Other
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.g22c0313m&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #G22C-0313
Other
1223 Ocean/Earth/Atmosphere Interactions (3339), 1239 Rotational Variations, 3319 General Circulation, 3346 Planetary Meteorology (5445, 5739), 3374 Tropical Meteorology
Scientific paper
Climate variability on interannual time scales is dominated by the El Nino / Southern Oscillation (ENSO), an ocean-atmosphere instability originating in the equatorial Pacific. ENSO has a strong signature in length-of-day (LOD), which can be accounted for almost entirely by atmospheric angular momentum (AAM) variations. It has been noted, however, that ENSO effects on polar motion (PM) are much weaker and hard to detect. In this study, we use the torque approach to explore Earth-atmosphere interaction associated with ENSO, and seek to understand why the large atmospheric fluctuations arising from ENSO are not effective in exciting PM variations. PM is affected by atmospheric torques acting in the equatorial plane, which arise largely from gravitational and surface pressure interactions with the Earth's bulge. Using the inverted barometer (IB) approximation for the effect of atmospheric loading on the ocean, we find that the bulge torque exhibits significant coherence with the Southern Oscillation Index (SOI), confirming that the atmosphere acts to force PM in association with ENSO. While the bulge torque is correlated with geodetic excitation at high (sub-annual) frequencies, however, the two series are not coherent at longer (interannual) periods, presumably due to the effects of other excitation sources (e.g. oceans) on these time scales. Local (i.e., non-bulge) torques are also found to be coherent with the SOI, in particular due to the interaction of surface pressure anomalies with the large-scale topography of Antarctica. The local torques can be directly related to wind term anomalies of equatorial AAM, largely associated with extratropical vortices located over the Pacific ocean.
de Viron Olivier
Dickey Jean O.
Marcus Steve L.
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