The surface UV-B irradiation in the Arctic: observations at the Polish polar station, Hornsund (77°N,15°E), 1996–1997

Abstract

Measurements of the UV-B radiation reaching ground level at the Polish polar station, Hornsund (Svalbard, 77° N , 15°30′E, 11 m a.s.l.), have been carried out since February 1996 by means of a temperature stabilized Robertson–Berger-type meter. The seasonal pattern of UV dose and UV index, and factors affecting the UV-B level there are studied for the period March–October of 1996 and 1997. The quality of the UV measurements is assured by comparisons of the instrument readings with those calculated from a radiative transfer model under clear-sky conditions. A statistical method is proposed to examine the year-to-year drift of the instrument readings. The maximum value of UV daily dose and UV index are found in late spring of 10.2 MED (1 MED=210 J eff m −2) and 2.5, respectively. The maximum UV irradiance at the midnight is ≅4 mW eff m −2 . The seasonal pattern of UV daily dose appears to be asymmetric relative to the summer solstice. All-weather UV measurements taken in early spring provided much higher (≅50%) UV irradiances than the corresponding measurements in late summer because of larger ground albedo and atmospheric transparency (due to smaller cloud/aerosol optical depth) in early spring. Depletion of total ozone is not the only source of the UV trend over Arctic. It is found that long-term (1965–1997) changes in the cloud cover over southern Svalbard had significant impact on the UV level there.