Int. J. Environ. Res. Public Health 2010, 7 951 5. Brief Summary of Our Knowledge about Geomagnetic Field, its Principle Parameters and Sources of Variation Earth currents flowing considerably deeper than at the Earth’s crust generate the Earth’s main magnetic field. Land geomagnetic force varies from 35 μT on the equator to 65 μT in regions close to Earth poles. Regular changes of solar activity and corresponding outer space plasma flow alterations induce global geophysical field fluctuations with a frequency range from 0,001 Hz to 10 Hz. The various manifestations of solar activity are driven by the changing amount and distribution of magnetic flux in the Sun. Solar activity dynamics was first discovered through observations of sunspots. Reliable counts of sunspots, integrated into an index called International sunspot number or Wolf number, date back from the present to at least the beginning of the 18th Century. In 1946, a better index of solar magnetic activity was discovered: the 10.7cm Solar Flux. This index represents measurement of radio emission from plasma concentrations formed in the solar corona by magnetic fields [81,82]. Potent blows of solar plasma (solar eruptions) reaching the Earth cause geomagnetic storms. A mediatory function in this process plays Ionosphere – upper part of Earth’s atmosphere at altitudes  70–1,000 kilometers. Blows of high-energy cosmic radiation comprising electrons, protons, ultraviolet and gamma-rays, etc., cause increase of ionization and intense currents in ionosphere (Figure 8). This generates potent electromagnetic fields throughout atmosphere, in oceans and even in the Earth crust. These fields and currents are able to influence any Earth organisms and their living conditions. Duration of geomagnetic storm average between one or two days, at this period amplitude of magnetic field fluctuations may vary from 200–300 nT and until 1000 nT, which exceeds normal background values in different frequency bands by 5,000–10,000-times [83]. Figure 8. Schematic picture of “Sun wind” consisting of plasma fluxes erupted from the Sun’s surface and their interaction with Earth’s magnetic field. Intensity of industrial magnetic fields can amount up to 120 μT, but contribution of the industrial (artificial) magnetic fields in total average intensity of environmental magnetic field is rather small because of mutual compensation (cancellation) of industrial magnetic fields [84,85]. 6. Possible Evidence of Regulatory Influence of Solar Cycles and Corresponding Geomagnetic Field Perturbations on Flu Epidemic Process