Synodic tendencies in the time series of fmin at South Pole, Antarctica

Abstract

At least three contemporaneous sequences of synodic polar cap absorption events (PCA) have been identified in the time series of ionosonde fmin obtained at the Antarctic station, South Pole, at maximum epoch of the recent solar cycle (1958). The sequence synodic periods (27·45, 27·45, and 27·2 days) are characteristic of the rotation of moderately low latitude regions of the sun. These results support the interpretation of similar synodic sequencies which occurred in 1961, associated with MeV proton streams in interplanetary space. Due to the proliferation of solar active regions at sunspot maximum, several proton streams may exist contemporaneously. It is concluded that the magnetic structures in interplanetary space, responsible for the guidance of MeV solar protons, existed for a substantial portion of the maximum and waning phases of the recent solar cycle.