Effects of short-term solar UV variability on the stratosphere

Changes in solar ultraviolet flux produce changes in ozone concentration in the upper stratosphere with associated radiative and dynamical effects. At low latitudes, the response of ozone mixing ratio to solar UV variations on the time scale of the solar rotation period is well characterized observationally. In addition, then is some provisional evidence for an ozone response at intermediate periods of 60-80 days. Current two-dimensional stratospheric models simulate the observed 27-day response amplitudes and phase lags with reasonable accuracy in the upper stratosphere. The observed response of total ozone on the 27-day time scale is also in approximate agreement with the same models although observed ozone sensitivities and phase lags are slightly larger than expected theoretically. Future studies of the 27-day response at higher latitudes and altitudes are needed to test more completely our understanding of the direct effects of solar UV variability on the middle atmosphere. (C) 1999 Elsevier Science Ltd. All rights reserved.