Total Ozone trends deduced from Nimbus 7 Toms data



The Total Ozone Mapping Spectrometer (TOMS) on the Nimbus 7 satellite has been measuring the total column amount of ozone over the globe for more than 11 years. Recent improvements in the data analysis have led to a technique for determining and removing drift in the calibration such that the data at the end of the record are precise to ±1.3% (2σ) relative to the data at the beginning of the record. A statistical model, including terms for seasonal variation, linear trend, quasi-biennial oscillation, solar cycle and second-order autoregressive noise has been fit to the TOMS time series of total ozone data. The linear trend obtained when this statistical model is fit to the TOMS data averaged between 65N and 65S latitudes is −0.26±0.14%/year or −3% over the 11.6 year time period from November, 1978 through May, 1990. The trend is near zero (0.0002±0.2 %/year) at the equator and increases towards both poles. At 50N the annually averaged trend is −0.5±.21%/year. The 50N trend over the 11.6 year time period shows a strong seasonal variation from more than −0.8%/year in winter and early spring (February and March) to about −0.2%/year in summer (July and August).