A comparison of ionospheric currents, magnetic variations, and electric fields at Arecibo

Ionospheric currents calculated from incoherent scatter measurements at Arecibo are compared to ground magnetic variations at San Juan and to electric fields measured in the F region for two slightly disturbed periods and one very disturbed period, comprising a total of 7 days of data. The measurements indicate that the currents primarily responsible for the ground magnetic variations were flowing in the ionosphere on the slightly disturbed days. On the very disturbed days the variation in the horizontal intensity appears to be primarily due to an asymmetric ring current of magnetospheric origin. The eastward wind had to be modeled above 130 km in the calculations. A semidiurnal S2,2 wind model consistent with the measured southward winds drives southward currents that produce a total D variation of 20–40 γ with approximately the observed phase, indicating that the S2,2 component should be included in theoretical Sq calculations. A diurnal component also appears to be necessary if the D variation is to be well reproduced. The electrostatic field was found to drive about as much net horizontal current as the neutral winds. The horizontal components of the electrostatic field tended to be perpendicular to the calculated ionospheric currents on all days.