Morphological Characteristics of Strong Thermal Emission Velocity Enhancement Emissions

Morphological characteristics of Strong Thermal Emission Velocity Enhancement (STEVE) are investigated during an event on July 17, 2018. We calibrate photographs from citizen scientists for scientific purposes. We determine the altitude profiles for STEVE emissions. The spectral continuum purplish STEVE emission peaks at 200 km, which is in the altitude range where redline‐only SAR emission could be generated. The green picket fence peaks at 110 km, similar to that of the typical green aurora. For both emissions, their altitudes of the peak emissions and the shapes of the altitude profiles are similar across different longitudes. In regions of two‐layer purplish STEVE emissions, the lower layer STEVE peaks at ∼130 km with slightly different peak altitudes at different longitudes. The green picket fence structures are separated by 14 km in longitude with a full width of half maximum of ∼5.3 km. They move westward at a roughly constant speed of ∼250 m/s, although they sometimes disappear and reappear. The purplish STEVE and green picket fence emissions are latitudinally narrow, and whether they are simultaneously collocated on the same magnetic field line depends on their latitudinal offset relative to their width. We demonstrate that the green picket fence and purplish STEVE emissions are located on magnetic field lines within a tenth (0.02°) of the latitudinal width of STEVE (0.2°). The fact suggests that different STEVE emissions are driven by the same narrow region either in the ionosphere or the magnetosphere, although their generation mechanisms differ. The morphological characteristics have important implications in determining how STEVE is generated.