The spatio-temporal structures and role of low- and high-frequency intraseasonal modes in Indian Summer monsoon rainfall observed in TRMM data

This study uses precipitation estimates from the Tropical Rainfall Measuring Mission to estimate the intensity and examine the spatiotemporal patterns in the modes found in intraseasonal timescale over the Indian monsoon region during boreal summer. Here, using multichannel singular spectrum analysis, two dominant modes of oscillations are found in the intraseasonal timescale with periodicity of 10–20-days and 20–60-days, respectively. 20–60-days mode shows northward propagation from the equatorial Indian Ocean linked with the eastward propagating modes of convective systems over the tropics. 10–20-days mode shows very complex structure with a northwestward propagating anomaly pattern emanating from the Indonesian coast moving towards central India. This pattern is found to have a possible interaction with a structure emerging from higher latitudes propagating southeastwards. The two intraseasonal modes contribute comparable amount to the total rainfall variability. The intensity of the 20–60-days (10–20-days) mode show significantly strong inverse (direct) relationship with all- India June–September rainfall and both the modes exhibit profound variability in their intensity in interannual scale. This study also establishes that the probability of getting good amount of rainfall (no rainfall) over central India increases significantly if the two intraseasonal modes exhibit positive (negative) anomalies over the region. Relation between the ISO intensities and sea surface temperature is also discussed. This study points towards the fact that the knowledge of ISO phases can increase the skill in the probabilistic forecasting of rainfall over India.