Forty-year (1971-2010) semiquantitative observations of visibility-cloud-precipitation in Korea and its implication for aerosol effects on regional climate

摘要

Forty-year (1971-2010) observations of cloud cover and types have been analyzed, and implications on the effects of aerosol-cloud feedback were explored. Cloud cover and types have been observed over Korea on the basis of visible (human-eye) attributes without any change in official observing instructions. Visibility has been used as an ongoing proxy measure of aerosol concentrations, and observed meteorological variables such as sunshine duration and precipitation have been employed to analyze aerosol causes and implications for urban and regional climate. The analysis revealed persistent decade-long patterns in Korea: steadily reduced visibility (-0.37 km/yr), consistently decreasing sunshine duration (-0.06 %/hr), and declining occurrence of light precipitation. Spatial distributions of sunshine duration and visibility exhibited more localized variations in the early period (1971-1990), and tended to be more uniform throughout Korea over more recent years (1991-2010), implying the recent regional-scale impact of cloud change over northeast Asia. Cloud analysis results showed that the five most common types were stratocumulus (S_c), cirrus (C_i), altostratus (A_s), stratus (S_t), and nimbostratus (N_s), with occurrences of 33%, 17%, 17%, 9%, and 8%, respectively. Occurrence of rarely precipitating or nonprecipitating low-level S_c clouds showed an increasing (+0.34%/yr), but no (or only minor) effects of aerosols on heavy precipitation such as cumulus cloud types were found. Cloud cover in the range of 6/10 to 8/10 units has increased by 31.5 ± 6.5%, and occurrences of both cloud-free (～2/10 units) and overcast (～8/10 units) conditions have decreased.