Rocket Measurements of Electron Energy Spectra From Earth’s Photoelectron Production Layer

<p> Photoelectrons are crucial to atmospheric physics. They heat the atmosphere, strengthen 28 planetary ambipolar electric fields, and enhance the outflow of ions to space. However, 29 there exist only a handful of measurements of their energy spectrum near the peak of 30 photoproduction. We present calibrated energy spectra of pristine photoelectrons at their 31 source by a prototype Dual Electrostatic Analyzer (DESA) instrument flown on July 11 32 2021 aboard the Dynamo-2 sounding rocket (NASA &numero; 36.357). Photopeaks arising from 33 30.4nm He-II spectral line were observed throughout the flight above 120km. DESA also 34 successfully resolved the rarely observed N2 absorption feature. Below 10eV observations 35 were in good agreement with the GLOW suprathermal electron. Above 10eV fluxes sub36 stantially deviated from the model by as much as an order of magnitude.</p>