In August‐September 1967 eleven barium vapor clouds were released during evening twilight between invariant magnetic latitudes of 67.3° to 68.1° from Andøya, Norwav. Two flights (8 releases) occurred during moderate negative bays in H, whereas the third flight (3 releases) took place during a positive bay in H. Visual auroral displays were observed in the vicinity during all flights. In the negative bay situation, barium ion cloud motions were eastward and closely parallel to auroral arc alignments. Electric fields transverse to the magnetic field with intensities of 10–130 mv/m directed southward were observed. During the positive bay event the barium clouds spanned the breakup transition region, with the two equatorward clouds moving westward while the poleward cloud went east. Observed reversals in direction were closely correlated with magnetic variations. North‐directed electric fields of up to 50 mv/m were found in the positive bay sector. In all events the ion cloud motions revealed that E was perpendicular to the ionospheric current, hence we conclude that the auroral electrojets, both eastward and westward, are essentially Hall currents. The results illustrate that the magnitude of E driving ionospheric currents cannot be deduced solely from ground magnetic observations because of the variable ionospheric electrical conductivity. There is evidence that while E is large near an auroral arc, the field within is very low. Large gradients and/or irregularities in the E field are found to exist most of the time. These are revealed on three different time‐space scales: from differences in velocity for parallel moving clouds, from velocity changes along the path of a given cloud, and in the form of rayed structure within a cloud.
Electrically neutral, luminous clouds are a by‐product of chemical releases conducted to create barium ion clouds for the measurement of electric fields. Wind measurements provided by the motions of these clouds are particularly valuable in that the motions can be directly compared with convective ion drift motions to test the importance of ion drag forces. Motion from multiple releases between 200 and 300 km from 15 rockets launched from four high‐latitude locations is analyzed in this paper. The observations in the evening and midnight hours at magnetic latitudes of ≥65° strongly suggest that in these regions ion drag is the dominant force in driving neutral winds between 200 and 300 km. This conclusion is based on both the agreement between ion and neutral drift directions and the fact that there are distinct changes in the wind associated with (a) the reversal in east‐west ion drift at the Harang discontinuity, and (b) the transition from auroral belt sunward ion drift and polar cap antisolar ion drift. In the morning sector it is evident that neutral wind observations cannot be directly interpreted in terms of ion drag; other factors must be considered, such as inertial effects from ion drag, a lack of sufficient ionization for strong coupling of ion neutral motions, and wind forces other than ion drag forces.
Twelve Ba+ clouds were released at invariant latitudes 76° to 78° from three rockets launched from Cape Parry, Northwest Territories, Canada, for the study of polar‐cap electric fields and their relationship to polar‐cap magnetic‐field disturbances. All flights occurred under conditions characterized by Kp≈3. E was typically between 20 and 40 volts/km, directed roughly from dawn toward dusk, and was more uniform in space and time than E fields observed in the auroral belt. The measurements showed a large angular difference between the directions of E and ΔH, the horizontal polar‐cap magnetic disturbance. This meant that ΔH could not be caused solely by ionospheric Hall currents in the form of a sheet across the polar cap; also the sign of the difference was opposite to that expected from other elements of the conductivity tensor. Various factors lead to the conclusion that ΔH is caused almost entirely by a source other than overhead ionospheric currents. This conclusion has the consequence that continuity for Hall current auroral electrojets cannot be achieved by way of the polar‐cap and midlatitude ionospheres as assumed in the past. A mutual solution for both the ΔH problem and the continuity problem was found in terms of a new model for continutity of the Hall current auroral electrojets. Continuity by way of field‐aligned currents is primarily a consequence of (grad N)/N being greater than (grad E)/E. N = electron density at 100–130 km. The large‐scale properties of grad N/grad E appear to be compatible with the net distribution of field‐aligned currents required to explain both the polar cap ΔH and the simultaneous disturbance observed on the low‐latitude side of the auroral belt. The net field‐aligned currents are equivalent to two sheet currents flowing ‘out of’ and ‘into’ the auroral‐belt ionosphere, respectively, in the magnetic local time sectors 20–24h and 8–12h. Cause and effect between field‐aligned currents and precipitating particles is implied, in that the distribution of grad N at 100–130 km depends on the distribution of the precipitation.
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