Differential Rotation
Together, differential rotation and convection produce the unique solar magnetic field, which in turn causes solar flares, prominences, coronal mass ejections, and other solar surface activity.
Because the Sun, like other stars, is not a solid, different parts rotate at different angular velocities. The rotation of the Sun's matter is dependent on its latitude. For example, at the equator the photospheric matter completes a full rotation in about 25 days while the photospheric matter at the poles makes a full rotation in about 36 days. This is differential rotation. The inner layers do not act the same way. The border between the inner and outer layers is called the tachocline, and the different rates on either side of this border rub together to create an electric current. The differing rotations at different latitudes cause changes in the originally vertical magnetic field lines. The faster rotation at the equator wraps the field lines around the sun until they are practically parallel to the equator. As they continue to wrap around, they get tangled and pop out of the surface. The peak of the sunspot cycle occurs when the lines are most tangled and chaotic. At that point there is a maximum number of sunspots and, as a result, a maximum amount of surface activity. The field lines reset at the end of the cycle, resulting in almost no sunspots, and the process begins again. |
Click the image to watch a video showing how differential rotation affects the magnetic field lines. (Credit to UCAR Center for Science Education)
|
Classifications
Solar flares can be classified as A, B, C, M, and X. Class A is the smallest energy output, while class X is the largest. Each represents an increase in energy output by 10 from the class preceding it. Each of these classes can be broken down further into subclasses 1 through 9, except for X, which can be higher than 9. For an example of a classification, the video posted under "Presentation" shows an M6.7 solar flare.
The classes below M do not release enough energy have any impact on earth, while M and X class solar flares may cause radio blackouts or radiation storms. Below is an image of the strongest solar flare on record. It was too strong for the sensors measuring it, which maxed out at an X28. A class X10 would be 10^1 times greater than an X, and an X20 would be 10^2 times greater. That means this solar flare emitted more than 10^2.8 times more energy than an X. |