A grid sensitivity study of the Weather Research and Forecasting (WRF) model for simulating surface winds over the small island state of Fiji

Abstract

A grid sensitivity study of the Weather Research and Forecasting (WRF) model was conducted for simulating the surface winds and the diurnal cycle over the small island developing state (SIDS) of Fiji. Two different sets of grid resolutions: 20 km -4 km -1.33 km and 15 km -5 km -1 km are used with the two-way nested approach and 1deg gridded input data from the National Centers for Environmental Prediction -(Final) Operational Global Analysis (NCEP-FNL) as initial and boundary conditions. Simulations are performed for an austral summer (January 2017) and austral winter (July 2017) month using the dynamical-downscaling approach and the tropical suite of the physics parameterization scheme to simulate the surface winds and the diurnal cycle of wind speed for both grid set-ups. The results revealed that the WRF model is able to capture the surface winds and the diurnal cycle of wind speed more accurately for the higher grid resolution of 1 km x 1 km in comparison with the 1.33 km x 1.33 km, indicating that the topographical representation is better in the higher grid resolution. For January (July) the bias reduced from 0.85 m/s (1.04 m/s) to 0.50 m/s (0.83 m/s), which is a reduction of 20.78 % (15.44 %). The Root Mean Square Error (RMSE) reduced from 2.08 m/s (2.55 m/s) to 1.96 m/s (2.50 m/s). The Standard Deviation Error (STDE) is 1.65 m/s (1.92 m/s), which is almost the same for both grids. The diurnal cycle correlation also improved from 0.69 (0.60) to 0.81 (0.75).

High-resolution mesoscale wind-resource assessment of Fiji using the Weather Research and Forecasting (WRF) model

“…Previous studies on the evaluation of the WRF model for simulating surface winds and the diurnal cycle of wind speed for the SIDS of Fiji showed that the standard 1.33 km by 1.33 km grid resolution in a 20 km -4 km -1.33 km grid nesting set up may not be an appropriate grid size to evaluate the surface winds for Fiji; as it was suspected that the topography was not properly resolved and a grid sensitivity study was recommended [24]. Following that recommendation, a grid sensitivity study of the WRF model for simulating the surface winds for the SIDS of Fiji was conducted and it was concluded that the 1 km by 1 km grid resolution of the 15 km -5 km -1 km grid configuration was appropriate to evaluate the wind resources for the SIDS of Fiji [25].…”

“…This paper is an enhancement of the WRF mesoscale wind resource assessment approach applied to small tropical islands from an initial study [24] followed by a grid sensitivity study [25] to finally, the decade-long mesoscale wind resource assessment of Fiji. This study is also an application and evaluation of the mesoscale wind resource modelling using the WRF model.…”

Evaluation of the mesoscale–microscale (WRF–WAsP) coupling methodology for wind resource parameters in Fiji

“…The wind direction at studied sites is dominantly southeasterly but in some cases it's in other directions because of local and island-scale circulations. Apart from the microscale studies, a few mesoscale studies including a Weather Research and Forecasting (WRF) model grid sensitivity study (Dayal et al, 2020a), a WRF model evaluation study (Dayal et al, 2020b) and a decade long mesoscale wind resource assessment study have been conducted for Fiji at a high-resolution of 1 km × 1 km at applicable wind turbine hub-heights to identify potential wind resource areas (Dayal et al, 2021a). A recent study also analyzed the wind resources at the existing 10 MW Butoni wind farm and reported that it is located on a weak wind speed regime of Wind Power Class 1 and has a capacity factor of 5.4% (Dayal et al, 2022).…”