Master Thesis
Convective boundary layer structures over the Tibetan Plateau
Kathrin Fuchs (12/2012-07/2013)
Support: Thomas Foken, Tobias Gerken
The atmospheric boundary layer is the layer that is directly influenced by the earth’s surface. The atmospheric boundary layer height is an important parameter of the atmospheric boundary layer. It corresponds to the height of turbulent mixing of pollutants and water vapour into the atmosphere within a time scale of about one hour. The conditions for the development of the atmospheric boundary layer on the Tibetan Plateau are special due to the high altitude and low air density. The Tibetan Plateau is the highest plateau in the world and a key region for the world’s climate. A high amount of incoming solar radiation reaches the surface due to the low atmospheric column above the plateau. The intense surface heating causes great diurnal and seasonal variation of surface fluxes. Energy and water cycles on the Tibetan Plateau strongly affect the the global atmospheric circulation. The importance for the climate on the global scale highlights the necessity of studying the behaviour of atmospheric parameters on the Tibetan Plateau, especially those involved in convection processes and the water cycle. However, there have been only few investigations of the atmospheric boundary layer development on the Plateau and it is still poorly understood. This study investigates the convective boundary layer height under the special conditions of the TP in the early monsoonal period. The goal of this study is to asses the performance of different methods for the determination of the mixed layer height from radiosoundings on the Tibetan Plateau. Furthermore, the performance of slab models, which model the evolution of the mixed layer height, is investigated. Therefore, modelled mixed layer heights are compared to mixed layer heights determined from radiosoundings. This study contributes to the validation of the Active Tracer High Resolution Atmospheric Model (ATHAM) which is applied at the Nam Tso area. The investigations are based on data acquired in the context of the Atmospheric Boundary Layer Experiment, Nam Tso, Tibet in July 2012 closed to the Nam Tso Lake.