Coronal Weather Report







Forecasting the Sun's Changing Coronal Magnetic Field

To forecast solar storms scientists must develop models of the Sun's coronal magnetic field which simulate how it changes with time. Understanding and modeling the dynamic behavior of the coronal magnetic field is key to developing a useful space weather report which will allow scientists to predict space weather storms.

Image Credit: HAO

Image Credit: HAO

Image Credit: SOHO

The structure of the Sun's outermost layer, the corona, changes dramatically with the 11 year solar cycle. The above image on the left shows the corona during solar minimum as seen in white light by a special camera with an occulting disk to create an artificial solar eclipse (a "coronagraph"). The white light comes from sunlight scattered by particles (electrons) in the corona. Notice the shape of the corona, which is concentrated near the equator of the Sun. There is very little corona visible near the poles. In contrast, the middle image shows the Sun's corona during solar maximum. During solar maximum the corona fills both polar and equatorial regions of the Sun.

The shape of the corona is largely determined by the Sun's global magnetic field. During solar minimum there are more open field lines near the poles than during solar maximum, these open field lines allow the coronal gas to escape into space. Closed magnetic field lines contain the gas and help define the shape of the visible corona. To progress from one magnetic field configuration to the other the Sun must eject magnetic field and plasma. This is accomplished by giant explosions called Coronal Mass Ejections. The above image on the right shows a coronal mass ejection just lifting off the limb of the Sun. You can click on the image to see a movie of several CME's exploding into space.

We'll investigate the process of constructing a coronal weather report on the next pages.

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