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<p>Land–atmosphere interactions play a critical role in the climate system. The long-term (monthly or longer) effects of land thermal anomalies have been extensively studied, but relatively less attention has been paid to their fast (synoptic) atmospheric responses. Based on the diagnostics of NCEP/DOE reanalysis and numerical experiments using RegCM5, this study investigates thermal effects of the land surface over West Asia, a climatically sensitive region for downstream impacts, on atmospheric circulation and rainfall over the South and East Asian monsoon regions. While anomalous conditions over Eurasia, including West Asia, are primarily modulated by a teleconnection pattern originating from the North Atlantic Ocean, the land surface heating over West Asia can further exert downstream influence on weather conditions on synoptic time scales. Specifically, the heating enhances lower-tropospheric water vapor transportation towards the southern Tibetan Plateau, inducing increased rainfall. Meanwhile, the heating generates significant Rossby wave source (<i>RWS</i>) to the north of Iranian Plateau in the upper troposphere, exciting a downstream wave train that reaches northeast Asia and triggers regional rainfall. In contrast, the land surface cooling over West Asia induces an opposite-phase <i>RWS</i> to the south of the Iranian Plateau, leading to asymmetry downstream responses over East Asia. Following either the surface heating or cooling, the maximum responses of the Rossby wave typically occur around 5&#xa0;days later. These results highlight the rapid relay effects of West Asian land surface anomalies on downstream synoptic variability, providing new insights into improving medium-range weather forecasts over East Asia.</p>

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Downstream impacts of the land-surface thermal anomalies over West Asia on synoptic-time-scale atmospheric variability

  • 期刊论文

  • 发表日期：

    2025年11月3日

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  • Yang Zhou,
  • Boyang Lei,
  • Pang-Chi Hsu,
  • Lei Han,
  • Shanlei Sun,
  • Mengke La,
  • Haishan Chen

摘要

Land–atmosphere interactions play a critical role in the climate system. The long-term (monthly or longer) effects of land thermal anomalies have been extensively studied, but relatively less attention has been paid to their fast (synoptic) atmospheric responses. Based on the diagnostics of NCEP/DOE reanalysis and numerical experiments using RegCM5, this study investigates thermal effects of the land surface over West Asia, a climatically sensitive region for downstream impacts, on atmospheric circulation and rainfall over the South and East Asian monsoon regions. While anomalous conditions over Eurasia, including West Asia, are primarily modulated by a teleconnection pattern originating from the North Atlantic Ocean, the land surface heating over West Asia can further exert downstream influence on weather conditions on synoptic time scales. Specifically, the heating enhances lower-tropospheric water vapor transportation towards the southern Tibetan Plateau, inducing increased rainfall. Meanwhile, the heating generates significant Rossby wave source (RWS) to the north of Iranian Plateau in the upper troposphere, exciting a downstream wave train that reaches northeast Asia and triggers regional rainfall. In contrast, the land surface cooling over West Asia induces an opposite-phase RWS to the south of the Iranian Plateau, leading to asymmetry downstream responses over East Asia. Following either the surface heating or cooling, the maximum responses of the Rossby wave typically occur around 5 days later. These results highlight the rapid relay effects of West Asian land surface anomalies on downstream synoptic variability, providing new insights into improving medium-range weather forecasts over East Asia.