Aurora Borealis

Luminous phenomenon of the upper atmosphere that occurs primarily at high latitudes.

Caused by the interaction of energetic particles (electrons and protons) from outside the atmosphere with atoms of the upper atmosphere.

Auroras in the Northern Hemisphere are called aurora borealis, or northern lights; in the Southern Hemisphere they are called aurora australis, or southern lights. Auroras are caused by the interaction of energetic particles (electrons and protons) from outside the atmosphere with atoms of the upper atmosphere. Such interaction occurs in zones surrounding the Earth's magnetic poles. During periods of intense solar activity, auroras occasionally extend to the middle latitudes.

Sources & Types of Aurora

Again, our understanding is very incomplete. A rough guess may point out three main sources:

Dynamo action with the solar wind flowing past Earth, possibly producing quiet auroral arcs ("directly driven" process). The circuit of the accelerating currents and their connection to the solar wind are uncertain.
Dynamo action involving plasma squeezed earthward by sudden convulsions of the magnetotail ("magnetic substorms"). Substorms tend to occur after prolonged spells (hours) during which the interplanetary magnetic field has an appreciable southward component, leading to a high rate of interconnection between its field lines and those of Earth. As a result the solar wind moves magnetic flux (tubes of magnetic field lines, moving together with their resident plasma) from the day side of Earth to the magnetotail, widening the obstacle it presents to the solar wind flow, and causing it to be squeezed harder. Ultimately the tail plasma is torn ("magnetic reconnection") --some blobs ("plasmoids") are squeezed tailwards and are carried away with the solar wind, others are squeezed earthwards where their motion feeds large outbursts of aurora, mainly around midnight ("unloading process"). Geomagnetic storms have similar effects, but with greater vigor. The big difference is the addition of many particles to the plasma trapped around Earth, enhancing the "ring current" which it carries. The resulting modification of the Earth's field allows aurora to be visible at middle latitudes, on field lines much closer to the equator.
Satellite images of the aurora from above show a "ring of fire" along the auroral oval (see above), often widest at midnight. That is the "diffuse aurora", not distinct enough to be seen by the eye. It does not seem to be associated with acceleration by electric currents (although currents and their arcs may be embedded in it) but to be due to electrons leaking out of the magnetotail.

Any magnetic trapping is leaky, there always exists a bundle of directions ("loss cone") around the guiding magnetic field lines where particles are not trapped but escape. In the radiation belts of Earth, once particles on such trajectories are gone, new ones only replace them very slowly, leaving such directions nearly "empty". In the magnetotail, however, particle trajectories seem to be constantly reshuffled, probably when the particles cross the very weak field near the equator. As a result the flow of electrons in all directions is nearly the same ("isotropic"), and that assures a steady supply of leaking electrons.

The energization of such electrons comes from magnetotail processes. The leakage of negative electrons does not leave the tail positively charged, because each leaked the electron lost to the atmosphere is quickly replaced by a low energy electron drawn upwards from the ionosphere. Such replacement of "hot" electrons by "cold" ones is in complete accord with the 2nd law of thermodynamics.

Other types of aurora have been observed from space, e.g. "poleward arcs" stretching sunward across the polar cap, the related "theta aurora", and "dayside arcs" near noon. These are relatively infrequent and poorly understood. Space does not allow discussion of other effects such as flickering aurora, "black aurora" and subvisual red arcs. In addition to all these, a weak glow (often deep red) has been observed around the two polar cusps, the "funnels" of field lines separating the ones that close on the day side of Earth from lines swept into the tail. The cusps allow a small amount of solar wind to reach the top of the atmosphere, producing an auroral glow.

Aurora Links

The Aurora Borealis (Northern Lights)
The greatest natural phenomenon above our earth. Alaska is situated right under a vast expanse of the auroral oval that is enjoyed in our skies 150 to 200+ nights a year.

Aurora Borealis
The Northern Lights over Long Island.

Photos of the Aurora Borealis
One of the most eerily beautiful sights in the night sky is the Aurora Borealis, or Northern Lights.

The Aurora Borealis and the Telegraph by Patti Norton
This occurs in the sky of the northern hemisphere. (The same phenomenon occurs in the southern hemisphere, where it is named the aurora australis.) The aurora borealis is a glowing or flickering light of natural origin which is sometimes seen at night in the sky.

Recording Auroral Observations
The following information is intended to help the auroral observer to make useful records of displays. Observations of a display should be recorded every 15 minutes unless the display is inactive such as a distant, unchanging glow.

The Aurora Page Photographs by Jan Curtis
In these nine pages are many incredible images, selected from the works of Jan Curtis. Photographs were taken in and around the Fairbanks, AK area.

AuroraWatch
What is an Aurora? What causes It? What do we know about the Aurora? Can we see any from the UK? This page will give you some background information about aurorae and how they are formed.

Aurora Information
Aurora Information Compiled by the Public Information and Education Outreach Office.

Tips on Viewing the Aurora
Being able to see the Aurora depends mainly on two factors, geomagnetic activity (the degree of disturbance of the earth's magnetic field at the time) and your geographic location. Further considerations are the weather at your location, and light pollution from city lights, full moon and so forth.

Northern Lights or Aurora Borealis
The Spirits of the North on Wabatongushi Lake.

Aurora Facts
Let's discover the Aurora Borealis!

The Aurora Page
A source for Information, links and images about the "Northern Lights" on-line since the Web began.

Aurora Borealis visible in Belgium
The northern light or aurora is a common phenomenon at high latitudes such as Norway or Finland but rather exceptional in Belgium. Presently, the Sun is at its peak level in its 11 year activity cycle which enhances the chances for such events.

Northern Dawn: The Aurora Borealis by Robert C. Moler
Astronomy provides many wondrous sights. There's the totally eclipsed sun whose time and location are known with high accuracy. Only the weather is an unknown.

Resources:

Nordlys - Of all naturally occuring heavenly phenomena, few come close to a night with a magnificent northern lights display. Flickering curtains of dancing light against the dark skies, northern lights is certainly one of the most spectacular of nature's phenomena.

Aurora Borealis - Winter Under The Northern Lights Churchill, Manitoba, Canada.

Aurora Watching in Minnesota - Did you know... that if conditions are just right, we can see the aurora borealis here in Minnesota?

The Northern Lights Planetarium - Aurora Borealis by Franck Pettersen.

Mysteries Zone Network: For everyone who enjoys a mystery stories. Feel free link to any page(s) from this site.
NOTE: Views expressed here are not endorsed by mysterieszone.com or any other sponsoring individuals or organizations.

2010 copyright by Mysteries Zone Resources, Privacy Policy