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

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 winter season (January–February 2018). Measurements include a north-south transect across the South Asian plume over the northern Indian Ocean and 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 steep increase in CCN concentration with an 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 (

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

Scientific Reports ◽

10.1038/s41598-020-74897-x ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Subin Jose ◽

Vijayakumar S. Nair ◽

S. Suresh Babu

Keyword(s):

Indian Ocean ◽

Indirect Effect ◽

Cloud Condensation Nuclei ◽

Satellite Observations ◽

Anthropogenic Emissions ◽

Anthropogenic Aerosols ◽

Northern Indian Ocean ◽

Aerosol Loading ◽

Cloud Water Content ◽

Cloud Tops

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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Supplementary material to "Mixing state of refractory black carbon aerosol in the South Asian outflow over the northern Indian Ocean during winter"

10.5194/acp-2020-836-supplement ◽

2020 ◽

Author(s):

Sobhan Kumar Kompalli ◽

Surendran Nair Suresh Babu ◽

Krishnaswamy Krishnamoorthy ◽

Sreedharan Krishnakumari Satheesh ◽

Mukunda M. Gogoi ◽

...

Keyword(s):

Indian Ocean ◽

Black Carbon ◽

South Asian ◽

Mixing State ◽

The South ◽

Northern Indian Ocean ◽

Supplementary Material ◽

Black Carbon Aerosol

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The Global Warming–Induced South Asian High Change and Its Uncertainty

Journal of Climate ◽

10.1175/jcli-d-15-0638.1 ◽

2016 ◽

Vol 29 (6) ◽

pp. 2259-2273 ◽

Cited By ~ 11

Author(s):

Xia Qu ◽

Gang Huang

Keyword(s):

Global Warming ◽

Indian Ocean ◽

South Asian ◽

Geopotential Height ◽

General Circulation ◽

South Asian High ◽

Latent Heating ◽

The South ◽

Northern Indian Ocean ◽

Circulation Change

Abstract Based on models from phase 5 of the Coupled Model Intercomparison Project (CMIP5), the present study investigates the South Asian high (SAH) change in response to global warming. Under global warming, the selected 16 coupled general circulation models all feature an elevation of geopotential height at 100 hPa to the south of the SAH climatological position; an easterly response is found over the northern Indian Ocean in all the models, while a westerly response is found over subtropical Asia. The ridges of the SAH shift equatorward in 75% of models. Using the linear baroclinic model, it is found that the combined effects of latent heating and the mean advection of stratification change (MASC) are mainly responsible for those responses. The MASC mainly leads to the aforementioned easterly and westerly responses; the latent heating contributes to the geopotential height response and the easterly response over the northern Indian Ocean. The most important intermodel diversity is found in the 100-hPa circulation change under global warming, accounting for more than half of the total intermodel variance. The intermodel spread of latent heating and the MASC are important factors in driving the 100-hPa circulation diversity. Furthermore, analysis shows that the projected uncertainties in humidity, vertical velocity, and global mean temperature change are the three most important sources of intermodel diversity for the 100-hPa circulation change.

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