Abstract:
Occurrence of spread F echoes at Kodaikanal for a period of about one year has been analysed and diurnal and seasonal characteristics have been found to exist in the frequency of occurrence of these echoes. It has been found that the phenomenon occurs only during night-time with largest frequency between 1900 and 0400 hours local time. While the seasonal variation is characterized by equinoctial maxima as in the case of geomagnetic activity, the day-to-day variations in scattering indicate a negative correction with the degree of magnetic activity. Thus, scattering persists for largest percentage of time during comparatively quiet periods and is often altogether absent on magnetically stormy nights. The phenomenon is discussed in relation to ionospheric irregularities and radio-star scintillation.
