Long-term Trends of Solar UV Radiation

Figure 1 shows increasing trend (confidence level: 99%) of annual accumulation of daily erythemal UV radiation at Tsukuba during the overall observation period, with an increase rate of 4.6% per decade (33.0 kJ/m² per decade). As per "Long-term Trends of Total Ozone," total ozone shows a slight increase in the 1990s and early 2000s, with no discernible trend in recent years. Accordingly, the increasing trend in erythemal UV radiation cannot be explained solely by overall ozone changes. This may be attributed to a decreasing tendency in aerosol optical extinction, air pollution and/or the weather condition changes over monitoring sites such as cloudiness (UNEP, 2022).

Brewer spectrophotometer

Figure 1: Time-series of the annual accumulation of daily erythemal UV radiation The observation of erythemal UV at Tsukuba (36.06°N, 140.13°E) in Japan started from 1990. Each annual accumulation is summed up monthly-mean equivalent values multiplied by the days of the month. The monthly-mean equivalent value is based on the calculation from daily values in which missing data are excluded. Open circles represent annual data that include at least one month with less than 20 daily data. The regression line covers the whole observation period (statistically significant at a confidence level of 99%).

Reference

UNEP (2022), Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: 2022 assessment report.

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