ULF Modulation of Auroral and Sub-Auroral Optical Emissions

Aurora have fascinated and captivated humans throughout history.  Science has taught us that auroral emissions are due to energetic particles, primarily electrons, streaming down the Earth’s magnetic field lines exciting the atmosphere and causing it to radiate light in beautiful displays of color forming arcs, spirals, and a variety of other dynamic features.  A recently discovered sub-auroral optical feature called STEVE, or Strong Thermal Emission Velocity Enhancement, was initially identified by citizen scientists.  STEVE appears as a narrow east-west band of whitish-purple light at latitudes below the typical auroral oval and is often accompanied by a bright green ‘picket fence’ emission.  Initial studies of this phenomena has found STEVE to be associated with a fast flow of ionized particles moving through the upper portion of the atmosphere and thus it is postulated to be due to a strong atmospheric heating mechanism, rather than typical auroral particle precipitation.  The mechanisms producing STEVE, the green picket fence, and other auroral forms are not well understood.  In my research I use a combination of high frequency (HF) radar data from the Super Dual Auroral Radar Network and all-sky imager data from the Redline Geospace Observatory (REGO) and the THEMIS ground network to study the ultra-low frequency (ULF) modulations of STEVE and other auroral emissions.  In this talk I will present the background, methods and results of my research on this topic and will show that ULF waves play a very important role in modulating both STEVE and other auroral forms.  The results have significant implications for understanding the physics of auroral/sub-auroral optical emissions via plasma heating and energetic particle precipitation.