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2. Study of atmospheric and oceanic excitations in the motin of earth's spin axis in space

Creator:
Vondrák, Jan and Ron, Cyril
Type:
article, model:article, and TEXT
Subject:
Earth orientation, nutation, geophysical excitation, and VLBI
Language:
English
Description:
In this review paper we study the atmospheric and oceanic effects in nutation. It is a continuation and summary of our previous studies that we made during the last five years or so. We use slightly modified methods and apply them to the most recent data (both atmospheric/oceanic excitation functions and combined solution of celestial pole offsets by International VLBI Service for Geodesy and Astrometry - IVS). We find th at the atmospheric and oceanic excitations provide significant changes in nutation, mostly with annual and semi-annual periods. The numerical integration of Brzeziński’s broadband Liouville equations yield Free Core Nutation (FCN) that is consistent with VLBI-based observed values. The analysis of VLBI observations shows small quasi-periodic fluctuations of the period and qua lity factor of retrograde FCN, ranging between 429.8 to 430.5 days and 17000 to 22000, respectively. To this end, we use resonant effects in several dominant forced nutation terms to calculate the period and quality factor of FCN in running 6-year intervals. Numerically integrated geophysical excitations are removed fro the observed celestial pole offsets, and the remaining part is used again to derive the period and quality factor of FCN in running intervals. Our conclusion is that the observed quasi-periodic variations of both parameters are not caused by these geophysical excitations, but another source should be searched for.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public