Abstracts for the 6th International GAME Conf.

3-5 December 2004

Kyoto Japan

Role of intra-seasonal oscillations in modulating seasonal summer monsoon rainfall over India

Dr. R.H. Kripalani (1), Dr. (Mrs) Ashwini Kulkarni (1), Mr. S.S. Sabade (1)

The summer monsoon rainfall variability is partly due to the external surface boundary forcing and partly due to its internal dynamics.Slowly varying surface boundary forcing during the preceding winter and pre-monsoon season provide the handle for seasonal prediction.However the variability associated with the internal dynamics within the monsoon season is difficult to predict. The intra-seasonal variability dominant during the monsoon season constitutes this internal dynamics.Hence in this study the relationship between the intra-seasonal variability and the inter-annual monsoon variability is examined using observed rainfall data for a 103- year period (1901-2003). Further the dynamical reasons for the relationship found are examined through the NCEP-NCAR reanalysis data for the period 1958-2003.Techniques of correlation and composite analysis ,band-pass filtering and wavelet analysis are used. Results reveal that the summer monsoon rainfall over India is positively related with the faster modes (3-7 day; 10-20 day)and inversly related with the slower mode (30-60 day).Even within the monsoon season, a change from active to weak spell clearly reveals that the period of oscillation increasing, and a change from weak to active spell shows periodicty length decreasing. To ascertain whether the behavior of the modes could be foreshadowed during the preceding winter / spring, lower troposphere circulation features over the Indo-Pacific region are determined during the extreme phases of these intra-seasonal oscillations.Preliminary analysis reveal that these modes show their origin over the Pacific region in particular over the north Pacific associated with the Aleutian Low during winter and the North Pacific sub-tropical high during summer.Further work is under progress.

Submittal Information

Name : Date :
    Dr. R.H.Kripalani
    30-Jul-04-18:16:15
Organization : Theme :
    Indian Institute of Tropical Meteorology
    Theme 3
Address : Presentation :
    NCL PO, Pashan, Pune 411008
    Poster or oral
Country : Abstract ID :
    INDIA
    T3DR30Jul04181615
Phone : Fax :
    91-20-25893600
    91-20-25893825
E-mail :
    krip@tropmet.res.in