Impact of Madden-Julian oscillation on onset of summer monsoon over India

The Madden-Julian oscillation (MJO) is identified as the dominant mode of intraseasonal variabilities (ISVs) in the tropical atmosphere. It is one of the most influencing factors, which can influence the onset phase of monsoon over India giving rise to early/delayed onset of summer monsoon onset over Kerala (MOK) in the southern tip of India. The aim of the present study is to find years in which northward propagating ISVs significantly contribute to the early/delayed MOK. Climatology of early and delayed onset of Indian summer monsoon is analyzed in association with MJO state for the period of 37 years (1979-2015). The results indicate strong MJO events are frequent and show relatively better association with the onset of summer monsoon over India as compared to the weak MJO events. With respect to the MJO phase, the result suggests that the MOK occur mostly in association with MJO phases 1, 2, 3, and 8. Out of these, the MJO phase 2 (convection centre over western equatorial Indian Ocean) is mostly associated with pre-onset (early onset) years, MJO phase 8 (convection center over western hemisphere) is mostly associated with post-onset (late onset) years, and MJO phases 1 and 3 (convection centers over eastern equatorial Indian Ocean or western hemisphere) are mostly associated with normal-onset years.