scholarly journals Retrieval of Key Aerosol Optical Parameters from Spectral Direct and Diffuse Irradiances Observed by a Radiometer with Nonideal Cosine Response Characteristic

2012 ◽  
Vol 29 (5) ◽  
pp. 683-696 ◽  
Author(s):  
Pradeep Khatri ◽  
Tamio Takamura ◽  
Akihiro Yamazaki ◽  
Yutaka Kondo
Keyword(s):  
Direct Effect ◽  
Radiative Forcing ◽  
Response Characteristic ◽  
Single Scattering ◽  
Optical Parameters ◽  
Aerosol Radiative Forcing ◽  
Aerosol Direct Effect ◽  
Diffuse Irradiance ◽  
Isotropic Distribution ◽  
Sky Radiance

Abstract The spectral direct and diffuse irradiances observed by a radiometer with a horizontal surface detector have been frequently used to study aerosol optical parameters, such as aerosol optical thickness (τaer) and single scattering albedo (ω). Such radiometers more or less lack an ideal cosine response. Generally, either the cosine error of observed diffuse irradiance was corrected by assuming an isotropic distribution of sky radiance or it was neglected in the past studies. This study presents an algorithm to retrieve τaer and ω from direct and diffuse irradiances observed by a radiometer with a nonideal cosine response characteristic by taking into account the cosine errors of observed irradiances in detail. The proposed algorithm considers the anisotropic distribution of sky radiance while correcting the cosine error of observed diffuse irradiance. This algorithm can also be used to calculate the cosine error correction factor of diffuse irradiance. The results show that the aerosol optical parameters and the aerosol direct effect (aerosol radiative forcing and the heating rate) can be heavily affected by the cosine errors of observed direct and diffuse irradiances. The study further shows that assuming the isotropic distribution of sky radiance while correcting the cosine error of observed diffuse irradiance can affect the retrieved ω at small and large solar zenith angles; thus, the estimated aerosol direct effect can be quantitatively affected. Because of the cosine errors, this study found the actual values of diffuse irradiances at different wavelengths were underestimated by around 5%–11%.

scholarly journals A Method to Estimate Aerosol Radiative Forcing from Spectral Optical Depths

2006 ◽  
Vol 63 (3) ◽  
pp. 1082-1092 ◽  
Author(s):  
S. K. Satheesh ◽  
J. Srinivasan
Keyword(s):  
Chemical Composition ◽  
Optical Depth ◽  
Radiative Forcing ◽  
Field Experiments ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Radiative Properties ◽  
Aerosol Radiative Forcing ◽  
Sky Radiance ◽  
Aerosol Radiative

Abstract Radiative forcing of aerosols is much more difficult to estimate than that of well-mixed gases due to the large spatial variability of aerosols and the lack of an adequate database on their radiative properties. Estimation of aerosol radiative forcing generally requires knowledge of its chemical composition, which is sparse. Ground-based sky radiance measurements [e.g., aerosol robotic network (AERONET)] can provide key parameters such as the single-scattering albedo, but in shipborne experiments over the ocean it is difficult to make sky radiance measurements and hence these experiments cannot provide parameters such as the single-scattering albedo. However, aerosol spectral optical depth data (cruise based as well as satellite retrieved) are available quite extensively over the ocean. Spectral optical depth measurements have been available since the 1970s, and spectral turbidity measurements (carried out at meteorological departments all over the world) have been available for several decades, while long-term continuous chemical composition information is not available. A new method to differentiate between scattering and absorbing aerosols is proposed here. This can be used to derive simple aerosol models that are optically equivalent and can simulate the observed aerosol optical properties and radiative fluxes, from spectral optical depth measurements. Thus, aerosol single-scattering albedo and, hence, aerosol radiative forcing can be estimated. Note that the proposed method is to estimate clear-sky aerosol radiative forcing (over regions where chemical composition data or sky radiance data are not available) and not to infer its exact chemical composition. Using several independent datasets from field experiments, it is demonstrated that the proposed method can be used to estimate aerosol radiative forcing (from spectral optical depths) with an accuracy of ±2 W m−2.

scholarly journals Radiative forcing of the desert aerosol at Ouarzazate (Morocco)

2018 ◽  
Vol 37 ◽  
pp. 03004
Author(s):  
Abdelouahid Tahiri ◽  
Mohamed Diouri
Keyword(s):  
Optical Properties ◽  
Atmospheric Aerosol ◽  
Radiative Forcing ◽  
Cloud Formation ◽  
Optical Parameters ◽  
Aerosol Radiative Forcing ◽  
Daily Average ◽  
Definition Of ◽  
Aerosol Radiative

