The intraseasonal fluctuation of Indian summer monsoon rainfall and its relation with monsoon intraseasonal oscillation (MISO) and Madden Julian oscillation (MJO)

The intraseasonal fluctuations of Indian summer monsoon rainfall (ISMR) are mainly controlled by northward propagating monsoon intraseasonal oscillation (MISO) and eastward propagating Madden Julian oscillation (MJO). In the current study, we examine the relationship between the intraseasonal fluctuations (active and break spells) of ISMR with the phase propagation and amplitude of MISO and MJO. We notice that active spells generally occur during MISO phases 2–5 (MJO phases 3–6), and break spells mainly occur during MISO phases 6–8 (MJO phases 6–8 and 1). The association of active/break spells with MISO phases is more prominent than with MJO phases. We show the phase composite of unfiltered and regression-based reconstructed rainfall for eight MISO and MJO phases, which is consistent with the earlier findings. We notice that the reconstructed field shows a systematic and well-organised northward propagation compared to the unfiltered field. Phase composite also indicates a lead-lag relationship between MISO and MJO phases. MISO phase composite shows more robust northward propagation than the MJO phase composite. MISO reconstructed rainfall explained more percentage variance than MJO reconstructed rainfall with reference to 20–90-day filtered rainfall. It is found that long active (> 7 days) predominantly occurs when either MISO or MJO, or both of them are active, and the associated signal is somewhere in between phases 2 and 5. A long break occurs when both (MISO and MJO) or at least one (MJO/MISO) is feeble, or even though associated signals are strong, they are primarily located in phases 1, 6, 7 and 8.