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    Direct Insertion of MODIS Radiances in a Global Aerosol Transport Model

    Source: Journal of the Atmospheric Sciences:;2007:;Volume( 064 ):;issue: 003::page 808
    Author:
    Weaver, Clark
    ,
    da Silva, Arlindo
    ,
    Chin, Mian
    ,
    Ginoux, Paul
    ,
    Dubovik, Oleg
    ,
    Flittner, Dave
    ,
    Zia, Aahmad
    ,
    Remer, Lorraine
    ,
    Holben, Brent
    ,
    Gregg, Watson
    DOI: 10.1175/JAS3838.1
    Publisher: American Meteorological Society
    Abstract: In this paper results are presented from a simple offline assimilation system that uses radiances from the Moderate Resolution Imaging Spectroradiometer (MODIS) channels that sense atmospheric aerosols over land and ocean. The MODIS information is directly inserted into the Goddard Chemistry and Aerosol Radiation Transport model (GOCART), which simulates the following five aerosol types: dust, sea salt, black carbon, organic carbon, and sulfate. The goal is to produce three-dimensional fields of these aerosol types for radiative forcing calculations. Products from this assimilation system are compared with ground-based measurements of aerosol optical depth (AOD) from the Aerosol Robotic Network (AERONET). Insertion of MODIS radiances draws the GOCART model closer to the AERONET AOD. However, there are still uncertainties with surface reflectivity over moderately bright surfaces and with the amount of absorbing aerosol. Also described is the assimilation cycle. The forward model takes the aerosol information from the GOCART model and calculates radiances based on optical parameters of the aerosol type, satellite viewing angle, and the particle growth from relative humidity. Because the GOCART model is driven by previously assimilated meteorology, these forward model radiances can be directly compared with the observed MODIS level-2 radiances. The offline assimilation system simply adjusts the aerosol loading in the GOCART model so that the observed minus forward model radiances agree. Minimal change is made to the GOCART aerosol vertical distribution, size distribution, and the ratio of the five different aerosol types. The loading in the GOCART model is updated with new MODIS observations every 6 h. Since the previously assimilated meteorology provides surface wind speed, radiance sensitivity to wind speed over rough ocean is taken into account. Over land the dark target approach, also used by the MODIS?atmosphere group retrieval, is used. If the underlying land surface is deemed dark enough, the surface reflectances at the 0.47- and 0.66-?m wavelengths are constant multiples of the observed 2.13-?m reflectance. Over ocean the assimilation AOD compares well with AERONET, over land less so. The results herein are also compared with AERONET-retrieved single-scattering albedo. This research is part of an ongoing effort at NASA Goddard to integrate aerosols into the Goddard Modeling and Assimilation Office (GMAO) products.
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      Direct Insertion of MODIS Radiances in a Global Aerosol Transport Model

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    http://yetl.yabesh.ir/yetl1/handle/yetl/4218424
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    • Journal of the Atmospheric Sciences

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    contributor authorWeaver, Clark
    contributor authorda Silva, Arlindo
    contributor authorChin, Mian
    contributor authorGinoux, Paul
    contributor authorDubovik, Oleg
    contributor authorFlittner, Dave
    contributor authorZia, Aahmad
    contributor authorRemer, Lorraine
    contributor authorHolben, Brent
    contributor authorGregg, Watson
    date accessioned2017-06-09T16:53:24Z
    date available2017-06-09T16:53:24Z
    date copyright2007/03/01
    date issued2007
    identifier issn0022-4928
    identifier otherams-76022.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4218424
    description abstractIn this paper results are presented from a simple offline assimilation system that uses radiances from the Moderate Resolution Imaging Spectroradiometer (MODIS) channels that sense atmospheric aerosols over land and ocean. The MODIS information is directly inserted into the Goddard Chemistry and Aerosol Radiation Transport model (GOCART), which simulates the following five aerosol types: dust, sea salt, black carbon, organic carbon, and sulfate. The goal is to produce three-dimensional fields of these aerosol types for radiative forcing calculations. Products from this assimilation system are compared with ground-based measurements of aerosol optical depth (AOD) from the Aerosol Robotic Network (AERONET). Insertion of MODIS radiances draws the GOCART model closer to the AERONET AOD. However, there are still uncertainties with surface reflectivity over moderately bright surfaces and with the amount of absorbing aerosol. Also described is the assimilation cycle. The forward model takes the aerosol information from the GOCART model and calculates radiances based on optical parameters of the aerosol type, satellite viewing angle, and the particle growth from relative humidity. Because the GOCART model is driven by previously assimilated meteorology, these forward model radiances can be directly compared with the observed MODIS level-2 radiances. The offline assimilation system simply adjusts the aerosol loading in the GOCART model so that the observed minus forward model radiances agree. Minimal change is made to the GOCART aerosol vertical distribution, size distribution, and the ratio of the five different aerosol types. The loading in the GOCART model is updated with new MODIS observations every 6 h. Since the previously assimilated meteorology provides surface wind speed, radiance sensitivity to wind speed over rough ocean is taken into account. Over land the dark target approach, also used by the MODIS?atmosphere group retrieval, is used. If the underlying land surface is deemed dark enough, the surface reflectances at the 0.47- and 0.66-?m wavelengths are constant multiples of the observed 2.13-?m reflectance. Over ocean the assimilation AOD compares well with AERONET, over land less so. The results herein are also compared with AERONET-retrieved single-scattering albedo. This research is part of an ongoing effort at NASA Goddard to integrate aerosols into the Goddard Modeling and Assimilation Office (GMAO) products.
    publisherAmerican Meteorological Society
    titleDirect Insertion of MODIS Radiances in a Global Aerosol Transport Model
    typeJournal Paper
    journal volume64
    journal issue3
    journal titleJournal of the Atmospheric Sciences
    identifier doi10.1175/JAS3838.1
    journal fristpage808
    journal lastpage827
    treeJournal of the Atmospheric Sciences:;2007:;Volume( 064 ):;issue: 003
    contenttypeFulltext
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    DSpace software copyright © 2002-2015  DuraSpace
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