The atmospheric aerosol contributes to the definition of the climate with direct effect, the diffusion and absorption of solar and terrestrial radiations, and indirect, the cloud formation process where aerosols behave as condensation nuclei and alter the optical properties. Satellites and ground-based networks (solar photometers) allow the terrestrial aerosol observation and the determination of impact. Desert aerosol considered among the main types of tropospheric aerosols whose optical property uncertainties are still quite important. The analysis concerns the optical parameters recorded in 2015 at Ouarzazate solar photometric station (AERONET/PHOTONS network, http://aeronet.gsfc.nasa.gov/) close to Saharan zone. The daily average aerosol optical depthτaer at 0.5μm, are relatively high in summer and less degree in spring (from 0.01 to 1.82). Daily average of the Angstrom coefficients α vary between 0.01 and 1.55. The daily average of aerosol radiative forcing at the surface range between -150W/m2 and -10 W/m2 with peaks recorded in summer, characterized locally by large loads of desert aerosol in agreement with the advections of the Southeast of Morocco. Those recorded at the Top of the atmosphere show a variation from -74 W/m2 to +24 W/m2

scholarly journals Column aerosol optical properties and aerosol radiative forcing during a serious haze-fog month over North China Plain in 2013 based on ground-based sunphotometer measurements

2013 ◽  
Vol 13 (11) ◽  
pp. 29685-29720 ◽  
Author(s):  
H. Che ◽  
X. Xia ◽  
J. Zhu ◽  
Z. Li ◽  
O. Dubovic ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
North China Plain ◽  
North China ◽  
Optical Parameters ◽  
Aerosol Radiative Forcing ◽  
Coarse Mode ◽  
Fine Mode ◽  
Rural Sites ◽  
Urban Sites ◽  
Aerosol Radiative

Abstract. In January 2013, North China Plain experienced several serious haze events. Cimel sunphotometer measurements at seven sites over rural, suburban and urban regions of North China Plain from 1 to 30 January 2013 were used to further our understanding of spatial-temporal variation of aerosol optical parameters and aerosol radiative forcing (ARF). It was found that Aerosol Optical Depth at 500 nm (AOD500 nm) during non-pollution periods at all stations was lower than 0.30 and increased significantly to greater than 1.00 as pollution events developed. The Angstrom exponent (Alpha) was larger than 0.80 for all stations most of the time. AOD500 nm averages increased from north to south during both polluted and non-polluted periods on the three urban sites in Beijing. The fine mode AOD during pollution periods is about a factor of 2.5 times larger than that during the non-pollution period at urban sites but a factor of 5.0 at suburban and rural sites. The fine mode fraction of AOD675 nm was higher than 80% for all sites during January 2013. The absorption AOD675 nm at rural sites was only about 0.01 during pollution periods, while ~0.03–0.07 and 0.01–0.03 during pollution and non-pollution periods at other sites, respectively. Single scattering albedo varied between 0.87 and 0.95 during January 2013 over North China Plain. The size distribution showed an obvious tri-peak pattern during the most serious period. The fine mode effective radius in the pollution period was about 0.01–0.08 μm larger than during non-pollution periods, while the coarse mode radius in pollution periods was about 0.06–0.38 μm less than that during non-pollution periods. The total, fine and coarse mode particle volumes varied by about 0.06–0.34 μm3, 0.03–0.23 μm3, and 0.03–0.10 μm3, respectively, throughout January 2013. During the most intense period (1–16 January), aerosol radiative forcing (ARF) at the surface exceeded −50 W m−2, −180 W m−2, and −200 W m−2 at rural, suburban, and urban sites, respectively. The ARF readings at the top of the atmosphere were approximately −30 W m−2 in rural and −40–60 W m−2 in urban areas. Positive ARF at the top of the atmosphere at the Huimin suburban site was found to be different from others as a result of the high surface albedo due to snow cover.

scholarly journals Contrasting variation in aerosol optical properties during dust episodes in the Middle East and Southwest Asia: Model results and ground measurement

2019 ◽  
Vol 99 ◽  
pp. 04006
Author(s):  
Khan Alam ◽  
Maqbool Ahmad
Keyword(s):  
Middle East ◽  
Radiative Forcing ◽  
Single Scattering ◽  
Dust Storms ◽  
Radiative Properties ◽  
Southwest Asia ◽  
Gulf Region ◽  
Aerosol Radiative Forcing ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Using Data

