Analysis of Indian monsoon daily rainfall on subseasonal to multidecadal time-scales using a hidden Markov model

A 70-year record of daily monsoon-season rainfall at a network of 13 stations in central western India is analyzed using a 4-state homogeneous hidden Markov model. The diagnosed states are seen to play distinct roles in the seasonal march of the monsoon, can be associated with 'active' and 'break' monsoon phases and capture the northward propagation of convective disturbances associated with the intraseasonal oscillation. Interannual variations in station rainfall are found to be associated with the alternation, from year to year, in the frequency of occurrence of wet and dry states; this mode of variability is well correlated with both all-India monsoon rainfall and an index characterizing the strength of the El Nino Southern Oscillation. Analysis of low-passed time series suggests that variations in state frequency are responsible for the modulation of monsoon rainfall on multidecadal time-scales as well. Copyright (C) 2008 Royal Meteorological Society.