Fantastic Aurora: Inside the Sun to Earth's Poles

Related video: http://www.youtube.com/watch?v=SrXJuhKiirI

Plasma from solar flares or coronal mass ejections travel along solar wind to ultimately produce aurora's in Earth's polar regions. This visually stunning explanatory video takes you on a journey from sun's interior to the Earth's upper atmosphere.

Auroral observations over the last 100 years reveal that peak periods of aurora occur close to the equinoxes-that is, during the months of March and April, and again September and October. Of the two yearly peaks, the greater peak of auroral events occurs during October. However, some of the strongest levels of geomagnetic storms are in the spring. The minimum activity yearly occurs during the months of June and July, with a lesser minimum during December.

Aurora is a direct result of solar plasma interacting with gasses in the upper atmosphere. Geomagnetic storms develop when strong gusts of solar wind and coronal mass ejections (CMEs) "hit" the Earth's magnetosphere in just the right way. The magnetosphere is filled with electrons and protons that are normally trapped by lines of magnetic force that prevent them from escaping to space or descending to the planet below. The impact of a CME breaks loose some of those trapped particles, causing them to rain down on the atmosphere. Gasses in the atmosphere start to glow under the impact of these particles. Different gasses give out various colors. Think of a neon sign and how the plasma inside the glass tube, when excited, glows with a bright color. These precipitating particles mostly follow the magnetic field lines that run from Earth's magnetic poles, and are concentrated in circular regions around the magnetic poles called "auroral ovals." These bands expand away from the poles during magnetic storms. The stronger the storm, the greater these ovals will expand. Sometimes they grow so large that people at middle latitudes, like California, can see these "Northern Lights."

When the molecules and atoms are struck by solar wind particles the stripping of one or more of their electrons ionizes them to such an extent that the ionized area is capable of reflecting radio signals at very high frequencies. This ionization occurs at an altitude of about 70 miles, very near the E layer of the ionosphere. The level of ionization depends on the energy and amount of solar wind particles able to enter the atmosphere.

While correlations exist between visible and radio aurora, radio aurora could exist without visual aurora. Statistically, a diurnal variation of the frequency of radio aurora contacts has been identified that suggests two strong peaks, one near 6 PM and the second around midnight, local time.

VHF auroral echoes, or reflections, are most effective when the angle of incidence of the signal from the transmitter, with the geomagnetic field line, equals the angle of reflection from the field line to the receiver. Radio aurora is observed almost exclusively in a sector centered on magnetic north. The strength of signals reflected from the aurora is dependent on the wavelength when equivalent power levels are employed. Six-meter reflections can be expected to be much stronger than 2-meter reflections for the same transmitter output power. The polarization of the reflected signals is nearly the same as that of the transmitted signal.

The planetary K index (Kp) is a good indicator of the expansion of the auroral oval, and the possible intensity of the aurora. When the K index is higher than 5, most readers in the northern states and in Canada can expect favorable aurora conditions. If the K index reached 8 or 9, it is possible for radio aurora to be observed by stations as far south as Florida.

Look for Aurora-mode propagation when the Kp rises above 4, and look for visual Aurora after dark when the Kp rises above 5. The higher the Kp, the more likely you may see the visual lights. But, you don't have to see them to hear their influence on propagation. Listen for stations from over the poles that sound raspy or fluttery on frequencies above 28 MHz, possibly up as high as 440 MHz. Sometimes aurora will enhance a path at certain frequencies, other times it will degrade the signals. Sometimes signals will fade quickly, and then come back with great strength. The reason for this is that the radio signal is being refracted off of the more highly ionized areas that are lit up. These ionized areas ebb and flow, so the ability to refract changes, sometimes quickly. I've observed the effect of Aurora and associated geomagnetic storminess even on lower HF frequencies.

More info about radio propagation and space weather: http://sunspotwatch.com/

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Movie Credit: University of Oslo/Department of Physics, NASA, Arcticlightphoto.no

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[7viviana]

Great , very simple and smart explanation

[pegasusmatrix]

Totally awesome, (and scientifically correct) video of our magnetosphere at work.

[OfficialTribe]

Yay plasma!

[simrehman123]

awsome sir...

[Lockemeister]

Great video!