Localized dayside proton aurora at high latitudes

Abstract

Two types of dayside localized proton‐induced auroral emissions on the dayside were identified in SI12 images from the Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) spacecraft. “Auroral oval spots” occurred at or toward the poleward edge of the dayside proton auroral oval. “Polar cap spots” occurred well into the polar cap. The polar cap spots occurred when the interplanetary magnetic field (IMF) was strongly northward and radially aligned along the Sun‐Earth line, which results in reconnection with northern lobe field lines. For the auroral oval spots that occurred during northward‐IMF only, there was a large azimuthal component of the IMF. During northward IMF conditions, a large azimuthal component of the IMF leads to reconnection at high latitudes on closed geomagnetic field lines. The reconnection site would map closer to auroral oval latitudes, which is consistent with the location of the auroral oval spots. The auroral oval spots were found to be much larger in size and total intensity than the polar cap spots, but the average intensities of the two types of spots were comparable. The average intensity of the auroral oval spots was proportional to the solar wind dynamic pressure and solar wind density, suggesting that the average intensity of the auroral oval spots is dependent on the number of protons precipitating from the reconnection site, rather than the proton energy. No clear trend was found for the polar cap spots, but there was a notable lack of polar cap spots for high solar wind dynamic pressures and densities.