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Aurorae

September 5, 2015

Aurorae

What they are, and how to find them!

 

 

They have mesmerized, and they have terrified. They have been called many names, including: the “Omen of War,” the “Dancing Spirits,” and “Game of Ball” by Native Americans. Aristotle described them as burning flames. Descartes thought they were moon or sunlight reflected off snow or ice crystals. But none of these are correct. The aurorae are the beautiful Northern Lights, also known as Aurora Borealis (or the Southern Lights, and Aurora Australis if you live in the southern hemisphere). These days, we know today that the aurorae are not our ancestors’ spirits in the sky, but a reaction of energy and particles that are visible to the naked eye best seen in the winter months near the poles.

 

The earth has a magnetic field, and the magnetosphere can be imagined as a buffer zone around the earth. There is an inconstant stream of particles emitted from the sun traveling towards the earth called the solar wind. “The interaction of Earth’s magnetic field with the magnetized solar wind is similar to that of a rock in a stream. The solar wind (stream) encounters Earth’s magnetosphere (rock) as an obstacle and moves around it, leaving a wake behind” (Moldwin). There are times when particles reach the magnetosphere and are “funneled down into the north and south poles where the field comes into and out of the Earth” (Moldwin).

 

Now at the poles, the particles are able to interact with the molecules in the outer atmosphere. These particles then excite oxygen and nitrogen molecules to the point that their electrons jump to higher energy levels. When these excited molecules return to their base energy level, they emit light (photons) at a certain wavelength specific to their element and this is what’s seen as aurorae.

 

The aurora zone forms an oval on both the northern and southern hemispheres, about 10 – 20 degrees from each magnetic pole. Scientists have found that there is a correlation between solar activity and the appearance of aurorae. With a solar wind that is constantly changing, oftentimes coronal mass ejections (CMEs) will cause storms in the magnetosphere. With these storms, the auroral oval expands and rapidly brightens around the northern and southern poles.

 

The different colors (usually seen are red, purple and green) depend on what type of molecule was excited, and at what altitude. Oxygen will emit green at lower heights and red at higher heights. Nitrogen will emit purple at lower heights and blue at higher heights.

 

Want to know if you’ll be able to see aurorae soon? The National Oceanic and Atmospheric Administration’s Space Weather Prediction Center has created an impressive forecast for the northern and southern hemispheres. The model will show a 3-day forecast, and they also produce a short-term 30-minutes forecast (Link Below).

 

http://www.swpc.noaa.gov/products/aurora-3-day-forecast

For further reading: An Introduction to Space Weather by Mark Moldwin

 

Questions, comments, or concerns? Contact us at ForecastingConsultantsLLC@gmail.com

 

-Gretchen Hansen

The Forecasting Consultants Team

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