OBSERVED LONG-TERM OZONE AND UV CHANGES

摘要

The ozone decline is continuing through 1999. Total columnar ozone has been decreasing over middle latitudes (20° - 60° between 1979 - to - present at rates of about 4% in winter/spring and about 2% per decade in the summer. This long-term trend was interrupted by periods of enhanced volcanic activity, which resulted to significant ozone losses (more than 5% per year) following large volcanic eruptions (El Chichon in 1982 and particularly Mt Pinatubo in 1991). Linked to the ozone decrease are well-documented global increases of the harmful UV-B solar radiation levels reaching ground level. The erythemal dose over middle latitudes is increasing at rates exceeding 5% per decade while the solar UV irradiance at the lower wavelengths is increasing by more than 10% per decade. The long-term UV variability has a QBO and regionally an ENSO component, which cannot be overlooked, even in comparison with the amplitude of the annual cycle.