Identification of the Low‐Altitude Plasmapause Projection Using Energetic Electron Spectra

On the nightside, the low‐altitude projection of the plasmapause is commonly associated with the ionospheric mid‐latitude trough, which is typically identified from ionospheric density measurements and is clearly manifested in total electron content (TEC) data. In the equatorial magnetosphere, the plasmapause, marks the outer boundary of the plasmasphere, which, in turn, is associated with intense whistler‐mode hiss waves. These waves efficiently scatter energetic electrons, producing a characteristic energy–‐shell structure in energetic electron fluxes. In this study, we identify this energy‐latitude structure in low‐altitude energetic electron measurements from the ELFIN CubeSats. We compare its latitudinal location with the position of the mid‐latitude trough inferred from TEC data and find a strong agreement between the two. Based on this relationship, we propose a new method for identifying the mid‐latitude trough, and thus the proxy of the low‐altitude projection of the plasmapause, using energetic electron measurements alone.