THE ANALYSIS OF ULTRAVIOLET-RADIATION IN THE DEAD-SEA BASIN, ISRAEL

The Dead Sea basin offers a unique site to study the attenuation of th e ultraviolet (UV) radiation, as it is situated at the lowest point on Earth, about 400 m below sea level, and the air above the Dead Sea is characterized by a relatively high aerosol content due to the very hi gh salt content of the Dead Sea. In view of its being an international ly recognized centre for climatotherapy, it is of interest to study bo th its UV intensity and attenuation as a function of wavelength relati ve to other sites. In order to provide a basis for intercomparison of the radiation intensity parameters measured at the Dead Sea, a second set of identical parameters were being measured simultaneously at a se cond site, located at a distance of ca. 65 km and to the west and situ ated above sea-level (Beer Sheva at +315 m.a.s.l.). The ultraviolet ra diation, both UV-B and UV-A, were monitored continuously at both sites using Solar Light Co. Inc. broad-band meters. In addition, sporadic m easurements utilizing a narrow-band spectroradiometer were performed t o ascertain the extent of site-specific spectral selectivity in the ul traviolet spectrum. The monthly average daily attenuation rates were f ound to vary from -10.2 to -17.3 per cent 1000 m(-1) and -3.3 to -8.7 per cent 1000 m(-1) for UV-B and UV-A, respectively. The average month ly values for UV-B and UV-A are -14.6 per cent 1000 m(-1) and -5.4 per cent 1000 m(-1), respectively. These values are in the range of value s reported previously for studies performed at high altitudes, e.g. in the Alps and the Andes. The relative attenuation in the ultraviolet r ange as a function of wavelength, i.e. site-specific spectral selectiv ity, decreases with increasing wavelength. Consequently, the spectral range most effective with regard to erythema undergoes the highest deg ree of attenuation. These findings are in accordance with radiation sc atter theory. (C) 1997 Royal Meteorological Society.