Buildup of aerosols over the Indian Region

Moorthy, K. Krishna; Babu, S. Suresh; Manoj, Mohanan R.; Satheesh, S. K.

doi:10.1002/grl.50165

Cited by 180 publications

(66 citation statements)

References 21 publications

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“…Aerosol emissions have been rising in India since the 1950s due to expansion of industry and the rapidly increasing population which uses cooking fires. Remote sensing and ground-based observations applied to aerosol measurements from the mid-1980s have shown an increasing trend in aerosol loading and aerosol optical depth (AOD) (Moorthy et al, 2013;Acharya and Sreekesh, 2013). Maximum concentrations are found pushed up against the foothills of the Himalayas in the northern plains of India during pre-monsoon season (Lau et al, 2006), and remain strong during June and July (Lau et al, 2008).…”

Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 99%

Impacts of 20th century aerosol emissions on the South Asian monsoon in the CMIP5 models

2015

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Abstract. Comparison of single-forcing varieties of 20thcentury historical experiments in a subset of models from the Fifth Coupled Model Intercomparison Project (CMIP5) reveals that South Asian summer monsoon rainfall increases towards the present day in Greenhouse Gas (GHG)-only experiments with respect to pre-industrial levels, while it decreases in anthropogenic aerosol-only experiments. Comparison of these single-forcing experiments with the all-forcings historical experiment suggests aerosol emissions have dominated South Asian monsoon rainfall trends in recent decades, especially during the 1950s to 1970s. The variations in South Asian monsoon rainfall in these experiments follows approximately the time evolution of inter-hemispheric temperature gradient over the same period, suggesting a contribution from the large-scale background state relating to the asymmetric distribution of aerosol emissions about the equator.By examining the 24 available all-forcings historical experiments, we show that models including aerosol indirect effects dominate the negative rainfall trend. Indeed, models including only the direct radiative effect of aerosol show an increase in monsoon rainfall, consistent with the dominance of increasing greenhouse gas emissions and planetary warming on monsoon rainfall in those models. For South Asia, reduced rainfall in the models with indirect effects is related to decreased evaporation at the land surface rather than from anomalies in horizontal moisture flux, suggesting the impact of indirect effects on local aerosol emissions. This is confirmed by examination of aerosol loading and cloud droplet number trends over the South Asia region. Thus, while remote aerosols and their asymmetric distribution about the equator play a role in setting the inter-hemispheric temperature distribution on which the South Asian monsoon, as one of the global monsoons, operates, the addition of indirect aerosol effects acting on very local aerosol emissions also plays a role in declining monsoon rainfall. The disparity between the response of monsoon rainfall to increasing aerosol emissions in models containing direct aerosol effects only and those also containing indirect effects needs to be urgently investigated since the suggested future decline in Asian anthropogenic aerosol emissions inherent to the representative concentration pathways (RCPs) used for future climate projection may turn out to be optimistic.In addition, both groups of models show declining rainfall over China, also relating to local aerosol mechanisms. We hypothesize that aerosol emissions over China are large enough, in the CMIP5 models, to cause declining monsoon rainfall even in the absence of indirect aerosol effects. The same is not true for India.

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Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 99%

Impacts of 20th century aerosol emissions on the South Asian monsoon in the CMIP5 models

2015

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“…The Indian subcontinent has been recognized as a major aerosol hot spot (Ramanathan et al, 2001;Kaufman et al, 2002;Lau et al, 2008), where the aerosol characteristics show large spatio-temporal variations (e.g., Prasad and Singh, 2007;Dey and Di Girolamo, 2010;Ramachandran et al, 2012).The aerosol loading continues to increase over the recent years (Dey and Di Girolamo, 2011;Kaskaoutis et al, 2011;Krishna Moorthy et al, 2013) as opposed to a decreasing global trend (Mishchenko et al, 2007).There is a growing evidence of the potential impacts of aerosols on monsoon circulation through dynamic and microphysical connections (Ramanathan et al, 2005;Gautam et al, 2009;Bollasina et al, 2011;Ganguly et al, 2012;Das et al, 2014) that strongly depends on the aerosol load (typically represented in terms of aerosol optical depth, AOD) and composition.…”

Section: Introductionmentioning

confidence: 99%

Satellite-Based Estimates of Aerosol Washout and Recovery over India during Monsoon

Chowdhury

Dey

Ghosh

et al. 2016

Aerosol Air Qual. Res.

