Monday, 1 June 2015

Strong Scintillation Coincident with Solar Eclipse Onset

The regular KAIRA experiment includes a beam pointing at the strong radio source Cassiopeia-A to monitor ionospheric scintillation.  Over the period of the solar eclipse on 20th March 2015 no obvious variation in this scintillation pattern has been noted so far, although the scintillation was very active because of the CME which hit a couple of days previously.  However, scintillation of Cygnus-A is different: In this case the line of sight to the radio source passed through the eclipse shadow. 
Although the experiment didn't include a dedicated beam on Cygnus-A (another frustration - the intention was to change Cas-A to Cyg-A, but this was forgotten in the lead-up to observation), it is obvious in a few of the regular riometry beams and, most importantly, it's an obvious source in the all-sky imaging.  The image shows the scintillation in amplitude (top plot) and phase (lower plot - see earlier 'blog posts for information on how this is calculated) found by analysing the intensity and location of Cygnus-A in the all-sky images taken every second.  The start of the visible eclipse from KAIRA was just after 09:00 UT, but the shadow in the F-region will have been larger and started earlier.  This corresponds neatly with the period of very strong amplitude scintillation, suggesting that this is associated with the onset of the eclipse.

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