Assessment of regional aerosol radiative effects under the SWAAMI campaign – Part 2: Clear-sky direct shortwave radiative forcing using multi-year assimilated data over the Indian subcontinent

Abstract. Clear-sky, direct shortwave aerosol radiative forcing (ARF) has been estimated over the Indian region, for the first time employing multi-year (2009–2013) gridded, assimilated aerosol products, as an important part of the South West Asian Aerosol Monsoon Interactions (SWAAMI) which is a joint Indo-UK research field campaign focused at understanding the variabilities in atmospheric aerosols and their interactions with the Indian summer monsoon. The aerosol datasets have been constructed following statistical assimilation of concurrent data from a dense network of ground-based observatories and multi-satellite products, as described in Part 1 of this two-part paper. The ARF, thus estimated, is assessed for its superiority or otherwise over other ARF estimates based on satellite-retrieved aerosol products, over the Indian region, by comparing the radiative fluxes (upward) at the top of the atmosphere (TOA) estimated using assimilated and satellite products with spatiotemporally matched radiative flux values provided by CERES (Clouds and Earth's Radiant Energy System) single-scan footprint (SSF) product. This clearly demonstrated improved accuracy of the forcing estimates using the assimilated vis-à-vis satellite-based aerosol datasets at regional, subregional and seasonal scales. The regional distribution of diurnally averaged ARF estimates has revealed (a) significant differences from similar estimates made using currently available satellite data, not only in terms of magnitude but also the sign of TOA forcing; (b) the largest magnitudes of surface cooling and atmospheric warming over the Indo-Gangetic Plain (IGP) and arid regions from north-western India; and (c) negative TOA forcing over most parts of the Indian region, except for three subregions – the IGP, north-western India and eastern parts of peninsular India where the TOA forcing changes to positive during pre-monsoon season. Aerosol-induced atmospheric warming rates, estimated using the assimilated data, demonstrate substantial spatial heterogeneities (∼0.2 to 2.0 K d−1) over the study domain with the IGP demonstrating relatively stronger atmospheric heating rates (∼0.6 to 2.0 K d−1). There exists a strong seasonality as well, with atmospheric warming being highest during pre-monsoon and lowest during winter seasons. It is to be noted that the present ARF estimates demonstrate substantially smaller uncertainties than their satellite counterparts, which is a natural consequence of reduced uncertainties in assimilated vis-à-vis satellite aerosol properties. The results demonstrate the potential application of the assimilated datasets and ARF estimates for improving accuracies of climate impact assessments at regional and subregional scales.

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Assessment of Regional Aerosol Radiative Effects under SWAAMI Campaign – PART 2: Clear-sky Direct Shortwave Radiative Forcing using Multi-year Assimilated Data

10.5194/acp-2020-454 ◽

2020 ◽

Author(s):

Harshavardhana Sunil Pathak ◽

Sreedharan Krishnakumari Satheesh ◽

Krishnaswamy Krishna Moorthy ◽

Ravi Shankar Nanjundiah

Keyword(s):

