RESEARCH ARTICLE


Impact of Downscaling on the Simulation of Seasonal Monsoon Rainfall Over the Indian Region Using a Global and Mesoscale Model



Surya K. Dutta1, Someshwar Das*, 1, S.C. Kar1, U.C. Mohanty2, P.C. Joshi2
1 National Centre for Medium Range Weather Forecasting, NOIDA, India
2 Centre for Atmospheric Science, IIT, Delhi, India
3 Space Application Centre, ISRO, Ahmedabad, India


© 2009 Duttaet al.;

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the SAARC Meteorological Research Centre, Agargaon, Sher-e-Bangla Nagar, Dhaka - 1207, Bangladesh; Tel: 00-880-2-9144374, Ext. 314; Fax: 00-880-2-9144373; E-mails: somesh07@yahoo.com, somesh03@gmail.com


Abstract

A global model (T80L18; Triangular Truncation at wave number 80 with 18 vertical layers) and a mesoscale model MM5 (nested at 90 and 30 km resolutions) are integrated for 5 monsoon years 1998-2002. The impact of dynamical downscaling from global to mesoscale in the simulations of Indian summer monsoon rainfall is studied.

Comparisons between the global and the mesoscale models show that, though the global model has an edge over the mesoscale model in simulating the all-India mean rainfall closer to the observation, the T80L18 model lacks in simulating the spatial variations in rainfall. The effect of downscaling is better represented in the rainfall variations produced by MM5 both quantitatively and qualitatively over the foothills of the Himalayas and along Nepal to North-eastern India. It is also seen that the mesoscale model is able to represent the dispersion (standard deviation) present in the observed rainfall over India. In the five monsoon seasons, RMSE of mean rainfall (monthly and seasonal) of T80L18 forecasts are mostly lower than that of MM5 forecasts. However, synoptic features like the Somali Jet and Tibetan anticyclone are better represented by MM5. This model has also simulated the regions of convection better than the T80L18 model. However, the MM5 simulations produced an anomalous circulation over the Saudi Arabian region (15-200 N and 45-500 E) in many cases. The mesoscale model simulates better wind fields than the global model in general. Over peninsular India T80L18 model showed higher temperature gradient but, over Central India this model has better temperature field as compared to MM5. Over southern and north-eastern India, the temperature field of T80L18 and MM5 are very similar.

Keywords: Downscaling, Monsoon, Rainfall, Mesoscale, Simulation, Forecast, TRMM.