Comment on “A new method of spectral analysis and its application to the Earth's free oscillations: The ‘Sompi’ Method” by S. Hori et al.

The "Sompi" method of Hori et al. [1989] (henceforth H89) is an autoregressive (AR) method for finding the exponentially decaying/growing sinusoidal components (henceforth simply "sinusolds") in a time series corrupted by noise.H89 made numerous references to an earlier study by Chao and Gilbert [1980] (henceforth CG80), which has described a similar spectral analysis method genetically (and perhaps a bit unfortunately) called the "AR" method.Both methods were applied in the two papers to study the Earth's free oscillation records.In this commentary I will contrast the two methods, since the comparisons made by H89 are superficial and can be misleading.For clarity, I will call CG80's "AR" method the "AR-FD"method (where FD stands for frequency domain; see below).