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.

中文翻译：

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马登-朱利安振荡影响下的印度-恒河平原强降雨条件

印度恒河平原 (IGP) 是人口稠密和农业生产区，具有强烈的年际和季节内降雨变化。IGP 的季节内降雨变化是由于赤道印度洋海面温度的变化。IGP 上的强降雨活动主要是对流驱动，这可能与马登-朱利安振荡 (MJO) 相关。1979-2012年特大暴雨阈值是基于对强降雨事件（日降雨量偏离百分比（PDR≥700%））的分析。极强MJO事件阈值显示MJO振幅偏离最高（PDA≤ 200%）。本研究旨在找出 IGP 上 60 天和 30 天降雨变化周期之间的同时关系，并与 1979-2012 年期间 MJO 振幅变化相关联。此外，还详细研究了 MJO 不同阶段的 30 天降雨变化周期。分析 IGPs 降雨的月和日变化以及 MJO 振幅，以发现重要的强降雨和 MJO 事件。结果表明，月降雨量变化是由于季风槽振荡等天气尺度天气系统和IGP上相应的压力波动引起的。观察到开始和撤退阶段异常强烈的降雨活动与 MJO 阶段 6-8 相关。观察到活动中断阶段的强降雨活动与 MJO 阶段 3-5 相关。沿喜马拉雅山山麓观察到中断阶段的强降雨事件。每日降雨量的变化是由于季风环流和 MJO 之间的相互作用。