Gerken, T; Biermann, T; Babel, W; Herzog, M; Ma, Y; Foken, T; Graf, HF: Surface-atmosphere interactions and convection triggering in the Nam Co Lake basin, Tibetan Plateau: Influence of soil moisture and wind direction.
Poster, AGU Fall Meeting 2013, San Francisco: 09.12.2013 - 13.12.2013

Surface-atmosphere interactions through the exchange of momentum, energy and water play a crucial role in the development of mesoscale circulations, clouds and convection, which in turn feed back to the surface. Atmospheric circulations modeling frameworks commonly have a too coarse resolution in order to fully capture these interactions. We use the cloud-resolving Active Tracer High-resolution Atmospheric Model (ATHAM) which is developed and used for mescoscale applications, in order to investigate the interactions between the surface and the atmosphere in a lake-land-atmosphere system on the Tibetan Plateau. Nam Co Lake, at 4730 m altitude, is surrounded by alpine steppe grassland and mountain chains. During the summer monsoon season there is a high variability of soil moisture with Bowen-ratios ranging from 0.5 to 3. Local water recycling is important. We identified two different mechanisms for convection triggering in the lake system that are dependent on the direction of the background wind: Triggering over topography, when the background wind and the lake-breeze have the same flow direction and triggering due to convergence between the lake-breeze front and the background wind. The type of convection triggering determines whether precipitation will occur within the basin. We will also present modeling studies investigating the impact of soil moisture in the generation of mesoscale circulations between the lake and the land surface and will show how the surface influences the evolution from boundary-layer clouds to moist convection. Additionally, the influence of clouds on the surface energy-balance is discussed.

Letzte Änderung 27.11.2013