Equatorial effects on nighttime Pc3 pulsations

Nighttime Pc3 pulsations observed simultaneously during the years 1976-1979 at Choutuppal (geomagnetic lat., 7.5 deg), an inland nonelectrojet station in India, and at Etaiyapuram (geomagnetic lat., -0.6 deg), a station in India near the dip equator, reveal an enhancement of the meridional component at the dip equator. The enhancement factor of these nighttime signals exhibits a local time variation reaching a maximum value of about 2.0 around midnight. It is also noted that, while the nighttime occurrences of Pc3s increase with an increase in solar activity, the percentage of nighttime enhancement shows an inverse relation. The results are analyzed in the light of a possible mechanism for nighttime enhancement of SCs, SIs, etc. at the dip equator.