RESULTS OF THE NEW AND OLD UMKEHR ALGORITHM COMPARED WITH OZONE SOUNDINGS

Vertical ozone distributions from regular Umkehr observations at Arosa, Switzerland, from 1956 to 1990 retrieved with the newly developed algorithm Of MATEER and DELUISI (1992, J. atmos. terr. Phys. 54, 537), using Bass-Paur absorption coefficients and described in this issue, are compared with the corresponding results obtained with the old routine [MATEER and DUETSCH (1964), NCAR, Boulder, Colorado, Part I, 105 pp.], officially in use at the World Ozone Data Center at Toronto. For the period 1967 1989 they are also compared with the sounding data obtained at Payerne, Switzerland with the Brewer-Mast electrochemical instrument. The annual mean values calculated from Umkehr observations increased, using the new algorithm, in layer 4 and to a lesser extent in layers 3 and 1. They decreased strongly in layer 2 and also 6 and became smaller, too, in layers 7 and 8. The new Umkehr yields annual mean values which are much closer to the sounding results than those of the old routine. The seasonal variation shows somewhat larger differences. There are big discrepancies between the trends obtained from both Umkehr algorithms and those calculated from the soundings in the region of the ozone maximum and in the troposphere. The former discrepancies may be due to the changes in the relation between total ozone and vertical distribution which occurred during the past 20 years and which are not taken into account in the definition of the a priori profiles in the new routine. It seems that useful trends can only be obtained in layer 6 and above using Umkehr observations.