Observations of Pi 2 pulsations at the Chung-Li (CNL) station are presented and interpreted. The geomagnetic latitude of this station is 13.8-degrees-N (L = 1.06). The power spectra of the observed Pi pulsations show both single and multiple peaks during daytime and nighttime. Typical periods of Pi pulsations observed are 30-100 s. The observed frequency ratios of the first three harmonics are found to be about 1:1.5:2. Large-amplitude pulsations are more frequently observed during local noon and midnight. The observed characteristics are explained on the basis of two cavity resonance models: (1) a magnetosphere cavity model (model A) that includes the plasmasphere and the plasma outside the plasmapause and (2) a plasmasphere cavity model (model B) that ignores the plasma outside the plasmapause. It is found that the presence of the plasma outside the plasmapause can significantly modify the amplitude and eigenfrequencies of the waves excited in the resonance cavity. The eigenfrequencies of the cavity waves also depend on the position and the density drop at the plasmapause. The eigenfrequencies as a function of the azimuthal wave number k(y) are also studied. It is found that for small k(y), the ratios of the eigenfrequencies of the first three harmonics in the radial direction calculated from model A are consistent with the observed values.
