Seasonal ozone variations in the upper mesosphere

Abstract

The global daytime ozone was measured by the Solar Mesosphere Explorer satellite (SME) for 5 years. The measurements extend through the mesosphere, covering from 50 km to over 90 km. The ozone in the upper mesosphere varies annually by up to a factor of 3. The observed seasonal variations may be summarized in several different ways. From year to year there is a great deal of repeatability of these variations. This repeatability occurs in most of the upper mesosphere outside the tropics. Near 0.01 mbar (80 km) the mid‐ and high‐latitude mixing ratio peaks each year in mid‐April. A secondary maximum in the altitude profile of ozone density usually occurs near 85 km. Changes in this structure are directly related to the April maximum and other seasonal changes seen at 0.01 mbar. The changing seasonal structure produces a “bump” at the ozone mixing ratio minimum that is largest just after spring equinox. This perturbation to the mixing ratio profile seems to move upward during the first half of the year. The seasonal changes of ozone were analyzed in terms of annual and semiannual structure. The variations generally have both an annual and semiannual component depending on altitude and latitude. The phases of the variations change quickly with both altitude and latitude. The semiannual component peaks in April, over most of the upper mesosphere.