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<p>The Low-Level Jet (LLJ) over the Arabian Sea (AS) is a critical component of the Indian Summer Monsoon Rainfall (ISMR), acting as a primary channel for moisture transport from the equatorial Indian Ocean through AS to the Indian subcontinent. This study examines the variability of the LLJ core zone (48°–68°E, 6°–16°N) during excess and deficit monsoon years from 1981 to 2020, using high-resolution reanalysis (ERA5), sea surface temperature (NOAA OISST), and gridded rainfall data from IMD. Seasonal (JJAS) and sub-seasonal (June–September) patterns during excess and deficit monsoon years are examined to evaluate the influence of the LLJ on monsoon dynamics. The excess monsoon years are consistently associated with strengthened westerlies in the LLJ core, enhanced cross-equatorial flow, increased moisture transport, cooler AS SST due to wind-driven upwelling, deeper monsoon troughs, and intensified convection, leading to above-normal rainfall. In contrast, deficit years exhibit weakened LLJ flow, warmer SST, reduced land–sea thermal contrast, suppressed convection, and significant rainfall deficits. Correlation patterns highlight strong positive links between LLJ strength and surface temperature, humidity, cloud cover, and rainfall during excess years, whereas in deficit years these relationships are weaker or reversed. Trend analysis reveals a statistically significant seasonal strengthening of the LLJ (0.021&#xa0;m&#xa0;s<sup>−1</sup>&#xa0;yr<sup>−1</sup>, 95%) and robust warming of SST (0.039&#xa0;°C&#xa0;yr<sup>−1</sup>, 95%), alongside increasing cloud cover and modest precipitation rises. Decadal analysis shows a shift from predominantly negative SST, temperature, and humidity anomalies in earlier decades to strongly positive anomalies post-2000, accompanied by enhanced late-season LLJ strength and modest increases in precipitation. These findings highlight the LLJ core region as a sensitive indicator and active modulator of monsoon variability, with important implications for seasonal rainfall prediction, agricultural planning, water resource management, and climate adaptation under a warming Indian Ocean.</p>

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Dynamics of the Arabian Sea Low-Level Jet and its influence on Indian monsoon extremes

  • 期刊论文

  • 发表日期：

    2026年5月15日

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  • Archana Sagalgile,
  • P. V. S. Raju,
  • Akshay Kulkarni

摘要

The Low-Level Jet (LLJ) over the Arabian Sea (AS) is a critical component of the Indian Summer Monsoon Rainfall (ISMR), acting as a primary channel for moisture transport from the equatorial Indian Ocean through AS to the Indian subcontinent. This study examines the variability of the LLJ core zone (48°–68°E, 6°–16°N) during excess and deficit monsoon years from 1981 to 2020, using high-resolution reanalysis (ERA5), sea surface temperature (NOAA OISST), and gridded rainfall data from IMD. Seasonal (JJAS) and sub-seasonal (June–September) patterns during excess and deficit monsoon years are examined to evaluate the influence of the LLJ on monsoon dynamics. The excess monsoon years are consistently associated with strengthened westerlies in the LLJ core, enhanced cross-equatorial flow, increased moisture transport, cooler AS SST due to wind-driven upwelling, deeper monsoon troughs, and intensified convection, leading to above-normal rainfall. In contrast, deficit years exhibit weakened LLJ flow, warmer SST, reduced land–sea thermal contrast, suppressed convection, and significant rainfall deficits. Correlation patterns highlight strong positive links between LLJ strength and surface temperature, humidity, cloud cover, and rainfall during excess years, whereas in deficit years these relationships are weaker or reversed. Trend analysis reveals a statistically significant seasonal strengthening of the LLJ (0.021 m s−1 yr−1, 95%) and robust warming of SST (0.039 °C yr−1, 95%), alongside increasing cloud cover and modest precipitation rises. Decadal analysis shows a shift from predominantly negative SST, temperature, and humidity anomalies in earlier decades to strongly positive anomalies post-2000, accompanied by enhanced late-season LLJ strength and modest increases in precipitation. These findings highlight the LLJ core region as a sensitive indicator and active modulator of monsoon variability, with important implications for seasonal rainfall prediction, agricultural planning, water resource management, and climate adaptation under a warming Indian Ocean.