4.4 WRF-LES in 250+ real sites: Learnings and Challenges

Montornès, Alex, Pau Casso, Gil Lizcano, Vortex, Spain, and Branko Kosovic, National Center for Atmospheric Research

We are entering a new era in atmospheric modeling. Increased computational resources now allow global models to reach resolution previously achievable only by limited area, mesoscale models. Horizontal grid cell size of global operational forecast models is now on the order of 10 km (approximately 9 km for ECMWF and 13 km for GFS) while global reanalysis data sets have resolution of few tens of kilometers (e.g. ERA-5). The value of limited area models, such as the Weather Research and Forecasting (WRF) model is therefore diminished. Does this mean the end of the mesocale models for operational forecasting and applications like wind resource assessment? Of course not. As global models reach mesoscales, limited area models will have to take advantage of available computational resources and explore new horizons, the microscale. A number for applications including wind energy, pollutant dispersion wildland fire spread prediction, etc. could benefit from turbulence resolving simulations. In recent years advances have been made in coupling mesoscale and microscale simulations. WRF model and algorithms implemented in it represent one of the platforms that enable nearly seamless coupling between mesoscale and microscale simulations.

Building on recent advances in mesoscale to microscale coupling by researchers from the National Center for Atmospheric Research, during the last three years Vortex has been working on the development of a seamless modeling chain based on the WRF's large-eddy simulation (LES) capabilities. This modeling chain produces realistic ten-minute time-series at 110 m grid cell size resolution for any region, under operational deadlines imposed by wind resource assessment. Last year, during 17th Annual WRF Users' Workshop, we presented our approach for solving some of the key limitations in the mesoscale-microscale coupling as well as an initial validation with promising results at eight sites with different hub heights, topographic complexity, meteorological regimes and climate features (Montornes et al., 2016).

We now propose a new contribution that can be divided in two parts. First we show an extended validation of one-year WRF-LES results at about hundred worldwide sites where measurements are available. In the second part, we will use the 250+ sites that we have launched during this year for exploration and analysis in this new modeling field. Finally, we will present current challenges in the mesoscale-microscale integration based on the WRF model with the goal of improving simulations for this new application of the limited area models.

Montornes, A., Casso, P., Lizcano, G., Kosovic, B.: WRF-LES in the real world: Towards a seamless modeling chain for wind industry applications. 17th Annual WRF Users' Workshop. 2016.