MULTIRATE ALIAS FROM PERIODICALLY INTERRUPTED SAMPLING OF TIME-SERIES- IS THE QBO-SOLAR ACTIVITY CYCLE OF NORTH POLAR TEMPERATURE AN EXAMPLE

Intermittent sampling of a time series, wherein a basic uniform sampli ng rate is interrupted by a switch which periodically turns the sampli ng on and off, defines two sampling rates and two Nyquist periods, N1 and N2, respectively twice the shorter and longer periods of sampling. Thus, if data sampled in this manner contains frequencies higher than 1/N2 (that of the interruption switch), alias of the spectrum takes p lace even though N1 may be of sufficiently high frequency to itself sa tisfy the nominal single sampler Nyquist criterion. This condition can lead to potentially gross misinterpretation of the true frequency spe ctrum. This paper formalizes the problem for the frequency domain, fol lowed by exploration of the possibility that such a corrupting effect may be present in the QBO-solar cycle relation reported by Labitzke an d coworkers.