Tropical Cyclone Activity over the Indian Ocean in the Warmer Climate - Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change - page 71

2. Data and Methodology and Discussion
Global cyclone tracks and cyclogenesis data have been obtained from the best
track archive from Joint Typhoon Warning Centre (JTWC) and National
Hurricane Centre (NHC) for 30 years from 1977 to 2006. This period falls
completely in the post-satellite era and observation of cyclone parameters is
considerably better than that in the pre-satellite era (Mohapatra et al., 2012).
Different ocean basins considered in the study are as per Webster et al. (2005),
viz., North Atlantic Ocean (NAO; 5 to 25 ° N, 90 to 20 ° W), West North Pacific
(WNP; 5 to 20 ° N, 120 to 180 ° E), East North Pacific (ENP; 5 to 20 ° N, 90 to
120 ° W), South West Pacific (SWP; 5 to 20 ° S, 155 to 180 ° E), North Indian
Ocean (NIO; 5 to 20 ° N, 55 to 90 ° E) and South Indian Ocean (SIO; 5 to 20 ° S,
50 to 115 ° E). TCs are classified into three groups according to their intensity
as class 1 (wind speed between 34 and 47 kt), class 2 (wind speed between 48
and 63 kt) and class 3 (wind speed 64 kt or more). This grouping is same as
classification of North Indian Ocean cyclones by Indian Meteorological
Department viz., cyclonic storm, severe cyclonic storm and very severe cyclonic
storm and above. To investigate the variation in cyclone activity in recent years,
storm frequency and storm days of these three groups for the two 15-year
periods 1977-1991 and 1992-2006 are examined for each of the ocean basins.
The changes in the regions of cyclogenesis have been studied in last 30
years for all the ocean basins. For this the number of storms originated in a
5 ° × 5 ° (longitude-latitude) box have been examined for the two 15-year periods
as considered above.
3. Results and Discussion
3.1 Frequency of Genesis
Group-wise distribution of storm frequency and storm days in these two periods
is shown in Table 1. It is seen that intense cyclones and their life time is increased
for all basins except for East and West North Pacific which show increase in
weaker cyclonic storms instead, in the recent years.
Further examination of maximum intensity (i.e. maximum sustained wind
speed attained by the intense system in a basin in a year) shows significant
increasing trend for the ocean basins NAO, SIO and SWP out of which SIO
has maximum trend, implying that cyclones are becoming more and more
intense in these ocean basins with the highest rate in SIO (Fig. 1).
3.2 Area of Genesis of TC
In the NIO the Arabian Sea experiences the increase (green) in the genesis of
cyclones whereas Bay of Bengal generally experiences decrease (red) of these
events (Fig. 3 to the left). In the SIO basin, decrease in the cyclogenesis events