The shape of the power spectrum of cosmic ray at ground level up to 7 × 10 Hz

The power spectral density of cosmic ray fluctuations observed at ground level during the years 1966–1968 has been calculated. In order to obtain the correct shape of the spectrum, the Fast Fourier Transform method with a triangular data window was used and corrections were made for uncorrelated errors and aliasing effects. When ignoring the Earth rotation peaks, the spectral index , for a sample of polar, middle latitude and equatorial stations, is ? 1.96 in the frequency range 3 × 10^?7–10^?4 Hz. A possible break around 10^?5 Hz, if existing, would be, on the whole, barely significant as a would change from ? 1.96 to ? 2.10. There are indications that beyond 10^?4 Hz up to 7 × 10^?3 Hz the spectrum continues with ? 2.