Dust storms deteriorated air quality over the Gulf Region, Iraq, Iran, and Pakistan during the last decade. The purpose of this study is to investigate the changes in aerosol optical and radiative properties during a dust episode over the various locations in the Middle East and Southwest Asia using data from the MODerate resolution Imaging Spectroradiometer (MODIS) and the Aerosol Robotic Network (AERONET) during March, 2012. Maximum aerosol optical depth (AOD) values were found to be 2.18, 1.30, 4.33 and 1.80 over Lahore, Kanpur, Kaust, and Mezaira, respectively. The Volume Size Distributions, Single Scattering Albedo, Refractive Index, and Asymmetry parameter indicated that coarse mode aerosols were predominant relative to fine mode aerosols during the dust event. The average shortwave aerosol radiative forcing (ARF) values at the earth’s surface were found to be -96±45 W m-2, -86±22 W m-2, -77±51 W m-2, and -75±40 W m-2, over Lahore, Kanpur, Kaust and Mezaira, respectively. Likewise, the averaged ARF values over Lahore, Kanpur, Kaust and Mezaira at the top of the atmosphere (TOA) were found to be -45±25 W m-2, -27±9 W m-2, -41±29 W m-2, and -75±40 W m-2, respectively. The large differences between surface and TOA forcing produced significant heating within the atmosphere.

scholarly journals Direct Aerosol Radiative Forcing Uncertainty Based on a Radiative Perturbation Analysis

2010 ◽  
Vol 23 (19) ◽  
pp. 5288-5293 ◽  
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.

scholarly journals Diurnal aerosol variations do affect daily averaged radiative forcing under heavy aerosol loading observed in Hefei, China

2015 ◽  
Vol 8 (7) ◽  
pp. 2901-2907 ◽  
Author(s):  
Z. Wang ◽  
D. Liu ◽  
Y. Wang ◽  
Z. Wang ◽  
G. Shi
Keyword(s):  
Temporal Resolution ◽  
Radiative Forcing ◽  
Single Scattering ◽  
High Temporal Resolution ◽  
Diurnal Changes ◽  
Data Set ◽  
Time Resolved ◽  
Aerosol Radiative Forcing ◽  
Aerosol Loading

Abstract. A strong diurnal variation of aerosol has been observed in many heavily polluted regions in China. This variation could affect the direct aerosol radiative forcing (DARF) evaluation if the daily averaged value is used as normal rather than the time-resolved values. To quantify the effect of using the daily averaged DARF, 196 days of high temporal resolution ground-based data collected in SKYNET Hefei site during the period from 2007 to 2013 is used to perform an assessment. We demonstrate that strong diurnal changes of heavy aerosol loading have an impact on the 24-h averaged DARF when daily averaged optical properties are used to retrieve this quantity. The DARF errors varying from −7.6 to 15.6 W m−2 absolutely and from 0.1 to 28.5 % relatively were found between the calculations using daily average aerosol properties, and those using time-resolved aerosol observations. These errors increase with increasing daily aerosol optical depth (AOD) and decreasing daily single-scattering albedo (SSA), indicating that the high temporal resolution DARF data set should be used in the model instead of the normal daily-averaged one, especially under heavy aerosol loading conditions for regional campaign studies. We also found that statistical errors (0.3 W m−2 absolutely and 11.8 % relatively) will be less, which means that the effect of using the daily averaged DARF can be weakened by using a long-term observational data set.

scholarly journals Observations and Modeling of the Surface Aerosol Radiative Forcing during UAE2

2008 ◽  
Vol 65 (9) ◽  
pp. 2877-2891 ◽  
Author(s):  
K. M. Markowicz ◽  
P. J. Flatau ◽  
J. Remiszewska ◽  
M. Witek ◽  
E. A. Reid ◽  
...  
Keyword(s):  
United Arab Emirates ◽  
Radiative Forcing ◽  
Sea Breeze ◽  
Single Scattering ◽  
Land Breeze ◽  
Gulf Region ◽  
Diurnal Variability ◽  
Aerosol Radiative Forcing ◽  
Aerosol Forcing ◽  
Aerosol Radiative

