Seasonal characteristics of CIE standard sky types in northeast China

This study is based on the fifteen standard sky models proposed by the International Commission of Illumination (CIE) and explores the sky luminance distribution throughout the severe cold regions of China. The experiment analysis is based on 22,829 sets of effective luminance data from January 2019 to December 2019. The Tregenza method and the normalization ratio method are used to analyze changes in the sky environment throughout the year in Northeast China. The results indicate that the standard sky models proposed by the CIE can represent the basic characteristics of the sky over a whole year in Harbin, but the frequency of each sky type is clearly different. Type V.4 (CIE standard clear sky, low illuminance probability) has a frequency exceeding 22% over the year, and is the most common type of sky in Harbin, while type VI.6 (white blue turned sky with broad solar corona) has the lowest frequency type. The use of these two methods indicates that the frequency of clear sky in Harbin over the year exceeds 50%, and this mainly occurs in spring, autumn and winter. The probability of overcast and partly cloudy skies is over 20%, and in summer an overcast sky is more probable. When comparing against different solar elevations, it is found that for solar elevations below 50°, V.4 is the most common sky type with a probability above 15%, whilst for solar elevations above 50°, type I.1 is the most frequent.