Ultraviolet radiation in partly snow covered terrain: Observations and three-dimensional simulations

Coastal regions with fiords and mountains with seasonally varying snowcover form complex environments for ultraviolet radiative transfer. The presence of snow causes enhanced levels of UV radiation, the quantitative interpret ation of which is only possible with detailed three-dimensional radiative t ransfer simulations. Such calculations of the irradiance at 340 nm have bee n performed for the location of Tromso, Norway, under cloudless and overcas t conditions, moving the snowline from 0 to 1000 m.a.s.l. and finally for s now free conditions. The evolution of the radiation enhancement as the snow line moves up is compare wit measurements made by a narrow bandwidth multic hannel filter instrument. For a cloudless sky the simulations and measureme nts exhibit a similar radiation enhancement of 23-27%. For the investigated overcast situation the radiation enhancement is about 40-60%.