Verification of WRF wind field hindcast forced by different initial and boundary conditions over the Persian Gulf: Comparison with synoptic data and QuikSCAT and ASCAT satellites data

The Persian Gulf with subtropical climate is located between latitudes of 23-30 degrees, whit its coast adjoiner to Iraq, Kuwait, Saudi Arabia, Qatar and United Arab Emirates from one side and to Iran from the other side. The Persian Gulf’s width in widest part is 370 km and its length is 990 km. For people living near the sea and the surrounding coastal area as well as construction of onshore and offshore structures, knowledge and understating of the wind field and its variability is essential. In addition, the most common effect of wind is seen in wind driven currents, swells, upwelling and down-welling systems. Moreover wind stress plays a key role in the modeling of air sea interaction phenomenon, e.g., determination of the drag coefficient. Although other factors such as wind palfern and oceanic current are also contributing to the in determination of this coefficient but the wind is the main governing factor. In other words, any inaccuracy in determination of the sea surface wind field could cause a large over or under estimations in atmospheric and oceanic estimations.
This work is devoted to verify the effects of different initial and boundary condition in global data (using reanalysis and analysis datasets) on numerical simulations of WRF (Weather Research and Forecasting) model over the Persian Gulf area. The main obstacle in the verification and evaluation of a model simulation is the lack of observation data with fine spatial and temporal resolution, in particular for offshore areas. Fortunately, in onshore areas, the existence of weather stations has solved the problem somehow, and for offshore areas satellite data are found to be the best dataset considering the spatial coverage. In the present study, simulations of WRF model are compared with different type of observation data. In this research, two types of data are used for verifying the model, i.e. Synoptic stations data and Satellite data (QuikSCAT and ASCAT).
The WRF model version 3.4.1 is employed with ARW dynamical core for simulating of sea surface wind field over the Persian Gulf region. Considering the connection and information exchange between the domains, a two way nesting method is applied in simulations. As the goal was just to verify the effects of different initial and boundary conditions on simulations, therefore, for all the simulations the number of domains and their analogous grid sizes are considered the same. For these simulations three domains are considered the main domain approximately covers the whole are of the Middle East, from West and some parts of Far East with 36km spatial grid spacing. First nested domain covers the southern half of Iran along with marginal countries of Persian Gulf, with a 12km spatial grid resolution and ultimately, the innermost domain of the Persian Gulf that also includes some parts of Oman Sea with 4km grid spacing. The time step for simulations is assumed 216seconds and the time period for each simulation is 30hours, from which the first 6 hours are assumed as spin-up time. To provide the initial and boundary conditions three datasets of ERA-Interim (ECMWF Re-Analysis Interim), NCEP-FNL and NCEP-R2 are employed.
Along with lots of effective factors, results from this research show that one of the sources of error in the WRF model wind simulations is the selection of initial and boundary conditions (input data). The obtained results of this work reveal that for the surface wind hindcast simulations over the Persian Gulf using WRF model, the ECMWF ERA-Interim data is a more suitable dataset to provide the initial and boundary conditions, rather than the NCEP-FNL and NCEP-R2 data. However, the NCEP-FNL is an alternative data set when the ERA-Interim data has some lacks.