The solar and dynamically induced oscillations in the stratosphere

Abstract

The temporal and spatial characteristics of short‐term fluctuations in the stratosphere are studied using 30 months of ozone, solar UV, and temperature data from the Nimbus 7 solar backscattered ultraviolet (SBUV) and the stratosphere and mesosphere sounder (SAMS) experiments. It is shown that the stratosphere is in a continuous state of oscillation, with periods varying between 3 to 7 weeks. These oscillations are manifestations of dynamically induced perturbations in the winter hemisphere and the 27‐day modulation of the solar UV radiation. Dynamically induced oscillations are global in extent and appear to be independent of solar activity. They are strongest at high latitudes during the fall‐spring epoch of each hemisphere. When the seasonal differences of the two hemispheres are taken into account, the high‐latitude oscillations in each hemisphere show significant negative correlation with lower latitudes which extends far beyond the tropics into the opposite hemisphere. Their phase shows the characteristics of meridional waves with poleward and equatorward propagations above and below 10 mbar, respectively. Both the multiple regression and cross‐spectral analyses of ozone, temperature, and solar flux data show the ozone mixing ratio to be much more sensitive to dynamically induced changes in temperature than to changes in solar UV flux. The solar‐induced changes in ozone are detectable only under favorable circumstances, that is, at low latitudes during periods of high solar activity. The estimated change in ozone mixing ratio in the upper stratosphere is about 3% over a solar cycle. This is comparable to a temperature‐induced change of about 2 K of dynamical origin.