ATMOSPHERIC EXCITATION OF POLAR MOTION DURING THE GIG-91 MEASUREMENT CAMPAIGN

Daily determinations of the Earth's pole position from Global Positioning System (GPS) observations acquired during the first GPS IERS and Geodynamics (GIG) experiment held during January 22, 1991 to February 13, 1991 are interpreted in terms of atmospheric wind and pressure fluctuations as parameterized by the atmospheric angular momentum (AAM) chi-functions. All available AAM chi-functions spanning the GIG '91 period have been collected and compared to the observations in the time and polar motion domains. The greatest level of agreement is obtained using die total (wind plus pressure) chi-functions from the Japanese Meteorological Agency (JMA) where the pressure term is computed by assuming the inverted barometer approximation. In this case, the correlation coefficient between the observed and JMA-induced polar motion series is 0.91 for the x-component and 0.72 for the y-component, the rms of the difference between the observed and JMA-induced series is 0.71 mas for the x-component and 0.69 mas for the y-component, and the percentage of the variance of the observed series explained by the JMA-induced series is 83% for the x-component and 48% for the y-component. Thus, it is demonstrated that atmospheric wind and pressure fluctuations are largely responsible for exciting the rapid polar motions observed during GIG '91.