The solar wind fluctuations cause variation in the strength and direction of the magnetic field measured near the earths' surface. Any abrupt changes in this dynamic medium are called geomagnetic disturbances. This impacts on HF communications as the ionosphere acts as a mirror bouncing and reflecting signals back down to earth. Solar Cycles Space weather depends on an 11-year solar cycle. Cycles vary in both intensity and length, and the solar activity is characterized by the appearance of sunspots on the sun.
Sunspots are regions of stronger magnetic field.
The solar maximum is the time when maximum spot numbers are visible. Sunspot numbers are those quoted for an average number over a 12-month period, and is the traditional measure of solar cycle status. Peak sunspot like highest rainfall is that for recorded worst cases, and 5 of the last 6 have been high magnitudes. Cycle 19 in 1957 peak had a sunspot number of 201, and the largest on record, Cycle 21 in 1979 had a peak sunspot number of 165 was the second largest, Cycle 22 in 1989 was equal third largest. At present it is in a rising phase, with cycle 23 predictions by IPS space Services are a large amplitude number on 2000 of 165 or greater.