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Last Post 4/12/2010 12:04 AM by Emilia Kilpua

CME/Solar Storm

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4/11/2010 2:10 PM
Stephanie C How can the speed of a solar CME be predicted? Thanks.

Emilia Kilpua

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4/12/2010 12:04 AM
Hi Stephanie,It is not an easy task to predict and measure the speed of a CME! As a matter of fact, it is even very difficult to predict when a CME eruption will occur at the Sun. At the times of high solar activity CMEs tend to be faster than during solar minimum. Also CMEs that are associated with solar flares and active regions are typically faster than CMEs that originate outside of the active regions. Close to the Sun CMEs are observed by a device called a coronagraph (see figure below) that measures visible light to determine the density structure in the corona. In coronagraph images CMEs appear as outward moving bright areas (increased density regions). Scientists track the movement of the CME front edge through a series of coronagraph images and calculate its average speed. However, the obtained speed is typically not the “true speed” of the CME, only a rough estimate. This is because of the complex process how coronagraph images are formed. STEREO observatory that consists of two identical spacecraft was launched in October 2006 and both spacecraft carry coronagraphs. With two spacecraft it is possible to determine the CME speed with much greater accuracy than with only one spacecraft.