Presentation on theme: "Xiaolei Niu and R. T. Pinker Department of Atmospheric and Oceanic Science, University of Maryland, College Park, Maryland Radiative Flux Estimates from."— Presentation transcript:
Xiaolei Niu and R. T. Pinker Department of Atmospheric and Oceanic Science, University of Maryland, College Park, Maryland Radiative Flux Estimates from the Advanced Baseline Imager (ABI): Synthesis of Angular Distribution Models 5th GOES Users' Conference, AMS 88, New Orleans, Jan 20-24, 2008. Objective Develop up-to-date ADMs for use with ABI’s shortwave observations for clear and cloudy conditions based on: theoretical simulations with a radiative transfer model on the Clouds and the Earth’s Radiant Energy System (CERES) observational models. Resulting improvements in inferred SW fluxes from the new ADMs will be evaluated against ground observations using an existing inference scheme for current GOES satellites that utilize ADMs based on ERBE observations. This approach is conducive to the development of consistent time series of radiative fluxes from new and from historical geostationary satellites observations that by now cover a period of over twenty years. Methodology for Deriving New ADMs (1) Theoretical ADMs are based on MODTRAN simulations for clear and cloudy conditions using IGBP land classifications (1) ADMs based on CERES observations Background Observations from the ABI sensor onboard the new generation of the NOAA geostationary satellites (GOES- R) will be used to improve estimates of surface shortwave (SW) radiative fluxes. They are of high spatial and temporal resolution in sixteen spectral channels which is conducive for improved information on clouds, aerosols, and state of the surface. Critical elements of an inference scheme for radiative flux estimates from satellite observations are: 1) transformation from narrow-band observations into broadband values; 2) application of Angular Distribution Models (ADMs) to correct for angular dependence of observations ADMs can be based on (1) theoretical computations or on (2) observations. Preliminary Results Summary The derived surface radiative fluxes with updated ADMs have shown improvements at low solar angles when compared against ground observations. The average absolute bias for hours between 06 - 10am, 14-18pm for SURFRAD sites decreased by about 5 (W/m 2 ). A comprehensive evaluation will be performed after introduction of updated narrow to broadband transformations as appropriate for ABI. Use will be made of SEVIRI and MODIS observations as proxy for ABI. Impact of New ADMs The (UMD/SRB) model is implemented with current GOES observations Existing ADMs in model are based on ERBE Here - replaced with the newly selected CERES ADMs. Anisotropic Factor at SZA 63.2°over Desert for Clear Sky (a) Simulation; (b) Bright Desert (CERES) Difference (W/m 2 ) in Monthly mean all sky surface SW downward flux for January (left) and July (right), 2000 using ERBE and CERES ADMs. Upper: Clear Sky; Lower: All Sky CERES IGBP OceanWater Bright Desert Bare Ground (Desert) Dark Desert Permanent Snow Snow/Ice Fresh Snow Sea Ice Low-Mod Shrub/Tree High-Mod Shrub/Tree Needle leaf Forest Broadleaf Forest Mixed Forest Woodland Wooded Grassland Closed Shrub Open Shrub Grassland Cropland Acknowledgement: This work is supported under the Cooperative Institute for Climate Studies Cooperative Agreement, NOAA Award number NA17EC1483. Conversion Factor Clear Sky? Correlate the anisotropic factor from CERES and simulations of relevant surface type Correlate the anisotropic factor from simulations and CERES of relevant cloud category Select case of highest correlation between MOTRAN simulations for each CERES category Apply selected CERES ADMs to UMD/SRB model when implemented with GOES Y N Number of CERES land ADMs < number of IGBP classes No complete match between CERES and MODTRAN cloud ADMs For CERES category Process of Selecting CERES ADMs for UMD/SRB Alternative options for synthesizing modeled and observed ADMs are under evaluation. ERBE and CERES ADMs Upper: Clear; Lower: Cloudy SZA: 60°-70°; Azimuth: 150°-170° Surface Types for ADMs
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