Abstract
The atmospheric surface pressure time series of Madras, Darwin, and Tahiti together with non-tidal length-of-day (LODR) variations and axial component of atmospheric angular momentum (AAM) were analyzed by wavelet transform as well as the combination of the Fourier transform band pass filter with the Hilbert transform (FTBPF + HT) to detect interannual and intra-seasonal oscillations in them. It was found that annual oscillations in the atmospheric surface pressure variations of Darwin and Tahiti stations are in phase and are about 180o out of phase in the atmospheric surface pressure variations of Madras station. The phase of the annual oscillation in atmospheric surface pressure variations of Madras station is slightly greater (~ 20o) than the phase of the annual oscillation in the LODR time series. The amplitude and phase variations of the annual and semi-annual oscillations computed by the FTBPF + HT combination in LODR and the axial component of AAM are very similar. The mean amplitudes of the semi-annual oscillation in the atmospheric surface pressure variations of Madras and Tahiti are of the order of 0.4 hPa, the phases of these oscillations are stable and the amplitude of the semi-annual oscillation in the atmospheric surface pressure variations of Darwin is negligible due to unstable phase of this oscillation. The atmospheric surface pressure variations of Madras, Darwin, and Tahiti stations show similar amplitude wideband signals with a central period of ~ 4 years (cutoff periods ranging from about 2.2 to 20 years) related to El Niño phenomenon. The amplitude maxima of this signal corresponding to the strongest El Niño events in 1982-83, 1997-98, and 2014-15 are also present in amplitude variations of this signal in the LODR and AAM χ3 time series.