1. Description of the dust storm event
Dust storms blew across Saudi Arabia region during mid-March, 2014. Arising from well inland, the dust and sand swept hundreds of kilometers over coastal Saudi Arabia, Bahrain and Qatar before pouring over the Gulf and across Iran on March 12. Dust is so thick in northern Saudi Arabia that the land is completely obscured from view according to the local news report. In the south, thinner plumes also streak across the United Arab Emirates (UAE).
Continued unstable weather, lasting several days, caused by a surface trough coming from the Red Sea area, brought gusty winds and produced rising dust and sand across the region in the following days.
On March 15, fresh, strong winds over Saudi Arabia were picking up sand and dust as Shamal winds increased. On March 16, northwest winds reached 23-29 mph (37-47 km/h), carrying blowing dust and sand. The lowest visibility was expected to be near 1,000-1,500 m (3,280 – 4,920 ft).
2. Evaluation of WRF-Chem dust forecast model with EUMETSAT observations
During this period, the PME WRF-Chem dust forecast model performance was evaluated with satellite images from the European Organization for the Exploration of Meteorological Satellites (EUMETSAT), the Meteosat Second Generation (MSG). The aerosol optical depth (AOD) (Figs. 1a, 2a) and RGB-dust (Figs. 1c, 2c) from EUMETSAT are used to compare with the model simulated AOD (Figs. 1b, 2b) and vertical integrated dust concentration (Figs. 1d, 2d). The RGB-dust product is RGB composite based upon infrared channels of SEVIRI (services through the 12 spectral bands of its radiometer). Dust appears pink or magenta in this RGB combination. Dry land looks from pale blue (daytime) to pale green (nighttime). Thick, high-level clouds have red-brown tones and thin high-level clouds appear very dark (nearly black).
The large AOD value at southeast of the Kingdom in EUMETSAT (Fig. 1a) is well captured by model (Fig. 1b) at 10z, March 13, 2014, which is consistent with RGB-dust (Fig. 1c) and vertical integrated dust concentration simulated by model (Fig. 1d). Similar results are also obtained at other time period (e.g., 10z, March 16, 2014, Fig. 2). In general, model can capture the dominant dust storm signal especially at the southern part of the Kingdom. The signal tends to be weak in the northern side of the Kingdom sometimes (e.g. Fig. 2b), which will be improved in the future work.
Figure 1. Comparisons of aerosol optical depth (a, b) and vertical integrated dust concentration (c, d) between observations from EUROSAT (a, c) and model outputs (b, d) at 2014031310. The unit for vertical integrated dust concentration in d) is ug/g.
Figure 2. Comparisons of aerosol optical depth (a, b) and vertical integrated dust concentration (c, d) between observations from EUROSAT (a, c) and model outputs (b, d) at 2014031610. The unit for vertical integrated dust concentration in d) is ug/g