Initial comparison of POLAR UVI and Sondrestrom IS radar estimates for auroral electron energy flux

Abstract

Calibrated images from the POLAR satellite ultraviolet imager (UVI) in the 165.5 to 174.5 nm portion of the N2 Lyman‐Birge‐Hopfield band (LBH‐long) can be used to estimate the energy flux (FE) of auroral electrons precipitating into the high‐latitude ionosphere. Similarly, electron density profiles, as measured by ground‐based incoherent‐scatter radar, can be used to estimate FE and mean energy (Eo) by solving a system of linear equations relating the E‐region ionization rate profile to a family of monoenergetic ion production profiles. A coordinated POLAR/Sondrestrom radar experiment, designed as an initial comparison of POLAR UVI and ground‐based estimates of FE for a stable auroral arc, was executed during a POLAR apogee on May 20, 1996 at the Sondrestrom radar facility (lat. 66.99°N, long. 50.95°W). Reconstructed energy distributions, based on radar‐measured Ne profiles, indicate an approximately 2 keV Maxwellian source with an energy flux of from 6.4 to 14 mW m−2. LBH‐long images, binned over 0.5° of latitude and 1.0° of longitude, were used to derive energy flux as well. The UVI‐derived FE time history agrees favorably with radar estimates both in absolute magnitude and in the trend for this period. This experiment suggests that reliable estimates for the precipitating electron source energy and its ionospheric response can be derived from either ground‐based radar or POLAR UVI images during summertime conditions.