{"title":"Distinctive Features of Monsoon-TC Joint Rainfall over Western North Pacific and its Relationship with the Maritime Continent Thermal Condition","authors":"Jingying Wang, Zhiwei Wu","doi":"10.1080/07055900.2023.2221217","DOIUrl":null,"url":null,"abstract":"ABSTRACT The East Asian summer monsoon (EASM) and tropical cyclones (TCs) in the Western North Pacific (WNP) are both responsible for the East Asian summer rainfall, yet most studies only examine their rainfall separately. In this study, the East Asian summer rainfall for the past 39-years (1983-2021, May to September) is divided into three categories: monsoon rainfall without TCs’ influence (monsoon-only rainfall), TC rainfall independent of monsoon (TC-only rainfall) and monsoon-TC joint (MS-TC) rainfall. Compared with the other two categories, MS-TC rainfall exhibits distinctive features. During strong MS-TC years, a distinct cyclonic anomaly centre prevails over tropical WNP with anomalous southeasterlies extending from the tropics to the subtropics. Large rainfall centres are located at the west edge of the northern Philippines, the Philippine Basin, and the Korean Peninsula. The WNP Subtropical High (WNPSH) withdrawals eastward, with an eastward extension of the monsoon trough. These circulation configurations provide favourable environmental conditions for more northward movements of TCs, including low-level positive relative vorticity and enhanced vertical motion in WNP. Observational and theoretical analysis results show that anomalous thermal conditions in the southern Maritime Continent (MC) (97.5°−112.5°E, 8°−18°S) in early spring (March to April) can be a precursor for anomalous MS-TC rainfall. Strong MS-TC rainfall is usually preceded by depressed convection and anomalous westerlies near the MC. These anomalies can persist through the following summer and induce the positive feedback of cooling sea surface temperature (SST) in MC and cyclonic anomalies in tropical WNP through the wind-evaporation-SST (WES) effect and local Hadley circulation anomalies. The linear baroclinic model (LBM) experiments demonstrate that enhanced convection in tropical WNP further maintains the anomalous cyclone through Gill's response, which in turn modulates the distribution and amount of MS-TC rainfall.","PeriodicalId":55434,"journal":{"name":"Atmosphere-Ocean","volume":" ","pages":""},"PeriodicalIF":1.6000,"publicationDate":"2023-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Atmosphere-Ocean","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.1080/07055900.2023.2221217","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"METEOROLOGY & ATMOSPHERIC SCIENCES","Score":null,"Total":0}
引用次数: 0
Abstract
ABSTRACT The East Asian summer monsoon (EASM) and tropical cyclones (TCs) in the Western North Pacific (WNP) are both responsible for the East Asian summer rainfall, yet most studies only examine their rainfall separately. In this study, the East Asian summer rainfall for the past 39-years (1983-2021, May to September) is divided into three categories: monsoon rainfall without TCs’ influence (monsoon-only rainfall), TC rainfall independent of monsoon (TC-only rainfall) and monsoon-TC joint (MS-TC) rainfall. Compared with the other two categories, MS-TC rainfall exhibits distinctive features. During strong MS-TC years, a distinct cyclonic anomaly centre prevails over tropical WNP with anomalous southeasterlies extending from the tropics to the subtropics. Large rainfall centres are located at the west edge of the northern Philippines, the Philippine Basin, and the Korean Peninsula. The WNP Subtropical High (WNPSH) withdrawals eastward, with an eastward extension of the monsoon trough. These circulation configurations provide favourable environmental conditions for more northward movements of TCs, including low-level positive relative vorticity and enhanced vertical motion in WNP. Observational and theoretical analysis results show that anomalous thermal conditions in the southern Maritime Continent (MC) (97.5°−112.5°E, 8°−18°S) in early spring (March to April) can be a precursor for anomalous MS-TC rainfall. Strong MS-TC rainfall is usually preceded by depressed convection and anomalous westerlies near the MC. These anomalies can persist through the following summer and induce the positive feedback of cooling sea surface temperature (SST) in MC and cyclonic anomalies in tropical WNP through the wind-evaporation-SST (WES) effect and local Hadley circulation anomalies. The linear baroclinic model (LBM) experiments demonstrate that enhanced convection in tropical WNP further maintains the anomalous cyclone through Gill's response, which in turn modulates the distribution and amount of MS-TC rainfall.
期刊介绍:
Atmosphere-Ocean is the principal scientific journal of the Canadian Meteorological and Oceanographic Society (CMOS). It contains results of original research, survey articles, notes and comments on published papers in all fields of the atmospheric, oceanographic and hydrological sciences. Arctic, coastal and mid- to high-latitude regions are areas of particular interest. Applied or fundamental research contributions in English or French on the following topics are welcomed:
climate and climatology;
observation technology, remote sensing;
forecasting, modelling, numerical methods;
physics, dynamics, chemistry, biogeochemistry;
boundary layers, pollution, aerosols;
circulation, cloud physics, hydrology, air-sea interactions;
waves, ice, energy exchange and related environmental topics.