Abstract Aerosol radiative forcing in the Persian Gulf region is derived from data collected during the United Arab Emirates (UAE) Unified Aerosol Experiment (UAE2). This campaign took place in August and September of 2004. The land–sea-breeze circulation modulates the diurnal variability of the aerosol properties and aerosol radiative forcing at the surface. Larger aerosol radiative forcing is observed during the land breeze in comparison to the sea breeze. The aerosol optical properties change as the onshore wind brings slightly cleaner air. The mean diurnal value of the surface aerosol forcing during the UAE2 campaign is about −20 W m−2, which corresponds to large aerosol optical thickness (0.45 at 500 nm). The aerosol forcing efficiency [i.e., broadband shortwave forcing per unit optical depth at 550 nm, W m−2 (τ500)−1] is −53 W m−2 (τ500)−1 and the average single scattering albedo is 0.93 at 550 nm.

scholarly journals Direct SW aerosol radiative forcing over Portugal

2008 ◽  
Vol 8 (3) ◽  
pp. 8585-8628 ◽  
Author(s):  
D. Santos ◽  
M. J. Costa ◽  
A. M. Silva
Keyword(s):  
Forest Fires ◽  
Spectral Reflectance ◽  
Radiative Forcing ◽  
Longwave Radiation ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Aerosol Radiative Forcing ◽  
Desert Dust ◽  
Average Value ◽  
Aerosol Radiative

Abstract. The estimation of radiative forcing due to desert dust and forest fires aerosols is a very important issue since these particles are very efficient at scattering and absorbing both short and longwave radiation. In this work, the evaluation of the aerosol radiative forcing at the top of the atmosphere over the south of Portugal is made, particularly in the regions of Évora and of Cabo da Roca. The radiative transfer calculations combine ground-based and satellite measurements, to estimate the top of the atmosphere direct SW aerosol radiative forcing. The method developed to retrieve the surface spectral reflectance is also presented, based on ground-based measurements of the aerosol optical properties combined with the satellite-measured radiances. The aerosol direct radiative effect is shown to be very sensitive to the underlying surface, since different surface spectral reflectance values may originate different forcing values. The results obtained also illustrate the importance of considering the actual aerosol properties, in this case measured by ground-based instrumentation, particularly the aerosol single scattering albedo, because different aerosol single scattering albedo values can flip the sign of the direct SW aerosol radiative forcing. The instantaneous direct SW aerosol radiative forcing values obtained at the top of the atmosphere are, in the majority of the cases, negative, indicating a tendency for cooling the Earth. For Desert Dust aerosols, over Évora land region, the average forcing efficiency is estimated to be −25 W/m2/AOT0.55 whereas for Cabo da Roca area, the average forcing efficiency is −46 W/m2/AOT0.55. In the presence of Forest Fire aerosols, over Cabo da Roca region, the average value of forcing efficiency is −28 W/m2/AOT0.55 and over Évora region an average value of −33 W/m2/AOT0.55 is found.

scholarly journals Multi-Satellite Retrieval of SSA using OMI-MODIS algorithm

2018 ◽  
Author(s):  
Kruthika Eswaran ◽  
Sreedharan Krishnakumari Satheesh ◽  
Jayaraman Srinivasan
Keyword(s):  
Radiative Forcing ◽  
Single Scattering ◽  
Retrieval Algorithm ◽  
Ozone Monitoring Instrument ◽  
Aerosol Composition ◽  
Aerosol Radiative Forcing ◽  
Aerosol Absorption ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Absorbing Aerosols ◽  
Aerosol Type

Abstract. Single scattering albedo (SSA) represents a unique identification of aerosol type and aerosol radiative forcing. However, SSA retrievals are highly uncertain due cloud contamination and aerosol composition. Recent improvement in the SSA retrieval algorithm has combined the superior cloud masking technique of Moderate Resolution Imaging Spectroradiometer (MODIS) and the better sensitivity of Ozone Monitoring Instrument (OMI) to aerosol absorption. The combined OMI-MODIS algorithm has been validated over a small spatial and temporal scale only. The present study validates the algorithm over global oceans for the period 2008–2012. The geographical heterogeneity in the aerosol type and concentration over the Atlantic Ocean, the Arabian Sea and the Bay of Bengal was useful to delineate the effect of aerosol type on the retrieval algorithm. We also noted that OMI overestimates SSA when absorbing aerosols were present closer to the surface. We attribute this overestimation to data discontinuity in the aerosol height climatology derived from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite. OMI uses pre-defined aerosol heights over regions where CALIPSO climatology is not present leading to overestimation of SSA. The importance of aerosol height was also studied using the Santa Barbara DISORT radiative transfer (SBDART) model. The results from the joint retrieval were validated with ground-based measurements and it was seen that OMI-MODIS SSA retrievals were better constrained than OMI only retrieval.

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