Characteristic Features of Heavy Rainfall over Gujarat and Rajasthan States of India due to Very Severe Cyclonic Storm Phet over the Arabian Sea (31 May to 07 June 2010) - Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change - page 407

scale are important for the forecaster as well as climate scientist as the little
rainfall causes severe flood over those area. The satellite based precipitation
product is only means for overcoming these difficulties. At the same time it is
very important to validate the satellite-derived product with the observed rainfall
to quantify the direct usability of the products. Therefore an inter-comparison
exercise is carried out between observed daily gauge data with TRMM 3B42-
V6 rainfall product for Rajasthan and Gujarat separately. Nair et al. (2009)
have compared the observed rainfall with the daily rainfall derived from TRMM
3B42 and found it to be most accurate over regions of moderate rainfall.
2. Data and Methodology
For this study, the physical process behind the rarest of the rare track and the
weakening of the system before landfall have been analysed with the help of
ECMWF analyses of low level (850 hPa) vorticity, upper level (200 hPa)
divergence, 200 hPa level winds and vertical wind shear between 200 and 850
hPa levels during the period from 31 st May to 7 th June. The spatial distribution
of rainfall over Rajasthan and Gujarat due to the cyclone Phet have also been
analysed based on actual rainfall recorded by rain gauges and the TRMM
estimated rainfall. Therefore 24 hr cumulative daily rainfall of all stations under
district-wise rainfall monitoring scheme (DRMS) and IMD observatory ending
at 0300 UTC of 7 th and 8 th June 2010 of Gujarat and Rajasthan have been
collected and analyzed. Inter-comparison is made between the daily observed
rainfall and TRMM 3B42-V6 rainfall estimate. The TRMM 3B42-V6 data at
0.25 × 0.25 spatial and 3 hourly temporal resolution is extracted between latitude
20.125-24.875 N, longitude 68.125-74.375E to cover Gujarat region and latitude
23.125-30.125, longitude 69.375-78.375 to cover Rajasthan state for 7 th and
8 th June 2010. The daily rainfall have been computed from the 3-hourly TRMM
rain rate and analyzed and compared with the observed rainfall data of the two
states separately. The correlation of observed heavy rainfall with the daily
rainfall derived from TRMM has been calculated and analysed.
3. Results and Discussion
The heavy rainfall characteristics over Gujarat and Rajasthan states and
associated physical features are presented and discussed in sections 3.1 and
3.2 respectively.
3.1 Heavy Rainfall over Gujarat
Gujarat state received fairly widespread rainfall on 6 th and 7 th June 2010 due
to the cyclone Phet and isolated heavy rains on 7 th June. It is found that the
state received 6% of normal seasonal rainfall due to the cyclone Phet. Figure 2
shows the inter comparison of observed rainfall and TRMM 3B42 daily rainfall
over Gujarat state ending at 0300 UTC of 7 th June 2010. From Fig. 2a and Fig. 2b,