  In solar physics, especially in exploratory stages of research, it is often
necessary to compare the power spectra of two or more time series. One may, for
instance, wish to estimate what the power spectrum of the combined data sets
might have been, or one may wish to estimate the significance of a particular
peak that shows up in two or more power spectra. One may also on occasion need
to search for a complex of peaks in a single power spectrum, such as a
fundamental and one or more harmonics, or a fundamental plus sidebands, etc.
Visual inspection can be revealing, but it can also be misleading. This leads
one to look for one or more ways of forming statistics, which readily lend
themselves to significance estimation, from two or more power spectra. We
derive formulas for statistics formed from the sum, the minimum, and the
product of two or more power spectra. A distinguishing feature of our formulae
is that, if each power spectrum has an exponential distribution, each statistic
also has an exponential distribution.
