The Northern Lights / Aurora Borealis
A North Dakota Perspective

By Lyndon Anderson


Science of the Northern Lights / Resources

The northern lights are not caused by light bouncing off the snow and ice in the polar regions.

Instead, the displays have their origin in the sun, 93 million miles from earth.   

The sun sends a constant gas of charged particles towards the earth at about 300 to 400 kilometers per second. This is called the solar wind.

When there is activity on the sun that causes the solar winds to flow faster, and when the faster solar wind is combined with a strong southerly component of the interplanetary magnetic field, we can often see the northern lights in North Dakota.

The above photographs were taken on October 28, 2001 & October 21, 2001.

What causes the solar winds to flow faster?

One is coronal mass ejections. These are big events in which billions of tons of charged particles are directed towards the earth at speeds as high as 2,000 kilometers per second. These winds reach the earth anywhere from 1 day to one week or so. Most do not hit the earth, but when they do chances of seeing the northern lights increase significantly in North Dakota.

Another is high speed solar wind from coronal holes on the sun. Coronal holes are regions with open magnetic field lines which point into space and are carried with the solar rotation. These field lines sometime "slip over" the earth, resulting in geomagnetic activity. In front of the sector with open field lines, there is a compression in the solar wind, with higher than normal density and after that, a rise in speed can be observed (sometimes as high as 1,000 kilometers per second). If there is a coronal hole on the sun, the effects can be observed about two days after it rotates through the central meridian of the sun.

When these charged particles reach the earth, they hit the magnetosphere, which usually deflects the potentially harmful solar wind. 

But, if the solar wind packs enough punch and creates a shockwave that impacts the earth's magnetosphere with a great force, and if there is a strong southerly component of the interplanetary magnetic field, the accelerated particles spiral along the magnetic field lines and into the earth's atmosphere near the polar regions. 

There, the electrons and protons impart energy to the atoms and molecules that they encounter and make them glow The Northern Lights!

The above three photographs were taken on March 18, 2002, November 5, 2001 & December 24, 2001.


Resources

There are a lot of resources on the northern lights that further explain the science. Three books that I often refer to include:

Also, numerous web sites a lot of educational information on the northern lights. Use a search engine to find them, or refer to Jan Curtis' web site which contains a lot of those links at: http://climate.gi.alaska.edu/Curtis/curtis.html


Page 1 - Overview of Information in Online Brochure
Page 2 - An Aurora Chasing Story
Page 3 - Beauty of the Northern Lights
This is Page 4 - Science of the Northern Lights / Resources
Page 5 - The Northern Lights in North Dakota
Page 6 - Northern Lights Forecasts
Page 7 - Putting it all Together
Page 8 - Photographing the Northern Lights
Page 9 - Okay, So You Have Photographs, Now What?


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