Occurrence of Aurora

The aurora is a near daily occurrence somewhere on Earth and there is almost always an aurora in the sky (both day and night, but in the daytime it is out-shined by sunlight). However, the following factors can increase your chance of seeing them:

·         Time of Day: Because the intensity of the light in an aurora is low, it can only be seen at night. Furthermore, the most active and brilliant displays usually occur near midnight. Therefore, the best time to observe the aurora is, on average, between 11 p.m. and 2 a.m.

·         Season: In the northern hemisphere, the best time to view an aurora is during the winter. At latitudes where auroras are common, it is typically light all night in the summer—so you rarely have warm weather and a good aurora. Furthermore, in most polar regions, the weather tends to be clear during the middle of winter—so often the best time to see an aurora is also the coldest.

·         Sun Rotation: It takes the sun 27 days to rotate one time around its axis, so 27 days after an aurora display, the active region on the sun that caused the aurora will face Earth again. Although solar activity in that region on the sun might have decreased in the mean time, there is still a greater chance of aurora 27 days after the last period of increased auroral activity.

·         Solar Activity: Auroral activity also correlates with the activity of the sun, which changes according to an 11-year solar cycle. In general, the more active the sun, the greater the number of auroras. Thus, auroral displays are more likely around the time of the solar maximum (when solar activity is high). Aurora displays remain frequent and strong for several years around solar maximum. During solar maximum, the auroras are not only more frequent and more active, but they also can come further south away from the poles (it should be noted, however, that bright and active auroras can be observed at any time during the solar cycle).

Auroras form in an oval band centred at each magnetic pole. The width of the band ranges from 10 to 1,000 kilometers (km) and it is approximately 3,000 km (1,900 miles) from the magnetic pole during quieter solar periods. If you live near this oval, you will see the aurora on most clear, dark nights. In the northern hemisphere, for example, prime viewing locations include Fairbanks, Alaska, many locations in northern and middle Canada, and in the northern parts of Russia and Scandinavia.

As auroral activity increases, the aurora not only increases in brightness, but it also tends to move further towards the equator. Auroral activity is directly linked to disturbances in Earth's magnetic and electrical current system. These increases in activity are known as geomagnetic storms. To determine how high the geomagnetic activity needs to be for aurora to occur in your area, see the table at NOAA's Space Environment Center.

People in the northern United States and northern Europe may see the aurora a few times in a decade, while people in southern Europe, the southern United States, and even Mexico, may see the aurora only once-in-a-lifetime. It should be noted that the auroral oval does not follow lines of equal latitude, so people on the East Coast of the United States have a higher likelihood of seeing aurora than those at the same latitude on the West Coast.

Geomagnetic storms and the resulting auroral activity, vary unpredictably throughout the year. Because geomagnetic activity often results from events on the sun, it can be predicted by looking at the sun and solar flares. For this reason, auroral forecasts can only be made two or three days in advance. NOAA's Space Environment Center issues forecasts of geomagnetic activity. Since 1979, NOAA's polar-orbiting satellites have been measuring the energy flux of particles into the auroral zones.


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Aurora by Menal Salim is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.
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