The response of stratospheric constituents to a solar eclipse, sunrise, and sunset

Abstract

The combination of measurements and detailed stratospheric modeling of time-dependent events can be used to confirm chemical mechanisms and their laboratory rate constants or to deduce additional atmospheric properties such as the temperature structure. Sunset, sunrise, and a solar eclipse are events that are characterized by a relatively strong forcing function of brief duration. For these time scales, the detailed time-dependent photochemical and vertical diffusion equations can be solved to predict the variations of minor constituents that are physically important and accessible to current measurement techniques. Careful simultaneous solutions of these equations have shown a significant daytime variation of ozone down to altitudes of about 30 km that can affect the interpretation of spectral absorption type experiments. The calculated sunset variations of [NO] and [HO] show a log linear concentration decay for limited time periods that can be readily converted into atmospheric temperatures by using known reaction rates up to about 70-km altitude. Measurements of the time-dependent behavior of [NO] and [NO₂] during the eclipse of February 26, 1979, are expected to be made from the U2 aircraft at 20-km altitude. If the measurements have sufficient sensitivity, they can be used along with the model predictions to confirm some laboratory chemical rate constants and to estimate the [ClO]/[ClNO₃] ratio at 20-km altitude.