Above-cloud aerosol radiative effects based on ORACLES 2016 and ORACLES 2017 aircraft experiments

Abstract

Abstract. Determining the direct aerosol radiative effect (DARE) of absorbing aerosols above clouds from satellite observations alone is a challenging task, in part because the radiative signal of the aerosol layer is not easily untangled from that of the clouds below. In this study, we use aircraft measurements from the NASA ObseRvations of CLouds above Aerosols and their intEractionS (ORACLES) project in the southeastern Atlantic to derive it with as few assumptions as possible. This is accomplished by using spectral irradiance measurements (Solar Spectral Flux Radiometer, SSFR) and aerosol optical depth (AOD) retrievals (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research, 4STAR) during vertical profiles (spirals) that minimize the albedo variability of the underlying cloud field – thus isolating aerosol radiative effects from those of the cloud field below. For two representative cases, we retrieve spectral aerosol single scattering albedo (SSA) and the asymmetry parameter (g) from these profile measurements and calculate DARE given the albedo range measured by SSFR on horizontal legs above clouds. For mid-visible wavelengths, we find SSA values from 0.80 to 0.85 and a significant spectral dependence of g. As the cloud albedo increases, the aerosol increasingly warms the column. The transition from a cooling to a warming top-of-aerosol radiative effect occurs at an albedo value (critical albedo) just above 0.2 in the mid-visible wavelength range. In a companion paper, we use the techniques introduced here to generalize our findings to all 2016 and 2017 measurements and parameterize aerosol radiative effects.

Modeling the smoky troposphere of the southeast Atlantic: a comparison to ORACLES airborne observations from September of 2016

“…Furthermore, GEOS-5 uses a robust atmospheric data assimilation system using the grid-point statistical interpolation (GSI) algorithm, which includes AOD assimilation from MODIS (Terra and Aqua), among others. Aerosols are treated online using GOCART (Goddard Chemistry Aerosol Radiation and Transport) (Chin et al, 2002;Colarco et al, 2010). Black and organic carbon aerosols are treated separately, with organic carbon aerosols represented as a function of the particulate organic matter (POM), with POM equal to 1.4 times the organic carbon mass (Textor et al, 2006).…”

“…Black and organic carbon aerosols are treated separately, with organic carbon aerosols represented as a function of the particulate organic matter (POM), with POM equal to 1.4 times the organic carbon mass (Textor et al, 2006). The single-moment mass is converted to an extinction using a black carbon mass extinction efficiency of 10.7 and 5.83 m 2 g −1 for POM, both at 550 nm (Colarco et al, 2010). The carbonaceous aerosols are coupled with the radiation module.…”

“…The NASA ER2 flew at about 20 km altitude with downward-viewing remote sensors. Their data sets have been applied to date to multiinstrument assessment of single scattering albedo (SSA) (Pistone et al, 2019), the above-cloud aerosol optical depths (ACAODs) (LeBlanc et al, 2020), BBA cloud-nucleating activity , and direct aerosol radiative effects (Cochrane et al, 2019).…”

Development of an Ozone Monitoring Instrument (OMI) aerosol index (AI) data assimilation scheme for aerosol modeling over bright surfaces – a step toward direct radiance assimilation in the UV spectrum

“…To convert from NAAPS mass loading concentrations to aerosol extinction and scattering profiles, we require aerosol optical properties for the four species at 354 and 388 nm, which are summarized in Table 1. The optical properties of ABF (assumed to be sulfate in this study), sea salt, dust, and smoke aerosols, including mass extinction efficiencies and single-scattering albedos at 354 and 388 nm, are adapted from NASA's Goddard Earth Observing System version 5 (GEOS-5) model (e.g., Colarco et al, 2014;Buchard et al, 2015). Note that the study period is July and August of 2007 over Africa, coinciding with the early biomass burning season associated with lower single-scattering albedo values (Eck et al, 2013).…”

Assessing the Potential of Geostationary Satellites for Aerosol Remote Sensing Based on Critical Surface Albedo

“…Boehmler et al used the implications of CSA to study the limits of aerosol retrieval over the bright surfaces of Nevada [33]. Recently, some works considered the CSA to study the above-cloud radiative effects of aerosols [34]. Finally, Zhang et al underlined the loss of accuracy that the retrieval of other atmospheric constituents, namely column-weighted CO 2 mixing ratio, suffers for surfaces close to CSA [35].…”