## 2 Data and Sea Breeze Cases  
The meteorological data observed by the Korea Meteorological Administration (KMA) are provided to users after data processing in the quality control (QC) system. The Automatic Weather Station (AWS) measures temperature, pressure, humidity, wind, and precipitation every minute. The Wind Profiler Radar (WPR) is an operating device that uses electromagnetic signals to remotely sense wind speed and direction at various altitudes above the ground every 10 min. In Yeongdong region, Bukgangneung (BGN) has the only WPR operating station. We employed 1 h interval data from 8 AWS and 1 WPR of the KMA near the coast of Yeongdong for optimization and validation (see Figure 1b). Table 1 describes the main attributes of the stations. The meteorological variables used in this study are 2 m temperature, 2 m relative humidity, and 10 m wind (speed and direction) of the AWSs, and the vertical wind structure from the WPR.  
We used the sea breeze selection algorithm of [PERSON] et al. [14] to select the sea breeze cases in the Yeongdong region. For the selection of the sea breeze cases, several meteorological variables at Gangneung (GN) and a buoy station over the sea near Okgye and Samcheok are used, including precipitation, wind direction, air temperature, and sea level pressure. Station GN is an Automated Surface Observing System (ASOS) station located about 5.2 km inland from the coast (Figure 1b). The buoy station is located approximately 70 km seaward from the coast between Okgye and Samcheok.  
Based on a data set from 2009 to 2018, [PERSON] et al. [14] reported that GN had a total of 595 days of sea breezes, which occurred most frequently in April--June with a total of 268 days. As the initial and boundary conditions for WRF are provided by the high-resolution global final analysis (FNL) data, which have been produced since July 2015 by the National Centre for Environmental Prediction (NCEP)'s Global Forecast System (GFS), we have selected our sea breeze cases for the period of April--June from 2016 to 2021. This period depicted the lowest monthly precipitation and the largest difference in surface temperature between sea and land.  
Although sea breeze is a day-by-day phenomenon routinely observed in coastal areas, it is hard to be discerned from the synoptic scale winds. Thus, we applied strict rules to select the sea breeze cases for this study, first by excluding the days with precipitation to reduce the impact of synoptic fields, and then by including the following days: (1) when the wind direction is sustained between 0\({}^{\circ}\) and 110\({}^{\circ}\) for more than 6 h during the daytime, considering the north-northwest-south-southeast orientation of the coastline in Yeongdong; (2) when the wind direction is sustained between 110\({}^{\circ}\) and 360\({}^{\circ}\) for more than 6 h during the nighttime; (3) when the land surface temperature is higher than the sea surface temperature for more than 6 consecutive h during the daytime; and (4) when the sea level pressure over the sea is 0.5 hPa higher than that over the land. Through this procedure, we have selected the following sea breeze cases for this study: 16 April 2018, 12 April 2019, and 3 May 2019 for optimization, and 17 April 2018, 11 April 2020, and 15 April 2021 for validation.