Shu Takeshita

Long-term trends of global solar ultraviolet-B, ultraviolet-A and total irradiances measured in Japan since 2001

Global and diffuse solar ultraviolet-B, ultraviolet-A, and Total irradiances have been measured at Shonan Campus of Tokai University (Kanagawa, Japan, 35°21’N, 139°11’E) since 1990. Analysis of data recorded from Apr. 2001 to Dec. 2015 shows that daily integrated global UV-B irradiance has decreasing in the long-term as -0.381 %/year for the 95 % confidence interval in this period. More detail evaluation is made on the data recorded from Jan. 2009 to Dec. 2015. In this period, an increase trend in global UV-B irradiance was obtained (+0.607 %/year). This result suggests that critical factor on increase in UV-B irradiance is not only ozone amount but also amount of aerosols, sunshine duration and solar cycle.

Estimation of global solar UV index from UV-B irradiance measured with a narrow-band UV-B radiometer

The global solar UV index is an indicator for notifying the level of harmful solar ultraviolet radiation reaching the surface of the earth and the general public. It was proposed by the WHO/WMO/UNEP/ICNIRP and was standardized by the CIE in 2003. This index is derived from the product of the spectral solar UV irradiance from 250 to 400 nm and the CIE standard of reference erythema spectrum. For calculation of the UV index, the measurement of spectral solar UV irradiance is needed. Spectral radiometry is the best method of measurement of solar UV irradiance, however spectral radiometers are cost prohibitive. On the other hand, a narrow-band solar UV-B radiometer is widely used for measurement of solar UV-B irradiance in the world. The Tokai Solar Radiation Monitoring Network, and the UV Monitoring Network-Japan performed by the National Institute for Environmental Studies are two examples of monitoring networks using narrow-band solar UV-B radiometer in Japan. In this paper an estimation method of the UV index from the measured UV-B irradiance with the narrow-band UV-B radiometer.

Evaluation of a calibration constant of a narrowband solar UV-B radiometer

Since 1990, global solar UV-B irradiance has been measured by a narrow-band solar UV-B radiometer at Hiratsuka, Japan. To detect long-term trend of global solar UV-B irradiance measured by the narrow-band solar UV-B radiometer, evaluation of a calibration constant of the radiometer for accurate measurement is essential. Thus, for estimating trend of global solar UV-B irradiance from 2000 to 2003, the calibration constant of the narrow-band solar UV-B radiometer was evaluated by applying three methods. The first method is based on a spectral irradiance standard lamp, which has been applied when evaluating long-term trend of global solar UV-B irradiance from October 1990 to September 2000. The second one is based on a reference narrow-band solar UV-B radiometer. Global solar UV-B irradiance measured by our narrow-band solar UV-B radiometer was compared with that of the reference narrow-band solar UV-B radiometer under natural sunlight. The third one is based on the total ozone amount. The results with three methods showed good agreement within 5%, leading to the conclusion that three methods are comparable in evaluating the calibration constant of the narrow-band solar UV-B radiometer.