performance along with punctual collocation analyses. On average, we find a systematic error (bias) of-0.92 ms-1 and-0.79 ms-1 and a random error (scaled MAD) of 6.49 ms-1 and 5.37 ms-1 for lidar and radiosondes, respectively

Unraveling Gravity Wave Coupling from Surface to Stratosphere above La Réunion's Maïdo Observatory (21°S, 55.5°E) from Doppler and Rayleigh lidar observations

International audienceThe study investigates the vertical wave coupling from the Earth's surface to the middle atmosphere over the Maïdo Observatory at La Réunion (21°S, 55.5°E). Wind velocity and temperature profiles from the ground-based instruments, including the LiWind Doppler Rayleigh-Mie and Li1200 Rayleigh Lidars, in conjunction with other observations (radiosoundings, COSMIC-2 radio-occultation, SABER) and ERA5 reanalysis, are analyzed to characterize gravity waves (GW) and their vertical propagation during the period from November 20th to November 24th, 2023. Notably, a tropospheric subtropical westerly jet manifested above La Réunion during this period and jet instabilities contributed to enhance GW activity in the troposphere. Wavelet methods are employed for denoising purposes and for highlighting multiscale GW from raw wind and temperature profiles. In particular, our analysis reveals the existence of a GW with a 5-km vertical wavelength and approximately a 24-hour period, propagating upward from lower troposphere to the middle atmosphere above La Réunion’s Maïdo Observatory. Among others, the horizontal distribution of this structure surrounding La Réunion is examined using COSMIC-2 radio-occultation and SABER data. In addition, the ERA5 analysis also provides supporting evidence of such structures and GW filtering in the stratosphere