Radiative Forcing ◽

Regional Distribution ◽

Radiant Energy ◽

Indian Region ◽

Western India ◽

Surface Cooling ◽

Clear Sky ◽

Atmospheric Warming ◽

North Western ◽

Aerosol Radiative

Abstract. Clear-sky, direct shortwave Aerosol Radiative Forcing (ARF) has been estimated over the Indian region, for the first time employing multi-year (2009–2013) gridded, assimilated aerosol products. The aerosol datasets have been constructed following statistical assimilation of concurrent data from a dense network of ground-based observatories, and multi-satellite products, as described in Part-1 of this two-part paper. The ARF, thus estimated, are assessed for their superiority or otherwise over other ARF estimates based on satellite-retrieved aerosol products, over the Indian region, by comparing the radiative fluxes (upward) at Top of Atmosphere (TOA) estimated using assimilated products with spatio-temporally matched radiative flux values provided by CERES (Clouds and Earth's Radiant Energy System) Single Scan Footprint (SSF) product. This clearly demonstrated improved accuracy of the forcing estimates using the assimilated vis-a-vis satellite-based aerosol datasets; at regional, sub-regional and seasonal scales. The regional distribution of diurnally averaged ARF estimates has revealed (a) significant differences from similar estimates made using currently available satellite data, not only in terms of magnitude but also sign of TOA forcing; (b) largest magnitudes of surface cooling and atmospheric warming over IGP and arid regions from north-western India; and (c) negative TOA forcing over most parts of the Indian region, except for three sub-regions – the Indo-Gangetic plains (IGP), north-western India and eastern parts of peninsular India where the TOA forcing changes to positive during pre-monsoon season. Aerosol induced atmospheric warming rates, estimated using the assimilated data, demonstrate substantial spatial heterogeneities (~ 0.2 to 2.0 K day−1) over the study domain with the IGP demonstrating relatively stronger atmospheric heating rates (~ 0.6 to 2.0 K day−1). There exists a strong seasonality as well; with atmospheric warming being highest during pre-monsoon and lowest during winter seasons. It is to be noted that the present ARF estimates demonstrate substantially smaller uncertainties than their satellite counterparts, which is a natural consequence of reduced uncertainties in assimilated vis-a-vis satellite aerosol properties. The results demonstrate the potential application of the assimilated datasets and ARF estimates for improving accuracies of climate impact assessments at regional and sub-regional scales.

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Assessment of aerosols optical properties and radiative forcing over an Urban site in North-Western India

Environmental Technology ◽

10.1080/09593330.2016.1221473 ◽

2016 ◽

Vol 38 (10) ◽

pp. 1232-1244 ◽

Cited By ~ 4

Author(s):

Vikram Mor ◽

Rajesh Dhankhar ◽

S. D. Attri ◽

V. K. Soni ◽

M. Sateesh ◽

...

Keyword(s):

Optical Properties ◽

Radiative Forcing ◽

Urban Site ◽

Western India ◽

North Western

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Aerosol absorption and radiative forcing

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-7171-2007 ◽

2007 ◽

Vol 7 (3) ◽

pp. 7171-7233 ◽

Cited By ~ 7

Author(s):

P. Stier ◽

J. H. Seinfeld ◽

S. Kinne ◽

O. Boucher

Keyword(s):

Optical Depth ◽

Radiative Forcing ◽

Radiative Properties ◽

Refractive Indices ◽

Anthropogenic Aerosol ◽

Clear Sky ◽

Aerosol Absorption ◽

Long Wave ◽

Aerosol Radiative ◽

Cloud Radiative Properties

Abstract. We present a comprehensive examination of aerosol absorption with a focus on evaluating the sensitivity of the global distribution of aerosol absorption to key uncertainties in the process representation. For this purpose we extended the comprehensive aerosol-climate model ECHAM5-HAM by effective medium approximations for the calculation of aerosol effective refractive indices, updated black carbon refractive indices, new cloud radiative properties considering the effect of aerosol inclusions, as well as by modules for the calculation of long-wave aerosol radiative properties and instantaneous aerosol forcing. The evaluation of the simulated aerosol absorption optical depth with the AERONET sun-photometer network shows a good agreement in the large scale global patterns. On a regional basis it becomes evident that the update of the BC refractive indices to Bond and Bergstrom (2006) significantly improves the previous underestimation of the aerosol absorption optical depth. In the global annual-mean, absorption acts to reduce the short-wave anthropogenic aerosol top-of-atmosphere (TOA) radiative forcing clear-sky from –0.79 to –0.53 W m−2 (33%) and all-sky from –0.47 to –0.13 W m−2 (72%). Our results confirm that basic assumptions about the BC refractive index play a key role for aerosol absorption and radiative forcing. The effect of the usage of more accurate effective medium approximations is comparably small. We demonstrate that the diversity in the AeroCom land-surface albedo fields contributes to the uncertainty in the simulated anthropogenic aerosol radiative forcings: the usage of an upper versus lower bound of the AeroCom land albedos introduces a global annual-mean TOA forcing range of 0.19 W m−2 (36%) clear-sky and of 0.12 W m−2 (92%) all-sky. The consideration of black carbon inclusions on cloud radiative properties results in a small global annual-mean all-sky absorption of 0.05 W m−2 and a positive TOA forcing perturbation of 0.02 W m−2. The long-wave aerosol radiative effects are small for anthropogenic aerosols but become of relevance for the larger natural dust and sea-salt aerosols.

