Vortragsreihe Ökologie und Umweltforschung WS 2008/09

Tibetan experiments: Status, data analysis, and potential applications

Eingeladen durch Prof Foken Mikrometeorologie.

Kun Yang, Institute of Tibetan Plateau, Chinese Academy of Sciences (yangk@itpcas.ac.cn)

In this talk, I will cover the following activities, which are being conducted at University of Tokyo and Institute of Tibetan Plateau:

1. On-going experiments. Current projects include Tibetan Observation and Research Platform (TORP), JICA China-Japan weather disaster project, and CAMP-Tibet follow-up project. These experiments will be introduced briefly.

2. Evaluation of surface radiation budget from remote sensing and surface energy budget from a land data assimilation system. The Plateau harsh condition represents an extreme of weather and climate and, therefore, the observations could be used to validate a scheme or a model’s universality. GEWEX-SRB (surface radiation budget) and ISCCP-FD (radiation flux data) as well as the latest University of Maryland SRB were evaluated, and systematic errors were detected. Furthermore, the University of Tokyo microwave land data assimilation system was evaluated with observed surface energy budget and significant improvements are shown.

3. Process studies. (1) Due to strong solar heating, there are very large ground-air temperature gradients near noon. We developed a scheme to parameterize sensible heat fluxes for very large ground-air temperature gradient and this scheme was widely evaluated across China. (2) Soils beneath alpine meadows on the Plateau exhibit a clear stratification: the topsoil has high soil organic matters and dense roots and thus a small particle density and high porosity, while the deep soil is sand. We analyzed the topsoil and found a heat insulation effect and high water potential in the topsoil. This soil stratification plays a key role in surface water and energy budget and retard the response of frozen soil to climate change. (3) PBL development and mountain-valley circulations. Given reliable surface heat fluxes, we simulated the PBL development. We showed the PBL can extend up to 3 km high. The interesting thing is that: the wind in the afternoon is downslope instead of upslope. This downslope triggers convection and a raindrop evaporative cooling effect, which suppresses the further growing of PBL.

4. Extension to climate change studies. We tried to fill in the gap between experimental studies and climate change studies by combining high-resolution experimental data and low-resolution CMA (Chinese Meteorological Administration) data. Indeed, we found experimental studies can contribute to our understanding of climatic trend of surface energy budget.

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