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<p>Monsoon depressions play a critical role in modulating a substantial portion of summer monsoon rainfall across the Indian subcontinent. A multitude of investigations has examined the architecture and dynamics of these systems; however, the heterogeneity of convection and precipitation patterns particularly over terrestrial regions, especially when employing extensive temporal datasets, has garnered comparatively limited focus. Consequently, it is imperative to investigate the variability of precipitation and the convective processes associated with these terrestrial intense rain-producing systems to augment our understanding and mitigate the hazards associated with hydro-meteorological calamities. Our stringent selection criteria, which persist for ≥ 36&#xa0;h over land and northwestward propagation, ensure a homogeneous sample that enables a detailed, process-level analysis of land-based monsoon deep depression (DD), providing insights not achievable with broader, less selective datasets. This study considers nine homogeneous DD systems, each lasting a minimum of 36&#xa0;h, over the Indian landmass from 1991 to 2020. The timespan is divided into early (1991–2000), mid (2001–2010), and recent (2011–2020) periods. Results reveal a notable increase in rainfall during the mid-and recent periods, contributing to cooler surface temperatures compared to the early period. A distinct peak in Q1 (apparent heat source) and Q2 (apparent moisture sink) is observed at middle-levels (700–400&#xa0;hPa) during the mid and recent periods, leading to significant atmospheric heating, enhanced convection, and increased rainfall. Stratiform rainfall also increased recently, with frozen hydrometeors emerging as dominant contributors. Additionally, elevated wind speeds in the southwest quadrant, combined with increased vorticity and stronger vertical velocity from the lower to mid-troposphere, fostered more intense convective systems over the land. It is also indicated that more El Niño, fewer La Niña, and higher negative IOD occurrences may lead to weaker systems during the early period compared to mid and recent.</p>

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Heterogeneity of rainfall and associated convection in monsoon depressions over the Indian land region from long-term datasets

  • 期刊论文

  • 发表日期：

    2026年3月30日

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  • Nikita Goswami,
  • Sandeep Pattnaik

摘要

Monsoon depressions play a critical role in modulating a substantial portion of summer monsoon rainfall across the Indian subcontinent. A multitude of investigations has examined the architecture and dynamics of these systems; however, the heterogeneity of convection and precipitation patterns particularly over terrestrial regions, especially when employing extensive temporal datasets, has garnered comparatively limited focus. Consequently, it is imperative to investigate the variability of precipitation and the convective processes associated with these terrestrial intense rain-producing systems to augment our understanding and mitigate the hazards associated with hydro-meteorological calamities. Our stringent selection criteria, which persist for ≥ 36 h over land and northwestward propagation, ensure a homogeneous sample that enables a detailed, process-level analysis of land-based monsoon deep depression (DD), providing insights not achievable with broader, less selective datasets. This study considers nine homogeneous DD systems, each lasting a minimum of 36 h, over the Indian landmass from 1991 to 2020. The timespan is divided into early (1991–2000), mid (2001–2010), and recent (2011–2020) periods. Results reveal a notable increase in rainfall during the mid-and recent periods, contributing to cooler surface temperatures compared to the early period. A distinct peak in Q1 (apparent heat source) and Q2 (apparent moisture sink) is observed at middle-levels (700–400 hPa) during the mid and recent periods, leading to significant atmospheric heating, enhanced convection, and increased rainfall. Stratiform rainfall also increased recently, with frozen hydrometeors emerging as dominant contributors. Additionally, elevated wind speeds in the southwest quadrant, combined with increased vorticity and stronger vertical velocity from the lower to mid-troposphere, fostered more intense convective systems over the land. It is also indicated that more El Niño, fewer La Niña, and higher negative IOD occurrences may lead to weaker systems during the early period compared to mid and recent.