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Clear-sky aerosol radiative forcing effects based on multi-site AERONET observations over Europe

Meteorology and Atmospheric Physics ◽

10.1007/s00703-006-0212-9 ◽

2006 ◽

Vol 96 (3-4) ◽

pp. 277-291 ◽

Cited By ~ 6

Author(s):

S. Gonzi ◽

O. Dubovik ◽

D. Baumgartner ◽

E. Putz

Keyword(s):

Radiative Forcing ◽

Aerosol Radiative Forcing ◽

Clear Sky ◽

Aerosol Radiative

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Direct Aerosol Radiative Forcing Uncertainty Based on a Radiative Perturbation Analysis

Journal of Climate ◽

10.1175/2010jcli3543.1 ◽

2010 ◽

Vol 23 (19) ◽

pp. 5288-5293 ◽

Cited By ~ 81

Author(s):

Norman G. Loeb ◽

Wenying Su

Keyword(s):

Radiative Forcing ◽

Single Scattering ◽

Single Scattering Albedo ◽

Aerosol Radiative Forcing ◽

Clear Sky ◽

Radiative Perturbation ◽

Sky Conditions ◽

Global Mean ◽

Aerosol Properties ◽

Aerosol Radiative

Abstract To provide a lower bound for the uncertainty in measurement-based clear- and all-sky direct aerosol radiative forcing (DARF), a radiative perturbation analysis is performed for the ideal case in which the perturbations in global mean aerosol properties are given by published values of systematic uncertainty in Aerosol Robotic Network (AERONET) aerosol measurements. DARF calculations for base-state climatological cloud and aerosol properties over ocean and land are performed, and then repeated after perturbing individual aerosol optical properties (aerosol optical depth, single-scattering albedo, asymmetry parameter, scale height, and anthropogenic fraction) from their base values, keeping all other parameters fixed. The total DARF uncertainty from all aerosol parameters combined is 0.5–1.0 W m−2, a factor of 2–4 greater than the value cited in the Intergovernmental Panel on Climate Change’s (IPCC’s) Fourth Assessment Report. Most of the total DARF uncertainty in this analysis is associated with single-scattering albedo uncertainty. Owing to the greater sensitivity to single-scattering albedo in cloudy columns, DARF uncertainty in all-sky conditions is greater than in clear-sky conditions, even though the global mean clear-sky DARF is more than twice as large as the all-sky DARF.

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MACv2-SP: a parameterization of anthropogenic aerosol optical properties and an associated Twomey effect for use in CMIP6

Geoscientific Model Development ◽

10.5194/gmd-10-433-2017 ◽

2017 ◽

Vol 10 (1) ◽

pp. 433-452 ◽

Cited By ~ 57

Author(s):

Bjorn Stevens ◽

Stephanie Fiedler ◽

Stefan Kinne ◽

Karsten Peters ◽

Sebastian Rast ◽

...

Keyword(s):

