Rajeevan et al. [2010] defined the active and break spells of ISMR during the peak monsoon months of July and August by using the normalized anomaly of the rainfall over monsoon core zone of India (MZI) calculated from the high resolution daily gridded rainfall data over India. The break (active) spell has been identified when the normalized rainfall anomaly over the MZI which is roughly from 18°N to 28°N and 65°E to 88°E [Rajeevan et al. 2010], is less (greater) than –1.0 (+1.0), consecutively for three days or more. This criterion holds good for daily data.

For pentad data we have defined active/break spells using long term pentad mean and standard deviation of rainfall. A criterion of ±40% has been used to identify the active and break spells of Indian summer monsoon for pentad data during JJAS. Figure shows the mean, ±1SD line as well as ±40% of the mean. It is found that ±40% line is within the ±1SD line. So we have suggested that when rainfall is less than -40% of the long term pentad mean, the spell has been defined as break; greater than 40%, the spell is active and otherwise normal.