Periodicity in intraseasonal variation of summer monsoon rainfall over Orissa, India in relation to synoptic disturbances |
| |
| Authors: | M Mohapatra U C Mohanty |
| |
| Institution: | (1) India Meteorological Department, Mausam Bhavan, New Delhi, India;(2) Centre for Atmospheric Sciences, Indian Institute of Technology, Delhi Hauz Khas, New Delhi, India |
| |
| Abstract: | Summary The summer monsoon rainfall over Orissa, a state of eastern India, shows characteristic intraseasonal and interannual variability,
due to interaction of basic westerly flow with orography and the synoptic scale monsoon disturbances including low-pressure
systems and cyclonic circulations extending upto mid-tropospheric level (LPSC). These systems normally develop over the north
Bay of Bengal and move west-northwestwards along the monsoon trough. The essence of this study is to find out the main features
of the intraseasonal variability of daily monsoon rainfall over Orissa in relation to synoptic systems like LPSC and its implication
on the interannual variation of rainfall. For this purpose, the actual and mean daily rainfall data of 31 uniformly distributed
stations, six homogeneous regions and Orissa as a whole during monsoon season (June–September) over a period of 20 years (1980–1999)
are subjected to auto-correlation and power spectrum analyses. The actual and average daily scores of significant EOFs and
actual daily occurrence along with daily probability of occurrence of the LPSC influencing rainfall over Orissa during the
same period are also subjected to auto-correlation and power spectrum analyses.
The intraseasonal variation of monsoon rainfall over Orissa and different homogeneous regions is dominated by the synoptic
mode (3–9 days) of variation due to the similar mode of variation in the occurrence of LPSC influencing the rainfall. The
seasonal rainfall and hence the interannual variation depends on the intraseasonal variation of rainfall modulated with the
synoptic mode of variation in the occurrence of the LPSC. The occurrence of LPSC over the northwest (NW) Bay/NW and adjoining
northeast (NE) Bay and its subsequent movement and persistence over Orissa and east Madhya Pradesh & Chhattisgarh in synoptic
mode (3–6 days) alongwith absence of similar mode in the occurrence of the LPSC over NE Bay, Gangetic West Bengal (GWB) in
the north and west central (WC) Bay to the south leads to excess rainfall over different homogeneous regions and Orissa as
a whole. The reverse is the case in deficient years over Orissa and all homogeneous regions except southwest Orissa. The occurrence
of the LPSC over GWB in synoptic mode (about 5 days) alongwith absence of synoptic mode in the occurrence of the LPSC over
NW Bay leads to deficient rainfall year over southwest Orissa.
Correspondence: U. C. Mohanty, Centre for Atmospheric Sciences, Indian Institute of Technology, Delhi Hauz Khas, New Delhi
110016, India |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
