Abstract
Previous work by Chun et al. [1999] has shown that the polar cap (PC) index can be used as a proxy indicator of the integrated Joule heating rate in the Northern Hemisphere. However, knowledge of the spatial distribution of Joule heating is also important. The PC index is a single magnetometer station‐derived index which measures the level of geomagnetic activity in the polar cap. A negative PC index corresponds to a condition related to lobe‐merging convection conditions in the polar cap, near‐zero PC indicates a quiet polar cap, and a positive PC indicates geomagnetically active periods. In this study we developed average patterns of Joule heating as a function of PC using 56 days (∼12,800 individual patterns) of Assimilative Mapping of Ionospheric Electrodynamics data from various case studies. With PC ranging from −3 to 8, we divide the Joule heating patterns into PC bins of 1.0, finding that there is a clear spatial evolution of Joule heating from negative PC to positive PC. When PC is negative, Joule heating on average is constrained to the high‐latitude dayside. As PC goes to zero, Joule heating disappears. When PC increases in the positive direction, Joule heating intensifies throughout the auroral oval, with primary heating occurring along the dawn/dusk flanks. Further analysis reveals that it is primarily changes in the electric potential and not the Pedersen conductance that accounts for Joule heating shifting from the auroral zone to the high‐latitude dayside when PC goes negative. We also find that the cross polar cap potential is linearly proportional to the PC index, consistent with previous studies. Finally, we compare the hemispheric energy budget between Joule heating and electron particle energy. We find that globally, Joule heating is roughly 4 times that of particle energy during geomagnetically active times (positive PC). During quiet times (zero PC), Joule heating and particle energy are equal contributors. When lobe‐merging conditions occur (negative PC), Joule heating again dominates over particle energy except during the winter season, when polar cap conductivity is driven more by particle precipitation.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have