More than 200 hours of ionospheric electric field measurements taken on balloons flown from three polar cap sites have been analyzed to determine average properties of the large‐scale polar cap electric field and its dependencies on the interplanetary magnetic field. The major component of this electric field was directed from dawn to dusk and produced an average polar cap potential drop of about 55 kV. The magnitude of this potential provides an upper limit of about 700 RE for the length of the magnetospheric tail and implies an energy input from the solar wind to the magnetosphere of about 5 × 1019 ergs/sec. The dawn to dusk component of the high‐latitude polar cap electric field responds to Bz, the northward component of the interplanetary magnetic field, on a time scale ≲1 hour and with an average increase of about 3 mV/m for each 1 γ decrease of Bz. The hourly averages of the electric field data at each of the three sites are well described by a two‐cell convection pattern whose location depends on the y component of the interplanetary magnetic field. When By is positive (negative), the two‐cell convection pattern shifts toward dawn (dusk) in the northern hemisphere with the following consequences: the maximum intensity of the northern polar cap dawn to dusk electric field component occurs at local morning (evening), and the auroral zone return flow reaches higher latitudes in the evening (morning). Evidence of the vector nature of the interaction between interplanetary and terrestrial magnetic fields is provided by the observation that the above By dependent signatures are most evident when Bz is most negative.

By using rocket‐borne Langmuir probes, electron temperature profiles have been obtained in five mid‐latitude sporadic E layers. The data show the electron temperature within the layers to be lower than the electron temperature at the adjacent altitudes. This is consistent with the layers' being maintained by a vertical redistribution of ionization. The magnitude of the observed electron temperature variation is, however, larger than expected.

The electric field in the ionosphere and the magnetic field at the earth's surface in the mid‐latitude region were both measured during a sudden impulse. Ionospheric conductivities deduced from this data were consistent with expectations, thus suggesting that the fluctuations in the magnetic field at the earth's surface were caused by overhead ionospheric currents that were driven by an electric field associated with the sudden impulse.

A double‐probe measurement of midlatitude ionospheric electric fields was made on a rocket flight near a large, artificial, barium plasma cloud. The measurement was made after ground sunset on February 1, 1971, near L = 1.8, 7 min after the release of the barium and 4 min before the visual onset of its striations. The cloud‐associated perturbation of the approximately 4‐mv/m electric field in an earth‐fixed frame of reference was in agreement with theoretical expectations based on the enhancement of the Pedersen conductivity produced by the cloud and lends support to the gradient drift instability model of striation formation. The motion of the leading edge of the barium cloud was consistent with that expected from the rocket electric field measurement. The ionospheric electric field in a frame of reference not rotating with the earth differed from the corotation electric field by about 20% during the flight.

Electron temperatures and electron densities measured on four rocket flights have been used to deduce electron heating rates in the E and lower F regions. Above 150 km heating rates at midday are found to be in good agreement with calculated values. Anomalies are found in heating rates at sunrise which are attributed to a source, such as joule heating, which does not produce ionization.