1. Introduction of the WRF-Chem dust forecast model
In collaboration with PME, NCAR developed a WRF-Chem based dust forecast system for Saudi Arabia. The preliminary WRF-Chem dust forecasts for the Saudi Arabian domain at 21.6 km resolution were started on an operational mode on December 18, 2013. The WRF-Chem domain is currently the same as the operational RTFDDA domain 1. The daily WRF-Chem runs were configured for the 18Z cycle initially; however, due to some conflicts with the daily operational RTFDDA runs and the postprocessing, the WRF-Chem runs were switched to the 06Z cycle at the end of January 2014. The analysis period is 24-h and the forecast length is 48-h. During the analysis period, the hourly analysis fields from the operational RTFDDA 4-cycle runs are combined and are used to provide dynamic information for WRF-Chem through grid nudging (Fig. 1). The chemical fields are also spun up during the analysis period.
The daily dust forecasts are displayed on the web. The displayed variables include aerosol optical depth (AOD) at 600 nm, dust concentrations at surface, and vertically integrated dust concentrations. The dust forecasts are constantly examined and compared with the WMO dust observations and forecasts in an effort to understand the strengths and weaknesses of the WRF-Chem modeling system.
Figure 1. Schematics of the WRF-Chem dust forecast system.
2. Structure of the WRF-Chem dust forecast system
2.1 Location of the model codes: the hydrohome directory
saudi-c3: /home/pmefdda/hydrohome
The hydrohome directory contains all the model source codes.
2.2 Location of the executables: the datbin directory
saudi-c3: /home/pmeop/datbin
The datbin directory contains some of the utility files that download the GFS data, SST data and NCEP observation data.
2.3 Where to submit the job: the GMODJOBS directory
saudi-c3: /home/pmefdda/data/GMODJOBS
All model jobs are placed under this directory using different job id names. For NCAR-PME real-time WRF-Chem dust runs, the job is named as GWRFDUST. All model run control files can be found under this directory and this is also where all the model jobs are submitted.
The emissions files are located under:
saudi-c3: /home/pmefdda/data/GMODJOBS/GWRFDUST/wrfrun
2.4 Where the jobs are running and where to find the model data: the cycles directory
saudi-c3: /home/pmefdda/data/cycles
The cycles directories are the directories where the jobs are actually running and where the model data are stored. For the WRF-Chem dust runs, the running directory is:
saudi-c3: /home/pmefdda/data/cycles/GWRFDUST/GFS_WCTRL
The scripts for doing post processing of the WRF-Chem dust forecasts are located under:
saudi-c3: /home/pmefdda/data/cycles/GWRFDUST/GFS_WCTRL/plots