Ph.D. Thesis in deep convection/stratospheric composition
Université de Reims Champagne-Ardenne (URCA)
GSMA (Groupe de Spectrométrie Moléculaire et Atmosphérique), where the PhD will take place, is a laboratory belonging to the University of Reims Champagne-Ardenne and CNRS (Centre National de la Recherche Scientifique). Its scientific specialties range from molecular spectrometry, laser sensor development, to atmospheric and planetary sciences.
Homepage: https://www.univ-reims.fr/presentation-du-laboratoire/gsma-umr-cnrs-7331,9558,17474.html
PhD title: “Study of deep convection cases flown over during the STRATEOLE 2 balloon campaigns and their impact on the lower equatorial stratosphere.
Supervisor : Pr. Emmanuel Riviere
“The French-American project Stratéole 2, supported by CNES on the French side, is dedicated to the study of the dynamics and composition of the equatorial lower stratosphere. Tropospheric air masses enter the stratosphere overwhelmingly through tropical regions and influence both its chemical composition and climate. Among the key species of the tropical lower stratosphere, water vapor is the subject of particular attention due to its climatic and chemical role. While the incoming amount of water vapor at the tropopause depend primarily on the coldest temperature encountered during the slow ascent to the stratosphere, other processes such as waves or deep convection can also modulate water vapor, and their quantification at the global scale is much less known. The Stratéole 2 project is based on three phases of a long-duration pressurized balloon (BPS) campaign above the tropical tropopause and flying over a large portion of the equatorial belt. Two campaigns have already been carried out and another is planned in 2026-27. The balloon-borne instruments measure wind components and temperature perturbations (TSEN and GPS) due to atmospheric waves, but also the size distribution of aerosols (LOAC and LPC) and particles, the morphologies of cloud layers under the balloon (BeCOOL), as well as the abundance of greenhouse gases (Pico-SDLA, RACHuTS). The water vapor measurements obtained by the Pico-SDLA instruments during these campaigns are at the heart of this doctoral project. Due to the long duration of the flights, the balloons can fly over all tropical regions and thus sample the geographic variability of the above-mentionned processes. This doctoral project focuses on deep convection, which is generally more violent and organized over continents than over oceans. Deep convection is one of the water vapor modulation processes that is subject to significant geographical variation.
We propose to study different cases of deep convection highlighted by observations from the Pico-SDLA instrument, during the different phases of the campaign. Of particular interest are cases of extreme convection, in which the top of the cloud structures has exceeded the tropopause (overshoots). The variability of the convection probed offers the opportunity to study the variability of its impact on the lower stratosphere, which is a missing piece in the parameterization of convection in global climate models. A case of continental convection, as well a case of maritime convection will be studied, and the priority case will be the study of extreme convection due to the influence of cyclone Rai, flown over by two Stratéole 2 balloon flights. While it is accepted that certain parts of cyclones can penetrate into the lower stratosphere, the quantification of their impact on stratospheric water vapor is very little studied, due to the difficulty of making high resolution measurements in the immediate vicinity of such systems. The flyover of an event by two Stratéole 2 flights is a unique opportunity to better quantify their impact.
The PhD student’s work will consist of mesoscale simulations of the various convective cases mentioned above to better quantify their impact on stratospheric water. The atmospheric model used is the Méso-NH model (Méteo-France and LAERO) on the GENCI (Idris or Cines) and ROMEO (University of Reims Champagne-Ardenne) supercomputers. This model includes a “model to satellite” approach allowing, from the calculated meteorological fields, to simulate the parameters measured by the satellite (brightness temperatures), helping to validate the simulations with comparable products. Once the simulations have been validated by satellite observations and balloon measurements, stratospheric water budgets will be carried out and will allow to quantify the budgets transported by the different types of convective system and their variability. The simulations will be carried out with different microphysical settings, notably at a single moment or at two moments, with a modulation of the estimated budgets.
Any application should be done before August 18, 2025 from the Adum website: https://adum.fr (you will have to create an account to manage your application) with the thesis reference 65997