Abstract
Abstract. A radiative transfer interface has been developed to simulate the UV aerosol index (AI) from the NASA Goddard Earth Observing System version 5 (GEOS-5) aerosol assimilated fields. The purpose of this work is to use the AI and aerosol absorption optical depth (AAOD) derived from the Ozone Monitoring Instrument (OMI) measurements as independent validation for the Modern Era Retrospective analysis for Research and Applications Aerosol Reanalysis (MERRAero). MERRAero is based on a version of the GEOS-5 model that is radiatively coupled to the Goddard Chemistry, Aerosol, Radiation, and Transport (GOCART) aerosol module and includes assimilation of aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. Since AI is dependent on aerosol concentration, optical properties and altitude of the aerosol layer, we make use of complementary observations to fully diagnose the model, including AOD from the Multi-angle Imaging SpectroRadiometer (MISR), aerosol retrievals from the AErosol RObotic NETwork (AERONET) and attenuated backscatter coefficients from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission to ascertain potential misplacement of plume height by the model. By sampling dust, biomass burning and pollution events in 2007 we have compared model-produced AI and AAOD with the corresponding OMI products, identifying regions where the model representation of absorbing aerosols was deficient. As a result of this study over the Saharan dust region, we have obtained a new set of dust aerosol optical properties that retains consistency with the MODIS AOD data that were assimilated, while resulting in better agreement with aerosol absorption measurements from OMI. The analysis conducted over the southern African and South American biomass burning regions indicates that revising the spectrally dependent aerosol absorption properties in the near-UV region improves the modeled-observed AI comparisons. Finally, during a period where the Asian region was mainly dominated by anthropogenic aerosols, we have performed a qualitative analysis in which the specification of anthropogenic emissions in GEOS-5 is adjusted to provide insight into discrepancies observed in AI comparisons.
Highlights
The concept of the UV aerosol index (AI) was first introduced in the context of observations made by the Total Ozone Mapping Spectrometer (TOMS) sensors in the late 1990s (Herman et al, 1997; Torres et al, 1998) and has since been extended to apply to measurements with the Ozone Monitoring Instrument (OMI)
Goddard Earth Observing System version 5 (GEOS-5) features a mature atmospheric data assimilation system that builds upon the Grid-point Statistical Interpolation (GSI) algorithm jointly developed with the National Centers for Environmental Prediction (NCEP) (Wu et al, 2002; Derber et al, 2003; Rienecker et al, 2008)
We examine the impact of applying a new set of dust optics on MERRAero-derived aerosol absorption optical depth (AAOD) by comparing it with AErosol RObotic NETwork (AERONET) retrievals. (Recall that the shortest wavelength for which AERONET retrieves single scattering albedo (SSA) is 440 nm.) As depicted in Fig. 5 the optical properties derived from the Optical Properties for Aerosols and Clouds (OPAC)-based baseline simulations are generally more absorptive than the AERONET retrievals
Summary
The concept of the UV aerosol index (AI) was first introduced in the context of observations made by the Total Ozone Mapping Spectrometer (TOMS) sensors in the late 1990s (Herman et al, 1997; Torres et al, 1998) and has since been extended to apply to measurements with the Ozone Monitoring Instrument (OMI). Using AI for detecting aerosol has been applied to other sensors such as GOME (de Graaf et al, 2005) and SCIAMACHY (de Graaf and Stammes, 2005; Penning de Vries et al, 2009) and models (Colarco et al, 2002; Ginoux and Torres, 2003; Yoshioka et al, 2005) In these model studies, simulations of AI and aerosol optical depth (AOD) were performed for dust plume cases and compared to corresponding observations in order to validate the model and constrain the model optical properties of dust aerosols. The key elements of GEOS-5 used for MERRAero are summarized below
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