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December 18: Pseudostreamers

     
  December 18: Pseudostreamers  
  Pseudostreamers  
 

 

Click on the above image for a link to a movie showing the pseudostreamer

 

 
 

The SWAP instrument is very good at imaging pseudostreamers, a type of structure often found in the corona. The pseudostremer has two side-by-side sets of closed loops in the lower corona, with open field on top of it. The open field comes together at a cusp region, which you can clearly see in the image above. The cusp is generally dark in SWAP, whereas the open field that immediately surounds it is bright. This is probably due to temperature differences. If plasma that is heated beyond about 1 Million degrees Kelvin no longer creates light in a wavelength that SWAP is sensitive to. The plasma in the cusp is likely dark because it is hot.

The two sections of open field on either side of the cusp both point in the same direction. The meeting point of these two feld regions is a radially-extended sheet of plasma that has more material than its surroundings. You can see these thin ray-like structures in white-light coronagraph images extending from the cusp region of the pseudostreamer. Pseudostreamers are distinguished from their close cousins, streamers, by the direction of the open field. The two open field regions in streamers point in oposite directions. Sometimes it can be hard to determine if a structure that you see in the corona is a streamer or a pseudostreamer because we can't directly measure the magnetic field in the corona, but in those cases that are very ambiguous, by putting together mutliple observations and deductions, you can almost always pick out which kind of structure it is. This paper explains how we used SWAP and several other instruments to see when a pseudostreamer broke up into two separate streamers.

SWAP observed the pseudostreamer in the picture above rotate around the sun for almost a full year! The movie shows you a portion of this year. In the movie you can also see a lot of other dynamic events like eruptions, flares, and jets.