Seasonal oscillations in regional and global atmospheric excitation of polar motion

Abstract

Time variable spectra of seasonal oscillations of global and regional atmospheric excitation functions of polar motion for the period 1948–1999 are computed from the NCEP/NCAR (National Centres for Environmental Prediction/ National Centre for Atmospheric Research) reanalysis Atmospheric Angular Momentum (AAM) data, namely from the pressure and the pressure with the inverted barometric (IB) correction. Amplitudes of the time variable spectra of seasonal oscillations of the global and regional atmospheric excitation functions of polar motion are variable. Contributions of atmospheric excitation function of polar motion from lands and especially from the Eurasia are the most important in the seasonal spectrum range of polar motion excitation function. The maps of the mean amplitudes of seasonal oscillations of atmospheric excitation functions of polar motion are computed for the fifty years period in 108 equal-weight sectors. They show the regions in which these oscillations are the most energetic. Correlations between the global and regional atmospheric excitation functions of polar motion and the geodetic excitation functions are investigated. The correlation coefficients computed between the global/regional atmospheric and geodetic excitation functions of polar motion became more stable and achieved the highest values of about 0.8 after 1970, 1975 and 1985 for annual, semi-annual and 120 days oscillations, respectively. The correlation coefficients in the Asia region are the closest to those of the global data.