A Purple Steve

16 Mar 2018

   ... The thin ribbon of purple light can be seen with the green aurora in the background - apparently some distance behind the purple Steve. What causes the purple colour? The image comes from the Alberta Aurora Chasers - and one Notanee Bourassa (who was photographing in the garden with his children). The phenomenon is known as a Steve - see https://phys.org/print440264089.html .... Steve is what it is called in a study at Science Advances (March 2018). Steve is not a normal aurora. These usually occur in oval shapes and last for hours and are predominantly greens, blues, and reds. Steves have been observed for between 20 minutes and an hour - big difference. Steve stands for Strong Thermal Emission Velocity Enhancement.

Satellite data show Steves consist of a fast moving stream of very hot particles dubbed a sub-auroral ion drift. These have been studied by scientists for several decades, we are told, but until now they were unaware they had a visual effect. Scientists now know there are unknown chemical processes taking place in the sub-auroral zone. Aurora occur in the lower latitudes but Steve auroral lights can be seen much further south. For example, the above image was captured in southern Canada.

Adam posted a link to a video of aurora that took place over the last couple of days across northern latitudes. Go to https://www.youtube.com/watch?v=iWHDoLax0Vk&feature=youtu.be ... and see for example ...