Note: What follows is a non-technical description of solar activity.
What's with this whole "Solar Tsunami" thing?
What's up with that? What does it mean? Is there a danger? What should we do about it?
A little background
The sun is our local star. It is made up mostly of Hydrogen, but also some helium and a trace of other elements. It is sometimes thought of as a 'burning ball of gas', which is sort of true. It is not 'burning' like wood or paper burns, but rather because there is so much stuff all gathered in one spot that way down in the middle of the sun the atoms of hydrogen are under so much pressure and so much heat that they actually join up and become helium. This releases a lot more heat, which keeps the process going.
We think of the Sun as being made up of gas, but it's actually a fourth state of matter called plasma. 'Plasma' happens when there is so much heat and energy that the electrons in the atoms can't take it, and they fly away from the nucleus of the atom. So the sun is made up of this 'soup' of particles (protons, neutrons, and electrons).
Solar Wind
The energy contained in the sun is so great that the surface of the sun is constantly boiling away, with the charged particles (meaning that each particle has a tiny positive or negative electrical charge) get blasted off of the sun and launched into space. This is called the 'Solar Wind', and when it hits the earth's magnetic field, it is directed toward the poles and causes aurora (northern and southern lights).
Solar Cycles
Sometimes you will hear terms like "solar maximum" or "solar minimum". These refer to a cycle in the solar activity. At some times the sun is very active, with lots of sunspots, solar flares and coronal mass ejections (CMEs), and sometimes it is very quiet. The sun goes through cycles of increased and decreased activity. The cycle runs about 11 years. The highest period of solar activity is called 'Solar Maximum'. It is normal, it happens every 11 years or so. The next solar maximum is predicted to occur in 2013.
Solar Magnetism
Because the solar material is a plasma, most of the particles in the sun carry an electric charge. This is what we mean when we talk about 'charged particles'. The electrical charges cause vast currents that flow through the sun, which creates magnetic fields. These magnetic fields extend out into space. These magnetic fields interact with the solar material and cause many of the things we see happening on the sun. Loops and prominences follow the magnetic field lines, and sunspots are caused when the magnetic field lines push aside the bright surface material and reveal darker, cooler material underneath.
As the solar cycle progresses, the magnetic field lines of the sun go from a very smooth and even configuration at solar minimum to a very twisted and tangled configuration at solar maximum. So at solar max we see a lot more of the effects on the surface of the sun than we do at solar minimum.
Solar 'pole shift'
Sometimes you will hear that the sun's poles will flip. This is sort of true, but misleading. The sun has an overall magnetic polarity, and at solar minimum it can almost be described as having 'poles'. There isn't a specific north and south magnetic pole of the sun. Over the course of the solar cycle, the magnetic field lines get twisted, wrapped around the sun, and very tangled. At solar maximum the magnetic field is very complicated, and you can't really see the overall magnetic polarity of the sun. After solar maximum the fields begin to settle down, and the sun's polarity re-establishes in the opposite orientation from where it started.
The sun's magnetic field doesn't switch instantly. It doesn't send out a 'blast of radiation'. The 'flip' has no consequences for us, other than the fact that it is tied to the solar cycle.
The 11-year long 'solar cycle' is actually 1/2 of the 22-year long solar magnetic cycle (north to south to north).
What is a solar flare?
A solar flare is an explosion on the surface of the sun. These are caused when the magnetic field lines essentially 'short out', allowing large currents to flow between two regions very quickly. You can see that these are much more likely to occur near solar maximum, when the magnetic field lines of the sun are very tangled, than they are during solar minimum, when the field lines are comparatively smooth.
Solar flares are classed by how strong they are (how much energy they release), with the highest classification of "X". Solar flares release energy in the form of radiation.
Are solar flares dangerous?
Not if you live on the surface of the earth. The magnetic field of the earth and the atmosphere of the earth protects us from the burst of solar radiation. If you were an astronaut on the way to the moon, then yes, they can be dangerous. If you were an astronaut on the International Space Station, they would be less dangerous, but you could still be exposed to quite a bit of radiation.
What is a CME (Coronal Mass Ejection)?
This is actually what many people think of when they think of a solar flare. A CME is a blob of charged particles thrown off of the sun. They are frequently associated with solar flares, but not always. Think of a CME as a 'gust' in the solar wind.
Are CMEs dangerous?
Generally not. CMEs can cause several effects on the surface of the earth, and some of those effects can be dangerous, but they are not dangerous to us by themselves. One of the things that a CME can cause (and whether or not they cause these effects depends on a bunch of variables, too many to go into here) are things like interference with communications (telephone, satellite, etc), power outages (they can cause an 'extra' current in power lines, which can damage equipment or trip breakers), and damage to satellites, but the most freqent effect is not dangerous, but rather beautiful, and that is aurora.
As the charged particles of the CME flow past the earth, they interact with the magnetic field of the earth, and flow back along the magnetic field lines until they reach the upper atmosphere at the north and south pole. There they interact with molecules in the upper atmosphere, causing them to glow.
I've never heard about this stuff until recently, what has changed?
Various space agencies around the world have launched a fleet of sattelites to study the sun. Being able to predict what the sun is going to do, and being able to give advance warning of CMEs and solar flares would be very beneficial to power companies, satellite operators, and space agencies who have personnel in space. With spacecraft like SOHO, STEREO and SDO we are studying the sun in a level of detail that we have not been able to do before, so when anything happens we have a lot more details on it.
In addition, we are emerging from a very deep and extended solar minimum. The sun has been very, very quiet recently, and so when something happens on the sun it gets the solar scientists very excited.
Combine these things with a public media that doesn't necessarily understand what's going on, and you get big, splashy, but inaccurate headlines.
Why did various news outlets talk about a 'solar tsunami' heading toward the earth?
That was scary, wasn't it? However, what happened is fairly simple. The sun had a flare and an associated CME. Sometimes the flares cause a shock-wave on the surface of the sun. This is one of those things that we hoped to be able to capture with SDO, and we did.
This shock-wave is sometimes called a 'solar tsunami' (it has a technical name too, but we'll call it that here). It is exciting to watch, because you can see this shock-wave travel across the surface of the sun and cause effects to solar loops and prominences very far away from where the original explosion occurred. These shock-waves can tell us a great deal about what is going on inside the sun too. That is why the solar physicists were so excited to have this one captured by SDO.
However, someone at the news outlets confused the CME (coronal mass ejection) with the 'solar tsunami'. I'm not sure whose fault that was, or perhaps someone just compared the CME to a tsunami… I don't know. So let's be clear here: The so-called 'solar tsunami' is a shock-wave on the surface of the sun. It doesn't leave the sun. The CME is not what we call a 'solar tsunami'.
Of course, people associate the word 'tsunami' with destruction, as in the Indian Ocean tsunami of 2004. This lead to a bunch of rather irresponsible statements by various people (for example, some self-proclaimed 'experts' on YouTube) that this was going to cause a problem for us.
Meanwhile the scientists were waiting in anticipation, because the CME might cause some spectacular aurora. It did, by the way, but they were only visible if you were very far north.
Conclusion
So, as we state on the Solar Flares page, all of this is normal activity. You are hearing more about this because we have a lot more data with the new spacecraft. None of this is a threat to us. The absolute worst case scenario involves some long-term power outages… and that is why we want to study the sun, so that we can try to predict these things, and prevent them from causing problems by knowing when they are going to happen.
LosingMyMind (guest) 02 Aug 2010 18:12
