Seasonal variation of vertical distribution of aerosol single scattering albedo over Indian sub-continent: RAWEX aircraft observations

Babu, S. Suresh; Nair, Vijayakumar S.; Gogoi, Mukunda M.; Moorthy, K. Krishna

doi:10.1016/j.atmosenv.2015.09.041

Cited by 40 publications

(57 citation statements)

References 45 publications

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“…The campaign mode measurements of the vertical distribution of the atmospheric aerosols were carried out in two phases using the instrumented aircraft (Beechcraft B200) of National Remote Sensing Centre (NRSC), Hyderabad [Babu et al, 2016]: (a) November-December 2012 (winter phase) and (b) April-May 2013 (spring phase). Seven base stations were selected to represent distinct regions of India: Central India (Hyderabad and Nagpur), Western India (Jaipur and Jodhpur), Indo-Gangetic Plain (Lucknow and Ranchi/Patna), and Himalayan foothills (Dehradun) ( Figure 1a).…”

Section: Campaign Details and Datamentioning

confidence: 99%

Large‐scale enhancement in aerosol absorption in the lower free troposphere over continental India during spring

Nair

Babu

Gogoi

et al. 2016

Geophysical Research Letters

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Aerosol absorption in the lower troposphere over continental India was assessed using extensive measurements of the vertical distribution of absorption coefficients aboard an instrumented aircraft. Measurements were made from seven base stations during winter (November–December 2012) and spring (April–May 2013), supplemented by the data from the networks of surface observatories. A definite enhancement in aerosol absorption has been observed in the lower free troposphere over the Indo‐Gangetic Plain (IGP) during spring, along with a reduction near the surface. The regional mean aerosol absorption optical depth (AAOD) over IGP, which was derived from aircraft observations (integrated from the ground to 3 km), increased from 0.020 ± 0.009 in winter to 0.048 ± 0.01 in spring. The columnar AAOD depicted weak and distinctly different seasonal variations than that of surface level black carbon mass concentrations. This contrasting difference in the seasonality indicates the presence of elevated layers of absorbing aerosols during spring in association with the long‐range transport and vertical convective lofting of aerosols.

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Section: Campaign Details and Datamentioning

confidence: 99%

Large‐scale enhancement in aerosol absorption in the lower free troposphere over continental India during spring

Nair

Babu

Gogoi

et al. 2016

Geophysical Research Letters

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“…Similar to the accumulation and confinement of aerosols, trace gases (O 3 , NO x , and CO) also shows significantly higher loading in winter compared to other seasons and non-IGP locations (Kar et al, 2010;Nair et al, 2007). Using instrumented aircraft measurements, Babu et al (2016) have shown that these high pollution episodes are confined only within the shallow boundary layer and extremely low concentration of pollutants exist in the free troposphere.…”

Section: 1029/2018jd029758mentioning

confidence: 87%

Modeling of the Effects of Wintertime Aerosols on Boundary Layer Properties Over the Indo Gangetic Plain

et al. 2019

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Wintertime fog and severe aerosol loading in the boundary layer over South Asia, especially Indo Gangetic Plain (IGP), causes disruptions in the day‐to‐day life of millions of people living in the region, and these heavy pollution episodes result in relentless effects on human health. Weather Research Forecasting model coupled with aerosol chemistry is used to investigate the radiative effects and feedbacks of aerosols on the evolution and structure of the planetary boundary layer over the region. In general, aerosols lead to cooling at the surface, which decreases the nonradiative fluxes (latent and sensible heat fluxes), weakens the turbulent diffusion, and inhibits/delays the growth of convective boundary layer. The impact was maximum over IGP where aerosol‐induced solar dimming (60–80 W/m2) led to a cooling of −0.6 to −2 ° C at the surface, which decreases the noontime boundary layer height by ∼200 m. This effect overwhelms the diabatic heating due to absorbing aerosols in the atmosphere. The significant decrease in sensible (∼11–23 W/m2) and latent heat flux (5–14 W/m2) was observed over IGP and western India. Aerosol boundary layer interaction increases the aerosol loading near the surface (PM2.5) by 3 to 30 μg/m3, which further deteriorate the air quality and visibility over the region. The aerosol forcing increases the relative humidity in the lower boundary layer and amplifies the aerosol forcing. The fog events over the Indian regions identified using INSAT‐3D observations coincide with the regions where aerosol‐boundary layer interactions are very significant. The aerosol‐boundary layer interaction has significance in forecasting fog events and planning mitigation strategies for improving the air quality over the region.

