Evaluation of the Regional Representation of ASOS Sunshine Observations

In this study, the hourly solar radiation and daily sunshine duration data compiled from Seoul (108), Daejeon (133), Gwangju (156), and Mokpo (165) in Automated Synoptic Observing Systems (ASOS) during March, June, September, and December from 2019 to 2023 were analyzed to evaluate the regional representation of sunshine observations in different geographical areas across the South Korea. Solar radiation data from Mokpo were compared with data from Seoul, Daejeon, and Gwangju using a hourly 1:1 match-up method. While solar radiations exhibited an increased dispersion with distance from Mokpo, data meeting clear sky conditions (cloud cover ≤ 2) showed a reduced dispersion at all sites with minimal distance-based differences. Daily sunshine duration had numerous outliers due to sky conditions, leading to high variability over time. However, when considering data with cloud cover ≤ 2.4 only, distinct seasonal differences in average sunshine duration were observed, with no discernible trend depending on latitude. Thus, ASOS sunshine observations appear to be representative for their respective regions.