Ultraviolet Observations and a Theory of STEVE

A search for ultraviolet (UV) emissions in satellite data during known STEVE (Strong Thermal Emission Velocity Enhancement) events found that simultaneous subauroral UV arcs (SUA) were usually, but not always present in the Southern Hemisphere despite coverage of the conjugate STEVE location. From 2005 to 2020 a systematic search for SUA found over 100 cases with a mean Magnetic Local Time (MLT) of 316°, standard deviation 13° and hemispheric asymmetry. Frequently coincident continuum UV and visible emissions, upwelling plasma flux, and downward Field Aligned Currents were observed. Occassionally coincident MeV protons were observed. A theory of solar MeV protons and comoving keV electrons following a Parker spiral can explain these phenomena.