What Happens in the Aurora
An aurora is a natural light display in the sky particularly in the high latitude (Arctic and Antarctic) regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere. The charged particles originate in the magnetosphere and solar wind and, on Earth, are directed by the Earth's magnetic field into the atmosphere. A team of scientists on Saturday night launched an instrument-laden, two-stage sounding rocket arcing through shimmering green aurora, 186 miles above the Earth. Instruments on board, including those built at University of New Hampshire's Space Science Center, sampled electric and magnetic fields as well as charged particles in Earth's upper atmosphere (ionosphere) that get sloshed back and forth by a specific form of electromagnetic energy known as Alfven waves.
The precision measurements from the 40-foot Terrier-Black Brant rocket's instruments will shed new light on the physical processes that create the northern lights and further our understanding of the complex sun-Earth connection.
These Alfven waves are thought to be a key driver of "discrete" aurora — the typical, well-defined band of shimmering lights about six miles thick and stretching east to west from horizon to horizon.
An Alfvén wave in a plasma is a low-frequency travel ling oscillation of the ions and the magnetic field. The ion mass density provides the inertia and the magnetic field line tension provides the restoring force. The wave generally propagates in the direction of the magnetic field.
According to Marc Lessard, an associate professor at the UNH Institute for the Study of Earth, Oceans, and Space (EOS) and department of physics, the Alfven resonator is a structure in the ionosphere that acts like a guitar string when plucked by energy delivered by the solar wind to Earth's magnetosphere high above.
The ionosphere is a part of the upper atmosphere, from about 85 km to 600 km altitude, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth.
"The ionosphere, some 62 miles up, is one end of the guitar string and there's another structure over a thousand miles up in space that is the other end of the string. When it gets plucked by incoming energy we can get a fundamental frequency and other harmonics along the background magnetic field sitting above the ionosphere," Lessard said.
The Alfven resonator is a narrow, confined area of space — a channel that is perhaps several hundreds of miles tall but only six miles wide.
It is hypothesized that energy from the sun accelerates a beam of electrons producing aurora and also increasing the overall electrical conductivity within the channel.
Understanding how the ionosphere participates in providing the downward current is a critical component of understanding magnetosphere-ionosphere coupling.
Magnetosphere-Ionosphere Coupling in the Alfvén resonator (MICA) will provide insight into these wave-driven aurora specifically.
For further information: http://www.adn.com/2012/02/20/2327339/rocket-blasts-through-northern.html or http://www.sify.com/news/nasa-rocket-blasts-into-gleaming-aurora-news-international-mcwokiaijjj.html