Abstract.The measurement of the directions of radio meteors with an interferometric system is beset by two problems: (1) The ambiguity in the measured directions for antennas spaced by more than )•/2 and (2) the effects of mutual impedance when the antennas are spaced at )•/2 and less to avoid these ambiguities. In this paper we discuss the effects of mutual impedance between spaced antennas and describe an interferometer which both minimizes these effects and avoids the ambiguities associated with spacings larger than )•/2. We have modeled a version of this design numerically and show that under ideal conditions an interferometer of total span 4.5)• can yield directions accurate to about 0.3 ø with a signal-to-noise ratio of 20 dB. Finally, we have tested the design with observations from the 1996 Geminid and 1997 Quadrantid meteor showers and find that even without a ground plane, the interferometer provides unambiguous directions to an accuracy of the order of 1.15 ø.

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The response of the ionospheric F region to the large solar flare that occurred near 1500 UT on August 7, 1972, has been monitored by means of Faraday rotation measurements made at 17 stations in North America, Europe, and Africa. With observations spanning more than 10 hours in local time and more than 70 deg in latitude, the first truly global morphology of a flare‐induced F region event was obtained. The sizes of the individual sudden increases in the total electron content (Sitec) ranged from 1.8 to 8.6 × 1016 el/m²; on a percentage basis, all the Sitec fell within the 15 to 30% range. No obvious relationship was found between the sizes of the increases and the solar zenith angles at the various subionospheric points, nor between the observed Sitec and the sudden flare effects (SFE) seen on nearby magnetometer recordings. The latitudinal behavior provided the only simple ordering parameter found in the data, the lower latitudes having larger observed increases than the higher latitudes. Millstone Hill incoherent scatter data showed that nearly 40% of the total content enhancement observed at that site came from heights above 300 km. All the Sitec had a rise time of about 10 min, during which the Tec rate of change showed an excellent correlation with the time development of the solar radio burst monitored at 35,000 MHz.