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<p>This study investigates the long-term aerosol optical properties observed at the High-Altitude Cloud Physics Laboratory (HACPL), Mahabaleshwar, a high-altitude station located in the Western Ghats, India, using ground-based measurements from a CIMEL Sun–sky radiometer for a five-year period (2015–2019). The analysis focuses on the temporal variability and seasonal characteristics of aerosols at this unique site, which plays a critical role in cloud–aerosol interactions, regional climate processes, and satellite data validation. Seasonal classification is defined as pre-monsoon (March–May), monsoon (June–September), post-monsoon (October–November), and winter (December–February). Aerosol optical depth (AOD), Angstrom exponent (α), single scattering albedo (SSA), and asymmetry factor (g) are analyzed to characterize fine- and coarse-mode aerosol contributions and their seasonal behavior. The AOD at 440&#xa0;nm (AOD₄₄₀) ranges from 0.02 to 0.96, with a five-year mean value of 0.36 and most daily mean values lying between 0.23 and 0.38. The Angstrom exponent varies from 0.07 to 1.65, indicating a dominance of fine-mode aerosols during the post-monsoon and winter seasons, while enhanced coarse-mode particle concentrations are observed during the pre-monsoon period. Cluster trajectory analysis reveals the predominance of continental air masses during post-monsoon and winter, contributing mainly to fine-mode aerosols, whereas air masses originating from the Arabian Sea and Gulf regions dominate during the pre-monsoon season, transporting dust and sea-salt aerosols associated with coarse-mode particles. Spectral analysis shows that SSA decreases with increasing wavelength during post-monsoon and winter, while it increases gradually with wavelength in the pre-monsoon season. The asymmetry factor (g) exhibits a clear wavelength dependence, with higher values of 0.72 (± 0.02) at 440&#xa0;nm and lower values of 0.67 (± 0.04) at 1020&#xa0;nm. Furthermore, a comparison between ground-based AOD observations and MODIS-Terra satellite data over the study region demonstrates strong agreement, with a coefficient of determination (R²) ≥ 0.71 and a statistically significant Pearson correlation (<i>p</i> &lt; 0.0001).</p>

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Long-term Observations of Aerosol Optical Properties Over a high-altitude Station in the Western Ghats, India

  • 期刊论文

  • 发表日期：

    2026年2月16日

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  • Rohit D. Patil,
  • Subrata Mukherjee,
  • P. P. Leena,
  • Sachin S. Patil,
  • V. Anilkumar,
  • S. M. Sonbawne,
  • S. K. Saha,
  • B. Padmakumari,
  • G. Pandithurai

摘要

This study investigates the long-term aerosol optical properties observed at the High-Altitude Cloud Physics Laboratory (HACPL), Mahabaleshwar, a high-altitude station located in the Western Ghats, India, using ground-based measurements from a CIMEL Sun–sky radiometer for a five-year period (2015–2019). The analysis focuses on the temporal variability and seasonal characteristics of aerosols at this unique site, which plays a critical role in cloud–aerosol interactions, regional climate processes, and satellite data validation. Seasonal classification is defined as pre-monsoon (March–May), monsoon (June–September), post-monsoon (October–November), and winter (December–February). Aerosol optical depth (AOD), Angstrom exponent (α), single scattering albedo (SSA), and asymmetry factor (g) are analyzed to characterize fine- and coarse-mode aerosol contributions and their seasonal behavior. The AOD at 440 nm (AOD₄₄₀) ranges from 0.02 to 0.96, with a five-year mean value of 0.36 and most daily mean values lying between 0.23 and 0.38. The Angstrom exponent varies from 0.07 to 1.65, indicating a dominance of fine-mode aerosols during the post-monsoon and winter seasons, while enhanced coarse-mode particle concentrations are observed during the pre-monsoon period. Cluster trajectory analysis reveals the predominance of continental air masses during post-monsoon and winter, contributing mainly to fine-mode aerosols, whereas air masses originating from the Arabian Sea and Gulf regions dominate during the pre-monsoon season, transporting dust and sea-salt aerosols associated with coarse-mode particles. Spectral analysis shows that SSA decreases with increasing wavelength during post-monsoon and winter, while it increases gradually with wavelength in the pre-monsoon season. The asymmetry factor (g) exhibits a clear wavelength dependence, with higher values of 0.72 (± 0.02) at 440 nm and lower values of 0.67 (± 0.04) at 1020 nm. Furthermore, a comparison between ground-based AOD observations and MODIS-Terra satellite data over the study region demonstrates strong agreement, with a coefficient of determination (R²) ≥ 0.71 and a statistically significant Pearson correlation (p < 0.0001).