1 STUDY OF PRECIPITATING SYSTEMS BY DOPPLER WEATHER RADAR AND TROPICAL RAINFALL MEASURING MISSION PRECIPITATION RADAR Sanjay Sharma (1) , G. Viswanathan (2) , Ranga Rao (3) , Diganta Kumar Sarma (4) , Mahen Konwar (5) . (1) Department of Physics, Kohima Science College, Jotsoma, Kohima, Nagaland, India- 797 002. E-Mail: sanjay_sharma11@hotmail.com (2) Radar Development Cell, ISTRAC, Department of Space, Bangalore, India- 560 058. E-mail: gemsvi@yahoo.com (3) As (2) above, E-mail: ksc_research@rediffmail.com (4) As (1) above, E- mail: digantasarma02@rediffmail.com (5) As (1) above, E- mail: mahenkonwar@rediffmail.com INTRODUCTION Doppler Weather Radar (DWR) is used to measure the areal rainfall and three dimensional structures of precipitating systems [1]. The DWR observations are increasingly being used as a data source for hydrological and numerical weather prediction models. DWR works on Doppler Principle with single and dual polarization. In addition to reflectivity, Doppler radar has the ability to estimate the mean radial velocity (V) of targets by measuring Doppler shift in the returned signal. The Precipitation Radar (PR) in Tropical Rainfall Measuring Mission (TRMM) is aimed in improving the measurement of precipitation from space to achieve more precise estimation of diabetic heating associated with tropical precipitating cloud systems. Precipitation Radar (PR) has the ability to give the vertical profile of latent heat and also precipitation [2]. PR observations are very useful because of its high resolution both in vertical as well as horizontal extent. Vertically it can detect rain profile in 80 different cells at every 0.25 km resolution. Along horizontal direction it can measure rain intensity over a swath of 220 km in 49 Field Of View (FOV) with resolution of ~4.3 km (5 km after 14 August 2001). It cannot sense rainfall rate below 0.5 mm h -1 . In the present paper the tropical precipitating systems are studied over Sriharikota (13.66 0 N, 80.23 0 E), India, by utilizing DWR [3] and TRMM-PR along with Disdrometer. The operating frequency of DWR and TRMM-PR are 2.8 GHz and 13.8 GHz respectively. One base products of DWR i.e. reflectivity factor Z (dBZ) and two data products from TRMM, namely 2A25 (Z profiles) [4] and 2A12 (latent heat profiles), are utilized for the present study. METHODOLOGY Simultaneous observations for DWR and PR are considered whenever there are precipitation echoes . Point to point comparisons of both the radars is obscured by their different scanning method and frequencies. PR is a nadir looking radar and performs a cross track scanning having a beam with of 0.71° and DWR scans in circles in radial directions with horizontal resolution of 0.3 km having beam width of 1°. Bolen et. al. 2000 [5] gives solution to these problems by constructing a three-dimensional volume averaging the PR data in vertical direction with height equal to the beam width of DWR at each horizontal grid point. The footprint of PR is ~5 km and within this region one latitude and longitude value is assigned. In the present paper for the comparison of PR and DWR reflectivity following methodology is adopted. With reference to PR, a threshold of ± 0.04° latitude and longitude is specified. The values of DWR reflectivity within this range are only considered for comparison. After getting different reflectivity values from DWR within this range for one FOV of PR we considered the nearest value with respect to PR reflectivity. OBSERVATIONS AND RESULTS Simultaneous observations of precipitation echoes from DWR and TRMM-PR are presented in figure 1(a b, c, d). Figure 1(a,b ) shows the observation on 6 th November 2003 and 1(c, d) shows