Spring “Predictability Barrier” and Indian Summer Monsoon

Abstract

Monthly correlation of Indian monsoon rainfall (IMR) index with various monsoon indices changes predominantly and peaks within summer season (Ailikun and Yasunari, 2001). There is transition in this lead and lagged correlation during spring (March, April and May). This spring transition could not be captured in many general circulation models (GCMs) and is termed as “predictability barrier” (Latif and Graham, 1991). It has been less investigated and hence reasons for dampening/reversal of associated large scale fields during spring are intriguing. Present study illustrates dynamics of spring predictability barrier with Indian summer (June, July, August and September) monsoon (ISM). In this study, based on data from 1979 to 2008, an internal dynamics between various monsoon indices and corresponding IMR anomaly is diagnosed. It is found that secular behaviour of El Nino– Southern Oscillation (ENSO) during preceding spring of monsoon months (June, July, August and September) gets reversed in succeeding spring. Though correlation between various monsoon indices and ISM index remains similar during preceding and succeeding springs with peaks during monsoon (June, July, August and September), corresponding large scale fields show that strong significant convection dominates over the southern equatorial eastern Pacific Ocean, northern equatorial western Pacific Ocean, Indonesian throughflow and weaker significant convection dominates over the Head Bay of Arabian Sea and western to central Indian sub-continent during preceding spring. Such patterns reverse during succeeding spring.