Thread by @intrepid_p

(1/16) Ever wondered about the different colours and types of Aurora phenomena? I have shot a lot over the years so thought I would do a thread on Aurora types. I will start with the classic overhead green aurora. These next few shots were taken during a G3 (KP7) solar storm.

(2/16) Green forms between 100–250 km altitude as oxygen atoms become excited as they interact with the the solar wind and emitting light at 557.7nm. In strong solar storms where the aurora is overhead green dominates as it is so much brighter due to proximity to the viewer.

(3/16) Above green can be bands of other colours. 2nd most common is the red/pink that forms at around 250–500km altitude from oxygen atoms emitting light at 630nm. Still oxygen atoms but but at a different covalence state due to the higher temperatures found at higher altitudes.

(4/16) The above shot shows both the green and red/pink bands. But in rare cases when observing a strong aurora from a distance and terrain blocks most of the green you can see just the red band. This is then called a "blood aruora".

(5/16) Note higher altitude band can sometimes be seen overhead also if there are gaps in the green band below. These were taken also in large G3 (KP) solar storm.

(6/16). Above the red band you can on very rare occasions get a blue/purple fringe that comes from the interaction of the solar wind with hydrogen and helium in the ionosphere (well above 500km). In this shot you can see green and red bands then the blue/purple band above.

(7/16) The green band in the shot above actually has a yellowish tinge. When looking at the auroral oval from a long way away the shallow angle of observation causes the green and red bands to overlap generating a dirty green or yellow. Light scattering adds to the red shift.

(8/16) The Southern Lights are also seen this way due to distances of the observer to the Aurora (unless in Antarctica). The shot below (from Tasmania) should not be calibrated to vivid green like the Northern Lights (same way the setting sun should not be recalibrated white)

(9/16) Below the green aurora (<95km) the density of molecules stops oxygen emitting light. It is technically possible in extreme storms to see a low altitude fringe of blue or red below the green layer from Nitrogen atoms either in its ionised or excited states respectively.

(10/16) 'Steve' is a phenomenon distinct from typical auroras, the POES-17 satellite detected no charged particles impacting with the ionosphere during the Steve event which was studied. This means that is likely produced by an entirely different yet unknown mechanism.

(11/16) 'Steve' seems to be related to a band of fast-moving ions and super-hot electrons passing through the ionosphere. It runs perpendicular to the normal Auroa at mid latitudes and often generates it's own green picket fence Aurora next to it.

(12/16). Steve is only now being characterised by science. I managed to capture Steve in a time-lapse at a remote hike in location over Berg Lake. You can clearly see the picket fence aurora here with Steve (the purple band) above it.

(13/16)
With the quality of data produced I co-authored a physics paper with a team from University of Saskatchewan, University of Western Ontario, NASA,GSFC, The New Jersey Institute of Technology, University of Calgary and Alberta Aurora Chasers.

(14/16) The work was able to determine Steve’s optical emissions ranged from 130-270km in altitude and the picket fence’s emissions ranging from 95-150 km altitude. Raw time-lapse used below. More into at peakd.com/photography/@i…

(15/16) Thanks for sticking with this thread! If you would like support my Aurora work please RT the thread. I have the rare blue/purple Aurora shot I talked about which was taken at 54 North in Canada up @withFND for 1ETH foundation.app/@intrepidphoto…

(16/16) Last one to finish. This is the coldest shot I have taken. With windchill temps were -50C (-58F). I had issues with my eyelids freezing shut and had to use handwarmers on my eyes to see while snowshoeing back home. 😳