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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 14755-14774, 2016
https://doi.org/10.5194/acp-16-14755-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
25 Nov 2016
Movement, drivers and bimodality of the South Asian High
Matthias Nützel, Martin Dameris, and Hella Garny Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
Abstract. The South Asian High (SAH) is an important component of the summer monsoon system in Asia. In this study we investigate the location and drivers of the SAH at 100 hPa during the boreal summers of 1979 to 2014 on interannual, seasonal and synoptic timescales using seven reanalyses and observational data. Our comparison of the different reanalyses focuses especially on the bimodality of the SAH, i.e. the two preferred modes of the SAH centre location: the Iranian Plateau to the west and the Tibetan Plateau to the east. We find that only the National Centers for Environmental Prediction–National Center of Atmospheric Research (NCEP–NCAR) reanalysis shows a clear bimodal structure of the SAH centre distribution with respect to daily and pentad (5 day) mean data. Furthermore, the distribution of the SAH centre location is highly variable from year to year. As in simple model studies, which connect the SAH to heating in the tropics, we find that the mean seasonal cycle of the SAH and its centre are dominated by the expansion of convection in the South Asian region (70–130° E  ×  15–30° N) on the south-eastern border of the SAH. A composite analysis of precipitation and outgoing long-wave radiation data with respect to the location of the SAH centre reveals that a more westward (eastward) location of the SAH is related to stronger (weaker) convection and rainfall over India and weaker (stronger) precipitation over the western Pacific.

Citation: Nützel, M., Dameris, M., and Garny, H.: Movement, drivers and bimodality of the South Asian High, Atmos. Chem. Phys., 16, 14755-14774, https://doi.org/10.5194/acp-16-14755-2016, 2016.
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Short summary
Using seven reanalyses, we study the movement and drivers of the upper tropospheric–lower stratospheric anticyclone (AC) that forms during the Asian summer monsoon and is debated to be an important pathway for air masses to the stratosphere. We find that the distribution of the AC's centre position, and especially the so-called bimodality, largely depends on the reanalysis. Furthermore, we can connect shifts of the AC to precipitation and convection anomalies over India and the western Pacific.
Using seven reanalyses, we study the movement and drivers of the upper tropospheric–lower...
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