Rg. Rastogi et al., NOCTURNAL VARIATIONS OF GEOMAGNETIC HORIZONTAL FIELD AT EQUATORIAL STATIONS, Geophysical research letters, 23(19), 1996, pp. 2601-2604
The nocturnal variations of the horizontal component (H) of the geomag
netic field at equatorial stations Koror, Trivandrum, Addis-Ababa and
Ibadan during any of the seasons of the period 1958-59 showed a steady
decrease after sunset throughout the nighttime hours. However, at Hua
ncayo a steady decrease after sunset to sunrise is seen only during th
e D-months. During the J and E months decrease is seen after sunset ti
ll about 22-23 hr and a slow and steady increase from midnight hours t
o sunrise. The nocturnal variations of H field at Huancayo show a rema
rkable similarity with tile corresponding variations of the horizontal
electric field in the ionosphere as determined by tile Doppler shifts
of backscatter echoes from tile E and F layers over Jicamarca. Thus,
genuine changes in the equatorial electric field and current in the io
nosphere over the American sector during the nighttime hours are clear
ly indicated.