IUGG 2003 Abstract

P05-Posters The Physical Oceanography of the Indian Ocean Monday, June 30 PM Location: Site D

TIME [ 1645-259 ] [ P05/30P/D-003 ] [ Poster ]

INDIAN WINTER MONSOON RAINFALL AND THE TROPICAL INDIAN OCEAN DIPOLE: PREDICTIVE RELATIONSHIPS AND THEIR VARIABILITY

Kumar S.R.U.Bhanu ODURY(Dept. of Meteorology and Oceanography, Andhra University, Visakhapatnam, India - 530 003)

Naidu Venkateswara CHENNU(Dept. of Meteorology and Oceanography, Andhra University, Visakhapatnam, India - 530 003) Rao R.L. SAI ( Dept. of Meteorology and Oceanography, Andhra University, Visakhapatnam, India - 530 003 )

The Indian winter monsoon rainfall during October through December accounts 30% to 60% of total yearly rainfall and is very crucial for both agriculture and economy for South India (south of 200 N). An attempt is made in the present study to predict the probable relationships between the winter monsoon rainfall and Indian Ocean Dipole (IOD)/anomalous temperatures over the western equatorial tropical Indian Ocean for the period 1959 - 1997. The IOD is a prominent coupled ocean-atmospheric phenomenon in the tropical Indian Ocean and it is defined as anomalous cooling of sea surface temperature (SST) in the eastern equatorial Indian Ocean ( 900 - 1100E and 100S - 00 ) and anomalous warming of SST in western equatorial Indian Ocean ( 500E - 700E and 100S - 100N ). Further the intensity of IOD is noted by anomalous SST gradient between the western equatorial Indian Ocean and southeastern equatorial Indian Ocean and it is called as Dipole Mode Index (DMI). When the DMI is positive, the phenomenon is represented as positive IOD and vice-versa. The northeasterlies in the form of surges are mainly coming from high-pressure region of northeast India from October onwards and picks up some moisture over Bay of Bengal and give more rain over south India. The strength of the cold surge from high pressure area over northeast India in terms of geopotential heights over northeast Indian stations namely Calcutta and Gauhati at 850 hPa and 700 hPa. The above pressure distribution during October, which releases northeasterlies over India, is related with western equatorial Indian Ocean SSTs during August and September. There is a significant positive relationship (r = 0.6) between the above two parameters which indicates that strong SST in the western equatorial Indian Ocean is responsible for the release of strong northeasterlies from the high pressure are over northeast India in the month of October. The above significant relationship continues even for geopotential heights of November and December over Gauhati and Calcutta. Secondly the SSTs over the western Indian Ocean are well correlated with the winter monsoon rainfall over South India. The highlight of the present study is that there is positive relationship between the SST in the western equatorial Indian Ocean in the June and the winter monsoon rainfall. Finally there is also a direct significant relationship between the IOD and winter monsoon rainfall. The above relationships are useful for the prediction of the winter monsoon activity.