Crooked River Aurora is a rare high altitude blue/purple aurora. The blue/purple fringe on the top comes from the interaction of the solar wind with hydrogen and helium in the ionosphere.
Below that is the reddish band or "blood aurora" that forms around 250–500 km from excited oxygen atoms emitting light at 630 nm. The bottom layer is the more typically seen green aurora that forms between 100–250 km by excited oxygen atoms emitting light at 557.7 nm.
