Tuesday, 19 September 2017

A Wolf in Sheep Clothing - 19th September

Just 2 weeks ago we had the largest solar flare for a decade and large active regions keeping solar observers pleasantly occupied in the declining phase of the solar cycle.  Now the face of the sun is virtually blank in white light, with only one small decaying active region.  You would be mistaken in thinking this means the sun is quiet; looking in ultra violet wavelengths with the Solar Dynamics Observatories AIA imaging rig reveals a large coronal hole is visible. These are the dark patches on the solar disk on the right, and their open magnetic field lines means that the solar wind flows freely from these regions.  As they are geo-effective it means the solar wind has been interacting with the magnetic field lines of our own planet and has been producing some great aurora in our polar regions.  It just shows that just because the sun might appear quiet in white light it doesn't mean it is actually being quiet!