An evaluation of the performance of Umkehr stations by Solar Backscattered Ultraviolet (SBUV) experiment

Until recently, Umkehr data taken by 20 Dobson stations around the world have been the principal source of information about the behavior of upper stratospheric ozone. Umkehr results are used also for detecting drifts in satellite instruments and for determining intersatellite biases. However, a systematic evaluation of the quality of Umkehr data taken by the various stations has been lacking. Five years of ozone profile data from the Solar Backscattered Ultraviolet (SBUV) have been used to examine and intercompare the quality of Umkehr stations, and to assess the degradation of their performance after the El Chichon volcano eruption in southern Mexico. In contrast to Umkehr, the SBUV ozone measurments in layers 7 through 9 (1-8 mb) were unaffected by the massive amounts of dust and gases ejected by El Chichon.