GISS Lunch Seminar
Speaker: Mathieu Ratinsky (LATMOS)
Title: Tropical dynamics in the UTLS: a new window with Aeolus

Abstract:
In 2018, the European Space Agency launched the Aeolus satellite, equipped with the ALADIN Doppler lidar instrument, designed to retrieve wind profiles on a global scale. As part of the work of a PhD thesis, our study examines how ALADIN identifies internal gravity waves (IGWs) in the upper troposphere and lower stratosphere region, known as UTLS. To do this, we isolated the disturbances caused by IGWs by subtracting the so-called "background" wind measurements provided by Aeolus from the individual measurements. A spectral analysis of these data enabled us to estimate the kinetic energy of IGWs in the UTLS throughout the Aeolus mission. This study represents the first attempt to reconstruct the global distribution of IGW activity using global wind information provided exclusively by the Aeolus mission. The analysis reveals well-known sources of IGW such as orography and tropical convection. The focus will be on the tropical UTLS region, where ALADIN has extensive stratospheric coverage, although an extratropical analysis will also be presented. Our analysis highlighted an area of increased IGW activity over the Indian Ocean during the boreal summer, slowly migrating from East Africa to the Pacific between June and December. The distribution and seasonal variation of Aeolus- derived IGW activity were cross-validated using global temperature profiling by EUMETSAT radio occultation (RO) satellites and ERA5 reanalysis. RO and ERA5 data were resampled to ALADIN vertical resolution and spectrally analyzed in the same way as ALADIN wind data to recover IGW potential energy. The derived IGW potential energy data confirm the seasonal variation in IGW kinetic energy observed by ALADIN, in particular the eastward migration, potentially linked to convection within the MJO (Madden-Julian oscillation). The results suggest that the interannual variation of IGW kinetic and potential energies in the UTLS is modulated by the quasi-biennial oscillation, while MJO-related waves may be characterized by shorter vertical wavelengths. Overall, this study highlights the potential of Aeolus wind profiling to improve our understanding of atmospheric dynamics, particularly in the UTLS region.