Physics Department Seminar University of Alaska Fairbanks


J O U R N A L    C L U B

 

White-washing the aurora: new results on broad-band emissions in aurora and aurora-like phenomena 


 
by
 
Don Hampton
UAF, Geophysical Institute


 


One of the most intriguing aspects of the aurora, especially in the age of low-cost, high-sensitivity cameras, is the vibrant colors they exhibit. From the striking green to deep reds and pink/violet colors, they present almost unnatural colors. This is due to the production of the optical emission by electron impact excitation of the atomic and molecular gases. Since the interactions excite quantum states in the electron orbitals, the permitted emission wavelengths are discrete and limited. This has been the backbone of studying the energy deposition and distribution of the precipitating electrons using ground-based and some satellite based studies. With advanced sensitivity and proliferation of multi-camera arrays in Alaska, Canada and Scandinavia, as well as a much expanded cadre of citizen science observers, we are finding that not all emissions are discrete. The discovery of the STEVE (Strong Thermal Emission Velocity Enhancement) phenomenon, and subsequent measurement with an imaging spectrograph showed that the emissions were broadband, not discrete. While associated with very high electron temperature, calculations do not support the idea that it is a blackbody glow. And more recently a new set of broadband filtered cameras in Canada have captured several active auroral events where the color characteristics did not follow normal red-green-blue ratios. Subsequent measurements with the same imaging spectrographs again show a distinct broadband emission overlaying the typical auroral emissions. I will present these examples (STEVE and broadband active aurora), and present a little speculation on the possible mechanism, though the measurements to date don't allow a definitive answer.




 


Friday, 07 March, 2025


Note: Hybrid meeting by Zoom and in the Globe Room: https://zoom.us/j/796501820?pwd=R2xEcXNwZGVRbG0va29iN2REU241UT09


3:45PM