Anthropogenic emissions from South Asia reverses the aerosol indirect effect over the northern Indian Ocean

Abstract Atmospheric aerosols play an important role in the formation of warm clouds by acting as efficient cloud condensation nuclei (CCN) and their interactions are believed to cool the Earth-Atmosphere system (‘first indirect effect or Twomey effect’) in a highly uncertain manner compared to the other forcing agents. Here we demonstrate using long-term (2003–2016) satellite observations (NASA’s A-train satellite constellations) over the northern Indian Ocean, that enhanced aerosol loading (due to anthropogenic emissions) can reverse the first indirect effect significantly. In contrast to Twomey effect, a statistically significant increase in cloud effective radius (CER, µm) is observed with respect to an increase in aerosol loading for clouds having low liquid water path (LWP < 75 g m−2) and drier cloud tops. Probable physical mechanisms for this effect are the intense competition for available water vapour due to higher concentrations of anthropogenic aerosols and entrainment of dry air on cloud tops. For such clouds, cloud water content showed a negative response to cloud droplet number concentrations and the estimated intrinsic radiative effect suggest a warming at the Top of the Atmosphere. Although uncertainties exist in quantifying aerosol-cloud interactions (ACI) using satellite observations, present study indicates the physical existence of anti-Twomey effect over the northern Indian Ocean during south Asian outflow.

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Exploring the First Aerosol Indirect Effect over the Maritime Continent Using a Ten-Year Collocated MODIS, CALIOP, and Model Dataset

10.5194/acp-2018-4 ◽

2018 ◽

Author(s):

Alexa D. Ross ◽

Robert E. Holz ◽

Gregory Quinn ◽

Jeffrey S. Reid ◽

Peng Xian ◽

...

Keyword(s):

Indirect Effect ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Effective Radius ◽

Satellite Observations ◽

Orthogonal Polarization ◽

High Background ◽

Aerosol Indirect Effect ◽

Moderate Resolution Imaging Spectroradiometer ◽

Complex Relationships

Abstract. Satellite observations and model simulations cannot, by themselves, give full insight into the complex relationships between aerosols and clouds. This is especially the case over the greater Southeast Asia, an area that is particularly sensitive to changes in precipitation yet possesses some of the world’s largest observability and predictability challenges. We present a new collocated dataset that combines satellite observations from Aqua's Moderate-resolution Imaging Spectroradiometer (MODIS) and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) with the Navy Aerosol Analysis and Prediction System (NAAPS). The dataset is designed with the capability to investigate aerosol-cloud relationships and provides coincident and vertically resolved cloud and aerosol observations for a ten-year period. Using model reanalysis aerosol fields from the NAAPS and coincident cloud liquid effective radius retrievals from MODIS (removing cirrus contamination using CALIOP), we investigate the first aerosol indirect effect. We find overall that as expected, aerosol loading anti-correlates with cloud effective radius, with maximum sensitivity in cumulous mediocris clouds with heights in the 3–4.5 km level. The highest susceptibility in droplet effective radius to modeled perturbations in particle concentrations were found in the more remote regions of the western Pacific Ocean and Indian Ocean. Conversely, there was much less variability in cloud droplet size near emission sources over both land and water. We hypothesize this is suggestive of a high background aerosol population already saturating the cloud condensation nuclei budget.

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Interactions between the MJO, Aerosols, and Convection over the Central Indian Ocean

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-16-0054.1 ◽

2017 ◽

Vol 74 (2) ◽

pp. 353-374 ◽

Cited By ~ 2

Author(s):

Douglas C. Stolz ◽

Steven A. Rutledge ◽

Weixin Xu ◽

Jeffrey R. Pierce

Keyword(s):

