Short periodic variations of polar motion and hemispheric atmospheric angular momentum excitation functions in the period 1984-1992
Abstract. Short periodic oscillations with the periods from 10 up to 110 days of the hemispheric components of effective atmospheric angular momentum (EAAM) excitation function and their correlation with polar motion excitation function have been analyzed. The EAAM data of the Japan Meteorological Agency (JMA) computed for the two hemispheres and the very long baseline interferometry (VLBI) polar motion NGS 92 R01 data (NGS 1992), determined by the National Geodetic Survey were applied. The distinct oscillations with periods of about 28, 35-55 and 60-80 days were detected in the χy-component of both polar motion excitation function and northern EAAM excitation functions containing wind and pressure, with and without inverted barometric correction terms. The χy-component of the polar motion excitation function is significanly correlated (correlation coefficient equal to 0.55-0.75) with the χy-components of the northern EAAM excitation functions mentioned above, which are mostly induced by the atmospheric circulation over lands. No meaningful correlation between polar motion excitation function and the southern EAAM excitation functions was found. The χx-components of the EAAM and polar motion excitation functions are not significantly correlated. The strong short periodic variation of the length of day (LOD) and χy in the early 1988 seems to be caused by the above-mentioned 35-55 days oscillations of the northern hemisphere atmosphere. This variation can be related to the rapid passing from the El Niño to the La Niña phenomenon or from the minimum to the maximum in the Southern Oscillation Index in 1987-1989.
