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

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

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 (

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

2020 ◽  
Vol 20 (5) ◽  
pp. 3135-3149 ◽  
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.

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

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

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

2016 ◽  
Vol 29 (6) ◽  
pp. 2259-2273 ◽  
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.

scholarly journals Mixing state of refractory black carbon aerosol in the South Asian outflow over the northern Indian Ocean during winter

2021 ◽  
Vol 21 (11) ◽  
pp. 9173-9199
Author(s):  
Sobhan Kumar Kompalli ◽  
Surendran Nair Suresh Babu ◽  
Krishnaswamy Krishna Moorthy ◽  
Sreedharan Krishnakumari Satheesh ◽  
Mukunda Madhab Gogoi ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Black Carbon ◽  
South Asian ◽  
Equatorial Indian Ocean ◽  
Mixing State ◽  
The South ◽  
Air Masses ◽  
Continental Outflow ◽  
Mass Concentrations

Abstract. Regional climatic implications of aerosol black carbon (BC), which has a wide variety of anthropogenic sources in large abundance, are well recognized over South Asia. Significant uncertainties remain in its quantification due to a lack of sufficient information on the microphysical properties (its concentration, size, and mixing state with other aerosol components) that determine the absorption potential of BC. In particular, the information on the mixing state of BC is extremely sparse over this region. In this study, the first observations of the size distribution and mixing state of individual refractory black carbon (rBC) particles in the South Asian outflow to the south-eastern Arabian Sea and the northern and equatorial Indian Ocean regions are presented based on measurements using a single particle soot photometer (SP2) aboard the Integrated Campaign for Aerosols, gases, and Radiation Budget (ICARB-2018) ship during winter 2018 (16 January to 13 February). The results revealed significant spatial heterogeneity of BC characteristics. The highest rBC mass concentrations (∼938±293 ng m−3) with the highest relative coating thickness (RCT; the ratio of BC core to its coating diameters) of ∼2.16±0.19 are found over the south-east Arabian Sea (SEAS) region, which is in the proximity of the continental outflow. As we move to farther oceanic regions, though the mass concentrations decreased by nearly half (∼546±80 ng m−3), BC still remained thickly coated (RCT∼2.05±0.07). The air over the remote equatorial Indian Ocean, which received considerable marine air masses compared to the other regions, showed the lowest rBC mass concentrations (∼206±114 ng m−3) with a moderately thick coating (RCT∼1.73±0.16). Even over oceanic regions far from the landmass, regions that received the outflow from the more industrialized east coast/the Bay of Bengal had a thicker coating (∼104 nm) compared to regions that received outflow from the west coast and/or peninsular India (∼86 nm). Although different regions of the ocean depicted contrasting concentrations and mixing state parameters due to the varied extent and nature of the continental outflow as well as the atmospheric lifetime of air masses, the modal parameters of rBC mass–size distributions (mean mass median diameters ∼ 0.19–0.20 µm) were similar over all regions. The mean fraction of BC-containing particles (FBC) varied in the range of 0.08–0.12 (suggesting significant amounts of non-BC particles), whereas the bulk mixing ratio of coating mass to rBC mass was highest (8.31±2.40) over the outflow regions compared to the remote ocean (4.24±1.45), highlighting the role of outflow in providing condensable material for coatings on rBC. These parameters, along with the information on the size-resolved mixing state of BC cores, throw light on the role of sources and secondary processing of their complex mixtures for coatings on BC under highly polluted conditions. Examination of the non-refractory sub-micrometre aerosol chemical composition obtained using the aerosol chemical speciation monitor (ACSM) suggested that the overall aerosol system was sulfate-dominated over the far-oceanic regions. In contrast, organics were equally prominent adjacent to the coastal landmass. An association between the BC mixing state and aerosol chemical composition suggested that sulfate was the probable dominant coating material on rBC cores.

scholarly journals Secular and orbital-scale variability of equatorial Indian Ocean summer monsoon winds during the late Miocene

