Rocket observations at the northern edge of the eastward electrojet

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Abstract
A Nike‐Tomahawk rocket was launched north over two quiet, late evening auroral arcs in March 1975. A northward magnetic disturbance was observed on the ground under the rocket trajectory. South of the arcs the northward electric field was 60 mV/m, indicating strong westward plasma flow. An eastward electrojet current layer was penetrated in the upward flight. Precipitating electrons were observed over each arc. The electric field decreased to below 20 mV/m over each arc and recovered to 50 mV/m between the arcs. Using the observed electron flux and a model of the ionosphere, the Hall and Pedersen conductivities were calculated. These conductivities were used, with the observed electric field, to calculate the eastward and northward components of the horizontal ionospheric currents. The eastward current calculated south of the first arc agreed well with the observed eastward electrojet current. The power dissipated by the Pedersen current Σp|E|² was also calculated and compared with the power carried by the precipitating electrons. The Joule power decreased abruptly in the auroral arcs, as the precipitating electron power increased. The total dissipated power was approximately the same inside the arcs, between them, and south of the luminosity. North of the aurora the electric field and dissipated power remained low. Field‐aligned currents carried by the observed electrons were about a factor of 3 lower than those inferred from the magnetic field measurements. Likewise, current continuity arguments to keep the auroral current system divergence free required a larger field‐aligned current than that obtained from the particle detectors.