Temporal and spatial variability of total ozone in Southwest Sweden revealed by two ground-based instruments

Abstract

This study deals with temporal and spatial variability of ozone in Southwest Sweden as measured by two ground-based instruments. Daily total ozone values measured by a Brewer ozone spectrophotometer at Norrköping, Sweden are analysed for the period 1988–1997. The analysis not only gives an estimate of the long term annual and seasonal trends, but also provides statistics of means and variability on various temporal scales. The highest decreasing trend was found in spring, while the smallest seasonal trend was in summer. On an annual basis, the long term trend is determined as −2.61 DU (0.79%) per year. The mean annual range of seasonal averages is as high as 96 DU (29.2%) with the maximum in October and the minimum in April. On average, variability in summer is much less than in winter whilst spring and autumn experience moderate variations. Large variations from day to day are found to be frequent. A spectral analysis on the daily values shows that the dominating oscillating periods are between 2.1 and 4.5 days, indicating the importance of the synoptic scale influences. Furthermore, the analysis reveals a trend of decreasing variability with decreasing ozone. To study the spatial variability, measurement from another similar instrument that is located in Oslo is compared to that in Norrköping. Daily values during 1994–1996 are compared, which shows a correlation coefficient of 0.90. However, the difference between the stations can still be considerable. The standard deviation of the difference is 21.8 DU and the maximum absolute difference is as high as 77.5 DU. This certainly has implications for the regional variability of surface UV. © 1998 Royal Meteorological Society