INTERMEDIATE-TERM EPOCHS IN SOLAR SOFT-X-RAY EMISSION

Observations of the daily 1- to 8-A solar X ray emission from 1977 to 1981 are analyzed from a terrestrial viewpoint. A high-resolution method of anharmonic frequency analysis is used to search for discrete frequencies in a finite time series and estimate the frequency, phase, and amplitude of each periodic component. Results suggest that near the boundary of an epoch the amplitude spectrum undergoes an episodic change in frequency, phase, and amplitude, after which a new spectrum appears that persists for the duration of the next epoch. Furthermore, these frequencies most closely corresponding to solar rotation are not normally distributed about a 27-28 day mean but occur at about 22, 25, and 34 days.