Spatial monsoon variability with respect to NAO and SO |
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| Authors: | S B Kakade S S Dugam |
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| Institution: | (1) Indian Institute of Tropical Meteorology, 411 008 Pune, India |
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| Abstract: | In this paper, the simultaneous effect of North Atlantic Oscillation (NAO) and Southern Oscillation (SO) on monsoon rainfall
over different homogeneous regions/subdivisions of India is studied. The simultaneous effect of both NAO and SO on Indian
summer monsoon rainfall (ISMR) is more important than their individual impact because both the oscillations exist simultaneously
throughout the year. To represent the simultaneous impact of NAO and SO, an index called effective strength index (ESI) has
been defined on the basis of monthly NAO and SO indices. The variation in the tendency of ESI from January through April has
been analyzed and reveals that when this tendency is decreasing, then the ESI value throughout the monsoon season (June–September)
of the year remains negative andvice versa. This study further suggests that during the negative phase of ESI tendency, almost all subdivisions of India show above-normal
rainfall andvice versa. The correlation analysis indicates that the ESI-tendency is showing an inverse and statistically significant relationship
with rainfall over 14 subdivisions of India. Area wise, about 50% of the total area of India shows statistically significant
association. Moreover, the ESI-tendency shows a significant relationship with rainfall over north west India, west central
India, central north east India, peninsular India and India as a whole. Thus, ESI-tendency can be used as a precursor for
the prediction of Indian summer monsoon rainfall on a smaller spatial scale. |
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| Keywords: | North Atlantic oscillation southern oscillation Indian summer monsoon rainfall effective strength index |
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