Spatio-temporal variability of summer monsoon rainfall over Orissa in relation to low pressure systems |
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| Authors: | M Mohapatra U C Mohanty |
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| Institution: | (1) India Meteorological Department, 781 015 Guwahati, Assam, India;(2) Centre for Atmospheric Sciences, Indian Institute of Technology, 110 016 Delhi, New Delhi, India |
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| Abstract: | The summer monsoon rainfall over Orissa occurs mostly due to low pressure systems (LPS) developing over the Bay of Bengal
and moving along the monsoon trough. A study is hence undertaken to find out characteristic features of the relationship between
LPS over different regions and rain-fall over Orissa during the summer monsoon season (June-September). For this purpose,
rainfall and rainy days over 31 selected stations in Orissa and LPS days over Orissa and adjoining land and sea regions during
different monsoon months and the season as a whole over a period of 20 years (1980-1999) are analysed. The principal objective
of this study is to find out the role of LPS on spatial and temporal variability of summer monsoon rainfall over Orissa.
The rainfall has been significantly less than normal over most parts of Orissa except the eastern side of Eastern Ghats during
July and hence during the season as a whole due to a significantly less number of LPS days over northwest Bay in July over
the period of 1980-1999. The seasonal rainfall shows higher interannual variation (increase in coefficient of variation by
about 5%) during 1980-1999 than that during 1901-1990 over most parts of Orissa except northeast Orissa. Most parts of Orissa,
especially the region extending from central part of coastal Orissa to western Orissa (central zone) and western side of the
Eastern Ghats get more seasonal monsoon rainfall with the development and persistence of LPS over northwest Bay and their
subsequent movement and persistence over Orissa. The north Orissa adjoining central zone also gets more seasonal rainfall
with development and persistence of LPS over northwest Bay. While the seasonal rainfall over the western side of the Eastern
Ghats is adversely affected due to increase in LPS days over west central Bay, Jharkhand and Bangladesh, that over the eastern
side of the Eastern Ghats is adversely affected due to increase in LPS days over all the regions to the north of Orissa. There
are significant decreasing trends in rainfall and number of rainy days over some parts of southwest Orissa during June and
decreasing trends in rainy days over some parts of north interior Orissa and central part of coastal Orissa during July over
the period of 1980-1999 |
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| Keywords: | Rainfall variability monsoon Orissa |
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