(music by Bruce Cockburn: The Northern Lights from Dancing in the Dragon's Jaws)
Go to Intro FLASH Slide Show...
(music by Bruce Cockburn: The Northern Lights from Dancing in the Dragon's Jaws)
The Northern Lights have been "immortalized" in "CAN- LIT" through R.W. Service's lines:
The Northern Lights have seen queer sights But the queerest they ever did see Was the night on the marge of Lake La Barge I cremated Sam MaGee...
The aurora are a direct result of the interaction between:
In a literal sense, the aurora tells us about what happens on the surface of the sun and the center of the earth! Let's consider each of the above three factors in a bit more detail:
The sun has its own magentic field that is manifest in sunspots on the surface and the delicate streamers that we see in the solar Corona:
 |
 |
The solar magnetic field stretches out into the solar system and controls the outward motion of charged particles ("the solar wind") gusting from the sun's surface.
A turbulent and at times gusty wind of charged particles (mostly electrons, protons and helium nuclei) is constantly blowing outward to give what is known as the solar wind. These charged particles whizz by at thousands of km/s. Occasionally a solar flare or coronal mass ejection event will dump an unusually large amount of matter into the solar wind:
 |
Earth's magnetic field provides us with a critical first defense against the solar wind! The magnetic field forms a region called the magnetosphere that surrounds the earth and both deflects and traps particles from the solar wind. The VanAllen radiation belts trap particles from the solar wind and these particles can slowly funnel down along the earth's magnetic field lines to enter earth's atmosphere. These particles contribute to some of the activity that we associate with aurora but are not the main cause. Gusts in the solar wind distort and buffet the magnetosphere and radiation belts. The solar wind acts like an electric current flowing across the magnetic field of the magnetosphere and this produces a dynamo effect - very strong electrical currents and a strong voltage potential are produced. The gusts also inject charged particles into the magnetosphere and these are accelerated down into the Earth's atmosphere producing the aurora that we see. Click to see a FLASH animation of this. During a bright auroral display the energy generated is enormous! Typical currents are tens of millions of amperes while the voltages are 40 000 to 50 000 volts. This means that a bright display rivals the power consumption of the US! Aurora also create havoc with power systems, radio communications and satellites! In fact, the great March 1989 aurora that blacked out parts of Quebec and left Montreal in the dark for hours is estimated to have cost Quebec Hydro nearly 1 Billion dollars!! Aurora, if not understood and compensated for, would also create extreme corrosion problems in northern pipelines.
|
The Earth's Magnetosphere |
|
|
The charged particles follow the magnetic field of the Earth and enter the atmosphere in a place called the auroral oval. Follow this link to see the oval as it is in real time. During intense auroral "storms" the oval swells and sinks to lower latitudes. The interaction between the solar wind and Earth's magnetic field also produces extremely low frequency radio waves. These are radio waves that have frequencies comparable to acoustic sound waves and can be heard with radio receivers specially designed to detect such waves. Hear low frequency radio waves produced by charged particles interacting with Earth's magnetic field.
|
|
This is part of a North America wide study of how the earth;s magentic field changes in response to auroral activity.
Our atmosphere is 79% Nitrogen and 21% Oxygen so it comes as no surprise that Nitrogen and Oxygen are the primary agents for the aurora. What is surprising, however, is just how these atoms (and their molecular forms) actually produce the aurora. The key is that high energy electrons "beam" down into the upper atmosphere where the gas density is so low that the average time between atomic collisions is from a second or so to a few minutes. When this happens the atoms are able to produce line transitions that cannot be produced on Earth - we just don't have good enough vacuums to do this! Astronomers call these transitions forbidden line transitions. The following table summarizes this:
| Colour(s) Present | Atoms or Molecules | Height |
|---|---|---|
| all red, glowing | Oxygen (630 nm) | 200 km - 400 km (click here for example ) |
| green | Oxygen atoms (558 nm) | 100 km - 150 km (click here for example ) |
| green, red at top | Oxygen atoms (630 nm and 558 nm) | green at 100- 150 km with red in upper regions (click here for example ) |
| green, red on lower border | Oxygen atoms (558 nm) and Nitrogen molecules (red) | red at 70 km - 100 km, green at approx. 100 km (click here for example ) |
| blue, purple | nitrogen molecules | 100 km - 200 km, twilight hours, sun illuminates, ionizes nitrogen molecules and scatters from auroral rays (click here for example ) |
For more on the aurora click here
Seeds:
Chp 8; all
Kaufmann:
Chp 18; 310-333
Web Sites to Explore ...