Optical Properties ◽

Radiative Forcing ◽

Industrial Emissions ◽

Max Planck ◽

Aerosol Optical Properties ◽

Anthropogenic Aerosol ◽

Aerosol Radiative Forcing ◽

Clear Sky ◽

Aerosol Forcing ◽

Aerosol Radiative

Abstract. A simple plume implementation of the second version (v2) of the Max Planck Institute Aerosol Climatology, MACv2-SP, is described. MACv2-SP provides a prescription of anthropogenic aerosol optical properties and an associated Twomey effect. It was created to provide a harmonized description of post-1850 anthropogenic aerosol radiative forcing for climate modeling studies. MACv2-SP has been designed to be easy to implement, change and use, and thereby enable studies exploring the climatic effects of different patterns of aerosol radiative forcing, including a Twomey effect. MACv2-SP is formulated in terms of nine spatial plumes associated with different major anthropogenic source regions. The shape of the plumes is fit to the Max Planck Institute Aerosol Climatology, version 2, whose present-day (2005) distribution is anchored by surface-based observations. Two types of plumes are considered: one predominantly associated with biomass burning, the other with industrial emissions. These differ in the prescription of their annual cycle and in their optical properties, thereby implicitly accounting for different contributions of absorbing aerosol to the different plumes. A Twomey effect for each plume is prescribed as a change in the host model's background cloud-droplet population density using relationships derived from satellite data. Year-to-year variations in the amplitude of the plumes over the historical period (1850–2016) are derived by scaling the plumes with associated national emission sources of SO2 and NH3. Experiments using MACv2-SP are performed with the Max Planck Institute Earth System Model. The globally and annually averaged instantaneous and effective aerosol radiative forcings are estimated to be −0.6 and −0.5 W m−2, respectively. Forcing from aerosol–cloud interactions (the Twomey effect) offsets the reduction of clear-sky forcing by clouds, so that the net effect of clouds on the aerosol forcing is small; hence, the clear-sky forcing, which is more readily measurable, provides a good estimate of the total aerosol forcing.

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Regional and monthly and clear-sky aerosol direct radiative effect (and forcing) derived from the GlobAEROSOL-AATSR satellite aerosol product

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-393-2013 ◽

2013 ◽

Vol 13 (1) ◽

pp. 393-410 ◽

Cited By ~ 9

Author(s):

G. E. Thomas ◽

N. Chalmers ◽

B. Harris ◽

R. G. Grainger ◽

E. J. Highwood

Keyword(s):

Optical Properties ◽

Radiative Forcing ◽

Radiative Effect ◽

Mean Values ◽

Clear Sky ◽

Aerosol Loading ◽

Uncertainty Estimates ◽

Wide Range ◽

Aerosol Radiative ◽

Radiation Scheme

Abstract. Using the GlobAEROSOL-AATSR dataset, estimates of the instantaneous, clear-sky, direct aerosol radiative effect and radiative forcing have been produced for the year 2006. Aerosol Robotic Network sun-photometer measurements have been used to characterise the random and systematic error in the GlobAEROSOL product for 22 regions covering the globe. Representative aerosol properties for each region were derived from the results of a wide range of literature sources and, along with the de-biased GlobAEROSOL AODs, were used to drive an offline version of the Met Office unified model radiation scheme. In addition to the mean AOD, best-estimate run of the radiation scheme, a range of additional calculations were done to propagate uncertainty estimates in the AOD, optical properties, surface albedo and errors due to the temporal and spatial averaging of the AOD fields. This analysis produced monthly, regional estimates of the clear-sky aerosol radiative effect and its uncertainty, which were combined to produce annual, global mean values of (−6.7 ± 3.9) W m−2 at the top of atmosphere (TOA) and (−12 ± 6) W m−2 at the surface. These results were then used to give estimates of regional, clear-sky aerosol direct radiative forcing, using modelled pre-industrial AOD fields for the year 1750 calculated for the AEROCOM PRE experiment. However, as it was not possible to quantify the uncertainty in the pre-industrial aerosol loading, these figures can only be taken as indicative and their uncertainties as lower bounds on the likely errors. Although the uncertainty on aerosol radiative effect presented here is considerably larger than most previous estimates, the explicit inclusion of the major sources of error in the calculations suggest that they are closer to the true constraint on this figure from similar methodologies, and point to the need for more, improved estimates of both global aerosol loading and aerosol optical properties.

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Radiative Impacts of Aerosols During COVID-19 Lockdown Period Over the Indian Region

Frontiers in Environmental Science ◽

10.3389/fenvs.2021.746090 ◽

2021 ◽

Vol 9 ◽

Author(s):

Rohini L. Bhawar ◽

Suvarna Fadnavis ◽

Vinay Kumar ◽

P. R. C. Rahul ◽

Tushar Sinha ◽

...

