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Skywatching

Protecting Earth from the Suns coronal mass ejections

Forecasting solar storms

Seeing the launch of a coronal mass ejection (CME) from the surface of the Sun is an awe-inspiring experience.

The story starts with a huge loop, many times bigger than the Earth, extending upward from a surface fizzing with the coming and going of small loops of magnetic field. It looks rather like a living pile carpet. The big loop writhes, suddenly jerks, snaps off at its roots and catapults off into space at speeds as high as thousands of kilometres a second.

At such speeds, it reaches our planet's orbit in maybe two days. If it hits us, it can cause massive magnetic storms and disruptions of our power, communications and transportation infrastructure. That has happened in the past, but we need to pay more attention today because we are more critically dependent on that infrastructure than ever before.

Imagine a few days with no Internet, anywhere. Imagine being on holiday in Paris, having had a lavish meal at a posh restaurant and then finding your credit card won't work because there is no communication with your financial institution.

We can certainly see when a coronal mass ejection is on its way. We see the loop against the solar disc and our solar radio telescopes pick up the explosion that sent it on its way. However, once we no longer see it against the solar disc it becomes invisible.

Because we have only a rough idea of the speed it is moving when we no longer see it, we don't know exactly when it will arrive. We need that information to warn those who might be affected by it.

The CME remains completely invisible until it is detected by the solar monitoring satellites located 1.5 million kilometres sunward of the Earth. At that point, we know how fast it is moving and can assess its threat potential, with a mere 15 minutes' notice to prepare for it.

Understandably, we would really like more notice than that. One possibility being explored is to detect the twinkling of radio sources when the CME passes between us and them, rather like looking though hot air. However, since the number of suitable cosmic radio sources is small, and detecting that twinkling can be challenging, even with large radio telescopes, other solutions are being sought. One of them is to go back to the launch of the CME from the Sun.

On the surface of the Sun we see areas of enhanced magnetic fields called active regions. These contain sunspots and lots of loops and other magnetic structures. Some new research suggests that by careful observation of an active region before, during and immediately after the launch, it may be possible to calculate the ejection speed of the CME, which would in turn enable us to accurately predict its arrival time at the Earth.

A simple analogy is launching a stretched elastic band. We stretch it, which stores energy in it. We then release it so it flies off at high speed. Most of that energy we stored in the stretching becomes kinetic energy, from which we can calculate the speed. Of course, the solar case is more complicated.

We need to estimate the energy stored in the stretched magnetic fields, the amount actually released and the mass of material ejected. From this we can calculate the speed. Considering the complexity of the solar magnetic fields, and that we have to infer the information from observations made 150 million kilometres away, this is quite an achievement.

This depends on our having appropriate instruments watching the Sun all the time. That is why, around the world, nations are committing more resources to keeping a close eye on the Sun and better understanding how the various aspects of the Sun's bad behaviour can impact our lives.

•••

• Venus lies low in the sunset glow.

• Around midnight, Saturn lies low in the south, and Jupiter and Mars close together in the northeast.

• There will be a “new” Moon Aug. 2.

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



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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]



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

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