Science & Tech

How to read a solar forecast 

The space weather forecast is a great resource for planning outings to see the northern lights. Here’s what the forecast really means.
  • Dec 31, 2012
  • 606 words
  • 3 minutes
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Dazzling displays of aurora borealis are a sought-after sight in Canada. The natural phenomenon is a visual manifestation of geomagnetic storms, which occur when energetic particles from the sun reach the Earth. Numerous online resources can help predict an occurrence, but the scientific language can make them difficult to understand.

The Canadian Space Weather Forecast Centre in Ottawa posts regional forecasts of geomagnetic field conditions across the country. Scientists develop forecasts by combining data from the ACE satellite 1.5 million kilometres away from Earth, various instruments pointed at the sun and magnetometers around the world.

Geomagnetic activity is strongest under the auroral oval, which is aligned with the magnetic north pole — not the geographical one. When geomagnetic activity is high, the auroral oval expands to lower latitudes, bringing the northern lights to southern Canada.

Here’s what you need to know about Space Weather Canada’s forecasts to predict when you’ll be able to see the northern lights near you:

1. Current conditions

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A sample forecast for the Western Auroral Region (Diagram: Space Weather Canada)

Space Weather Canada posts current geomagnetic field conditions on its homepage for Canada’s three zones: the polar cap, auroral and sub-auroral zones. Updated every five minutes, activity is classified as either quiet, unsettled, active or storm.

For a more detailed look at the current conditions near you, explore the regional forecasts for the upcoming three to six hours, which are updated every fifteen minutes using measurements taken from magnetic observatories across Canada. Colour labels ranging from green to red correspond to the K index. This forecast switches to a system of five classifications: quiet, unsettled, active, stormy or major storm. If the forecasted conditions are labelled “stormy” or “major storm” at the station closest to you, and the sky is clear and dark, there is a chance of a visible aurora.

2. Short-term forecast

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Short-term forecasts show geomagnetic activity for the next 24 hours. (Diagram: Space Weather Canada)

To plan further ahead, explore the short-term forecasts on Space Weather Canada. Several  charts and graphs display 24-hour forecasts, as well as a look back at the geomagnetic activity of the past 48 hours. Depending on the rate of ejection, particles from solar storms take one to three days to reach Earth. Space Weather Canada displays the data in charts organized by both geographical regions and zones. Keep in mind that the hourly forecasts are shown in Universal Time (UT). Though the definition varies, UT is essentially the same as Greenwich Mean Time (GMT). 

For a more specific reading, look at the forecast data itself, measured in nanoteslas, or nT. Normal geomagnetic activity is below 100 nanoteslas. In the sub-auroral zone, this is the case 99.5 percent of the year.

3. Long-term forecast

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Long-term forecasts are broken down into the polar cap, auroral and sub-auroral zones. (Diagram: Space Weather Canda)

Space Weather Canada’s long-term forecasts show the predicted magnetic activity over a 27-day period. Check the prediction for the polar cap, auroral and sub-auroral zones. Like the current geomagnetic field conditions, this information is classified under one of four coloured labels: quiet, unsettled, active and stormy.

Remember, the long-term forecasts are just predictions. It is not always possible to know when a solar storm will erupt on the sun, but when one does, space weather forecasters can predict when the ejected particles will reach Earth.

For more information and to few the latest forecasts, visit spaceweather.ca.

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