Magnetic Reconnection, Part Deux

From the feedback I got from my last post I wanted to clarify a few things, mostly the Interplanetary Magnetic Field generated by the Sun. But first, the x,y,z axis scheme. Below is an image of a three dimensional axis:

The orbits of the planets reside in the x-y plane along with the Sun itself.  In astronomy, this is known as the plane of ecliptic. As the solar wind spreads out through the Solar System, it takes the IMF field lines with it. Because the Sun rotates just like the Earth, the solar wind, and thus, the IMF looks like the pattern you see from a water sprinkler when looking down on it towards x-y plane.

imf_big
Courtesy: NASA

However, the IMF is not flat along the x-y plane.  In addition to the sprinkler type formation seen above, it also has a wavy type feature as well.  This is represented in the image below:

Courtesy: NASA

The z-axis is up and down.  When the IMF slopes upward, it is said to have a positive Bz value as B is used in physics to represent a magnetic field.  The Earth’s magnetic field flows from the geographical South to North Pole and also has a positive Bz value.  When two magnetic fields are flowing in the same direction the probability of reconnection is low.  When the IMF is sloping downwards, it has a negative Bz value.  In this case, the probability of reconnection is high which brings along with it a high chance of auroral activity and magnetic storms.  This is why if you visit a space weather website to check out possible aurora, you’ll want to be on the lookout for a negative Bz value.

 

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