On the build-up of dust aerosols and possible indirect effect during Indian summer monsoon break spells using recent satellite observations of aerosols and cloud properties

Abstract. Monsoonal rainfall is the primary source of surface water in India. Using 12 years of in-situ and satellite observations, we examined association of aerosol loading with cloud fraction, cloud top pressure, cloud top temperature, and daily surface rainfall over Indian summer monsoon region (ISMR). The analyses showed positive correlations between aerosol loading and cloud properties as well as rainfall. A decrease in outgoing longwave radiation and increase in reflected shortwave radiation at the top of the atmosphere with an increase in aerosol loading further supported a seminal role of aerosols on cloud systems. Significant perturbation in liquid- and ice-phase microphysics was also evident over ISMR. For the polluted cases, delay in the onset of collision-coalescence processes and 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 bigger sized ice-phase hydrometeors and, therefore, implies that the delayed rain processes eventually lead to more surface rainfall. Numerical simulation of a typical rainfall event case over ISMR using spectral bin microphysical scheme coupled with Weather Research Forecasting (WRF-SBM) model was also performed. Simulated microphysics also illustrated the initial suppression of warm rain coupled with 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 and thereby increasing surface rainfall over the ISMR. While the meteorological variability influence the strength of the observed positive associations, our results suggest that the persistent aerosol-associated deepening of cloud systems and 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 ISMR.

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Investigation of the aerosol–cloud–rainfall association over the Indian summer monsoon region

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-5185-2017 ◽

2017 ◽

Vol 17 (8) ◽

pp. 5185-5204 ◽

Cited By ~ 26

Author(s):

Chandan Sarangi ◽

Sachchida Nand Tripathi ◽

Vijay P. Kanawade ◽

Ilan Koren ◽

D. Sivanand Pai

Keyword(s):

Summer Monsoon ◽

Indian Summer Monsoon ◽

Satellite Observations ◽

Monsoon Region ◽

Cloud Systems ◽

Aerosol Cloud ◽

Aerosol Loading ◽

Surface Rainfall ◽

Summer Monsoon Region ◽

Ice Phase

Abstract. 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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Evaluation of cloud properties in the NCEP CFSv2 model and its linkage with Indian summer monsoon

Theoretical and Applied Climatology ◽

10.1007/s00704-015-1404-3 ◽

2015 ◽

Vol 124 (1-2) ◽

pp. 31-41 ◽

Cited By ~ 11

Author(s):

Anupam Hazra ◽

Hemantkumar S. Chaudhari ◽

Ashish Dhakate

Keyword(s):

Summer Monsoon ◽

Indian Summer Monsoon ◽

Cloud Properties

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Consistent response of Indian summer monsoon to Middle East dust in observations and simulations

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-15571-2015 ◽

2015 ◽

Vol 15 (11) ◽

pp. 15571-15619 ◽

Cited By ~ 4

Author(s):

Q. Jin ◽

J. Wei ◽

Z.-L. Yang ◽

B. Pu ◽

J. Huang

Keyword(s):

Boundary Layer ◽

Middle East ◽

Summer Monsoon ◽

Indian Summer Monsoon ◽

Arabian Sea ◽

Dust Emission ◽

Shortwave Radiation ◽

Dust Aerosols ◽

Northern India ◽

Southwest India

Abstract. The response of the Indian summer monsoon (ISM) circulation and precipitation to Middle East dust aerosols on sub-seasonal timescales is studied using observations and the Weather Research and Forecasting model with chemistry (WRF-Chem). Satellite data shows that the ISM rainfall in coastal southwest India, central and northern India, and Pakistan are closely associated with Middle East dust aerosols. The physical mechanism behind this dust–ISM rainfall connection is examined through ensemble simulations with and without dust emission. Each ensemble includes 16 members with various physical and chemical schemes to consider the model uncertainties in parameterizing shortwave radiation, the planetary boundary layer, and aerosol chemical mixing rules. Experiments show that dust aerosols increase rainfall by about 0.44 mm day−1 (~ 10%) in coastal southwest India, central and northern India, and northern Pakistan, a pattern consistent with the observed relationship. The ensemble mean rainfall response over India shows much stronger spatial correlation with the observed rainfall response than any of the ensemble members. The largest modeling uncertainties are from the boundary layer schemes, followed by shortwave radiation schemes. In WRF-Chem, the dust AOD over the Middle East shows the strongest correlation with the ISM rainfall response when dust AOD leads rainfall response by about 11 days. Further analyses show that the increased ISM rainfall is related to the enhanced southwesterly flow and moisture transport from the Arabian Sea to the Indian subcontinent, which are associated with the development of an anomalous low pressure system over the Arabian Sea, the southern Arabian Peninsula, and the Iranian Plateau due to dust-induced heating in the lower troposphere (800–500 hPa). This study demonstrates a thermodynamic mechanism that links remote desert dust emission in the Middle East to the ISM circulation and precipitation variability on sub-seasonal timescales, which may have implications for ISM rainfall forecasts.

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