Atmospheric semidiurnal lunar tide climatology simulated by the Whole Atmosphere Community Climate Model

The atmospheric semidiurnal lunar tide is added to the Whole Atmosphere Community Climate Model (WACCM) through inclusion of an additional forcing mechanism. The simulated climatology of the semidiurnal lunar tide in surface pressure and zonal and meridional winds in the mesosphere and lower thermosphere (MLT) is presented. Prior observations and modeling results demonstrate characteristic seasonal and latitudinal variability of the semidiurnal lunar tide in surface pressure, and the WACCM reproduces these features. In the MLT, the WACCM simulations reveal a primarily semiannual variation with maxima near December and June solstice. The peak amplitudes in the MLT zonal and meridional winds are similar to 5-10 ms(-1), and occur at mid to high latitudes in the summer hemisphere. We have further compared the WACCM simulation results in the MLT with those from the Global Scale Wave Model (GSWM). The overall latitude and seasonal variations are consistent between these two models. However, the GSWM peak amplitudes are similar to 2-3 times larger than those in the WACCM. This is thought to be related to deficiencies in the GSWM and not the WACCM simulations. With the exception of smaller amplitudes during Northern Hemisphere summer months, the WACCM simulations of the semidiurnal lunar tide in the MLT are also shown to be generally consistent with prior observations and modeling results. The reduced amplitudes in the WACCM simulations during Northern Hemisphere summer months are thought to be related to the influence of the cold-pole bias in WACCM on the propagation of the lunar tide during these months.