Regionalization of seasonal precipitation over the Tibetan Plateau and associated large-scale atmospheric systems

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  • 1 Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden
  • 2 Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden
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Abstract

Precipitation over the Tibetan Plateau (TP) has major societal impacts in South and East Asia, but its spatiotemporal variations are not well understood mainly because of the sparsely distributed in-situ observation sites. With help of the Global Precipitation Measurement satellite product IMERG and ERA5 reanalysis, distinct precipitation seasonality features over the TP were objectively classified using a self-organizing map algorithm fed with ten-day averaged precipitation from 2000 to 2019. The classification reveals three main precipitation regimes with distinct seasonality of precipitation: winter peak, centered at the western plateau; early summer peak, found on the eastern plateau; and late summer peak, mainly located on the southwestern plateau. On a year-to-year basis, the winter peak regime is relatively robust, while the early summer and late summer peak regimes tend to shift mainly between the central and northern TP, but are robust in the eastern and southwestern TP. A composite analysis shows that the winter peak regime experiences larger amounts of precipitation in winter and early spring when the westerly jet is anomalously strong to the north of the TP. Precipitation variations in the late summer peak regime are associated with intensity changes in the South Asian High and Indian summer monsoon. The precipitation in the early summer peak regime is correlated with the Indian summer monsoon together with anticyclonic circulation over the western North Pacific. The results provide a basic understanding of precipitation seasonality variations over the TP and associated large-scale conditions.

Correspondence to: Deliang Chen (deliang@gvc.gu.se)

Abstract

Precipitation over the Tibetan Plateau (TP) has major societal impacts in South and East Asia, but its spatiotemporal variations are not well understood mainly because of the sparsely distributed in-situ observation sites. With help of the Global Precipitation Measurement satellite product IMERG and ERA5 reanalysis, distinct precipitation seasonality features over the TP were objectively classified using a self-organizing map algorithm fed with ten-day averaged precipitation from 2000 to 2019. The classification reveals three main precipitation regimes with distinct seasonality of precipitation: winter peak, centered at the western plateau; early summer peak, found on the eastern plateau; and late summer peak, mainly located on the southwestern plateau. On a year-to-year basis, the winter peak regime is relatively robust, while the early summer and late summer peak regimes tend to shift mainly between the central and northern TP, but are robust in the eastern and southwestern TP. A composite analysis shows that the winter peak regime experiences larger amounts of precipitation in winter and early spring when the westerly jet is anomalously strong to the north of the TP. Precipitation variations in the late summer peak regime are associated with intensity changes in the South Asian High and Indian summer monsoon. The precipitation in the early summer peak regime is correlated with the Indian summer monsoon together with anticyclonic circulation over the western North Pacific. The results provide a basic understanding of precipitation seasonality variations over the TP and associated large-scale conditions.

Correspondence to: Deliang Chen (deliang@gvc.gu.se)
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