The TRR 181 seminar Series/Joint Seminar is held by Prof. Dr. Riwal Plougonven (LMD Laboratoire de Meteorologie Dynamique, Ecole Polytechnique, Paris) on January 29th, 1:30 pm in Bundesstr. 53, Hamburg, room 22/23.

Long-duration balloon observations of gravity waves in the tropical lower stratosphere

Abstract

The Laboratoire de Météorologie Dynamique coordinates long duration balloon campaigns in the equatorial lower stratosphere (Strateole 2 project, coordinated by Albert Hertzog). The objectives and some selected outcomes of the first two campaigns (Nov. 2019 - Feb. 2020, and Oct. 2021 - Jan. 2022) will be briefly presented. 

We will then focus on the contribution of these observations to the understanding of gravity waves. The quasi-Lagrangian behavior of the superpressure balloons gives access to intrinsic frequencies of the underlying motions. This provides unique and valuable information on gravity waves in particular. These observations have allowed to quantify the spectra in frequency of the waves, their momentum fluxes, their intermittency and to probe their relationship to the underlying convection. These informations are of interest for the modelling community given the role of gravity waves in driving middle atmospheric circulations, notably the Quasi-Biennal Oscillation. 

To situate these results in a broader context, we will question how they may help the development of parameterizations of gravity waves in climate models. As a reference dataset about lower stratospheric gravity waves, these observations have been used to evaluate parameterizations, and also to train Machine Learning methods to estimate gravity wave momentum fluxes from knowledge of the large-scale flow. Interest and limitations of these approaches will be discussed. 

The presentation will draw from work of several colleagues, within LMD and beyond: Albert Hertzog, Aurelien Podglajen, Milena Corcos, Sothea Has, Aurélie Fischer and Francois Lott to name a few.