On the adequacy of the fixed locations of the surface‐based international network for inferring interannual ozone variability

Abstract

The consistency between interannual global ozone variations inferred from observations at the limited number of station locations of the surface‐based international ozone network and those derived from satellite observations with nearly complete global coverage has been investigated. Monthly ozone averages based upon the complete set of total ozone soundings derived from the backscattered ultraviolet instrument on the Nimbus 4 satellite have been compared with averages derived from a subset of these measurements taken within the vicinity of the stations of the surface‐based network. Comparisons have been made as well between averages derived from backscattered ultraviolet measurements over station locations and those derived from observations with the Dobson and M‐83 instruments. The number of stations in the north temperate zone appears adequate to represent monthly ozone averages to within 0.5%, except during the early phase of the northern hemisphere spring maximum when the total ozone fields change appreciably over scales well below global. However, the geographical distribution of stations does not properly represent different latitudes. The resultant error in the derived change in north temperate zone ozone between 1970 and 1971 is 0.5%. In the tropical and south temperate zones, ozone averages for use in deriving seasonal variability and trends are generally uncertain by about 1%. The precision is poorer than for the north temperate zone because the number of stations is appreciably smaller. However, in the south temperate zone, the average from the sample may differ from the average derived from the full data set by as much as 5% in some months, when major local maxima or minima in ozone appear southeast of Australia, where southern stations are concentrated. The uncertainty in the global averages which results is comparable in size to typical year‐to‐year changes.