COMPARISON OF SBUV AND SAGE-II OZONE PROFILES - IMPLICATIONS FOR OZONE TRENDS

Solar backscattered ultraviolet (SBUV) ozone profiles have been compar ed with Stratospheric Aerosol and Gas Experiment (SAGE) II profiles ov er the period October 1984 through June 1990, when data are available from both instruments. SBUV measurements were selected to closely matc h the SAGE II latitude/longitude measurement pattern. There are signif icant differences between the SAGE II sunrise and the sunset zonal mea n ozone profiles in the equatorial zone, particularly in the upper str atosphere, that may be connected with extreme SAGE II solar azimuth an gles for tropical sunrise measurements. Calculation of the average sun set bias between SBUV and SAGE II ozone profiles shows that allowing f or diurnal variation in Umkehr layer 10, SBUV and SAGE II agree to wit hin +/-5% for the entire stratosphere in the northern midlatitude zone . The worst agreement is seen at southern midlatitudes near the ozone peak (disagreements of +/-10%), apparently the result of the SBUV ozon e profile peaking at a lower altitude than SAGE. The integrated ozone columns (cumulative above 15 km) agree very well, to within +/-2.3% in all zones for both sunset and sunrise measurements. A comparison of t he time dependence of SBUV and SAGE II shows that there was less than +/-5% relative drift over the 5.5 years for all altitudes except below 25 km, where the SBUV vertical resolution is poor. The best agreement with SAGE is seen in the integrated column ozone (cumulative above 15 km), where SAGE II has a 1% negative trend relative to SBUV over the comparison period. There is a persistent disagreement of the two instr uments in Umkehr layers 9 and 10 of +/-4% over the 5.5-year comparison period. In the equatorial zone this disagreement may be caused in par t by a large positive trend (0.8 degrees K per year) in the National M eteorologica Center temperatures used to convert the SAGE II measureme nt of ozone density versus altitude to a pressure scale for comparison with SBUV. In the middle stratosphere (30-40 km), SBUV shows a 2-4% n egative drift relative to SAGE II. If the actual ozone trends are cons idered, SBUV and SAGE II agree in showing little ozone change (less th an 2%) between 1984 and 1990, except in layer 3 where SAGE II measures a large ozone decrease. But over 11 years, SBUV measured a 7% per dec ade ozone decrease between 40 and 50 km, decreasing in magnitude at lo wer altitudes, in good agreement with 11-year trends derived from the average of 5 Umkehr stations.