{"title":"Role of Intraseasonal Oscillation in Linking the Stepwise Onset of Summer Monsoon in the Northern Indian Ocean","authors":"Kuiping Li, Qin He, Yang Yang","doi":"10.1002/asl.1313","DOIUrl":null,"url":null,"abstract":"<p>The summer monsoon onset in the northern Indian Ocean is crucial for the densely populated South Asia, as it ends the pre-monsoon heatwave and kicks off the rainy agricultural season. Climatologically, this onset occurs in two distinct phases: first in the Bay of Bengal (BoB), followed by the Arabian Sea (AS). However, the possible mechanistic linkage between these phases remains unclear. Based on observational analysis, this study investigates how the BoB monsoon onset preconditions the subsequent AS monsoon onset, with particular focus on the pivotal trigger of the AS monsoon—the intraseasonal oscillation (ISO-AS). We demonstrate that the BoB monsoon onset establishes an easterly vertical wind shear across the northern Indian Ocean. The shear environment interacts with the ascending motion of the ISO-AS, which develops approximately 1 month later, enhancing cyclonic vorticity north of the convection center of the ISO-AS. This process, in turn, promotes moisture convergence in the boundary layer and facilitates the northward propagation of the ISO-AS, ultimately triggering the summer monsoon onset in the AS. By elucidating the stepwise nature of monsoon onset in the northern Indian Ocean, this work offers valuable insights for improving predictions of the Asian summer monsoon.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"26 9","pages":""},"PeriodicalIF":2.0000,"publicationDate":"2025-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1313","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Atmospheric Science Letters","FirstCategoryId":"89","ListUrlMain":"https://rmets.onlinelibrary.wiley.com/doi/10.1002/asl.1313","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"METEOROLOGY & ATMOSPHERIC SCIENCES","Score":null,"Total":0}
引用次数: 0
Abstract
The summer monsoon onset in the northern Indian Ocean is crucial for the densely populated South Asia, as it ends the pre-monsoon heatwave and kicks off the rainy agricultural season. Climatologically, this onset occurs in two distinct phases: first in the Bay of Bengal (BoB), followed by the Arabian Sea (AS). However, the possible mechanistic linkage between these phases remains unclear. Based on observational analysis, this study investigates how the BoB monsoon onset preconditions the subsequent AS monsoon onset, with particular focus on the pivotal trigger of the AS monsoon—the intraseasonal oscillation (ISO-AS). We demonstrate that the BoB monsoon onset establishes an easterly vertical wind shear across the northern Indian Ocean. The shear environment interacts with the ascending motion of the ISO-AS, which develops approximately 1 month later, enhancing cyclonic vorticity north of the convection center of the ISO-AS. This process, in turn, promotes moisture convergence in the boundary layer and facilitates the northward propagation of the ISO-AS, ultimately triggering the summer monsoon onset in the AS. By elucidating the stepwise nature of monsoon onset in the northern Indian Ocean, this work offers valuable insights for improving predictions of the Asian summer monsoon.
期刊介绍:
Atmospheric Science Letters (ASL) is a wholly Open Access electronic journal. Its aim is to provide a fully peer reviewed publication route for new shorter contributions in the field of atmospheric and closely related sciences. Through its ability to publish shorter contributions more rapidly than conventional journals, ASL offers a framework that promotes new understanding and creates scientific debate - providing a platform for discussing scientific issues and techniques.
We encourage the presentation of multi-disciplinary work and contributions that utilise ideas and techniques from parallel areas. We particularly welcome contributions that maximise the visualisation capabilities offered by a purely on-line journal. ASL welcomes papers in the fields of: Dynamical meteorology; Ocean-atmosphere systems; Climate change, variability and impacts; New or improved observations from instrumentation; Hydrometeorology; Numerical weather prediction; Data assimilation and ensemble forecasting; Physical processes of the atmosphere; Land surface-atmosphere systems.