## 4 Results
### Simulations
The smaller potential temperature variation below \(\sim\)1 km on 18 January was well-reproduced in the four simulations, except for the large decrease in the potential temperature from \(\sim\)1800 LST on 18 January. The simulation with the MYNN scheme showed the rapid increase in the potential temperature below \(\sim\)1 km compared with the other simulations. Additionally, the height of the layer with a nearly constant potential temperature was the highest in the MYNN scheme (\(\sim\)1 km) and similar to that in the observation. Thus, we considered the MYNN scheme as the most accurate scheme in simulating the CBL development during the daytime on 17 January. This result is in line with that of another optimization study of WRF physical parameterization schemes [32]. At the initial stage of moisture advection on 17 January, the simulated water vapor mixing ratio near the surface was generally smaller than that at the upper level (height of \(\sim\)1 km), whereas the observed water vapor mixing ratio was the largest near the surface. This implied that the advected moist air was not well-mixed with the pre-existing air near the surface in the simulations. The small-scale turbulences that play a large role in the mixing of air were not accurately reproduced by the PBL schemes in the study. Additionally, the amount of the advected moisture in the four simulations was generally less than that in the observation. From \(\sim\)1800 LST on 18 January, the simulated water vapor mixing ratio below \(\sim\)1 km decreased with time in general. We found that the simulated moisture advection ended earlier than the observed one, as shown in the 2-m air temperature time series. The simulation with the MYNN scheme showed the strongest moisture advection among the four simulations. Due to the strongest moisture advection and highest CBL \begin{table}
\begin{tabular}{c c c c c c c c c} \hline  & \multicolumn{4}{c}{**MBE**} & \multicolumn{4}{c}{**RMSE**} \\ \hline  & **YSU** & **MYJ** & **MYNN** & **ACM2** & **YSU** & **MYJ** & **MYNN** & **ACM2** \\ \hline
2-m air temperature (°C) & \(-0.93\) & \(-0.20\) & \(-0.53\) & \(-0.96\) & \(1.88\) & \(1.48\) & \(1.64\) & \(1.84\) \\
10-m wind speed (m s\({}^{-1}\)) & \(-1.38\) & \(-0.69\) & \(-1.62\) & \(-1.55\) & \(1.80\) & \(1.30\) & \(1.98\) & \(1.85\) \\ \hline
925 hPa air temperature (°C) & 0.20 & 0.24 & 0.47 & 0.28 & 0.80 & 0.76 & \(1.19\) & \(0.78\) \\
925 hPa wind speed (m s\({}^{-1}\)) & \(-0.65\) & \(-0.74\) & \(-0.62\) & \(-0.27\) & \(2.34\) & \(2.45\) & \(2.64\) & \(1.90\) \\ \hline
850 hPa air temperature (°C) & 0.22 & 0.25 & 0.86 & 0.62 & 1.41 & 1.35 & \(1.82\) & \(1.24\) \\
850 hPa wind speed (m s\({}^{-1}\)) & \(-0.58\) & \(-0.49\) & \(-1.53\) & \(-0.18\) & \(2.79\) & \(2.92\) & \(3.31\) & \(2.98\) \\ \hline \end{tabular}
\end{table} 
Table 1: Mean bias error (MBE) and root mean square error (RMSE) of the simulated 2-m, 925 hPa, and 850 hPa air temperature and 10-m, 925 hPa, and 850 hPa wind speed. height, the water vapor mixing ratio increased above 2 km, similar to the observation. Therefore, we concluded that the simulation with the MYNN scheme performed the best in simulating the moisture advection from ~1900 LST on 17 January. To demonstrate the structures of the lower troposphere in the four simulations in detail, the vertical profiles of the simulated and observed potential temperature are shown in Figure 8. From 1000 to 1500 LST on 17 January, the CBL developed from the initial to the mature stage (Figure 8a,b). At the initial stage, the CBL height in the observations (~0.2 km) was similar to those in the simulations with the MYJ and MYNN schemes, and smaller than those in the simulation with the YSU and ACM2 schemes. At the mature stage, the CBL developed up to ~1.1 km. The CBL heights of the four simulations were smaller than the observed value; the simulation with the MYNN scheme showed the highest CBL height (~0.9 km), which was the closest to the observed CBL height.