Keep shooting photos even between substorms! Here is a Tall Blue Ray (TBR), possibly a Giant Blue Ray (GBR), captured by Javor Kac from W Slovenia (45°N MLAT) during the 25 September 2023 G2 storm. This blue ray formed *after* a substorm - the substorm lasted about 10 minutes with red pillars / rays reaching about 10° high in the sky. After it faded and only some faint, photographically (barely) detectable red glow remained, this blue ray formed - reaching some 50° high in the sky! Reds 10°, blue 50°! Preliminary triangulation suggests this blue ray reached ~3500 km high!
Various kinds of blue rays all share the same characteristic: they are exceptionally tall. And the blue color, sharing the same emission mechanism - resonant sunlight scattering on ionized molecular nitrogen (N2 ) at very high altitudes, even above the oxygen reds. But being very tall they can be seen very far equatorward, with the lower (red and blue) parts of the auroral oval being below the horizon. I wonder just how often these tall blue rays are seen from lower mid and low latitudes, with nothing else popping above the northern horizon?
This great diagram was made by Geoff Cloake using observations by the GBR group.