Response of the middle atmosphere to the 11-year solar cycle simulated with the Whole Atmosphere Community Climate Model

Abstract

A long-term numerical experiment has been conducted using the Whole Atmosphere Community Climate Model (WACCM) to investigate the response of the middle atmosphere to time-varying spectral solar irradiance over multiple 11-year cycles, modeled on the basis of observed 10.7-cm radio flux (F10.7). The model domain covers from the Earth's surface to the lower thermosphere with approximately two-degree horizontal resolution and 66 vertical layers. Sea surface temperatures are prescribed by a climatological annual cycle, and boundary data for chemical compositions are held constant. The experiment does not include spontaneous nor imposed quasi-biennial oscillation. Temperature and ozone differences near the stratopause between solar max and min, typically 0.8 K and 1.6% corresponding to approximately 100 units of F10.7 variation, have general agreement with the current scientific understanding. The model's dynamical responses as an indirect solar effect are substantially weak during winter against evidences from past empirical studies. The indirect solar signal tends to appear when the polar vortex becomes weak. The most striking signal is more frequent stratospheric sudden warmings during solar max in the Northern Hemisphere late winter through early spring, supporting observed tendencies. This modulation has an aspect of the annular mode and results in a major impact on the troposphere in early spring. Such a signal, however, does not appear in the Southern Hemisphere where the model has a westerly bias. There is no marked response in the equatorial lower stratosphere. Copyright 2009 by the American Geophysical Union.