[CQ-Contest] What happened

[N7DF]

The surprising propagation that occurred on Sunday afternoon appears to have been the result of a major shift in the interplanetary magnetic field as evidenced by the NOAA plots
 
http://www.swpc.noaa.gov/ace/MAG_3d.html
 
http://spaceweather.com/glossary/imf.html
 
All day saturday the earth-sun flux path (Bz) was positive or north oriented but it shifted about 0300Z allowing the solar wind to penetrate the northern hemisphere until about 2000Z when it began to "ring" creating sparadic bursts of high energy areas in the ionosphere.   This was evidenced by the "spotlight" opening that many prople enjoyed with good runs into limited areas.
 
This was one of the most clearcut cause and effect examples I have ever seen.  It probably would not have been evident if it had not been for all the contest activity.