Abstract The timing of the Indian Summer Monsoon Rainfall (ISMR) onset significantly influences agriculture, food security, livelihoods, and the Indian economy. While the drivers of climatological ISMR onset are well discussed, the causes of delayed ISMR onset remain unclear. This study shows that the delay is primarily driven by anomalous high pressure over the Arabian Sea and anomalous low pressure over the Mascarene High, which weakens the regional Hadley circulation and, consequently, the lowâlevel moist southwesterly winds over the Arabian Sea. This weakening of southwesterlies directly delays the ISMR onset. When the ocean forces the atmosphere over the Arabian Sea, it alters the earlier delaying conditions and creates a favorable environment for the ISMR onset. The key novelty of this study is understanding the combined role of the Mascarene High, regional Hadley circulation, and Arabian Sea airâsea interactions in regulating delayed ISMR onset, offering new insights for improving ISMR onset prediction.
Observations from the Little Bunker
Last updated: February 24, 2026 10:22 PM
Atmospheric COâ
429.9 ppm
+17.3
ppm/year
Atmospheric CHâ
1946.47 ppb
+6.49
ppb/year
Global Temperature
+1.48 °C
Peak: +1.73°C
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8.1 billion
+67
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