HR: 1330h
AN: A12B-0083    [PDF]
TI: Preliminary Results from an Aerosol Assimilation System of MODIS Radiances Using the GOCART Aerosol Transport Model
AU: * Weaver, C
EM: weaver@blueberry.gsfc.nasa.gov
AF: GEST / UMBC, 1000 Hilltop Circle, Baltimore, MD 21250 United States
AU: da Silva, A
EM: dasilva@gmao.gsfc.nasa.gov
AF: NASA / GSFC, Code 910.3, Greenbelt, MD 20771 United States
AU: Chin, M
EM: chin@rondo.gsfc.nasa.gov
AF: NASA / GSFC, Code 910.3, Greenbelt, MD 20771 United States
AU: Ginoux, P
EM: Paul.Ginoux@noaa.gov
AF: NOAA GFDL Princeton University, Forrestal Campus, Route 1, Princeton, NJ 08542 United States
AB: We present results from a simple off-line assimilation system of the radiances from the 7 MODIS channels that sense aerosols over ocean. The Goddard Chemistry and Aerosol Radiation Transport Model (GOCART), which is driven by assimilated meteorology, simulates five aerosol types: dust, seasalt, black carbon, organic carbon and sulfate. This presentation focuses on the forward model that 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 level2 radiances. The off-line assimilation system simply adjusts the aerosol loading in the GOCART model so that the observed minus forward model (O-F) 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 hours. A necessary but not sufficient criterion for success of an assimilation system is that O-F radiance differences are smaller than those of a free-running GOCART model without observational updates. We analyze those geographic locations where the assimilation appears better than the free-running GOCART model and those locations where the updates are being rejected by the GOCART model. We also examine the O-F radiance differences in terms of the scattering angle and discuss possible contributions to these differences from: particle non-sphericity, incorrect refractive indexes, missing small particles, and water leaving radiance from the ocean. We also compare results with an assimilation of MODIS retrieved optical depths. This research is part of an ongoing effort at NASA Goddard to integrate aerosols into the Goddard Modeling and Assimilation Office (GMAO) products.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 3337 Numerical modeling and data assimilation
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting