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Is there a magnetospheric ground state? Do the position and size of the auroral oval depend on the magnetic dipole tilt angle at quiet magnetospheric conditions? In order to address these questions, northern hemisphere images of the aurora at 1356 Å, obtained by Polar BEAR at solar minimum (beginning of 1987), were related to high temporal resolution IMP 8 measurements of the interplanetary magnetic field, to solar wind velocity, and to the ground‐based activity index Kp. The first problem was addressed by a two‐dimensional correlation study of the repeatability of auroral emissions in corrected geomagnetic space at conditions of minimum energy transfer from the magnetosphere. The correlation measure of auroral images was 0.6‐0.85. Error simulations indicate that given the uncertainties in pixel position and intensity, the maximum expected value of the correlation measure is 0.65‐0.9. The notion of a ground state magnetosphere is therefore supported by our data. Repeatability was found at the same level regardless of time or reconfigurations of the magnetosphere between images and independent of magnetic time sector. The second problem was addressed by relating latitudinal shifts of the aurora with dipole tilt angle without resorting to auroral boundary specification. Our data indicate that the latitude of the continuous aurora is related to the dipole tilt angle at quiet magnetospheric conditions. In the winter hemisphere a 10° increase in the dipole tilt angle causes a 1° decrease (increase) in the latitude of auroral emissions at noon (midnight). The magnetic local time distribution of the latitudinal shifts with dipole tilt angle support a simple model in which the dipole tilt angle determines the position of the center of the auroral circle along the magnetic meridian 1320‐0120 MLT (for IMF By positive) and does not affect its radius.

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A bright and long-lived Sun-aligned auroral arc was observed over the north magnetic pole from 1120 to 1220 UT, December 14, 1990 at Eureka, Canada. It was monitored through its full lifetime with high resolution with an all-sky imager and a meridian scanning spectrometer. Its measured off-zenith 5577-/• intensity reached 12 kR. The recorded electron flux obtained boy a DMSP F9 overpass at 1124:15 UT was 56 ergs/(cm 2 s st), yielding an inferred 5577-A intensity in that region of the arc of at least 80 kR. The arc drifted slowly in the dusk to dawn direction during its early stages, then reversed its drift direction during later stages. The characteristics of the polar arc (its intensity, duration, and small-scale dynamics) were very similar to those of auroral oval arcs and strongly suggest that the polar arc occurred on closed magnetic field lines. Emissions on the duskside of the arc further suggest that the region of closed magnetic field lines extended from the evening sector to the magnetic pole. The inference is that the interplanetary magnetic field was most likely B• northward and By positive during the period of appearance of the arc.