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I want to ride my solar cycle February 8, 2011

Posted by mareserinitatis in physics, solar physics, Uncategorized.
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A little while back, I posted a bit of an intro to solar physics.  I spent time talking about sunspots and how they are a visible expression of the sun’s magnetic field.

Most people are aware that sunspots tend to occur in cycles.  There’s been a lot in the press the past couple years about how Sunspot Cycle 24 has been off to a slow start.  In fact, you may have seen this graphic:

This graph shows the sunspot activity from 1995-2009.  As you can see, the sunspots will increase and then decrease in intensity in approximately an eleven-year cycle.  At the end of one increase in intensity, the dipolar part of the sun’s magnetic field will reverse: that is, north pole becomes south and vice versa.  After another 11 years and another sunspot cycle, it flips back to it’s original orientation.  This means that the magnetic cycle is 22 years.

There are other cycles in sunspots, though.  Sunspot cycles will increase and decrease in intensity on a scale of about 80 years.  This is called the Gleissberg cycle.  You can kind of see this in the dark trend line:

You can also see that there are periods of very low activity.  These are called minimum, and there is a lot of study looking at what causes these.  Originally, it was thought that the Maunder Minimum may have been an artifact of poor observational practices, but there are other records confirming the existence of this Minimum.  (I’ll probably talk more about those at a later time.)

There are other cycles of varying lengths which have been proposed, some of which have periodicity of thousands of years.  But why do these matter?

There are several reasons we care, although I’ll only mention a few here.  First, space weather is becoming more and more important with the presence of satellites.  When solar activity increases, this directly affects satellite communications as well as various systems on Earth.  Understanding cycles can provide some predictability and could, in the future, allow us to prepare and protect such systems.  Second, these behaviors give us information as to what is going on inside the sun.  That information is helpful in figuring out how it works and what we can expect it to do.  Given the sun is the primary source of energy on the planet, we really ought to understand how it works.  Finally, solar energy output and variability directly impacts the Earth’s climate.  It is important to understand how the sun works so that we can differentiate it from other factors and forcing functions that are operating on the climate system.

All this talk about cycles has made me realize that there is one cycle the sun doesn’t have: a bicycle.



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