Modes of variability in atmospheric and oceanic excitation of polar motion

Author: Rui M. Ponte, David Salstein and J. Nastula
Date: 
April 21, 2002 - April 26, 2002
Type: 
Presentation
Venue: 
EGS General Assembly, Nice
Citation: 

Salstein, D., J. Nastula, and R.M. Ponte, 2002. Modes of variability in atmospheric and oceanic excitation of polar motion, EGS General Assembly, Nice, April 2002.

The redistribution of atmospheric and oceanic mass and changes in the circulation of these two fluids are essential mechanisms exciting motions of EarthSs pole. Such variations in the mass and motion of these fluids have large-scale patterns, and the strong modes that explain the variance contained in these patterns are responsible for the largest polar motion excitations. Using a fine-sector resolution of the fluid mass and motion fields taken from the atmospheric reanalysis of the U.S. National Centers for Environmental Prediction-National Center for Atmospheric Research and from the near-global oceanic model of Ponte and Stammer (1999, J. Geophys. Res.), we deter- mine, using both real and complex eigenvector analysis, fundamental modes of the regional excitation functions for polar motion for an 11-year period. The first mode of the atmospheric mass term, in particular, explains 50 percent of total variance, when the Inverted Barometer relationship, the isostatic adjustment of the ocean to overly- ing sea surface pressure, is considered, though 25 percent when it is not considered. The time series of the modes may be identified with seasonal fluctuations. Likewise, oceanic excitation variance (first mode for velocity and mass accounts for 30 and 15 percent of total variance, respectively) also has a strong seasonal component. Other modes have power at higher seasonal harmonics.We assess the regional contributions to these modes displaying seasonal variations.