When long-term observations are obtained from  one site only, the day/night alternance induces regular gaps in  the time series. These regular gaps  induce so-called daily aliases in the frequency domain:  each oscillation frequency will appear surounded by spurious peaks separated by 11.55microHz (1/24 hours). The amplitude of the closest daily aliases can be almost equivalent to the amplitude of the central peak associated with the oscillation frequency. This makes the detection of the oscillation frequencies very ambiguous.

In the STEPHI campaigns, we showed that three-sites observations, by suppressing the regularity of the gaps,  allow to remove this ambiguity , even taking into account usual interruptions due to bad weather.