## 2 Materials and Methods  
The cloud products of the geostationary satellite Communication, Ocean, and Meteorological Satellite (COMS) were used to analyze the occurrence frequency and characteristics of seedable clouds around the Korean Peninsula [31]. COMS, located at 0\({}^{\circ}\) N and 128.2\({}^{\circ}\) E, observes the Korean Peninsula area at a spatial resolution of 4 km \(\times\) 4 km every 15 min. Unlike polar-orbiting satellites or ground observation equipment, the cloud products of geostationary satellites are appropriate for analyzing the characteristics of clouds generated around the Korean Peninsula because they can continuously observe clouds over a wide area [32; 33]. The data used for analysis consisted of cloud fraction (CF), cloud top height (CTH), cloud top temperature (CTP), cloud phase, cloud top pressure (CTP), cloud optical thickness (COT), and rainfall intensity (RI) information collected from hourly data between 0900 and 1800 LST observed from December 2016 to November 2019. It is dangerous to conduct precipitation enhancement experiments at night because atmospheric aircraft needs to fly around the top and bottom of clouds. Therefore, most experiments were conducted in the daytime when a safe field of view was ensured. To detect seedable clouds using satellite data, clouds were classified using the algorithm shown in Figure 1. For satellite data, the grid data around a reference grid of an area of \(5\times 5\) grids was averaged. This was necessary because the data characteristics may not be continuous due to the grid data calculated by each grid of satellite data. Seedable clouds were defined as having a CF exceeding 80%, a CTH within 1-4 km, and a RI below 5 mm/h [28]. The CF represents the percentage of the clouds detected within \(7\times 7\) grids around the reference grid [34]. Since the uncertainty of cloud detection increased as CF decreased toward the edge of the cloud [35], sufficient CF, i.e., exceeding 80%, was defined as a condition in this study. Additionally, for a cloud to be used for seeding, it must have a suitable CTH and little or no natural precipitation. The minimum and maximum CTH were set using the minimum and maximum CTH and combustion rate of flares specified by experiments conducted by [PERSON] et al. [21] and NIMS [36]. Because of the nature of passive sensors in geostationary satellites, low-level atmospheric information of clouds observed by the satellite cannot be determined. As a result, lower-level clouds with a top height exceeding 4 km were not detected. Figure 1: Flow chart of seedable cloud detection algorithm using COMS data (CF is cloud fraction, CTH is cloud top height, RI is rainfall intensity, CTT is cloud top temperature). In precipitation enhancement experiments using atmospheric aircraft, the seeding material serves as an artificial cloud seed, which might help to develop the cloud while causing rainfall (snowfall). The precipitation development process varies with temperature. Therefore, the seeding materials for cold and warm clouds are different [37; 38]. For cold clouds, dry ice or silver iodide (AgI), which serves as the nucleus of ice, are seeded to cause snowfall or rainfall. In warm clouds, hygroscopic calcium chloride (CaCl\({}_{2}\)) or sodium chloride (NaCl) are seeded to cause rainfall [39; 40; 41]. The seedable clouds can be classified as ice or water phase clouds based on satellite images [31]. If a mixed phase is observed, it is classified as an ice-cloud phase if the CTT is below \(-5\,^{\circ}\)C, whereas it is classified as a water-cloud phase if the CTT is \(-5\,^{\circ}\)C or higher [25]. The occurrence frequency of seedable clouds can then be analyzed accordingly [28]. Clouds that could not be classified or did not correspond to the weather conditions presented in this study were excluded from the analysis. In addition, the occurrence frequency of seedable clouds occurred on land and sea and occurrence frequency according to cloud types were analyzed.