Regional high -frequency signals in atmospheric and oceanic excitation of polar motion Original Research Article

Atmospheric and oceanic variability have been shown to play a role in the excitation of polar motion at periods longer than about 5 days, but there is still a large drop in coherence between combined oceanic-atmospheric and geodetic series at about 8 or 9 days. Improving the agreement at these high frequencies will require better estimates of oceanic angular momentum (OAM) and atmospheric angular momentum (AAM). Determining which regions are the most important for excitation of polar motion may provide clues to the present quality of AAM and OAM estimates and ways to improve them. For this purpose regional patterns of the standard deviation of atmospheric and oceanic excitation with periods shorter than 10 days are analysed and compared. The role of regional mass (oceanic bottom pressure and atmospheric surface pressure) and motion (currents and winds) signals in contributing to global polar motion excitation is also examined by computing the fractional covariance between local and global time series. Midlatitude regions were found to be places of strong local oceanic and atmospheric signals. Important oceanic excitation signals include circulation and mass fluxes associated with subtropical and higher latitude regions.