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The Relation of Intraseasonal Variations With Local Onset and Demise of the Indian Summer Monsoon
Author(s) -
Karmakar Nirupam,
Misra Vasubandhu
Publication year - 2019
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2018jd029642
Subject(s) - demise , climatology , equator , monsoon , environmental science , atmospheric sciences , geology , geography , geodesy , political science , law , latitude
Two of the most important hydroclimatic features of the Indian summer monsoon (ISM) rainfall are its onset/demise and intraseasonal oscillations (ISOs) manifested by the active‐break cycles. In this study, we aim to understand the quantitative association between these two phenomena. An objective definition of local onset/demise of the ISM based on more than a century‐long India Meteorological Department rain gauge observation is taken into consideration. Using multichannel singular spectrum analysis we isolate northward‐propagating low‐frequency (20–60 days; LF‐ISO) and northwestward propagating high‐frequency (10–20 days; HF‐ISO) ISOs from the daily ISM rainfall. Our results suggest that a large number of local onset (59%) and demise (62%) events occur during positive developing phases and positive decaying phases of two ISOs, respectively, with phase locking between LF‐ISO and HF‐ISO being particularly important. Local onset is largely associated with favorable phases of ISOs across India except for LF‐ISO over eastern India and HF‐ISO over western Ghats and central India (CI). We find that local demise is more coherent with the ISO phases, especially with HF‐ISO across the domain. We performed a case study to understand large‐scale association with the onset of the ISM over CI. In 44 of total 58 cases (1948–2005), when CI onset occurred during favorable LF‐ISO or HF‐ISO phase, they are either linked with a northward propagation of convection from the equator in LF‐ISO time scale (28 cases) or westward propagating structures from the western Pacific in HF‐ISO time scale (27 cases).