Representation of Deep Moist Convection In NCMRWF Global T80 Analysis / Forecast System: Results From Different Experiments A. K. Mitra and S. Das National Center for Medium Range Weather Forecasting (NCMRWF) Mausam Bhawan Complex, Lodhi Road, New Delhi – 110003, India MEGHA-TROPIQUES 2 nd Scientific Workshop, 2-6 July 2001, Paris, France. ABSTRACT The onset and maintenance of the Asian summer monsoon is greatly influenced by moist convection. Deep moist convection also plays a key role in controlling the heat, moisture and momentum distribution in the atmosphere through sub-grid scale transport and condensation. It plays an important role in the maintenance of the general circulation and climate. In a global analysis-forecast system the initial condition representing the moisture, divergence and associated heating play key role in deciding the forecast quality. Realistic representation of moist convection in the atmospheric model through parameterization is also essential to properly simulate the precipitation, cloudiness and cloud radiation feedback. The parameterization schemes vary in complexities from simple moist convective adjustment to sophisticated mass flux type schemes. The impact of three different types of convection parameterization schemes is studied for summer monsoon period. The capability of different schemes in T80 model to predict monsoon rainfall and associated circulation in medium range is reported. The impact of these different schemes on simulating the mean monsoon flow and rainfall is also studied. Observed rainfall by merging satellite and gauge data is prepared for Indian monsoon region, which is compared with the model simulated values in different experiments. In order to investigate the impact of different cumulus parameterization schemes in the simulation of the Asian summer monsoon, the operational T80 model of NCMRWF has been integrated for an active monsoon phase (July) using KUO, RAS and SAS convection schemes. Results have been compared with the mean analysis of wind fields obtained from the NCMRWF global data assimilation system (ANA) and other available observations. 1. INTRODUCTION: Convection plays a dominant role in the tropics, in particular for the development and maintenance of the Asian summer monsoon. It affects the tropical circulation through the release of latent heat, vertical transport of heat, moisture and momentum and, through the interaction of clouds with radiation. Several methods have been proposed to parameterize the effects of cumulus convection in the large-scale numerical weather prediction models. The two most widely used schemes among them are the Kuo’s scheme (Kuo, 1974) and the Arakawa-Schubert scheme (Arakawa and Schubert, 1974, hereafter referred to as A-S). The latter scheme is known for its sound physical basis, but it is also computationally very expensive. Many techniques have been proposed in the recent past to simplify this scheme, viz., the Simplified Arakawa-Schubert scheme (SAS) developed by Grell (1993), Pan and Wu (1995), and the Relaxed Arakawa-Schubert scheme (RAS) proposed by Moorthi and Suarez (1992). The present operational model at the National Center for Medium Range Weather Forecasting (NCMRWF) uses a Kuo-type cumulus parameterization scheme based on Anthes (1977). Perpetual integrations have been carried out for the month of July, a period when the monsoon is generally very active over the Indian subcontinent using SAS, RAS and KUO. Almost all the operational NWP