Blanketing sporadicElayer near the magnetic equator

A study of the ionograms obtained at Kodaikanal (dip latitude 1.7°N) during the period 1954–1966 has shown that the daily variation of the occurrence of the blanketing type of Es (Esb) has a major peak around 1700 LT in the evening and a minor peak around 0800 LT in the morning and is practically inhibited around midday hours when the electrojet currents are maximum. Further, Esb is most frequent during local summer months and in years of minimum solar activity. In individual cases, Esb occurs during the period of very weak or reversed electrojet currents. The ionospheric drifts during these occasions show predominantly a north-south component. It is suggested that the equatorial Esb is due to the transport and accumulation of long-lived metallic ions from tropical latitudes to the magnetic equator by equatorward winds during the period when the electrojet currents are very weak and the upward Hall polarization field is thus absent.