Global amoral images acquired from the Polar ultraviolet imager in the Nort
hern Hemisphere during the winter of 1996 and the summer of 1997 (4 weeks b
efore and after solstice) are used to study seasonal effects on auroral acc
eleration and precipitation. The energy flux of precipitating electrons is
inferred from auroral luminosity in the long-wavelength bands (1600-1800 An
gstrom) of N-2 Lyman-Birge-Hopfield (LBHl) auroral emissions, and the mean
energy of precipitating electrons is inferred from the intensity ratio of L
BHl to LBHs (1400-1600 Angstrom, the shorter wavelength of LBH bands) auror
al emissions. Results indicate that dayside and nightside regions of aurora
reveal different seasonal effects: nightside (similar to 1900-0300 MLT) au
roral power is suppressed in summer, while dayside auroral power is enhance
d in summer and forms the so-called postnoon auroral hot spots, all by a fa
ctor of similar to2. The average energy of precipitating electrons is highe
r in the dark than in the sunlit hemisphere, while the number flux is lower
in the dark than in the sunlit hemisphere for all regions. These changes,
up to a factor of similar to3, are local time and latitude dependent. The s
uppression of the nightside auroral power in summer is associated with a la
rge decrease in the electron energy, whereas the enhancement of dayside aur
ora in summer is associated with a large increase in the electron number fl
ux. The increase of dayside auroral power in summer may be associated with
the large-scale upward field-aligned currents, which peak in summer. Result
s are also discussed in the context of a conductivity feedback instability
and a cyclotron maser instability. The asymmetric seasonal effects on the d
ayside and nightside auroras suggest a voltage generator for the dayside ma
gnetosphere and a current generator for the nightside magnetosphere.