2021 ◽  
Author(s):  
Clara T. Bolton ◽  
Emmeline Gray ◽  
Wolfgang Kuhnt ◽  
Ann E. Holbourn ◽  
Julia Lübbers ◽  
...  
Keyword(s):  
Indian Ocean ◽  
South Asian ◽  
Summer Monsoon ◽  
Late Miocene ◽  
Asian Monsoon ◽  
Equatorial Indian Ocean ◽  
South Asian Monsoon ◽  
The South ◽  
Near Surface ◽  
Monsoon Winds

Abstract. In the modern northern Indian Ocean, biological productivity is intimately linked to near-surface oceanographic dynamics forced by the South Asian, or Indian, monsoon. In the late Pleistocene, this strong seasonal signal is transferred to the sedimentary record as strong variance in the precession band (19–23 kyr) because precession dominates low-latitude insolation variations and drives seasonal contrast in oceanographic conditions. In addition, internal climate system feedbacks (e.g. ice-sheet albedo, carbon cycle, topography) play a key role in monsoon variability. Little is known about orbital-scale variability of the monsoon in the pre-Pleistocene, when atmospheric CO2 levels and global temperatures were higher. In addition, many questions remain open regarding the timing of the initiation and intensification of the South Asian monsoon during the Miocene, an interval of significant global climate change that culminated in bipolar glaciation. Here, we present new high-resolution (< 1 kyr) records of export productivity and sediment accumulation from International Ocean Discovery Program Site U1443 in the southernmost Bay of Bengal spanning the late Miocene and earliest Pliocene (9 to 5 million years ago). Underpinned by a new orbitally-tuned benthic isotope stratigraphy, we use X-Ray Fluorescence-derived biogenic barium variations to discern productivity trends and rhythms. Our data show strong eccentricity-modulated precession-band productivity variations throughout the late Miocene, interpreted to reflect insolation forcing of summer monsoon wind strength in the equatorial Indian Ocean. On long timescales, our data support the interpretation that South Asian monsoon winds were already established by 9 Ma, with no apparent intensification over the late Miocene.

scholarly journals On aerosol hygroscopicity, cloud condensation nuclei (CCN) spectra and critical supersaturation measured at two remote islands of Korea between 2006 and 2009

2011 ◽  
Vol 11 (24) ◽  
pp. 12627-12645 ◽  
Author(s):  
J. H. Kim ◽  
S. S. Yum ◽  
S. Shim ◽  
S.-C. Yoon ◽  
J. G. Hudson ◽  
...  
Keyword(s):  
Korean Peninsula ◽  
Total Concentration ◽  
Cloud Condensation Nuclei ◽  
Geometric Mean ◽  
Aerosol Size Distribution ◽  
Monitoring Site ◽  
Hygroscopic Growth ◽  
Condensation Nuclei ◽  
Critical Supersaturation ◽  
Better Than

