Geoscience Reference
In-Depth Information
Chapter 25
GSI/WRF Regional Data Assimilation System
and Its Application in the Weather Forecasts
over Southwest Asia
Jianjun Xu and Alfred M. Powell, Jr.
Abstract
In this study, the impact of directly assimilating Advanced TIROS
Operational Vertical Sounder (ATOVS) radiances using the Community Radiative
Transfer Model (CRTM) was evaluated to determine the impact on forecasts over
Southwest Asia. The CRTM was developed by the Center for Satellite Applications
and Research (STAR) and its application was promoted by the Joint Center for
Satellite Data Assimilation (JCSDA). The ATOVS radiance data from the National
Environmental Satellite Data and Information Service (NESDIS), the Gridpoint Sta-
tistical Interpolation (GSI) three-dimensional variational analysis (3DVAR) system
from the National Centers for Environmental Prediction (NCEP), and the Advanced
Research WRF (WRF-ARW) model from the National Center for Atmospheric
Research (NCAR) were employed in this study.
First, this paper will describe the forecasting errors encountered from running
the WRF-ARW model in the complex terrain of Southwest Asia from 1-31 May
2006. The subsequent statistical evaluation is designed to assess the model's surface
and upper-air forecast accuracy. The results show that the model biases caused by
inadequate parameterizations of physical processes are relatively small, except for
the 2-m temperature, as compared to the nonsystematic errors resulting in part
from the uncertainty in initial conditions. The total model forecast errors at the
surface show a substantial spatial heterogeneity and the errors are relatively larger
in higher elevation mountain areas. The performance of 2-m temperature forecasts
is different from the other surface variables' forecasts; the model forecast errors
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