POLAR UVI -- Sondrestrom Comparison, May 20, 1996
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 (IS) radar, can be used to
estimate FE and mean energy (E0) 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/IS 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 IS radar facility (lat. 66.99o
N, long. 50.95o 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 0.5o of
latitude and 1o 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 IS radar
or POLAR UVI images during summertime conditions.
The solid line gives the
energy flux FE derived from the brightest pixel in the
0.5o of latitude times 1o of longitude bin
over the radar beam, the dashed line gives the average FE
in this bin. The symbols represent the energy flux derived from the
radar data.
This is a portion of a UVI image, and the position where the
Sonrestrom Radar beam was pointed in indicated. There is also a
figure showing a portion of
the same image in greater enlargement.