Causes of the aurora
As pointed out in my post planets with green aurora have oxygen last Monday, the aurora is related to free electrons falling back to their normal orbits around the atoms’ nucleus. Most of the free electrons exist at heights above 60 km (~37 miles). Here their occurrence is so huge that they influence radio-wave propagation. The ion concentration increases with altitude to a maximum concentration at about 300 km (186 miles) above mean sea level.
Why you can receive shortwave radio in mid- and low latitudes at night
The ionosphere shows three distinct layers, called the D-, E-, and F-layer. Recall the ionization depends on solar radiation. After sunset, the ion concentration goes down especially in the D- and E-layer that are closer to the Earth than the F-layer.
The D-layer absorbs AM radio-waves. However, the D- and E-layer are non-existent at night because the sunbeams passing the globe do not reach them on the night side. Thus, at night, the AM radio-waves propagate to the F-layer that reflects them back to Earth. The Earth’s surface reflects the AM radio-waves as well. Consequently, at night, AM radio-waves can overcome the Earth’s curvature and AM broadcasts can be received far away from the radio station.
Aurora affected radio communication during WWII
Since these layers are related to the aurora, aurora activity strongly affects radio-wave propagation. During WWII, as part of the lend-lease act male pilots flew aircrafts from Fairbanks to Russia. Women flew them from the Lower 48s to Fairbanks, but weren’t allowed to fly the combat zone leg. I once met one of them, and she was a tough cookie in the most positive sense.
Aurora activity often affected radio communication. Thus, Fairbanks became an aurora research center. Today we still have disturbances in local cell phone calls due to aurora activity.
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Focus Alaska is a weekly series covering Alaska lifestyle, story telling, street style, events, insider travel tips, and curiosa.
Since this post talks about military inspired research, I picked a military inspired look. Here I am wearing an utility jacket with a distressed belt and a Civil War inspired leather hat. I love the color combination of barely pink with olive and brown. ❤ So chic. To sweeten up the look I added the layered mesh skirt c/o Lookbook Store to create a street style weekend look. Well, one could also state it the other way around, to toughen up the sweet ballerina skirt I added military inspired items. Your choice. 😉
Come back tomorrow for five tips on how to wear snake print in an office appropriate way.
Photos: G. Kramm
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