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“…These heterogeneities are primarily because of wide di- 25 versity in geography, anthropogenic activities and meteorological features at meso-scale and synoptic scale. As demonstrated by the past studies Shine, 1995, 1997;Heintzenberg and Helas, 1997;Russell et al, 2002;Takemura et al, 2002;Loeb and Su, 2010;Babu et al, 2016), a small change in the SSA can even alter the sign of aerosol radiative forcing (at top of atmosphere) from positive (warming) to negative (cooling), especially over highly reflecting surfaces. The large spatial heterogeneity in the surface reflectance of the land-mass over this region, and its seasonality makes the aerosol radiative forc-certainties by systematically combining multiple datasets (which individually may have higher uncertainties) (Kalnay, 2003;Lewis et al, 2006).…”

Section: Introductionmentioning

confidence: 91%

“…The merged, gridded datasets of AOD and AAOD over the domain enable estimation of SSA, the critically important aerosol parameter for radiative forcing estimation. The importance of the accurate estimation of SSA for climate impact assessment of aerosols has been underlined by numerous studies in the past Shine, 1995, 1997;Heintzenberg and Helas, 1997;Russell et al, 2002;Takemura et al, 2002;Loeb and Su, 2010;Babu et al, 2016). Takemura et al (2002) have shown 15 that the small changes in SSA can even alter the sign of aerosol radiative forcing (ARF) at TOA, while (Loeb and Su, 2010) have demonstrated that uncertainties in SSA could even be the largest contributor to the uncertainties in total direct ARF in clear as well as all sky conditions.…”

Section: Ssa Estimationmentioning

confidence: 99%

Assessment of Regional Aerosol Radiative Effects under SWAAMI Campaign – Part 1: Quality-enhanced Estimation of Columnar Aerosol Extinction and Absorption Over the Indian Subcontinent

Pathak¹,

Satheesh²,

Nanjundiah³

et al. 2019

Preprint

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Abstract. Improving the accuracy of regional aerosol climate impact assessment calls for an improvement in the accuracy of regional aerosol radiative effects (ARE) estimation. One of the most important means of achieving this is to use spatially homogeneous and temporally continuous datasets of critical aerosol properties, such as spectral aerosol optical depth (AOD) and single scattering albedo (SSA), which are the most important parameters for estimating aerosol radiative effects. However, observations do not provide the above; the space-borne observations though provide wide spatial coverage, are temporally snapshots and suffer from possible sensor degradation over extended periods. On the other hand, the ground-based measurements provide more accurate and temporally continuous data, but are spatially near-point observations. Realizing the need for spatially homogeneous and temporally continuous datasets on one hand and the near-non-existence of such data over the south Asian region (which is one of the regions where aerosols show large heterogeneity in most of their properties), construction of accurate gridded aerosol products by synthesizing the long-term space-borne and ground-based data, has been taken up as an important objective of the South West Asian Aerosol Monsoon Interactions (SWAAMI), a joint Indo-UK field campaign, aiming at characterizing aerosol-monsoon links and their variabilities over the Indian region. In the Part-1 of this two-part paper, we present spatially homogeneous gridded datasets of AOD and absorption AOD (AAOD), generated for the first time over this region. These data products are developed by merging the highly accurate aerosol measurements from the dense networks of 44 (for AOD) and 34 (for AAOD) ground-based observatories of Aerosol Radiative Forcing NETwork (ARFINET) and AErosol RObotic NETwork (AERONET) spread across the Indian region, with satellite-retrieved AOD and AAOD, following statistical assimilation schemes. The satellite data used for AOD assimilation includes AODs retrieved from MODerate Imaging Spectroradiometer (MODIS) and Multiangle Imaging SpectroRadiometer (MISR) over the same domain. For AAOD, the ground-based Black Carbon (BC) mass concentration measurements from the network of 34 ARFINET observatories and satellite-based (Kalpana-1, INSAT-3A) infrared (IR) radiance measurements, are blended with gridded AAODs (500&#8201;nm, monthly mean) derived from Ozone Monitoring Instrument (OMI)-retrieved AAODs (at 354&#8201;nm and 388&#8201;nm). The details of the assimilation methods and the gridded datasets generated are presented in this paper. The merged, gridded AOD and AAOD products thus generated, are validated against the data from independent ground-based observatories, which were not used for the assimilation process, but are representative of different subregions of the complex domain. This validation exercise revealed that the independent ground-based measurements are better confirmed by merged datasets than the respective satellite products. As ensured by assimilation techniques employed, the uncertainties in merged AODs and AAODs are significantly less than those in corresponding satellite products. These merged products also exhibit all important, large-scale spatial and temporal features which are already reported for this region. Nonetheless, the merged AODs and AAODs are significantly different in magnitude, from the respective satellite products. On the background of above mentioned quality enhancements demonstrated by merged products, we have employed them for deriving the columnar SSA and analysed its spatio-temporal characteristics. The columnar SSA thus derived has demonstrated distinct seasonal variation, over various representative subregions of the study domain. The uncertainties in the derived SSA are observed to be substantially less than those in OMI SSA. On the backdrop of these benefits, the merged datasets are employed for the estimation of regional aerosol radiative effects (direct), the results of which would be presented in a companion paper; Part-2 of this two-part paper.

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Seasonal variation of vertical distribution of aerosol single scattering albedo over Indian sub-continent: RAWEX aircraft observations

Cited by 40 publications

References 45 publications

Large‐scale enhancement in aerosol absorption in the lower free troposphere over continental India during spring

Large‐scale enhancement in aerosol absorption in the lower free troposphere over continental India during spring

Modeling of the Effects of Wintertime Aerosols on Boundary Layer Properties Over the Indo Gangetic Plain

Assessment of Regional Aerosol Radiative Effects under SWAAMI Campaign – Part 1: Quality-enhanced Estimation of Columnar Aerosol Extinction and Absorption Over the Indian Subcontinent

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