Slide 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) Slide 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. Slide 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. Slide 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 Slide 5 Slide 6 Slide 7 Subdivisional Rainfall over India- 1994 Slide 8 Subdivisional Rainfall over India- 1995 Slide 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 Slide 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.