238404
Skywatching

The science behind solar storms and the Northern Lights

Northern Lights science

From Penticton, the recent aurora looked like a hollow tower, made of finely combed fibres, with us looking up the middle.

There were patches of green and one of red. It covered most of the sky, except near the northern horizon. This display was unusual in that it was seen at low latitudes.

Northern lights displays are usually in the north. The artist that produced the display was the Sun. It was active for some time, producing lots of small flares. One of these flares occurred close to a huge, stressed magnetic loop, loaded with plasma (gas so hot electrons were escaping from its atoms.). The shock wave from the flare was too much for the loop.

The magnetic fields snapped and the loop with its contents were catapulted into space at thousands of kilometres a second—in our direction. These catapulted lumps of solar plasma and magnetic fields are known as “coronal mass ejections” (CMEs), because they come from the solar corona, its upper atmosphere. They are often referred to as “solar storms.”

When a CME hits the Earth's magnetic field, a magnetic storm is triggered. It is those magnetic storms that produce power outages and other disruptions of our infrastructure. High-energy particles move along the lines of the Earth's magnetic field, downward towards the Polar Regions. When those particles collide with oxygen and nitrogen atoms in our atmosphere, coloured light is produced, and we have an aurora.

This particular CME was a particularly big one. Its interaction with our planet's magnetic field was so violent, high-energy particles were accelerated down to the atmosphere at lower latitudes, leading to auroras being seen in places where they are extremely rare.

Some large CMEs can produce brilliant auroral displays and widespread power and other disruptions. The CME of November 1989 and the giant magnetic storm it produced was an example. Other CMEs, maybe as large, trigger the auroral displays but produce no power outages.

When we see a CME moving away from the Sun in our direction, it would be extremely useful to know in advance its potential for causing damage. It would also be useful to know exactly when it is due to arrive. However, at the moment we have trouble with both those requirements.

When the CME is launched, we see it against the solar disc, and our radio and other telescopes detect the emissions from the flare that may have triggered it. Then it becomes invisible. At that point we have only a rough idea of the speed it is moving, and no idea how much that speed changes due to encounters with other magnetic fields in the solar corona.

The next time we "see" the CME is when it passes the satellites sitting around 1.5 million kilometres sunward. That leaves us with about 15 minutes warning, depending on how quickly the CME is moving.

The other thing we would like to know is the orientation of the magnetic field in the CME compared with that of the Earth's magnetic field.

If they are in the same direction, it is rather like the collision of two balloons. On the other hand, if they are in opposing directions, we get annihilation of magnetic flux and energy releases that stimulate a stronger magnetic storm. The satellites that give us the 15 or so minutes' warning also tell us about the magnetic field in the CME. Storms with just one orientation of the magnetic field are rare.

Most CME's have magnetic fields pointing in many directions, making the consequences for us as it sweeps past complicated and hard to predict.

Canada and many other countries have various "stethoscopes" monitoring solar activity. However, we are still a long way from being consistently able to predict the precise arrival times and how much damage they might produce.

•••

• Just before dawn, look for Mars in the dawn glow and for Saturn higher and further to the west.

• The Moon will be full on May 23.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.



More Skywatching articles

237535
About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]



239192
The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

Previous Stories



237582


239430