The Surface-Pressure Signature of Atmospheric Tides in Modern Climate Models

Although atmospheric tides driven by solar heating are readily detectable at Earth’s surface as variations in air pressure (Hagan et al. 2003) the output of climate-oriented atmospheric general circulation models (GCMs) has rarely been examined for atmospheric tides. In this work we search for the tides in output from GCM / climate models contributing to the latest assessment report of the Intergovernmental Panel on Climate Change (IPCC; Randall et al. 2007). We also examine output from the Whole-Atmosphere Community Climate Model (WACCM), which extends from Earth’s surface to the thermosphere. We examine pressure near the surface because it is the best-observed signature of the tides, and because it is the most readily available output at high time-frequency from the IPCC models. We find surprising consistency among observations and all model simulations, despite variation of the altitudes of model upper boundaries from 30 to 75 km in the IPCC models and > 130 km for WACCM. Our results are compatable with previous suggestions that placing a GCM’s upper boundary at low altitude leads to compensating errors—reducing the forcing of the tides in the ozone layer but also introducing a spurious reflected wave at the upper boundary, which propagates to the surface (Lindzen et al. 1968; Zwiers and Hamilton 1986; Hamilton et al. 2008).