Using a Network of Scintillometers and Ceilometers for Validation of the WRF-mesoscale Model

Limited area models and meso-scale models are frequently used for detailed weather forecasting, for atmospheric and climate research, and to provide input for air quality models. To forecast the wind and temperature profiles correctly in the lowest part of the ABL, in particular the the atmospheric boundary-layer (ABL) scheme and the land-surface (LS) scheme are important. Usually the ABL schemes for these models are validated against local observations (turbulent fluxes and tower observations). However, since the model calculates fluxes and profiles on a grid scale, one should also validate calculated and observed turbulent surface fluxes on a larger spatial scale than just by local eddy correlation observations.

In this study we evaluate the ABL scheme and the land-surface scheme of the meso-scale model WRF by means of a network of scintillometers and ceilometers over different terrain types in the Netherlands in addition to the Cabauw tower observations. A scintillometer is a measurement device that uses a light beam that travels from a transmitter to a receiver over a path length of typically 500 m to 10 km. The degree of light beam attenuation is a measure for the turbulence intensity, and this is used to derive the area averaged turbulent heat fluxes. As such it is an ideal device for model validation in heterogeneous terrain. A ceilometer is measurement device that measures the boundary-layer height, which is usually unavailable from routine observations. Since WRF recently introduced the YSU scheme with convective non-local momentum transport and prescribed entrainment, we will pay special attention to this upgrade. This will be shown for e.g. the GABLS3 case study period.

The main findings are that WRF estimates the wind and temperature profiles well, but overestimates the turbulent surface fluxes. The introduction of the nonlocal momentum mixing slightly improves the wind profiles during the day, but it appears to be especially beneficial for the representation of the night time low-level jet.