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A Satellite Observation-based Analysis of Aerosol-cloud-precipitation Interaction during the February 2016 Unseasonal Heatwave Episode over Indian Region

Category: Aerosol Physics and Instrumentation

Volume: 19 | Issue: 7 | Pages: 1508-1525
DOI: 10.4209/aaqr.2018.04.0144
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Sunny Kant1, Jagabandhu Panda 1, M.G. Manoj2

  • 1 Department of Earth and Atmospheric Sciences, National Institute of Technology Rourkela, Odisha-769008, India
  • 2 Cochin University of Science and Technology, Kerala- 682022, India

Highlights

  • ACP interaction during an unseasonal heatwave episode over India is analysed.
  • Meteorological conditions supported moisture transport and cloud formation.
  • Radiative and microphysical effect observed during pre-mature and mature phases.
  • Invigoration effect seen during dissipating phase of the unseasonal heatwave episode.

Abstract

Aerosol-cloud-precipitation (ACP) interaction during the February 2016 unseasonal heatwave episode over India is analyzed and presented. Moderate Resolution Imaging Spectroradiometer (MODIS) datasets from the Aqua satellite are used to examine the relationship between aerosol and cloud parameters, viz., the aerosol optical depth (AOD), Ångström exponent (AE), cloud fraction, ice and liquid cloud effective radius, cloud optical depth, cloud top temperature, and ice and liquid cloud water path. Furthermore, the Tropical Rainfall Measuring Mission (TRMM) dataset is used to analyze the rainfall during the dissipating phase of the heatwave episode. The prevailing meteorological conditions during the pre-mature, mature, and dissipating phases of the episode are identified by analyzing the near-surface temperature, relative humidity, and vertically integrated moisture flux convergence via 0.25°-resolution ERA-Interim datasets. Back-trajectory analysis is conducted to determine the origin of air masses and transported aerosols. Hot and dry westerly winds dominate during the pre-mature and mature phases, and consequently, significant aerosol transport is observed. The AOD reaches a maximum of 1.6 during the three phases, with the AE being in the range of 0.8–1.7, indicating the presence of both fine- and coarse-mode aerosols. Due to microphysical processes, clouds respond fairly strongly to aerosols in the presence of favorable dynamic and thermodynamic atmospheric conditions. The suppression of precipitation during the pre-mature and mature phases is primarily attributable to weak aerosol-cloud interaction. A major rainfall event in the region comprising northern Odisha, eastern Jharkhand, and most parts of West Bengal, which is situated north of the minimum vertically integrated moisture flux zone, occurs during the dissipating phase. This rainfall event results from the unseasonal transport of moisture from the neighboring Bay of Bengal, the presence of appreciable aerosol loading, and the consequent ACP interaction.

Keywords

Aerosol-cloud interaction Heatwave Aerosol optical depth (AOD) Rainfall


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