Interactions between tropical low marine clouds and wind profiles using ALADIN/Aeolus

Abstract

Low clouds such as cumulus and stratocumulus cover a great part of the tropical belt all year long. Variables affecting the formation and dissipation of these clouds like the Sea Surface Temperature or humidity have been studied for a long time now. However, wind profiles could previously only be obtained by radiosondes (localized) or airborne measurements (regional). From 2018 to 2023, ESA ALADIN/Aeolus Doppler Wind LIDAR has orbited the Earth, collecting wind profiles at a global scale, between the surface and 20 km of altitude. This instrument has opened new perspectives regarding wind-cloud interactions with co-located low cloud profiles and wind profiles.   In a Large Eddy Simulation Helfer et al.[1]  have shown that wind shear can have an impact on the development of trade wind cumulus clouds in the first kilometers of the atmosphere. Mieslinger et al.[2]  have shown combining ERA5 wind and ASTER imagery, that stronger surface wind are correlated with a more important cloud cover. In our study, we will see how ALADIN/Aeolus can help us to better understand interactions between low clouds and wind with co-located observed wind profiles and cloud profiles. We will focus on the subtropical marine boundary layer, around strong subsidence regions, like the descending branch of the Hadley cell. In these regions, low clouds are present in number and ALADIN is rarely attenuated due to the rare occurrence of mid and high altitude clouds[3].   [1] Helfer et al. - How Wind Shear Affects Trade-wind Cumulus Convection (2020) [2] Mielsinger et al. - How Wind Shear Affects Trade-wind Cumulus Convection (2020) [3] Chepfer et al. - The GCM oriented CALIPSO Cloud Product (CALIPSO-GOCCP) (2010)