  Threshold systems appear to underlie the global behaviour of physical
phenomena very unlike at a first look. The usual experimental fingerprint of
threshold system grounded phenomena is the presence of power laws. Experimental
evidence has been found, for example, in superconductor vortex avalanches, sand
piles, the brain, 4He superfluidity and earthquakes. Double power-laws have
been found in social networks, in the luminosity of some galactic nuclei and,
very recently, in solar flares, among others. Here we show evidences that point
to a threshold system as the source for magnetic storms detected on the Earth.
We based our analysis on series of data acquired during many years in the
network of magnetic observatories of the National Observatory (Brazil). In
particular we focused our attention on October 2000 month of the Vassouras
Observatory (RJ, Brazil), which have been active since 1915. We have found both
power laws and double power laws for some relevant distributions.
