Assimilation of Satellite Aerosol Observations Into NASA LaRC’s CERES SYN1deg Data Product – Validation and Effect on Surface Radiative Transfer Results

Poster PDF

Description

NASA’s Clouds and the Earth’s Radiant Energy System (CERES) project produces the SYN1deg data product, providing climate quality, hourly, globally gridded and temporally complete maps of top of atmosphere (TOA), in atmosphere, and surface irradiances. TOA fluxes are derived from CERES instruments and geostationary satellites. In addition, TOA, in atmosphere, and surface irradiances are computed using the Langley Fu and Liou radiative transfer model. Meteorological profiles are provided by Global Modeling and Assimilation Office’s GEOS-541 reanalysis product. Cloud properties are derived solely from Terra and Aqua MODIS imagers between 60 and 90, and from MODIS and available geo-stationary satellites between 60N and 60S. In addition to cloud properties and meteorological profiles, aerosol optical depth and type profiles and aerosol optical properties are needed to estimate TOA, in atmosphere, and surface irradiances. Aerosol optical depths are derived from MODIS and a global aerosol transport model (MATCH) is used to determine aerosol type profiles. As the temporal record of the radiation data product lengthens, it is more likely that aerosol optical depths used in irradiance computations are derived from multiple satellite instruments with different algorithms. Consistent aerosol optical depths derived from multiple satellite instruments are essential in producing radiation climate data records. In this poster, we compare aerosol optical depths derived from MODIS and VIIRS by two different algorithms to examine how these aerosol optical depths differ. We then relate satellite-derived aerosol optical depth differences to SYN1deg downward shortwave irradiance bias. Based on this result, we derive uncertainty associated with different instruments/algorithms used in aerosol optical depth retrieval impacting on surface shortwave irradiances at various temporal and spatial scales, as well as, the uncertainty in the downward shortwave irradiance time series when multiple satellites and algorithms are used to derive aerosol optical depth. We also compare satellite derived aerosol optical depths and SYN1deg shortwave irradiance with those observed at ARM sites. Differences are used to derive uncertainty in satellite derived aerosol optical depth and SYN1deg shortwave irradiance. We then use this uncertainty to assess how the uncertainty caused by different instruments and algorithms is comparable to the uncertainty due to aerosol optical depth retrieval.