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Introduction

This exercise illustrate the basic structure and flow of a cycling data assimilation system, as shown in this chart (time doesn't match with the new case). It consists of running the GSI analysis with an ARW netcdf background field, and then the GSI analysis provides the initial fields for running a WRF-ARW forecast. The forecast output can be used as the GSI background for next GSI analysis.

The regional NAM BE is employed as the background error covariance and only conventional observations are assimilated in this example.

There are 4 steps in this GSI-ARW cycling data assimilation exercise:

• Step 1: GSI Data Analysis for 12Z of August 12, 2018. This step is similar to the online exercise ARW 3DVAR with conventional data (PrepBUFR)
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• Step 2: WRF-ARW model forecast at 12Z of August 12, 2018, using the GSI analysis from step 1.
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• Step 3: GSI Data Analysis for 18Z of August 12, 2018, using the 6-hour forecast output from step 2.
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• Step 4: WRF-ARW model forecast at 18Z of August 12, 2018, using the GSI analysis from step 3.
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