Abstract
In this paper, the NCEP–NCAR daily reanalysis data are used to investigate the characteristics of the atmospheric heat source/sink (AHSS) over South Asia (SA) and southern Indian Ocean (SIO). The thermal differences between these two regions and their influence on the outbreak of the Indian summer monsoon (ISM) are explored. Composite analysis and correlation analysis are applied. The results indicate that the intraseasonal variability of AHSS is significant in SA but insignificant in the SIO. Large inland areas in the Northern Hemisphere still behave as a heat sink in March, similar to the situation in winter. Significant differences are found in the distribution of AHSS between the ocean and land, with distinct land–ocean thermal contrast in April, and the pattern presents in the transitional period right before the ISM onset. In May, strong heat centers appear over the areas from the Indochina Peninsula to the Bay of Bengal and south of the Tibetan Plateau (TP), which is a typical pattern of AHSS distribution during the monsoon season. The timing of SA–SIO thermal difference turning positive is about 15 pentads in advance of the onset of the ISM. Then, after the thermal differences have turned positive, a pre-monsoon meridional circulation cell develops due to the near-surface heat center and the negative thermal contrast center, after which the meridional circulation of the ISM gradually establishes. In years of early (late) conversion of the SA–SIO thermal difference turning from negative to positive, the AHSS at all levels over the TP and SIO converts later (earlier) than normal and the establishment of the ascending and descending branches of the ISM’s meridional circulation is later (earlier) too. Meanwhile, the establishment of the South Asian high over the TP is later (earlier) than normal and the conversion of the Mascarene high from winter to summer mode occurs anomalously late (early). As a result, the onset of the ISM is later (earlier) than normal. However, the difference in vorticity between early and late conversion only shows in the changes of strong vorticity centers’ location in the upper and lower troposphere.
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Acknowledgments
The authors would like to acknowledge the data providers, NCEP, for the NCEP–NCAR data, which are available at http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html. We also thank Prof. Shihua Lyu and Prof. Shigong Wang for their advice.
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Supported by the National Natural Science Foundation of China (91537214, 41275079, 41405069, 41305077, and 41505078), China Meteorological Administration Special Public Welfare Research Fund (GYHY201506001), Scientific Research Fund of Sichuan Education Department (16ZA0203), and Chengdu University of Information Technology Scientific Research Fund (J201516, J201518, and KYTZ201517).
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Zhang, Y., Fan, G., Hua, W. et al. Differences in atmospheric heat source between the Tibetan Plateau–South Asia region and the southern Indian Ocean and their impacts on the Indian summer monsoon outbreak. J Meteorol Res 31, 540–554 (2017). https://doi.org/10.1007/s13351-017-6042-5
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DOI: https://doi.org/10.1007/s13351-017-6042-5