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<p>The low-level jet (LLJ) over the Arabian Sea is a critical component of the South Asian summer monsoon. A deeper understanding of its vertical characteristics is essential to South Asian summer precipitation. Based on ERA-5 reanalysis data, this study examines the vertical characteristics and climatic effects of the LLJ at four pressure levels (750&#xa0;hPa, 825&#xa0;hPa, 925&#xa0;hPa, and 1000&#xa0;hPa). It shows that the wind speed core is located at 925&#xa0;hPa, the 750&#xa0;hPa has the highest variability, and shows&#xa0;a significant upward trend. The empirical orthogonal function analysis identifies a consistent change mode (77.33% variance contribution) and an opposite change mode between upper and lower levels (20.44% variance contribution). The sensible heat flux over the Tibetan Plateau, global warming, and the Pacific Decadal Oscillation (PDO) collectively contribute to the upward trend at 750&#xa0;hPa. The PDO and the Eastern Pacific type of El Niño-Southern Oscillation show significant negative correlations with the first mode, through teleconnections that modulate the Tropical Easterly Jet and Walker Circulation. The Indian Ocean Basin mode exhibits a significant positive correlation with the second mode, by altering the land-sea thermal contrast and South Asian High. While the lower-level LLJ transports more moisture, the upper-level LLJ correlates more strongly with precipitation across India, the upper-level LLJ serves as a robust&#xa0;indicator of&#xa0;large-scale ascending motion, and the orographic forcing of the Western Ghats also plays a key role. These findings highlight the vertical heterogeneity of the LLJ, providing new insights into monsoon dynamics.</p>

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Vertical characteristics of the low-level jet over the Arabian Sea

  • 期刊论文

  • 发表日期：

    2026年3月2日

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  • Xinming Zhang,
  • Guocan Wu

摘要

The low-level jet (LLJ) over the Arabian Sea is a critical component of the South Asian summer monsoon. A deeper understanding of its vertical characteristics is essential to South Asian summer precipitation. Based on ERA-5 reanalysis data, this study examines the vertical characteristics and climatic effects of the LLJ at four pressure levels (750 hPa, 825 hPa, 925 hPa, and 1000 hPa). It shows that the wind speed core is located at 925 hPa, the 750 hPa has the highest variability, and shows a significant upward trend. The empirical orthogonal function analysis identifies a consistent change mode (77.33% variance contribution) and an opposite change mode between upper and lower levels (20.44% variance contribution). The sensible heat flux over the Tibetan Plateau, global warming, and the Pacific Decadal Oscillation (PDO) collectively contribute to the upward trend at 750 hPa. The PDO and the Eastern Pacific type of El Niño-Southern Oscillation show significant negative correlations with the first mode, through teleconnections that modulate the Tropical Easterly Jet and Walker Circulation. The Indian Ocean Basin mode exhibits a significant positive correlation with the second mode, by altering the land-sea thermal contrast and South Asian High. While the lower-level LLJ transports more moisture, the upper-level LLJ correlates more strongly with precipitation across India, the upper-level LLJ serves as a robust indicator of large-scale ascending motion, and the orographic forcing of the Western Ghats also plays a key role. These findings highlight the vertical heterogeneity of the LLJ, providing new insights into monsoon dynamics.