Investigation of the aerosol–cloud–rainfall association over the Indian summer monsoon region
Monsoonal rainfall is the primary source of surface water in India. Using 12 years of in situ and satellite observations, we examined the association of aerosol loading with cloud fraction, cloud top pressure, cloud top temperature, and daily surface rainfall over the Indian summer monsoon region (I...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/17/5185/2017/acp-17-5185-2017.pdf |
| Summary: | Monsoonal rainfall is the
primary source of surface water in India. Using 12 years of in situ and
satellite observations, we examined the association of aerosol loading with
cloud fraction, cloud top pressure, cloud top temperature, and daily surface
rainfall over the Indian summer monsoon region (ISMR). Our results showed
positive correlations between aerosol loading and cloud properties as well as
rainfall. A decrease in outgoing longwave radiation and an increase in
reflected shortwave radiation at the top of the atmosphere with an increase
in aerosol loading further indicates a possible seminal role of aerosols in
the deepening of cloud systems. Significant perturbation in liquid- and
ice-phase microphysics was also evident over the ISMR. For the polluted
cases, delay in the onset of collision–coalescence processes and an
enhancement in the condensation efficiency allows for more condensate mass to
be lifted up to the mixed colder phases. This results in the higher mass
concentration of larger-sized ice-phase hydrometeors and, therefore, implies
that the delayed rain processes eventually lead to more surface rainfall. A
numerical simulation of a typical rainfall event case over the ISMR using a
spectral bin microphysical scheme coupled with the Weather Research
Forecasting (WRF-SBM) model was also performed. Simulated microphysics also
illustrated that the initial suppression of warm rain coupled with an
increase in updraft velocity under high aerosol loading leads to enhanced
super-cooled liquid droplets above freezing level and ice-phase hydrometeors,
resulting in increased accumulated surface rainfall. Thus, both observational
and numerical analysis suggest that high aerosol loading may induce cloud
invigoration, thereby increasing surface rainfall over the ISMR. While the
meteorological variability influences the strength of the observed positive
association, our results suggest that the persistent aerosol-associated
deepening of cloud systems and an intensification of surface rain amounts was
applicable to all the meteorological sub-regimes over the ISMR. Hence, we
believe that these results provide a step forward in our ability to address
aerosol–cloud–rainfall associations based on satellite observations over
the ISMR. |
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| ISSN: | 1680-7316 1680-7324 |