Abstract
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), Angstrom 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.
Highlights
Extreme hot weather is frequent in summer over India
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
The 1000 hPa mean temperature over the study area at different phases of the unseasonal heatwave scenario superposed with wind field is depicted in Figs. 1(a)–(c), and Fig. 1(d) illustrates the 30-year (1985–2015) climatological mean temperature and wind derived from ERA-Interim data
Summary
Extreme hot weather is frequent in summer over India. The prevailing warm winds ( known as “loo”) during summer typically bring in heatwave conditions over India during March–June. Other areas in eastern parts of India, including West Bengal, Jharkhand, Bihar, and Odisha, were influenced by the 2015 pre-monsoon heatwave condition (Bhadram et al, 2005). It may be noted that the heatwave condition would certainly create an unstable environment and may induce transport of air masses from neighboring regions, which may contain aerosols as well as moisture. It is not understood clearly how ACP interaction takes place over India during an unseasonal heatwave episode. 19–30 May 1984 26–31 May 1988 07–13 Jun 1993 21–28 May 1998 16–24 Mar 2004 18–27 Mar 2010 18–24 May 2013
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