Nocturnal variations of geomagnetic horizontal field at equatorial stations

The nocturnal variations of the horizontal component (H) of the geomagnetic 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 Huancayo a steady decrease after sunset to sunrise is seen only during the D-months. During the J and E months decrease is seen after sunset till about 22-23 hr and a slow and steady increase from midnight hours to sunrise. The nocturnal variations of H field at Huancayo show a remarkable similarity with the corresponding variations of the horizontal electric field in the ionosphere as determined by the Doppler shifts of backscatter echoes from the E and F layers over Jicamarca. Thus, genuine changes in the equatorial electric field and current in the ionosphere over the American sector during the nighttime hours are clearly indicated.

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