Spatiotemporal variability of total cloud cover measured by visual observation stations and their comparison with ERA5 reanalysis over South Korea

Abstract

This analysis investigates the spatiotemporal variation of total cloud cover (TCC) across South Korea from 96 visual observation stations (VOS) during the years 2010-2019. The thin-plate spline interpolation technique is used to interpolate the spatial variation of TCC within the country. The annual average of TCC distribution is closely related to topographical features and does not show excessive variation, with 50-56% over land. The seasonal TCC distribution has the lowest (highest) pattern in spring (summer), with a minimum (maximum) pattern of approximately 45% (95%). The lowest pattern in spring and highest pattern in summer may be due to the combined effect of lower cloud cover with TCC during March, and higher cloud cover with TCC from June to July. Interpolated VOS data are compared with the TCC obtained from ERA5 reanalysis products. The correlation coefficient between VOS and ERA5 is higher than 0.80 on the eastern coast, and approximately 0.20-0.40 on the western coast, indicating a strong and poor sampling effect. The largest variability between VOS and ERA5 is observed during the winter season, with a percentage deviation of −70-20%, possibly due to inaccurate cloud detection under cold low-level atmospheric temperatures or snow cover. In summer, variability is −35-40%, which is slightly less than that in winter, possibly because of the incorrect detection of frequently occurring cumulus clouds. Principal component analysis of the TCC variability used to examine the relationship with other climate parameters. The first principal component, containing the major portion, correlated with precipitation, diurnal temperature, humidity, atmospheric pressure, and wind speed, with correlation coefficients of 0.293, 0.246, −0.360, −0.258, and 0.470, respectively, indicating positive or negative relationship. We believe the outcomes from this study will contribute a better understanding of climate over South Korea and establish links between East Asia and the Pacific Ocean cloud formation.

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