The hysteresis variation in F2-layer parameters.

The variations in f₀F2 and M(3000) F2 with sunspot number for the 19th solar cycle are studied to assess the difference between the rising and falling parts of the solar cycle. Such differences, which may be termed hysteresis is evaluated for several stations. In the case f₀F2 the magnitude of hysteresis is found to vary systematically with geomagnetic latitude, being minimum at equatorial and high latitudes, and a maximum at mid latitudes on either side of the equator. The M(3000) F2 factor also shows considerable hysteresis, but without any systematic latitude variation. The results are discussed in the light of a hysteresis effect observed in the variation of magnetic activity with the sunspot number.