Abstract. Aerosol size distribution, total concentration (i.e. condensation nuclei (CN) concentration, NCN), cloud condensation nuclei (CCN) concentration (NCCN), hygroscopicity at ~90% relative humidity (RH) were measured at a background monitoring site at Gosan, Jeju Island, south of the Korean Peninsula in August 2006, April to May 2007 and August to October 2008. Similar measurements took place in August 2009 at another background site (Baengnyeongdo Comprehensive Monitoring Observatory, BCMO) on the island of Baengnyeongdo, off the west coast of the Korean Peninsula. Both islands were found to be influenced by continental sources regardless of season and year. Average values for all of the measured NCCN at 0.2, 0.6 and 1.0% supersaturations (S), NCN, and geometric mean diameter (Dg) from both islands were in the range of 1043–3051 cm−3, 2076–4360 cm−3, 2713–4694 cm−3, 3890–5117 cm−3 and 81–98 nm, respectively. Although the differences in Dg and NCN were small between Gosan and BCMO, NCCN at various S was much higher at the latter, which is closer to China. Most of the aerosols were internally mixed and no notable differences in hygroscopicity were found between the days of strong pollution influence and the non-pollution days for both islands. During the 2008 and 2009 campaigns, critical supersaturation for CCN nucleation (Sc) for selected particle sizes was measured. Particles of 100 nm diameters had mean Sc of 0.19 ± 0.02% during 2008 and those of 81 and 110 nm diameters had mean Sc of 0.26 ± 0.07% and 0.17 ± 0.04%, respectively, during 2009. The values of the hygroscopicity parameter (κ), estimated from measured Sc, were mostly higher than the κ values obtained from the measured hygroscopic growth at ~90% RH. For the 2008 campaign, NCCN at 0.2, 0.6 and 1.0% S were predicted based on measured dry particle size distributions and various ways of representing particle hygroscopicity. The best closure was obtained when temporally varying and size-resolved hygroscopicity information from the HTDMA was used, for which the average relative deviations from the measured values were 28 ± 20% for 0.2% S (mostly under-prediction), 25 ± 52% for 0.6% (balanced between over- and under-prediction) and 19 ± 15% for 1.0% S (balanced). Prescribing a constant hygroscopicity parameter suggested in the literature (κ = 0.3) for all sizes and times resulted in average relative deviations of 28–41% where over-prediction was dominant. When constant hygroscopicity was assumed, the relative deviation tended to increase with decreasing NCCN, which was accompanied by an increase of the sub-100 nm fraction. These results suggest that hygroscopicity information for particles of diameters smaller than 100 nm is crucial for more accurate predictions of NCCN. For confirmation when κ = 0.17, the average κ for sub-100 nm particles in this study, was applied for sub-100 nm and κ = 0.3 for all other sizes, the CCN closure became significantly better than that with κ = 0.3 for all sizes.

scholarly journals Systematic Errors in South Asian Monsoon Simulation: Importance of Equatorial Indian Ocean Processes

2017 ◽  
Vol 30 (20) ◽  
pp. 8159-8178 ◽  
Author(s):  
H. Annamalai ◽  
Bunmei Taguchi ◽  
Julian P. McCreary ◽  
Motoki Nagura ◽  
Toru Miyama
Keyword(s):  
Indian Ocean ◽  
South Asia ◽  
South Asian ◽  
Coupled Model ◽  
Equatorial Indian Ocean ◽  
Coupled Processes ◽  
Cmip5 Models ◽  
Model Errors ◽  
Bjerknes Feedback ◽  
Sst Bias

Abstract Forecasting monsoon rainfall using dynamical climate models has met with little success, partly due to models’ inability to represent the monsoon climatological state accurately. In this article the nature and dynamical causes of their biases are investigated. The approach is to analyze errors in multimodel-mean climatological fields determined from CMIP5, and to carry out sensitivity experiments using a coupled model [the Coupled Model for the Earth Simulator (CFES)] that does represent the monsoon realistically. Precipitation errors in the CMIP5 models persist throughout the annual cycle, with positive (negative) errors occurring over the near-equatorial western Indian Ocean (South Asia). Model errors indicate that an easterly wind stress bias Δτ along the equator begins during April–May and peaks during November; the severity of the Δτ is that the Wyrtki jets, eastward-flowing equatorial currents during the intermonsoon seasons (April–May and October–November), are almost eliminated. An erroneous east–west SST gradient (warm west and cold east) develops in June. The structure of the model errors indicates that they arise from Bjerknes feedback in the equatorial Indian Ocean (EIO). Vertically integrated moisture and moist static energy budgets confirm that warm SST bias in the western EIO anchors moist processes that cause the positive precipitation bias there. In CFES sensitivity experiments in which Δτ or warm SST bias over the western EIO is artificially introduced, errors in the EIO are similar to those in the CMIP5 models; moreover, precipitation over South Asia is reduced. An overall implication of these results is that South Asian rainfall errors in CMIP5 models are linked to errors of coupled processes in the western EIO, and in coupled models correct representation of EIO coupled processes (Bjerknes feedback) is a necessary condition for realistic monsoon simulation.

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

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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