ULTRAVIOLET-RADIATION IN THE ARCTIC - THE IMPACT OF POTENTIAL OZONE DEPLETIONS AND CLOUD EFFECTS

An atmospheric radiation model is used to study the combined effects of ozone depletions/redistributions and particulate clouds on atmospheric heating/photolysis rates and ultraviolet radiation reaching the biosphere. Four types of particulate clouds prevalent in the summertime Arctic are considered: stratospheric aerosols, tropospheric aerosols (Arctic haze), cirrus clouds, and stratus clouds. The effects of ozone depletion and vertical redistributions of ozone are also examined. The main findings are as follows: (1) stratus clouds provide significant protection from ultraviolet radiation exposure, but while stratospheric aerosols imply increased UVB exposure, Arctic haze results in a decrease; (2) a redistribution of ozone from the stratosphere to the troposphere tends to decrease UV exposure, but for low solar elevations an increase may occur, (3) a 20% ozone depletion leads to about 0.4 K/d cooling in the lower stratosphere, while redistribution of ozone from the stratosphere to the troposphere implies a warming of about 0.015 K/d in the upper troposphere; (4) stratus clouds may cause a large warming in the middle and upper stratosphere (0.8 K/d); (5) clouds have little effect on ozone photolysis leading to O(1D) production at altitudes higher than 25 lan; (6) for ozone photolysis leading to O(3P) production photolysis rates may increase by 50% or more throughout the atmosphere due to multiple scattering by stratus clouds.