Interannual variation patterns of total ozone and lower stratospheric temperature in observations and model simulations

摘要

We report results from a multiple linear regression analysis oflong-term total ozone observations (1979 to 2000, by TOMS/SBUV), of temperaturereanalyses (1958 to 2000, NCEP), and of two chemistry-climate model simulations(1960 to 1999, by ECHAM4.L39(DLR)/CHEM (=E39/C), and MAECHAM4-CHEM). The model runs are transientexperiments, where observed sea surface temperatures, increasing source gasconcentrations (CO₂, CFCs, CH₄, N₂O, NO_x), 11-year solar cycle,volcanic aerosols and the quasi-biennial oscillation (QBO) are all accountedfor. MAECHAM4-CHEM covers the atmosphere from the surface up to 0.01 hPa (≈80 km).For a proper representation of middle atmosphere (MA) dynamics, itincludes a parametrization for momentum deposition by dissipating gravity wavespectra. E39/C, on the other hand, has its top layer centered at 10 hPa(≈30 km). It is targeted on processes near the tropopause, and has morelevels in this region. Despite some problems, both models generally reproduce the observed amplitudes and much ofthe observed low-latitude patterns of the various modes of interannual variability intotal ozone and lower stratospherictemperature. In most aspects MAECHAM4-CHEM performs slightly better than E39/C.MAECHAM4-CHEM overestimates the long-term decline of total ozone, whereas underestimates the decline over Antarctica and at northern mid-latitudes. Thetrue long-term decline in winter and spring above the Arctic may be underestimatedby a lack of TOMS/SBUV observations in winter, particularly in the cold 1990s.Main contributions to the observed interannualvariations of total ozone and lower stratospheric temperature at 50 hPa comefrom a linear trend (up to -10 DU/decade at high northern latitudes, up to -40 DU/decadeat high southern latitudes, and around -0.7 K/decade over much of the globe),from the intensity of the polar vortices (more than 40 DU, or 8 K peak to peak),the QBO (up to 20 DU, or 2 K peak to peak), and from tropospheric weather (upto 20 DU, or 2 K peak to peak). Smaller variations are related to the 11-yearsolar cycle (generally less than 15 DU, or 1 K), or to ENSO (up to 10 DU, or1 K). These observed variations are replicated well in the simulations.Volcanic eruptions have resulted in sporadic changes (up to -30 DU, or+3 K). At low latitudes, patterns are zonally symmetric.At higher latitudes, however, strong, zonally non-symmetric signals are foundclose to the Aleutian Islands or south of Australia. Such asymmetric featuresappear in the model runs as well, but often at different longitudes than in theobservations. The results point to a key role of the zonally asymmetric Aleutian(or Australian) stratospheric anti-cyclones for interannual variations athigh-latitudes, and for coupling between polar vortex strength, QBO, 11-year solarcycle and ENSO.