Further evidence for a global correlation of the Earth-ionosphere cavity resonances

The Stanford ELF/VLF Radio Noise Survey provides digital time series in the ELF range and VLF analog recordings of one horizontal magnetic field component at different locations around the globe. Three sites, Arrival Heights in Antarctica, Søndrestrømfjord in Greenland and Stanford in California, are chosen to investigate the natural magnetic noise in the frequency range of the Earth‐ionosphere cavity resonances (6–60 Hz). The resonances are interpreted as pure resonance phenomena and the associated parameters are derived in a robust manner by use of the complex exponential algorithm. The resulting amplitudes of the first and second resonances exhibit a pronounced diurnal variation and a distinct day to day variability of the same order during the time interval from January to April 1990. The day to day variability is well correlated between all of the three different sites. They also exhibit a 20–30 day variation that is related to the solar rotation period, expressed by means of sunspot numbers.