Laboratoire des Écoulements Géophysiques et Industriels

Nos tutelles


Nos partenaires


Accueil > Actualités > Séminaires > Séminaires 2020

Mardi 4 février 2020 à 11h00 - LEGI K118 [en]Tuesday, January 8, 2019 at 11:00 am - LEGI K118

Sara Bacer, LEGI/MEIGE & Atmospheric Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany

Titre/Title : Global numerical simulations of atmospheric ice crystals

Contact : Chantal Staquet (équipe MEIGE)

Résumé/Abstract : Clouds play a fundamental role in the atmosphere by influencing the global radiative energy budget, however, their representation in numerical models is still one of the main sources of uncertainties in climate predictions. In particular, the ice crystal formation process is very challenging, as multiple mechanisms occur for ice nucleation depending on aerosol characteristics and environmental conditions. A comprehensive ice nucleation parameterization (Barahona and Nenes, 2009, hereafter BN09) has been implemented in the global chemistry-climate model EMAC in order to improve the representation of ice crystal number concentration (ICNC). BN09 takes into account the competition for water vapour between homogeneous and heterogeneous nucleation in cirrus clouds, the presence of pre-existing ice crystals, and the influence of different precursor aerosols on heterogeneous nucleation. The implementation of BN09 has allowed to simulate processes which were neglected by the standard configuration of EMAC. The modelled ICNCs obtained by using BN09 in cirrus clouds agree with the observations, as BN09 strongly reduces ICNC in the upper troposphere. We found that the effect of pre-existing ice crystals is the main cause of such reduction and homogeneous ice nucleation is the dominant nucleation mechanism in cirrus clouds. Focusing on the contributions of different precursor aerosols to heterogeneous nucleation, we found that most of the new ice crystals in cirrus clouds derive from soluble organic compounds and in mixed-phase clouds from black carbon.