Indian Ocean ◽

Large Scale ◽

Transport Model ◽

Cloud Condensation Nuclei ◽

Vertical Wind Shear ◽

Equatorial Indian Ocean ◽

Satellite Observations ◽

Chemical Transport Model ◽

Initial Development ◽

Convective Clouds

Abstract This study examines covariability of boundary layer cloud condensation nuclei (CCN) concentrations [estimated using the GEOS 3D chemical transport model (GEOS-Chem)], convective clouds, precipitation, and lightning observed over the central equatorial Indian Ocean (CIO). Three distinct Madden–Julian oscillation (MJO) episodes were observed during the recent Dynamics of the MJO (DYNAMO; 2011/12) field campaign. Coherent relationships between CCN, rainfall, and lightning are apparent in time series from DYNAMO and more lightning located north of the equator is noted, compared to south of the equator. More-polluted environments north of the equator contained deep convective clouds that had stronger radar reflectivities (~2–3 dB) in the mixed-phase region (5–10-km altitude) compared to south of the equator. Following discussion of the MJO episodes that occurred during DYNAMO, 22 cycles of the MJO observed during boreal cold seasons in the years 2004–11 are examined with the aid of TRMM satellite observations. Climatological results suggest that horizontal transport of continental aerosols from proximal landmasses by the large-scale circulation after active MJO convection reinforces the meridional gradient of CCN concentrations in the CIO. Satellite observations depicted comparable aggregate cold cloud feature area in both regions in similar thermodynamic environments, leading to the suggestion that higher CCN concentrations north of the equator act to invigorate convection. Direct comparisons of convective intensity metrics to CCN support the aerosol hypothesis; however, in line with previous studies, it is acknowledged that conditional instability, vertical wind shear, and environmental moisture can modulate the initial development of deep convection over the CIO during select phases of the MJO.

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Interactive comment on “Cloud Condensation Nuclei properties of South Asian outflow over the northern Indian Ocean during winter” by Vijayakumar S. Nair et al.

10.5194/acp-2019-828-ac1 ◽

2020 ◽

Author(s):

Vijayakumar S Nair

Keyword(s):

Indian Ocean ◽

South Asian ◽

Cloud Condensation Nuclei ◽

Condensation Nuclei ◽

Northern Indian Ocean

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The Role of the Aerosol Indirect Effect in the Northern Indian Ocean Warming Simulated by CMIP5 Models

Atmospheric and Oceanic Science Letters ◽

10.1080/16742834.2014.11447199 ◽

2014 ◽

Vol 7 (5) ◽

pp. 411-416 ◽

Cited By ~ 3

Author(s):

Hu Ning ◽

Li Li-Juan ◽

Wang Bin

Keyword(s):

Indian Ocean ◽

Indirect Effect ◽

Ocean Warming ◽

Cmip5 Models ◽

Northern Indian Ocean ◽

Aerosol Indirect Effect ◽

Indian Ocean Warming

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Cloud Condensation Nuclei properties of South Asian outflow over the northern Indian Ocean during winter

10.5194/acp-2019-828 ◽

2019 ◽

Author(s):

Vijayakumar S. Nair ◽

Jayachandran Venugopalan Nair ◽

Sobhan Kumar Kompalli ◽

Mukunda M. Gogoi ◽

S. Suresh Babu

Keyword(s):

Indian Ocean ◽

South Asian ◽

Cloud Condensation Nuclei ◽

Geometric Mean ◽

Equatorial Indian Ocean ◽

Radiation Budget ◽

Condensation Nuclei ◽

The South ◽

Northern Indian Ocean ◽

Activation Efficiency

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Exploring the first aerosol indirect effect over Southeast Asia using a 10-year collocated MODIS, CALIOP, and model dataset

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-12747-2018 ◽

2018 ◽

Vol 18 (17) ◽

pp. 12747-12764 ◽

Cited By ~ 4

Author(s):

Alexa D. Ross ◽

Robert E. Holz ◽

Gregory Quinn ◽

Jeffrey S. Reid ◽

Peng Xian ◽

...