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Large aerosol optical depth (AOD) observed over the Indian subcontinent during the monsoon season in the satellite data challenges the common notion of aerosol washout by monsoon rain. Here, we examined recovery of aerosol field after washout by monsoon rain over various rainfall homogeneous zones of India in view of the duration of rainfall, recovery time and source strength. Mean (± 1 standard deviation) seasonal aerosol optical depth, AOD is highest over the central northeast 1 (0.74 ± 0.22) followed by central northeast 2 (0.60 ± 0.11), northwest (0.61 ± 0.15), west-central (0.54 ± 0.13), northeast (0.29 ± 0.08), peninsular India (0.39 ± 0.07) and hilly region (0.33 ± 0.08) in the monsoon season. Post-washout aerosol recovery in India is not a linear function to the recovery period relative to the two successive satellite overpasses. Fastest recovery is observed in the central northeast region dominated by anthropogenic emission. In general, washout is more for 9-hour spell than 3-hour spell, but not spatially uniform over the various rainfall homogeneous zones. In central northeast region it is observed that updraft plays an important role in post precipitation aerosol build up whereas in dustdominated northwest India, monsoon rainfall (whenever occurs) suppresses dust emission because of the increased soil moisture and therefore inhibits the recovery. The number of grids where washout outweighs recovery during the monsoon season for a 3-hour rainfall increases by 5.6% with an increase in rain rate from < 2 mm day -1 to > 4 mm day -1 , while the corresponding increase for a 9-hour rainfall event is 2.8%. AOD reduces in 'cloudy-sky' condition relative to 'clear-sky' condition because aerosols are scavenged by cloud drops as the clouds grow vertically during the monsoon. Quantitatively, AOD decreases by 16% per 100 hPa increase in cloud base height.

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“…Numerous studies examining the aerosol radiative forcing over India resulted in high spatio-temporal variability also exhibiting significant uncertainties, mainly due to the different sources, land use, aerosol types and properties as well as the influence of dynamic and synoptic meteorology and the mixing (internal and external) processes in the atmosphere (Lawrence and Lelieveld, 2010). With the increase in population, urbanization, industrialization and demands for energy, the aerosol loading over Indian sub-continent is gradually increasing, exhibiting large spatio-temporal variability in its trends (Kaskaoutis et al, 2011;Ramachandran et al, 2012;Moorthy et al, 2013). In order to understand the dynamics and variability of aerosol, systematic measurements of aerosol properties are needed at many locations to support the validation of the satellite algorithms and the inputs in general circulation and chemical transport models.…”

Section: Introductionmentioning

confidence: 99%

Seasonal Variability of Atmospheric Aerosol Parameters over Greater Noida Using Ground Sunphotometer Observations

Sharma

Kaskaoutis

Singh

et al. 2014

Aerosol Air Qual. Res.

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Atmospheric aerosols over northern India are subject of significant temporal and spatial variability and many studies have been carried out to investigate their physico-chemical and optical properties. The present work emphasizes on examining the aerosol optical properties and types over Greater Noida, Delhi region, using ground-based sun photometer data during the period 2010-2012. The analysis reveals a relatively high mean aerosol optical depth at 500 nm (AOD 500 = 0.82 ± 0.39), associated with a moderate Angstrom exponent α 440-870 of 0.95 ± 0.37. Both parameters, exhibit significant daily, monthly and seasonal variability with higher values of AOD 500 during post-monsoon (0.98 ± 0.50) and winter (0.87 ± 0.35) seasons associated with high α values (> 1.1) suggesting significant urban and biomass-burning contribution. On monthly basis, the highest AOD is found during July and November and the lowest one in the transition months of March and September. The aerosol-type discrimination via the relationship AOD vs. α shows a clear dominance of urban/industrial and biomass-burning aerosols during post-monsoon and winter in fractions of 74.5% and 72%, respectively, while aerosols of desert-dust characteristics were most frequent in pre-monsoon (41.7%) and monsoon (21%) seasons. In general, the analysis shows a rather well-mixed aerosol type under very turbid atmosphere, which is associated with the long range transport of pollutants through the westerly winds from the Thar desert and biomass burning in the western parts of India.

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Buildup of aerosols over the Indian Region

Cited by 180 publications

References 21 publications

Impacts of 20th century aerosol emissions on the South Asian monsoon in the CMIP5 models

Impacts of 20th century aerosol emissions on the South Asian monsoon in the CMIP5 models

Satellite-Based Estimates of Aerosol Washout and Recovery over India during Monsoon

Seasonal Variability of Atmospheric Aerosol Parameters over Greater Noida Using Ground Sunphotometer Observations

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