Signals of northward propagating Monsoon Intra-seasonal Oscillations (MISOs) in the RegCM4.7 CORDEX-CORE simulation over South Asia domain

Abstract

The northward propagation of intra-seasonal oscillations (ISO) is closely associated with the seasonal and sub-seasonal cycle of the Indian summer monsoon (ISM). This northward propagating monsoon ISO (MISO) is prominent at 25–90 days during the ISM and are very complex in nature. In this study, we use a simulation with REGional Climate Model v4.7 (RegCM4.7) output to attempt to better understand one of the major modes of ISO during the period 1981 to 2016. The model forced with EIN75 initial and boundary condition and EIN75 SST forcing is found to successfully capture the major signals of MISO. The propagating features of the MISO circulation pattern are broadly characterized using extended empirical orthogonal function (EEOF) and two major MISO indices (MISO-1 and MISO-2). The regions between the Indian subcontinent and the Indian ocean (IO) are found to be crucial for the MISO propagation during the 25–90 day oscillation. Half of the lifecycle of the MISO is found to be 15 days, i.e., the period necessary for the alteration from break phase to active monsoon phase. Simulated MISO indexes in phase space diagrams also reveal northward propagating signals that further help to explain potential mechanisms behind the MISO rainfall propagation from the IO to the Himalayan foothills.