Spatio-temporal characteristics in the clearness index derived from global solar radiation observations in Korea

Yeonjin Jung, Hana Lee, Jaemin Kim, Youngbum Cho, Jhoon Kim, Yun Gon Lee

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Abstract

The spatio-temporal characteristics of the clearness index (KT) were investigated using daily global solar irradiance measurements (290-2800 nm) for the period of 2000-2014 at 21 sites in Korea, a complex region in East Asia with a distinct monsoon season and heavy aerosol loading year-round. The annual mean KT value for all sites is 0.46, with values of 0.63 and 0.25 for clear and overcast skies, respectively. The seasonal variations in monthly average KT show a minimum of 0.37 in July at all sites except for Jeju, where the value was 0.29 in January. The maximum value (KT = 0.51) is observed in October, followed by a secondary peak (KT = 0.49) during February-April. The lowest KT value (KT = 0.42) was observed at both the Seoul and Jeju sites, and the highest (KT = 0.48) in the southeastern regions. Increases in average KT exceeding 4% per decade were observed in the middle and southeastern regions, with the maximum (+8% per decade) at the Daegu site. Decreasing trends (< -4% per decade) were observed in the southwestern regions, with the maximum (-7% per decade) at the Mokpo site. Cloud amount, relative humidity, and aerosol optical depth together explained 57% of the variance in daily mean KT values. The contributions of these three variables to variations in KT are 42%, 9% and 6%, respectively. Thus, the variations in KT in Korea can be primarily attributed to the presence of clouds and water vapor, with relatively weak aerosol effects.

Original languageEnglish
Article number55
JournalAtmosphere
Volume7
Issue number4
DOIs
Publication statusPublished - 2016

All Science Journal Classification (ASJC) codes

  • Environmental Science (miscellaneous)

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