Longitudinal variations of nighttime electron auroral precipitation in both the Northern and Southern hemispheres from the TIMED global ultraviolet imager

Using 6 years of Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) global ultraviolet imager auroral observations in both hemispheres, we have studied the longitudinal variations of auroral precipitation during the magnetic nighttime period of 2100 - 0300 magnetic local time. There was a strong seasonal dependence of the longitudinal variations of the aurora: (1) During solstices and for both hemispheres, auroral precipitation peaked between magnetic longitude (MLON) 210°E and 360°E in June and between MLON 120°E and 300°E in December. (2) In the equinoxes, the auroral longitudinal pattern was generally similar to that in local summer in each hemisphere, except that in the Northern Hemisphere the maximum precipitation was usually located in more westward longitudes in equinox than in summer. (3) The ratios between the maximum and the minimum of the precipitation energy flux along longitudes varied between 1.3 and 1.9, which were similar to those in previous studies. These features of the auroral longitudinal patterns did not change much from Kp = 1 to Kp = 4 conditions. Since the longitudinal distribution of auroral precipitation changed greatly with season in each hemisphere, the longitudinal variations of the magnetic field strength, which do not change with season, might not be the only process that caused the observed longitudinal variations of the aurora. Further data analysis shows that there was a significant negative correlation (coefficient |r| = ~0.4 - 0.8) between the peak auroral precipitation intensity and the solar-EUV-produced ionospheric conductivity of the same hemisphere (in summer and equinox) or of the conjugate hemisphere (in winter). These results indicate the important effects of solar-EUV-produced ionospheric conductivity, which has significant longitudinal variations, on the longitudinal patterns of the aurora at magnetic nighttime. Our results also suggest that the interhemispheric coupling during solstices might be an important factor that contributes to the longitudinal variations of the nighttime aurora. Our correlation analysis indicates that the hemispheric differences in the conjugate magnetic field strengths also contribute to the longitudinal variations of the aurora, although they appear not to be a major factor.