A Study On Comparison Of The Boundary Layer Parameterization Schemes In The WRF Model During Clear And Cloudy Days

One mesoscale mode, WRF model (3.4), is used to evaluate the model performances of simulating different meteorological conditions and boundary layer structural characteristics in Shou County in China during clear and cloudy days with five boundary layer parameterization schemes. The five boundary layer parameterization schemes are ACM2, BL, MYJ, MYNN2.5, YSU, respectively. Results show that:(1) During clear days, the non-local boundary layer parameterization (PBL) schemes can reproduce the weather condition well with higher simulated temperature and lower humidity in the daytime comparing to other schemes, but the simulated wind speed and wind direction are poor. At night, all PBL schemes have similar results. In detail, ACM2 scheme has greater ability to simulate temperature and humidity, while MYJ scheme does on wind speed and wind direction. When surface is heated by the sun, turbulent mixing strengthens and unstable stratification lasts. Simulation results are best from non-local schemes. These non-local schemes show higher mixing layer height, higher temperature, lower humidity and stronger turbulent movement, then more matter and energy can be carried to the upper air. Comparing with these three non-local schemes (MYN, MYJ, BL), the BL scheme can’t simulate the characteristics of potential temperature and relative humidity in lower atmosphere accurately, especially the wind speed and wind direction. All five schemes can successfully reproduce thermal inversion, humid inversion and low-level jet.(2) During cloudy days, ACM2 and YSU schemes have greater ability to simulate the time of cloud existence, cloud base height, thickness of the cloud. These results from BL scheme are poor. ACM2 scheme shows better short and long wave radiations because of its good ability in simulating cloud. Simulation results of 2m temperature and specific humidity are best when we use ACM2 scheme, but local schemes have advantages in the prediction of wind speed and wind direction. No significant differences of sensible heat flux, latent heat flux and friction velocity are found among the five boundary layer schemes; Under weak unstable conditions during the day, non-local schemes considered the large eddy transport can reflect the potential temperature and humidity profiles better. Except MYJ, other schemes can successfully simulate the wind speed profiles and wind direction. Under the weak stable condition at night, five schemes all can simulate the weak unstable stratification, inverse wet structure, jet stream and so on.(3) From above we can see that PBL schemes have different effects on basic meteorological fields under different weather conditions (clear and cloudy days). PBL schemes do little impact on short wave radiation during clear days. But during cloudy days, the simulated 2m temperature is different because of their different ability to simulate short wave radiation. Each PBL scheme has similar simulated results (time serious and vertical profile of 2m temperature,2m relative humidity, 10m wind speed and wind direction, potential temperature) under clear and cloudy days. Analyzing the simulated planetary boundary layer height (PBLH), non-local PBL schemes show stronger turbulent movement and higher PBLH than local schemes. While, comparing with the height from the profile of potential temperature, the error is large under clear days but small deviation is shown under cloudy days. At night, all schemes simulate similar results.