The evolution of Indian summer monsoon in 1997 and 1983 |
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| Authors: | J Srinivasan Ravi S Nanjundiah |
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| Institution: | (1) Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore 560012, India, IN |
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| Abstract: | Summary During most El-Ni?o events the Indian summer monsoon rainfall has been below normal. El-Ni?o that occurred during 1997 was
one of the strongest in the 20th century, but did not have an adverse impact on the Indian summer monsoon rainfall in 1997.
This is despite the fact that most parameters observed in May 1997 suggested that the Indian summer monsoon rainfall may be
below normal. This intriguing feature of the 1997 Indian summer monsoon rainfall has been examined by studying the evolution
of various parameters from May to August. The behavior of the 1997 monsoon is related to its evolution during June and July,
with westward migration of cloudbands from West Pacific that increased convection over Bay of Bengal. We find that there exists
a significant correlation between convective activity over Bay of Bengal and winds over the Arabian Sea with the latter lagging
convection over Bay of Bengal by about three days. The convective activity over Bay of Bengal induces stronger winds over
the Arabian Sea and this in turn enhances advection of moisture into the Indian landmass and leads to increased precipitable
water and strength of the monsoon. Using a simple thermodynamic model we show that increased precipitable water during July
leads to increased rainfall. A similar behavior has also been noticed during the 1983 monsoon, with precursors indicating
a possible poor monsoon but subsequent events changed the course of the monsoon.
Received May 21, 2001 Revised October 10, 2001 |
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