1. Effect of Tibetan snow on Indian Summer monsoon rainfall using RegCM2.5 M. S. Shekhar & S. K. Dash Indian Institute of Technology Delhi Hauz Khas, New Delhi -110016 India Workshop on Theory and use of Regional Climate Model (RegCM3)

2. Introduction  The summer monsoon of southwest Asia is the largest anomaly of general circulation.  Interannual variations of summer monsoon rainfall affects agriculture, water resources and the economy of the country.  The slowly varying boundary conditions at the surface of earth provides required memory in the climate system to predict averaged monsoon circulation and rainfall.  There exist an inverse relationship between Indian summer monsoon rainfall and the extent of Eurasian snow cover in the preceding season.

3. Objectives  To simulate Indian summer monsoon circulation features and Rainfall over the Indian region using RegCM2.5.  To conduct sensitivity experiments by using snow depth over Tibet to study its effect on Indian summer monsoon rainfall.

4. Domain Information Central Latitude- 20 o N Central Longitude- 80 o E 115 Points along the longitudinal direction 55 o E to 105 o E and 5oS to 45oN Grid distance- 110 Km 101 Points along the latitudinal direction Data used PSU/NCAR global 30’ resolution terrain and landuse data. Monthly OI SST available from NCEP ECMWF TOGA/WCRP uninitialized data 4 times daily Mercator Projection

7. Subdivisional Rainfall over India- 1994

8. Subdivisional Rainfall over India- 1995

9. GrellSnowIMD June24.6418.1827.46 July30.0524.2440.54 Aug22.216.9929.92 Sep12.7210.1415.37 89.6169.55113.29 All India Rainfall-1994All India Rainfall-1995 GrellSnowIMD June8.067.7317.54 July32.6623.9135.67 Aug31.6729.9729.14 Sep19.9419.8823.16 92.3381.49105.51

10. Conclusions The Regional Climate Model (RegCM3) is able to simulate the monsoon circulation over India reasonably well. The rainfall simulated in mm/day in Grell convection scheme is closer to the observed rainfall of the India Meteorological Department compared to the Kuo. The inverse snow-ISMR relationship is confirmed by using snow depth as the boundary condition in RegCM3. The All India rainfall is reduced by almost 20-25% in the high Tibetan snow experiment than in the control experiment.