Keyword(s):

Southeast Asia ◽

Indirect Effect ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Effective Radius ◽

Satellite Observations ◽

Droplet Growth ◽

Orthogonal Polarization ◽

Aerosol Indirect Effect ◽

Moderate Resolution Imaging Spectroradiometer

Abstract. Satellite observations and model simulations cannot, by themselves, give full insight into the complex relationships between aerosols and clouds. This is especially true over Southeast Asia, an area that is particularly sensitive to changes in precipitation yet poses some of the world's largest observability and predictability challenges. We present a new collocated dataset, the Curtain Cloud-Aerosol Regional A-Train dataset, or CCARA. CCARA includes collocated satellite observations from Aqua's Moderate-resolution Imaging Spectroradiometer (MODIS) and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) with the Navy Aerosol Analysis and Prediction System (NAAPS). The CCARA dataset is designed with the capability to investigate aerosol–cloud relationships in regions with limited aerosol retrievals due to high cloud amounts by leveraging the NAAPS model reanalysis of aerosol concentration in these regions. This combined aerosol and cloud dataset provides coincident and vertically resolved cloud and aerosol observations for 2006–2016. Using the model reanalysis aerosol fields from the NAAPS and coincident cloud liquid effective radius retrievals from MODIS (cirrus contamination using CALIOP), we investigate the first aerosol indirect effect in Southeast Asia. We find that, as expected, aerosol loading anti-correlates with cloud effective radius, with maximum sensitivity in cumulous mediocris clouds with heights in the 3–4.5 km level. The highest susceptibilities in droplet effective radius to modeled perturbations in particle concentrations were found in the more remote and pristine regions of the western Pacific Ocean and Indian Ocean. Conversely, there was much less variability in cloud droplet size near emission sources over both land and water. We hypothesize this is suggestive of a high aerosol background already saturated with cloud condensation nuclei even during the relatively clean periods, in contrast to the remote ocean regions, which have periods where the aerosol concentrations are low enough to allow for larger droplet growth.

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Cloud condensation nuclei properties of South Asian outflow over the northern Indian Ocean during winter

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-3135-2020 ◽

2020 ◽

Vol 20 (5) ◽

pp. 3135-3149 ◽

Cited By ~ 4

Author(s):

Vijayakumar S. Nair ◽

Venugopalan Nair Jayachandran ◽

Sobhan Kumar Kompalli ◽

Mukunda M. Gogoi ◽

S. Suresh Babu

Keyword(s):

Indian Ocean ◽

Size Distribution ◽

South Asian ◽

Cloud Condensation Nuclei ◽

Equatorial Indian Ocean ◽

Number Concentration ◽

Condensation Nuclei ◽

Northern Indian Ocean ◽

Number Size Distribution ◽

Activation Efficiency

Abstract. Extensive measurements of cloud condensation nuclei (CCN) and condensation nuclei (CN) concentrations in the South Asian outflow to the northern Indian Ocean were carried out on board an instrumented research vessel, as part of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) during the winter season (January–February 2018). Measurements include a north–south transect across the South Asian plume over the northern Indian Ocean and an east–west transect over the equatorial Indian Ocean (∼2∘ S), which is far away from the continental sources. South Asian outflow over the northern Indian Ocean is characterized by the high values of CCN number concentration (∼5000 cm−3), low CCN activation efficiency (∼25 %) and a steep increase in CCN concentration with the increase in supersaturation. In contrast, low CCN concentration (∼1000 cm−3) with flat supersaturation spectra was found over the equatorial Indian Ocean. The CCN properties exhibited significant dependence on the geometric mean diameter (GMD) of the aerosol number size distribution, and CCN activation efficiency decreased to low values (<20 %) at the time of new-particle formation events over near-coastal and remote oceanic regions. The analysis of the activation efficiencies for the “similar” aerosol size distributions over the northern Indian Ocean indicated the primary role of aerosol number size distribution on CCN activation efficiency. The dependence of CCN properties and activation efficiency on size-segregated aerosol number concentration, especially during the ultrafine (<100 nm) particle events, is investigated in detail for the first time over the region.

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