Physics Department Seminar University of Alaska Fairbanks

J O U R N A L    C L U B


Electrodynamics-Electron Correlative Experiment

Marilia Samara and John Bonnell
University of California Berkely

The goal of the GREECE mission is to make, “High resolution rocket and ground-based investigations of small-scale auroral structure and dynamics”. The aurora is one of the most dramatic open air manifestations of electrodynamics on the planet. The auroral light is produced when energetic electrons (think of the electron gun in an old-style TV or com- puter monitor, or in a particle accelerator) crash into atoms and molecules in the Earth’s upper atmosphere at 100-500 km altitude (60-300 miles) and cause them to emit light - red, green, crimson, violet and other visible and invisble wavelengths, depending upon altitude and energy - which one can then see from the ground. But that light is only the tip of the iceberg, and represents the end product of complex and only mildly understood electro- magnetic processes occurring further up along the Earth’s magnetic field. These processes are known to take the energy and forces contained in the fluid-like flows of ionized gas at those higher altitudes and and convert them into electric currents and voltages much like the way that a turbine in the core of a hydroelectric dam converts the flow of water into electrical power.What’s not well understood is why sometimes the auroral displays form placid, large-scale arcs and curtains across broad swaths of the sky (tens to hundreds of km north-to-south, and thousands of km east-to-west for tens of minutes to hours), only to break up into very-highly-structured and rapidly changing arcs, swirls, curls, pillars, even ‘flames’ (tens to hundreds of meters, with changes occuring on fraction of a second time scales - factors of 1000 in both cases!). GREECE is a tool and experiment all in one to make the measurements needed to better understand how this cascade from large to small and placid to active happens. To find out more about how that will be done, please visit :

Friday, 7 February 2014
Globe Room, Elvey Bldg.
3:45 PM