Effect of Short-Term Solar Ultraviolet Flux Variability in a Coupled Model of Photochemistry and Dynamics

Abstract

Variability in the solar ultraviolet radiative flux is known to cause changes in the chemistry and dynamics of the middle and upper atmosphere. Specifically, the 27-day solar rotation signal in irradiance has been correlated with responses in temperature and ozone. This study investigates the ozone and temperature responses in the upper stratosphere and mesosphere through analytic formulations and the Johns Hopkins University Applied Physics Laboratory (JHU/APL) 2D chemical?dynamical coupled model. From a simple ozone?temperature coupled analytical model, conditions are derived that would yield the greater sensitivities and negative phase lags in the ozone response as observed in the upper stratosphere. Using the JHU/APL photochemical model, both the diurnal and 27-day solar ultraviolet flux forcings are coupled to examine the effects of localized photochemistry on ozone response. A strong local-time dependence of the ozone response is then systematically explored. The JHU/APL 2D model is integrated with 27-day solar ultraviolet flux forcing consistently parameterized in both photolysis and heating rate calculations to quantitatively study the temperature and ozone responses and the temperature feedback on the ozone. The temperature response is always positive in the model and is consistent with the correlation studies from the observations. The greater phase lag near the equatorial mesopause and the reduced amplitude of the temperature response suggest an indirect dynamical effect. Furthermore, an alternative explanation of the well-known negative phase lag of O3 responses in the upper stratosphere is provided. As a result, it is shown that two major observed features of ozone response in the upper-middle atmosphere as simulated by the model may be explained by a single mechanism of negative forcing due to the catalytic destruction of ozone by an increasing solar UV radiation.