NAME =  Hara, Masayuki  
ORGANIZATION =  Frontier Research Center for Global Change, Japan Agency for Marine-Earth Science and Technology  
ADDRESS =  3173-25 Showa-machi, Kanazawa-ku Yokohama Kanagawa 236-0001  
COUNTRY =  Japan  
PHONE =  +81-45-778-5545  
FAX =  +81-45-778-5706  
E-MAIL =  hara.masayuki@jamstec.go.jp  
POSTER_ONLY =  no  
THEME =  T4  
DATE =  09-Aug-04-14:51:34  
ABSID = T4HM09Aug04145134 
TITLE = The generation mechanism of the Western Disturbances over the Himalayas 
AUTHOR_1 = Hara, Masayuki 
INSTITUTION_1 = Frontier Research Center for Global Change, Japan Agency for Marine-Earth Science Technology 
PRESENTER = AUTHOR_1 
AUTHOR_2 = Kimura, Fujio 
INSTITUTION_2 = Institute of Life and Environmental Sciences, University of Tsukuba 
AUTHOR_3 = Yasunari, Tetsuzo 
INSTITUTION_3 = Hydrospheric Atmospheric Research Center (HyARC), Nagoya University 
ABSTRACT = In winter, the western disturbances that generate and develop over the western area of the 
Himalayas bring much snow in the central Himalayas (Lang and Barros, 2004). We analyzed 
and simulated a typical case of the western disturbances using a regional meteorological 
model. We also investegate the characteristics of the cyclone using an f-plane shallow water 
equations model (SWEM). When a synoptic trough passed over the Tibetan plateau, the 
southern part of the trough was cut off and a meso-alpha-scale quasi-stationary cyclone 
formed aloft in the southwest of the Himalayas. Although the generated cyclone is almost 
stationary and moves eastward very slowly, the remaining northern part of the trough moves 
eastward faster than the subtropical westerlies. The southwestern moist winds at low level 
flowed into the cyclone from the Arabian Sea and the Bay of Bengal. The southwestern winds 
forced orographically and the upwind over the Himalayas caused snow along the southern of 
the Himalayas. These properties also can be seen in the results of the SWEM simulations. The 
vertical structure of the cyclone is barotropic and extends up to the tropopause. The phase 
velocity and vertical/horizontal structure of the cyclone agree well with the theoretical 
solution of the topographic Rossby wave in a stratified quasi-geostrophic fluid.