Intense rainfall conditions over Indo-Gangetic Plains under the influence of Madden-Julian oscillation

摘要

The Indo-Gangetic Plains (IGPs) are densely populated and agriculturally productive areas with strong interannual and intraseasonal rainfall variability. The intraseasonal rainfall variability over IGPs is due to variation in sea surface temperature in the equatorial Indian Ocean. The intense rainfall activity over IGPs is mainly convection-driven, which may be linked with Madden-Julian Oscillation (MJO). The threshold for exceptionally heavy rainfall during the period 1979-2012 is based on the analysis of heavy rainfall episodes (percentage departure in daily rainfall (PDR >= 700%). The thresholds for extremely strong MJO events show highest departure in MJO amplitude (PDA <= 200%). The present study aims to find the simultaneous relationship between 60 and 30-day cycles of rainfall variability over IGPs and linked with MJO amplitude variability for the period 1979-2012. Further, the 30-day cycle of rainfall variability is elaborately studied for different phases of MJO. The monthly and daily variability of IGPs rainfall as well as MJO amplitude is analysed to find important intense rainfall and MJO events. The results suggest that the monthly rainfall variability is caused due to synoptic scale weather systems like monsoon trough oscillation and corresponding pressure fluctuations over IGPs. The exceptionally intense rainfall activity during onset and retreat phases is observed to be associated with MJO phases 6-8. The intense rainfall activity during active-break phase is observed to be associated with MJO phases 3-5. The intense rainfall events during break phase are observed along foothills of Himalaya. The day-to-day rainfall variability is due to interaction between monsoon circulation and MJO.