Characteristics of the DW1 Tidal Wave in ERA Interim and WACCM: Implications for Nutation

Atmospheric tides are global-scale harmonic oscillations in atmospheric variables such as temperature, wind and pressure. They are excited by diurnal solar heating, which is absorbed by water vapor in the troposphere and ozone in the stratosphere. Maximum amplitudes are found in the mesosphere and lower thermosphere where the tides represent a major component of atmospheric variability. Through vertical coupling processes, subdiurnal components of the atmospheric tides are also present in surface pressure. It is well known that variations in wind and mass in the atmosphere excite variations in the rotation of the solid Earth via the conservation of angular momentum. When separated into zonally averaged waves for individual tidal periods of 24, 12 and 8 hours, atmospheric tidal variations are dominated by sun-synchronous migrating tides (i.e. DW1, SW2 and TW3). Since DW1 and its modulations over the seasons of the year primarily contribute to the nutation of the Earth, its characteristic variations in vertically varying temperature and wind fields will be described here. This will allow us to discuss the dominating excitation and coupling processes as reproduced by both the Whole Atmosphere Community Climate Model (WACCM) and the latest ECMWF re-analysis, ERA Interim.