Realistic semiannual oscillation simulated in a middle atmosphere general circulation model

Although several general circulation modelling studies have presented simulations containing a tropical middle atmosphere semiannual oscillation (6 month period), none so far have been able to reproduce the observed amplitude and vertical structure extending into the mesosphere. Here we present simulations with the Canadian Middle Atmosphere Model which utilize a nonlinear broad-spectrum gravity-wave parameterization [Medvedev and Klaassen, 1995, 2000] and exhibit a semiannual oscillation in good agreement with observations.