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Abstract
Abstract. The minimum eddy diffusivity (Kzmin) in the planetary boundary layer (PBL) scheme can influence the model performance when simulating meteorological parameters such as temperature. However, detailed studies on the sensitivities of the simulated temperatures to the settings of Kzmin are still lacking. Thus, in this study we evaluated the performance of the ACM2 (Asymmetrical Convective Model version 2) scheme in the WRF (Weather Research and Forecasting) model with different Kzmin settings when simulating the spatiotemporal distribution of the temperature in the region of Beijing, China. Five constant values and a function were implemented in the model to calculate Kzmin, and the simulation results with different Kzmin settings were compared and analyzed. The results show that the increase in Kzmin leads to an elevation of the 2 m temperature, especially at nighttime. We figured out that the deviation in the 2 m temperature at night is mainly caused by the different estimations of the turbulent mixing under stable conditions in simulation scenarios with different Kzmin settings. Moreover, the spatial distribution of the temperature deviation indicates that under various underlying surface categories, the change in Kzmin exerts a distinct influence on the prediction of the 2 m temperature. This influence was found to be stronger during the nighttime than during the daytime, in plain areas than in mountain areas, and in urban areas than in non-urban areas. During the night in the urban areas, the influence on the simulated 2 m temperature brought about by the change in Kzmin is the strongest. In addition, the model performance using a functional-type Kzmin in the ACM2 scheme for capturing the spatiotemporal distribution of the temperature in this region was also compared with that using a constant Kzmin.
Highlights
The planetary boundary layer (PBL) is a thin layer at the bottom of the atmosphere, which responds to a surface change within an hour or less (Stull, 1988)
The simulation results of the 2 m temperature and the 10 m wind speed were compared with the observational data provided by the above-mentioned IAP, CAS station, and four automatic weather stations (AWSs) to evaluate the model performance
We evaluated the performance of the Asymmetrical Convective Model version 2 (ACM2) scheme with different Kzmin settings in the estimation of the 2 m temperature (T2), surface skin temperature (TSK), and near-surface air temperature (T_level1) in the area of Beijing, China
Summary
The planetary boundary layer (PBL) is a thin layer at the bottom of the atmosphere, which responds to a surface change within an hour or less (Stull, 1988). Within the PBL a noticeable diurnal change in the temperature usually occurs, mainly caused by the warming and cooling of the ambient air by the ground surface during the daytime and the nighttime through turbulent mixing. Turbulence in the PBL is an important form of air motion and plays a critical role in vertically diffusing momentum, heat, moisture, and pollutants (Du et al, 2020). It is essential to accurately estimate the effects of turbulence on the vertical mixing within the PBL in weather and air quality models. The vertical mixing caused by turbulence is usually parameterized using PBL closure schemes.
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