| description abstract | The National Science Foundation scanning spectroradiometer at Palmer Station, Antarctica (64°46?S, 64°04?W) provides hourly ground-based measurements of solar ultraviolet (UV) irradiance at the, earth's surface. These measurements define the UV radiation environment of the region and, in conjunction with a daily record of sky conditions and radiative transfer modeling, permit a quantitative understanding of the role of cloud cover in regulating UV radiation levels at the Antarctic surface, including the period of the springtime ozone depletion. The transmission properties of cloud types over the Antarctic Peninsula are quantified by taking the ratio of UV-A irradiances measured under them to UV-A irradiances calculated for clear skies and the same solar zenith angle, and the results are then generalized to the UV-B. Under the averse overcast sky in the region, UV irradiance at all wavelengths is slightly greater than half of the value for clear skies. Under the thickest overcast layers, UV irradiance at all wavelengths is roughly 20% what it would be if the sky were clear. In a seasonally averaged sense cloudiness has no effect on the percentage enhancement in UV-B surface irradiance that results from the springtime ozone depletion. However, when considering time scales of hours to several days, an increase in cloud cover can be discussed in terms of its ability to attenuate the solar irradiance; in some cases giving a surface UV-B level comparable to that found under an unperturbed ozone column and clear skies. Depending on the amount of ozone depletion and the type of cloud cover, there will always be a wavelength below which surface radiation levels are excessive during spring. | |
