UV radiation in New Zealand: North-to-south differences between two sites, and relationship to other latitudes
Results from inter-calibrated broad-band UV monitors located near the northern and southern extremes of New Zealand are used to show differences in UV radiation over a full year of observations in 1994. These measurements are compared with model calculations to investigate the relative importance of the factors that modulate UV (e.g. solar zenith angle, cloud cover, ozone). The dominant factor is solar zenith angle, causing large seasonal variations, especially in the south. The north receives approximately 10% more UV than the south in summer, and twice the UV in winter, so that averaged over the year the north receives 25% more UV. Clouds reduced the annual clear-sky UV dose by 25-30%, and day-to-day variations in ozone cause UV fluctuations of 10%. Seasonal changes in ozone also cause significant changes in UV. These differences in UV within New Zealand are related to those elsewhere in the world, and the magnitudes of these differences are related to the magnitude of trends in UV caused by ozone depletion in recent years.