Seasonal and hemispheric variations of the total auroral precipitation energy flux from TIMED/GUVI

The auroral hemispheric power (HP) has been calculated from the averaged energy flux derived from Far-ultraviolet emission observations made by the global ultraviolet imager (GUVI) instrument on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite during 2002-2007. This HP was used to study how variations in seasonal and hemispheric asymmetries changed with changing geomagnetic activity. Our results showed that there were persistent seasonal and hemispheric differences in quiet conditions. There were HP differences of about 1-3 GW between the summer and winter seasons in each hemisphere and also between the two hemispheres during each solstice period for low geomagnetic activity (Kp < 3). The summer-winter asymmetry was 4%-35% when HP was low. These summer-winter differences became negligible when geomagnetic activity was moderate to active. Similarly, there were also HP differences of about 2 GW between local summers of the two hemispheres during geomagnetically quiet conditions (Kp < 3) but not during higher Kp conditions. The hemispheric asymmetries between the two summer solstices were about 10%-20% during quiet conditions, whereas there was no apparent hemispheric asymmetry between the two winter solstices under all Kp 1-5 conditions. Solar illumination effects were probably the primary cause of the seasonal and hemispheric variations of the auroral hemispheric power for these geomagnetically quiet conditions. During moderate and active conditions the conductivities were driven more by the production of ionization due to precipitation, so the precipitation was more symmetric.