Aerosol Characterization and Direct Radiative Forcing Assessment over the Ocean. Part I: Methodology and Sensitivity Analysis

A method based on the synergistic use of low earth orbit (LEO) and geostationary earth orbit (GEO) satellitedata for aerosol-type characterization, as well as aerosol optical thickness (AOT) retrieval and monitoring overthe ocean, is presented. These properties are used for the estimation of the direct shortwave aerosol radiativeforcing at the top of the atmosphere. The synergy serves the purpose of monitoring aerosol events at the GEOtime and space scales while maintaining the accuracy level achieved with LEO instruments. Aerosol opticalproperties representative of the atmospheric conditions are obtained from the inversion of high-spectral-resolutionmeasurements from the Global Ozone Monitoring Experiment (GOME). The aerosol optical properties are inputfor radiative transfer calculations for the retrieval of the AOT from GEO visible broadband measurements,avoiding the use of fixed aerosol models available in the literature. The retrieved effective aerosol opticalproperties represent an essential component for the aerosol radiative forcing assessment. A sensitivity analysisis also presented to quantify the effects that changes on the aerosol model may have on modeled results ofspectral reflectance, AOT, and direct shortwave aerosol radiative forcing at the top of the atmosphere. The impacton modeled values of the physical assumptions on surface reflectance and vertical profiles of ozone and watervapor are analyzed. Results show that the aerosol model is the main factor influencing the investigated radiativevariables. Results of the application of the method to several significant aerosol events, as well as their validation,are presented in a companion paper