Depletion and Natural Variability of the Ozone Layer from TOMS Observations

Afbraak en natuurlijke variabiliteit van de ozonlaag afgeleid uit TOMS waarnemingen


A statistical trend analysis of the TOMS total ozone data was performed from November 1978 through June 1994. The temporal dependency of the ozone column is described by the model, accounting for seasonal variation, linear anthropogenic trend, quasi-biennial oscillations (QBO), influence of the 11-year solar cycle and month-to-month correlation in ozone values. Year-round and monthly trends, QBO coefficients and solar cycle coefficients were calculated for all grid cells (1 degree latitude x 1.25 degree longitude) of the TOMS column ozone data, as well as for zonal means over 10 degrees latitudinal bands. Zonal mean ozone trends are listed in tabular form in Appendix E. Year-round depletion trend is -4.4+-2.7% per decade in the latitudinal range of 50 degrees N-60 degrees N. The maximum ozone depletion at these latitudes occurs in February, reaching the values of -8.2+-3.3% per decade, the minimum depletion of -2.9+-2.7% per decade occurs in August. Processes leading to low amounts of ozone are also reviewed. The effect of Mt. Pinatubo eruption was investigated, revealing long-term year-round ozone trends which became about 1% per decade more negative in the northern hemisphere and the Tropics after the Mt. Pinatubo eruption. Monthly trends were about 2% per decade more negative in the mid-latitude winter/spring in the northern hemisphere than before the Mt. Pinatubo eruption. There were no substantial changes in ozone trends in the southern hemisphere mid-latitudes. The increase in the ozone depletion rates after the Mt. Pinatubo eruption is mainly the result of enhanced heterogeneous "denoxification" reaction on the surface of aerosol particles in combination with the presence of chlorine from CFC emissions. Year-round ozone trends in the northern hemisphere reached the values of up to -6% per decade. The maximum year-round ozone depletion in this area apply to the areas above the UK, south of Norway and Sweden, some northern and far eastern parts of Russia, and the west coast and northern part of Canada. The largest ozone depletion at high northern latitudes is reached in March. The areas above the UK, northern France, Benelux, northern part of Scandinavia and large parts of Russia had high absolute trend values equal to about -10% per decade and more. There are also areas of enhanced ozone depletion above the western part of USA, northern part of Canada, part of Pacific Ocean and a small part of Atlantic Ocean. The monthly trends from September to November at high latitudes of the southern hemisphere showed strong ozone depletion of more than -10% per decade in almost the whole area south of 60 degrees S. The ozone depletion reaches its maximum in October, when trends in the polar region were about -30% per decade and those above the most southern part of South America and the Falkland Islands were about -10% per decade. The yearly difference between the maximum and minimum QBO in ozone (about 3-4% of the ozone column) can explain the part of inter-annual variations in the total ozone. In spring 1993 the QBO in ozone worked to reduce the total ozone and thus to worsen the situation in addition to the ozone destruction caused by Mt. Pinatubo aerosols. In spring 1994 QBO in ozone was positive, thus contributing to the recovery to normal total ozone values. The solar cycle extremes are responsible for 1% to 2% change in the ozone column. Comparisons are presented of the TOMS ozone data and trends as a function of latitude and season with the results of the RIVM 2D stratosphere model.

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