Séminaire
Very deep convection transports tropospheric air and water directly into the stratosphere. This transport may be underestimated by the general circulation models due to their coarse resolution, limiting our capability to predict the future climate. The efficiency of this transport is analysed using Meso-NH numerical simulation of two cases during boreal winter and summer. The very deep thunderstorm Hector the Convector is simulated with a resolution of 100 m and more than 1 billion grid points. This so-called Giga Large-Eddy Simulation is the finest ever used for a case of very deep convection. It allows us to represent the full Hector across the scales, from the mesoscale organisation to the most energetic eddies. The 200-km large thunderstorm is organised at the surface by the convergence lines. The latter appear along the sea breeze fronts and are intensified by the cold pools. The 10-km wide updrafts that overshoot into the stratosphere develop above these convergence lines and are characterized by a weak dilution. The km-scale eddies produce the irreversible mixing between the overshoots and the stratospheric air and finally the hydration. Recent investigations of the troposphere-to-stratosphere transport of water over a very large domain (covering India, China and the Himalaya range) confirm the convective importance in the contrasted framework of the Asian monsoon. The vertical transport by very deep convective systems over China is reproduced by the model, up to the lower stratosphere at altitudes matching with space lidar and infrared imagery observations. The resulted pockets of vapour-enriched air are then transported over India in two days, which explains the hydration features measured along the Geophysica aircraft track during the 2017 StratoClim campaign. The seminar will be given in English, or in French depending on the audience.
marie-pierre.lefebvre@lmd.jussieu.fr