Title: Variational assimilation of MODIS aersosol optical depth over east Asia region

Authors: Zhiquan Liu (JCSDA)
Quanhua Liu (JCSDA)
Hui-Chuan Lin (NCAR)
Craig Schwartz (NCAR)

Capability of assimilating NASA MODIS Aerosol Optical Depth (AOD) product is developed in NCEP GSI 3DVAR data assimilation system. Community Radiative Transfer Model (CRTM) is extended to include aerosol's absorption and scattering effects for visible and near infrared bands. This allows CRTM served as the AOD observation operator and used in data assimilation system. The corresponding Jacobian model of AOD forward operator is also developed to facilitate the gradient's calculation of the cost function as required by variational iteration procedure. In addition, analysis variables in the GSI system are expanded to include 14 aerosol species in order to initializing GOCART aerosol module, which is built in the WRF-Chem model. The newly developed AOD assimilation system is applied to dust storm case occurred in March 2010 over East Asia region. This dust storm is under-predicted by the WRF-Chem model initialized from NCEP global meteorological field. The statistics of the amplitude and length-scale of the aerosol background error is obtained. This is important for determining the relative weighting of the AOD observation and the background from a short-term forecast as well as the propagation of observation information from observed areas to unobserved areas. Assimilating MODIS AOD observation improves clearly the aerosol analysis and forecast when comparing independent AERONET AOD observations.

GMAO Head: Michele Rienecker Global Modeling and Assimilation Office NASA Goddard Space Flight Center

Curator: Nikki Privé Last Updated: May 27 2011