Monsoon is derived from an Arabic word that means seasons. The Indian summer monsoon (June-July-August-September; JJAS), which is also a part of the annually reversing wind system [Goswami 2005], is one of the most dynamic land-atmosphere-ocean coupled systems over the tropics [Webster et al. 1998] . Rainfall within the summer monsoon season is mainly punctuated by the northward propagating monsoon intraseasonal oscillations (MISOs) with timescales of 30-60 days [Yasunari 1979, 1980, 1981; Sikka and Gadgil 1980] that manifests as spells of heavy rainfall and periods of quiescent rainfall, instead of a continuous deluge.

These spells are termed as 'active' and 'break' spells respectively, which contribute to the sub-seasonal or intraseasonal variability (ISV) of the Indian summer monsoon. As the socio-economical growth of the Indian subcontinent is strongly interlaced with the summer monsoon rainfall, understanding the complex space–time characteristics of MISO, its realistic simulation and prediction at the extended range have received considerable attention in recent years