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monsoon and then very marginal formation of these systems in pre-monsoon.
However, decadal trend of D and above in monsoon and post-monsoon of AS
in Fig. 3c shows that it has followed increasing trend from 0.2 to 1 and 1.7
respectively from 1891 to 1970s which then decreased sharply to 0.9 and 1
respectively in 1992. Thereafter in contrast to D and above decrease in monsoon
and post-monsoon over BoB as in Fig. 3d, frequencies of systems in AS have
then followed sharply increasing trend from 2000 to 2006 from 0.6 to 2 in
monsoon while their frequencies do not show much variation in post-monsoon
after 1992. Post-monsoon's D and above are higher in AS than monsoon till
2002 but thereafter it is monsoon's D and above, higher for AS basin. Figure
3d also shows increasing monsoon depressions of BoB from 1912 to 1940s
from 4 to 7.6. Thereafter, it was a decreasing trend till 1997 when it was reduced
from 7.6 to 1.7, a 78% decrease of their decadal frequencies in 1990-2000
compared to 1935-1950, a most dominant climate shifting in their genesis over
this sea areas compared to any other sea of the globe and compared to any
other season. Even during some monsoons e.g. 2002, 2010 and 2012, not a
single system of D and above has been formed compared to their normal of 8
in 1980s. But their trends in post-monsoon as seen from Fig. 3d, are increasing
trend from 2 to 5 during 1891-1970 followed by relatively less decreasing
trend to 3 by 2011 in comparison with those in monsoon as discussed.
Similarly, seasonal frequencies of D and above in BoB from Fig. 3d show
it is both monsoon and post-monsoon that continued to follow same decadal
trend of increasing and decreasing as was their annual over Indian region in
Fig. 2d except two differences. First, it is the D and above, in monsoon having
near or little higher frequencies during latest of 2005-2011 over India compared
to those of post-monsoon as in Fig. 2d while in Fig. 3d, monsoon's D and
above, alone forming over BoB continued to remain below those of post-
monsoon for very long period consistently during recent of 1982-2011 which
is matter of worry. But, continuity of near or higher systems in monsoon over
India was mainly due to some recovery in formation of depressions with
frequencies increasing over AS that occurred in monsoon. Secondly, the
differences between total cyclonic systems formed in three different seasons
in a year over Indian region and BoB are that their frequencies in monsoon and
post-monsoon over India, have got another increasing trend prominently around
1970s due to increasing formation over AS as observed in Fig. 3c while for
BoB, such an increasing phase was not observed so prominently in Fig. 3d.
SCS and above in Figs 3e and 3f for pre- and post-monsoon show their decadal
frequencies variation for BoB same as was their epochal variation in their
annual frequencies and it reached highest values in 1970s followed by
decreasing trend with only exception that such decreasing trend predominantly
continued in post-monsoon till 2011. However, it was stagnated in case of pre-
monsoon from 1990 with overall increasing trend if linear trend line fitted for
whole period 1891-2011. But in case of AS, it has decreased in pre-monsoon
with very slow rate and vice-versa in post-monsoon.
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