Seasonal effects on sudden phase anomaly normalization

The size of a Sudden Phase Anomaly (SPA) corresponding to a given incident x-ray flux depends on the time of day of the event, the season of the year, the length of the path considered and the radiation spectrum. It is necessary to determine the influence of each of these factors if the measured phase advance is to serve as an accurate indicator either of the size of the ionospheric disturbance or of the magnitude of the responsible flare. In the paper the effect of changing season is considered. For a given x-ray flux and solar zenith angle, it is found that the D-layer is more responsive in summer than in winter.