Keyword(s):

Optical Depth ◽

Biomass Burning ◽

Atmospheric Aerosols ◽

Radiative Forcing ◽

Central India ◽

Indian Region ◽

Ozone Monitoring Instrument ◽

Gangetic Plain ◽

Outbreak Period ◽

The Government

The COVID-19 lockdown restrictions influenced global atmospheric aerosols. We report aerosol variations over India using multiple remote sensing datasets [Moderate Resolution Imaging Spectroradiometer (MODIS), Ozone Monitoring Instrument (OMI), Cloud-Aerosol Lidar, and Infrared Pathfinder (CALIPSO)], and model reanalysis [Copernicus Atmosphere Monitoring Service (CAMS)] during the lockdown implemented during the COVID-19 pandemic outbreak period from March 25 to April 14, 2020. Our analysis shows that, during this period, MODIS and CALIPSO showed a 30–40% reduction in aerosol optical depth (AOD) over the Indo-Gangetic Plain (IGP) with respect to decadal climatology (2010–2019). The absorbing aerosol index and dust optical depth measurements also showed a notable reduction over the Indian region, highlighting less emission of anthropogenic dust and also a reduced dust transport from West Asia during the lockdown period. On the contrary, central India showed an ∼12% AOD enhancement. CALIPSO measurements revealed that this increase was due to transported biomass burning aerosols. Analysis of MODIS fire data product and CAMS fire fluxes (black carbon, SO2, organic carbon, and nitrates) showed intense fire activity all over India but densely clustered over central India. Thus, we show that the lockdown restrictions implemented at the government level have significantly improved the air quality over northern India but fires offset its effects over central India. The biomass-burning aerosols formed a layer near 2–4 km (AOD 0.08–0.1) that produced heating at 3–4 K/day and a consequent negative radiative forcing at the surface of ∼−65 W/m2 (±40 W/m2) over the central Indian region.

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Evaluation of clear sky models to estimate the surface direct aerosol radiative effect over Germany

10.5194/egusphere-egu21-7294 ◽

2021 ◽

Author(s):

Jonas Witthuhn ◽

Anja Hünerbein ◽

Hartwig Deneke ◽

Florian Filipitsch ◽

Stefan Wacker

Keyword(s):

Radiative Forcing ◽

Power Plants ◽

Climate System ◽

Radiation Budget ◽

Radiative Effect ◽

Clear Sky ◽

A Value ◽

Reference Simulation ◽

One Year ◽

Aerosol Radiative

The radiation budget of the earth and its climate system is driven by the solar radiation, which interacts with gases, aerosol particles and clouds. Focusing on aerosol, a fundamental measure is the radiative forcing resulting from aerosol-radiation interactions (RFari) which is also known as the aerosol direct radiative effect. Quantifying the surface RFari on regional scales aids the understanding of the role of aerosol in the climate system and is important for the planning of solar energy systems.This study is based on a one year dataset (2015) of shortwave broadband global and diffuse horizontal irradiance measured with shaded and unshaded pyranometers at 26 station across Germany within the German Weather Service (DWD) observational network. A variety of clear-sky models are utilized to quantify RFari with a clear sky fitting technique. Clear sky models used are MMAC, MRM v.6.1, METSTAT, ESRA, Heliosat-1, CEM and the simplified Solis model. As these models have not been designed to estimate the clear sky irradiance without the presence of aerosol, we evaluated the accuracy of RFari with an reference simulation.The reference RFari is simulated using the TROPOS (Leibniz Institute of Tropospheric Research) Cloud and Aerosol Radiative Simulator (T-CARS) utilizing the offline version of the ECMWF radiation scheme (ecRad) with input data of meteorological state of the atmosphere, trace-gases and aerosol from CAMS reanalysis.The clear sky fitting approach for this set of clear sky models agrees well with T-CARS, showing an RMSE of 6.7 Wm-2 and an correlation of 0.75. The annual mean of surface RFari over the observation stations in Germany shows a value of -13.2 Wm-2 as an average over all clear sky models, compared to -13.4 Wm-2 from T-CARS. Out of this set of clear sky models, best performance is shown by the ESRA and MRM v6.1 models. Although, the accuracy of the annual mean RFari from the clear sky fitting approach is strongly depended on the number available clear-sky irradiance measurements and its distribution over the year. Therefore, this approach is not recommended for climatological studies, but may serve as valuable information for e.g. the evaluation of power generation and the influence by aerosol of photo-voltaic power plants.

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