Forcing of the Mesospheric Semi-Annual Oscillation in the Whole Atmosphere Community Climate Model

The mesosopheric semi-annual oscillation (MSAO) of the zonal winds is a prominent feature of the tropical atmosphere. The MSAO is out of phase with the underlying stratospheric semi-annual oscillation (SAO) and is believed to be forced by selective transmission of gravity waves and Kelvin waves propagating from the troposphere. Using NCAR's Whole Atmosphere Community Climate Model, we show that the MSAO can be forced by a combination of planetary waves and gravity waves. The forcing of the MSAO by planetary waves is strongest in January, when the 2-day wave amplitudes are the largest.