SIMULATIONS VS. OBSERVATIONS OF SUPERCOOLED CLOUD LIQUID WATER AT GROUND LEVEL; SENSITIVITY TO MODEL RESOLUTION AND CLOUD MICROPHYSICS PARAMETERIZATIONS

摘要

We investigate the potential for predicting episodes of in-cloud icing at ground level, by using a stateof-the-art numerical weather prediction model. For this purpose, we run the Weather Research and Forecasting (WRF) model at different horizontal resolutions, and with different microphysics schemes. Predicted values of supercooled cloud liquid water content SLWC and median volume droplet diameter (MVD) are validated against precise rotating multi cylinder measurements on a hill top in the northern Finland. We obtain the overall best result, with mean absolute error (MAE) of predicted SLWC as low as 0.08 g/m3 when the highest model resolution is applied together with the Thompson microphysics scheme. The quality of the SLWC predictions decreases dramatically with decreasing model resolution. A systematic difference in predictive skill is also found between the microphysics schemes applied. A comparison between measured and predicted MVD shows that when setting the droplet concentration equal to 250 cm-1, the model predicts MVD ranging from 12 -20 urn, which corresponds well with the measurements. However, the variation from case to case is not captured by the current microphysics schemes.