HR: 1330h
AN: H12C-1007    [PDF]
TI: Model-Based Analysis on the Mountain-Valley Circulation in the CEOP Reference Site
AU: * Tamura, T
EM: tamura@hydra.t.u-tokyo.ac.jp
AF: Department of Civil Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan
AU: Koike, T
EM: tkoike@hydra.t.u-tokyo.ac.jp
AF: Department of Civil Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan
AU: Yang, K
EM: yangk@hydra.t.u-tokyo.ac.jp
AF: Department of Civil Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan
AB: The mountain-valley circulation system in the Tibetan Plateau, one of the Coordinated Enhanced Observing Period (CEOP) reference sites, has been investigated. We set the target area around Naqu, which is located between the two mountain ranges running east to west in the north and the south. GEWEX Asian Monsoon Experiment-Tibet Intensive Observation Period of 1998 (GAME-Tibet IOP) data showed the diurnal variation of the convective activities and mountain-valley circulations. Wind from mountain to valley, accompanied by convection over the mountain range was observed during the afternoon while the wind direction changed at night with the mountain convection disappearing. At the same time, the convective precipitation areas moving from mountain to valley were observed by Doppler radar. Sometimes this convective precipitation system induced the vorticity. By using the atmosphere-land coupled regional model to investigate this phenomenon, we successfully clarified the mechanism of diurnal circulation going through the following steps. The convective clouds develop over the mountains encouraged by latent energy release. It leads to deep convective clouds with a high cloud bottom, while it also makes a huge amount of precipitation because of the relatively small saturation pressure. At the same time, these convections can bring down the westerly momentum in the upper troposphere with their downward stream. Then, this precipitation cools the surrounding air mass (by 2 to 4 K) by strong evaporation due to the relatively dry surrounding atmosphere. This significant amount of cold air mass under the cloud bottom induces a pressure gradient (meso-high) in the direction of the valley. As the wind blows from mountain to valley, lined convections are formed with cold air mass, with pushing up comparatively warm air mass in the valley. On the other hand, the contrast in the strength of westerly between inside and outside of the meso-high makes vorticity. For this validation, we made a comparison between the observation data and the simulation data. And these simulation data indicated pretty good correspondence with the observation data.
DE: 1800 HYDROLOGY
DE: 3314 Convective processes
DE: 3322 Land/atmosphere interactions
DE: 3329 Mesoscale meteorology
DE: 3337 Numerical modeling and data assimilation
SC: Hydrology [H]
MN: 2003 Fall Meeting