According to the article on the Cassini Solstice Mission website dating back to December 9, 2009:
The six-sided shape remains a mystery. Scientists think the hexagon is a meandering jet stream at 77 degrees north latitude, but they don't know what controls the path the stream takes. These images also show new phenomena for scientists to decipher, such as waves that can now be seen radiating from the corners of the hexagon where the jet takes its hardest turns. These images confirm the presence of a multi-walled structure in each of the hexagon's six sides, and the structure now can be seen extending to the top of Saturn's cloud layer.
And the article is equipped with links to the movie of the hexagon jet stream:
This movie from Cassini, made possible only as Saturn's north pole emerged from
winter darkness, shows new details of a jet stream that follows a hexagon-shaped
path and has long puzzled scientists. (Source: NASA JPL)
As the time passed, we now have more observational data and more photographs of this phenomena, than we had back in 2009. For example this photograph of Saturn's stormy north was published on August 5, 2013:
This view is centered on Saturn's north pole. North is up and rotated 33 degrees to the left. The image
was taken with the Cassini spacecraft wide-angle camera on June 14, 2013 using a spectral filter
sensitive to wavelengths of near-infrared light centered at 752 nanometers. (Source: NASA JPL)
Saturn's north polar hexagon appears to be a long-lived feature of the atmosphere, having been spotted in images of Saturn in the early 1980s, again in the 1990s, and then by the Cassini spacecraft in the past several years.
Source: The Persistent Hexagon, October 8, 2008, NASA JPL Cassini Solstice Mission
My question is, have we by now (since that article in 2009) been able to decipher the reason behind these mysterious hexagonal jet streams around Saturn's north pole, and what is it? Please back any possible theories with links to actual data and references.