Conjugacy of visual auroras during magnetically quiet periods

The spatial and temporal conjugacy of auroras at high latitudes has been investigated by flying two NC-135 jet aircraft, equipped with all-sky and narrow-field cameras, along magnetically conjugate paths crossing the northern and southern auroral zones along the dipole 256° meridian. The flights were centered about magnetic midnight on March 12, 14, and 16, 1967. Magnetic activity was very low throughout this period; nevertheless, auroras were observed between dp latitudes 66° and 71° during each flight. A visual examination of all the data and a quantitative analysis of selected film frames indicate that, within the limits of error in the measurements and aircraft navigation, all the observed auroras were conjugate according to the GSFC 12/66 model of the main geomagnetic field. In most cases when the relative positions of aircraft and aurora were the same in both hemispheres, the conjugate auroras exhibited remarkably detailed similarity (point conjugacy) in their shape, intensity, and in their spatial and temporal variations. There is a tendency for the southern auroras to be located slightly eastward of the northern conjugate auroras. Such a displacement appears to be consistent with a slight asymmetric distortion of the main geomagnetic field due to solar wind pressure and earth dipole-sun geometry at the date and time of the measurements. These results suggest that, during magnetically very quiet times, auroras located at dp latitudes up to 71° are caused by a symmetrical injection of electrons and protons near the equatorial plane and onto magnetic field lines that are closed, stable, and relatively undistorted by external magnetic fields. Preliminary results from similar conjugate flights conducted during March 1968, a magnetically disturbed period, are briefly described. A visual inspection of these data has revealed substantial deviations in auroral conjugacy and a considerably more complex behavior of particle precipitation than that occurring during magnetically quiet periods.

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