Net radiative effects of dust in the tropical North Atlantic based on integrated satellite observations and in situ measurements

Abstract

In this study, we integrate recent in situ measurements with satellite retrievals of dust physical and radiative properties to quantify dust direct radiative effects on shortwave (SW) and longwave (LW) radiation (denoted as DRE SW and DRE LW , respectively) in the tropical North Atlantic during the summer months from 2007 to 2010. Through linear regression of the CERES-measured top-ofatmosphere (TOA) flux versus satellite aerosol optical depth (AOD) retrievals, we estimate the instantaneous DRE SW efficiency at the TOA to be −49.7 ± 7.1 W m −2 AOD −1 and −36.5±4.8 W m −2 AOD −1 based on AOD from MODIS and CALIOP, respectively. We then perform various sensitivity studies based on recent measurements of dust particle size distribution (PSD), refractive index, and particle shape distribution to determine how the dust microphysical and optical properties affect DRE estimates and its agreement with the above-mentioned satellite-derived DREs. Our analysis shows that a good agreement with the observation-based estimates of instantaneous DRE SW and DRE LW can be achieved through a combination of recently observed PSD with substantial presence of coarse particles, a less absorptive SW refractive index, and spheroid shapes. Based on this optimal combination of dust physical properties we further estimate the diurnal mean dust DRE SW in the region of −10 W m −2 at TOA and −26 W m −2 at the surface, respectively, of which ∼ 30 % is canceled out by the positive DRE LW . This yields a net DRE of about −6.9 and −18.3 W m −2 at TOA and the surface, respectively. Our study suggests that the LW flux contains useful information on dust particle size, which could be used together with SW observations to achieve a more holistic understanding of the dust radiative effect.Published by Copernicus Publications on behalf of the European Geosciences Union.

Estimates of African Dust Deposition Along the Trans‐Atlantic Transit Using the Decadelong Record of Aerosol Measurements from CALIOP, MODIS, MISR, and IASI

“…The IASI to MODIS DOD ratio of 0.65 better reflects the wavelength dependence of DOD, which has been used to convert IASI thermal infrared DOD to DOD at 0.55 μm (shown in Figure ) for dust deposition calculations. This wavelength dependence also agrees well with recent radiative transfer modeling (Song et al, ) that yields the DOD 10 to 0.5 μm ratio of about 0.7 when the PSD for the transported dust is taken from a recent aircraft campaign (Ryder et al, ). However, the same study using the size distribution retrieved from AERONET observations yields a much smaller ratio of 0.4 (Song et al, ), because the AERONET retrieval is arguably biased toward smaller sizes as a result of limited sun photometer spectral coverage.…”

Direct Radiative Effect by Mineral Dust Aerosols Constrained by New Microphysical and Spectral Optical Data

“…These 19 samples were selected from a much larger assemblage to represent the global variability of the dust content of LW‐active minerals (clays, quartz, and calcite) and, therefore, of LW CRI. Published radiative closure studies based on aircraft radiation data (Granados‐Muñoz et al, ; Meloni et al, ) and satellite radiance observations (Banks et al, ; Liuzzi et al, ; Song et al, ) confirm the improved capability of the DB17 data set to represent the regional variations in the dust LW DRE compared to the V73 CRI.…”

Estimation of the Dust Aerosol Shortwave Direct Forcing Over Land Based on an Equi‐albedo Method From Satellite Measurements

“…Research notes that DRF dust in SW depends on the SZA. As the SZA declines, the E dust ( τ dust ) correspondingly decreases (Song et al, ). We have estimated the instantaneous E dust ( τ dust ) with the data of MODIS and CERES onboard the Aqua satellite, which are observed at noon (1:30 p.m. local time), so that the estimating of E dust ( τ dust ) is reasonable.…”