May 20, 2019

05.03.11: A New Breed of Sundog?

NASA’s Solar Dynamics Observatory is well on the path to producing some ground-breaking solar science this Solar Cycle #24, and that trend started the minute it left the launch pad. On February 11th, 2010, SDO lifted off atop an Atlas V rocket, and gave viewers a memorable sight.

A high thin cirrus had formed, and a sundog, sometimes known as a mock sun, could be seen high above the launch pad. As SDO pierced the cloud layer, viewers were awed as the rocket punctured the layer of cloud, sent ripples through it, and destroyed the sundog. The video in of itself was uber-cool:

But there’s more than meets the eye… notice a “mock-contrail” that seems to follow SDO upward? This rare phenomenon sent atmospheric researchers scrambling; not only did SDO send shockwaves through the cloud layer, but some pretty funky physics was going on. Sundogs are a pretty typical sight whenever there is a high thin cirrus aloft with lots of ice crystals oriented in the proper direction… these can be full haloes or arcs of stunning complexity, and we’ve seen some from Arctic latitudes that are quite bright and beautiful. But what optics expert Les Cowley and partner Robert Greenler believe occurred in the case of SDO was a rocket induced halo. Just how does this occur? Well, the compression wave of the rocket actually destroyed the symmetry of the old halo and organized the ice crystals into a new array of tiny spinning tops with an 8°- 12° degree orientation… anytime you’ve got directional orientation in ice crystals, they act like million little tiny prisms and viola, a “rocket halo” is born. In any event, SDO put on a stunning show… it was as if she couldn’t wait to start doing some solar science! Next launch, we’ll add rocket halos to our list of atmospheric phenomena to be on the lookout for, along with noctilucent clouds, shadow contrails and more!

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