Solar radiation budget and radiative forcing due to aerosols and clouds

Abstract

[1] This study integrates global data sets for aerosols, cloud physical properties, and shortwave radiation fluxes with a Monte Carlo Aerosol-Cloud-Radiation (MACR) model to estimate both the surface and the top-of-atmosphere (TOA) solar radiation budget as well as atmospheric column solar absorption. The study also quantifies the radiative forcing of aerosols and that of clouds. The observational input to MACR includes data from the Multiangle Imaging Spectroradiometer (MISR) for aerosol optical depths, single scattering albedos, and asymmetry factors; satellite retrieved column water vapor amount; the Total Ozone Mapping Spectrometer (TOMS) total ozone amount; and cloud fraction and cloud optical depth from the Cloud and Earth's Radiant Energy System (CERES) cloud data. The present radiation budget estimates account for the diurnal variation in cloud properties. The model was validated against instantaneous, daily and monthly solar fluxes from the ground-based Baseline Surface Radiation Network (BSRN) network, the Global Energy Balance Archive (GEBA) surface solar flux data, and CERES TOA measurements. The agreement between simulated and observed values are within experimental errors, for all of the cases considered here: instantaneous fluxes and monthly mean fluxes at stations around the world and TOA fluxes and cloud forcing for global annual mean and zonal mean fluxes; in addition the estimated aerosol forcing at TOA also agrees with other observationally derived estimates. Overall, such agreements suggest that global data sets of aerosols and cloud parameters released by recent satellite experiments (MISR, MODIS and CERES) meet the required accuracy to use them as input to simulate the radiative fluxes within instrumental errors. Last, the atmospheric solar absorption derived in this study should be treated as an improved estimate when compared with earlier published studies. The main source of improvement in the present estimate is the use of global distribution of observed parameters for model input such as aerosols and clouds. The agreement between simulated and observed solar fluxes at the surface supports our conclusion that the present estimate is an improvement over previous studies. MACR with the global input data was used to simulate the global and regional solar radiation budget, aerosol radiative forcing and cloud radiative forcing for a 3-year period from 2000 to 2002. We estimate the planetary albedo for a 3-year average to be 28.9 ± 1.2% to be compared with CERES estimate of 28.6% and ERBE's estimate of 29.6%. Without clouds (including aerosols) the planetary albedo is only 15.0 ± 0.6%. The global mean TOA shortwave cloud forcing is À47.5 ± 4 W m À2 , comparing well with the CERES and ERBE estimates of À46.5 and À48 W m TOA and the surface are À6.0 ± 1 W m À2 and À11.0 ± 2 W m À2 , respectively. In the presence of clouds the aerosol radiative forcing is À3.0 ± 1 W m À2 (at TOA) and À7.0 ± 2 W m À2 (at the surface). The study also documents the significant regional variations in the solar radi...

Response to “Toward unified satellite climatology of aerosol properties. 3. MODIS versus MISR versus AERONET”

“…Many successful applications of these data to global-and regional-scale questions are already presented in the literature. They range from assessing zonal mean or global aerosol short-wave forcing [37][38][39][40][41][42] and regional long-wave forcing [43], to improving aerosol forecasting through data assimilation [44,45], monitoring dust and pollution plume evolution [46,47] and air quality [48,49], mapping aerosol air mass type evolution [50], and validating aerosol transport model AOD simulations [51,52]. In each case, ways of exploiting the strengths of the MISR and MODIS data have been found, and in many cases, independent validation was performed specific to the application.…”

Impacts of 3D Aerosol, Cloud, and Water Vapor Variations on the Recent Brightening during the South Asian Monsoon Season

“…The water vapor importantly decreases the incident solar radiation at the surface due to its absorption of solar radiation [12]. Figure 6a,c exhibit the vertical relative humidity (RH) in all-sky and clear conditions, which consistently and gradually decreased with a maximum decrement of approximately 10% during the monsoon season in South Asia from 2006 to 2015.…”

Tracking Earth’s Energy: From El Niño to Global Warming

“…Both at the surface and TOA the imbalance is the same and, as noted above, is estimated to be 0.9 W m -2 . Updates in Trenberth et al (2009) included revised absorption in the atmosphere by water vapor and aerosols, since Kim and Ramanathan (2008) found that updated spectroscopic parameters and continuum absorption for water vapor increased the absorption by 4-6 W m -2…”