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aurora aurora

 

There are few events in the night that rival the magical dance of Aurora. She’s a temptress – teasing in the evening with a green arc that embraces the horizon, promising more, coyly withdrawing, then flirting again. At 10, she may send out a beam of light to the zenith, and then, a moment later, covers up and stretches out across the distant trees again, snuggling low for the rest of the night. But some nights, she feels more alluring, building slowly toward midnight and then erupting in a fury of dancing lights, with brilliant-coloured curtains down low and pulsing energy-laden green and purple heartbeats aloft, high above the Dipper and the North Star. As we watch her ballet, we can’t help but feel sorrow for those who stay behind in the cities, unaware of that enchanting temptress dancing in the dark skies.

 

 

The following maps display 20-year averages of satellite-measured cloud amount. The data are acquired by polar-orbiting satellites that have a nominal equator-crossing time of 2 a.m.

Cloud measurements such as these have biases caused by the difficulty of extracting a cloud signal from the infrared wavelengths that must necessarily be used at night. You will find that they don't agree well with the data in the table, and so they should be used for making comparisons between sites rather than as an indication of the absolute probability of suitable aurora-watching skies.

In general, inland sites in winter are sunnier than those along an open-water coast. In North America, winter locks away the moisture and weather systems tend to be forced to lower latitudes, leaving a high frequency of clear skies. In Europe, the best spots are well inland where Atlantic Ocean and Norwegian Sea moisture has difficulty reaching. November is a very cloudy month in North America, but less so in inland Sweden.

The surface-based cloud measurements in the table are those at midnight, or close to midnight if relevant observations are missing. The "time" column is the UT hour of those measurements. The "number of observations" column shows how many nightly reports are incorporated into the average. All of the columns show 20 or 21-year averages, usually from 1992 to 2012.

 

map of January cloud cover over North America Satellite-derived cloud cover maps for January and November. These maps should be used for comparative purposes between sites.
Map of average cloud cover over North Americal for November In November, lakes across northern Canada and Alaska are not frozen, but cold airmasses are making frequent excursions to lower latitudes. Cloudiness is high across eastern parts of the Great Plains and the eastern provinces, brought on by moisture carried by the northwesterly flows from the lakes in Manitoba and northern Saskatchewan.
map showing average cloud cover over Europe for January This map shows that inland areas have the least amount of cloud in the depths of winter, while coastal regions are affected by nearby open water.
map of average cloud cover over Europe in November There is less difference between November and January cloudiness in northern Europe because the freezing moisture-locking temperatures are less common and of shorter duration. This is a reflection of the greater continentality of the middle of North Americal (and Russia).
 

table of weather statistics for northern Europe and North America

Good luck on your Quest!

Links:

Spaceweather.com

NASA satellite image of the auroral oval

Space Weather Canada

Météo Spatiale Canada

University of Alaska Geophysical Institute

 

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Updated March 2012