ULF Wave Electromagnetic Energy Flux into the Ionosphere: Joule Heating Implications

Thursday, 18 December 2014
Michael Hartinger1, Mark Moldwin1, Shasha Zou1, John W Bonnell2 and Vassilis Angelopoulos3, (1)University of Michigan, Ann Arbor, MI, United States, (2)University of California Berkeley, Berkeley, CA, United States, (3)University of California Los Angeles, Los Angeles, CA, United States
Ultra Low Frequency (ULF) waves - such as standing Alfven waves - are one mechanism for coupling the inner magnetosphere to the Earth’s ionosphere. For example, they transfer energy from the solar wind or ring current into the Earth's ionosphere via Joule heating. In this study, we use NASA Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite data to investigate the spatial, frequency, and geomagnetic activity dependence of the ULF wave Poynting vector (electromagnetic energy flux) mapped to the ionosphere. We use these measurements to estimate Joule heating rates. We compare these rates to empirical models of Joule heating associated with large scale, static (on ULF wave timescales) current systems, finding that ULF waves usually contribute little to the global, integrated Joule heating rate. However, there are extreme cases when ULF waves make significant contributions to global Joule heating. Finally, we find ULF waves routinely make significant contributions to local Joule heating rates near the noon and midnight local time sectors, where static current systems nominally contribute less to Joule heating; the most important contributions come from lower frequency (<7 mHz) waves.