Construction and Quality of Best Tracks Parameters for Study of Climate Change Impact on Tropical Cyclones over the North Indian Ocean during Satellite Era - Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change - page 8

decreases with increase in intensity of CDs like other ocean basins (Lander,
2008; Nakazawa and Hoshino, 2009). The difference in intensity based on
visible and infrared imageries of Kalpana-1 and INSAT 3A satellites and the
microwave imageries based on polar orbiting satellites is higher in case of
lower intensity of the system such as depression and CS. It then decreases in
case of SCS and VSCS.

3. Frequency of CD, CS, SCS and VSCS

Comparing the genesis of depression over 2.5 × 2.5 degree blocks of the Bay
of Bengal (BOB) and Arabian Sea (AS) during pre-satellite era (1891-1960)
and satellite era (1961-2009), there has been increase in the frequency of genesis
over the data sparse sea areas (Mohapatra et al., 2012). The frequency of genesis
of depression over the head BOB has decreased during satellite era. Genesis of
depression could have been over-estimated during pre-satellite era over this
region due to climatological bias, as this region is prone for monsoon
depressions.
The average, standard deviation (SD) and coefficient of variation (CV) of
frequencies of CDs over the NIO are shown in Table 3 for the period of 1961-
2010. About 11 CDs develop over the NIO during a year including nine and
two over the BOB and AS respectively. Out of these about five intensify into
CS or above intensity storms (wind speed of 34 knots or more) including about
four over BoB and one over the AS. About three SCS or above intensity storms
(wind speed of 48 knots or more) are formed over the NIO during a year. It
includes two over the BoB and one over the AS. However, there is large
interannual variation in the frequency of CD, CS and SCS as shown in Table 3.
Due to lower frequency over the AS, the interannual variation is also higher
over this sub-basin than over the BOB.

Table 3: Mean, standard deviation (SD) and coefficient of variation (CV) of
frequency of (i) CD, (ii) CS and above and (iii) SCS and above intensity

Parameter CDs CS and above SCS and above

BOB AS NIO BOB AS NIO BOB AS NIO

Mean 8.6 2.2 10.8 3.6 1.1 4.7 2.3 0.7 3.0

SD 3.1 1.5 3.6 1.5 1.0 1.7 1.3 0.8 1.6

CV 35.5 69.2 33.0 42.5 94.1 36.1 57.5 124.1 54.6

Considering the frequency of VSCS or higher intensity storms during
satellite era (1965-2010), there have been about two VSCS per year (Table 4).
The frequency is maximum during post-monsoon season (Oct-Dec) followed
by pre-monsoon (March-May) and monsoon (June-September) season. As the
frequency of VSCS is less, the analysis has not been carried out for the sub-
basins of BOB and AS.