THE SEASONAL-VARIATION OF WATER-VAPOR AND OZONE IN THE UPPER MESOSPHERE - IMPLICATIONS FOR VERTICAL TRANSPORT AND OZONE PHOTOCHEMISTRY

The data indicate that the water vapor seasonal variation at mid-latitudes in the upper mesosphere is dominated by an annual component with low mixing ratios in winter and high mixing ratios in summer. The vertical distribution of water vapor in the upper mesosphere (up to 80 km) is controlled by advective rather than diffusive processes. This is consistent with the low mesospheric Kzz values (~105 cm2 s-1) deduced from the vertical gradient of the microwave water vapor measurements. However, it is difficult to reconcile the predominantly annual water vapor variation with the semiannual variation in ozone at 78 km observed by the Solar Mesosphere Explorer. We perform a series of one-dimensional photochemical/vertical transport model calculations which verify that the seasonal variation of water vapor cannot be the mechanism for the semiannual ozone variation. -from Authors