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Tropical semiannual oscillation in MLS temperature and ozone
from Ray et al. J. Atmos. Sci. vol. 51, 3045-3052, 1994


time series by pressure level of the deviation of MLS temperature from 1991-1994 over the equator
time series by pressure level of the deviation of MLS ozone from 1991-1994 over the equator

Time-height cross-section of MLS temperature (first figure above, K) and ozone (second figure above, ppmv) deviations from the 2-year (Oct 1991 - Sep 1993) mean over the equator. The horizontal axis is UARS day number: UARS day 20 is 1 Oct 1991, day 200 is 29 Mar 1992, day 380 is 25 Sep 1992, day 560 is 24 Mar 1993, day 740 is 20 Sep 1993.

The time series shown in these figures reveal the semiannual oscillation (SAO) as the dominant pattern of variability, with the largest negative temperature and positive ozone deviations (~10K and 1.2ppmv) occurring in the upper stratosphere, around the stratopause for temperature and at 3 hPa for ozone. The negative temperature and positive ozone deviations occur almost simultaneously over a large depth, extending down into the middle stratosphere during the solstice seasons. The positive temperature (8-10K and 1.2 ppmv) occurring in the upper stratosphere, around the stratopause for temperature and at 3 hPa for ozone. The negative temperature and positive ozone deviations occur almost simultaneously over a large depth, extending down into the middle stratosphere during the solstice seasons. The positive temperature (8-10K) and negative ozone (-1ppmv) deviations originate near the stratosphere and descend more gradually to the middle stratosphere over a period of about 2 months during the equinox seasons.

In the upper stratosphere, temperature and ozone deviations are a half-cycle out of phase, as expected from the inversely temperature-dependent photochemical control of ozone in this region. As the deviations descend below 10 hPa the two fields become out of phase by only several weeks or less due to the transition of ozone from photochemical to dynamical control and the vertical gradient of ozone becoming positive (as for temperature) in this region.

For further discussing of these data and analyses see Ray et al. J. Atmos. Sci. vol. 51, 3045-3052, 1994.

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