Instabilities and Structure in the High-Latitude Ionosphere - The Earth's Ionosphere: Plasma Physics and Electrodynamics - page 522

( C s ) required for two-stream instability. It is clear from this study that both the
gradient drift and the two-stream condition play a role in the auroral electrojet.
A controversy over interpretation of the phase velocity of meter-wavelength
waves at high latitudes has been resolved by simultaneous coherent scatter radar
and incoherent scatter radar observations. The STARE coherent scatter Doppler
data at first were interpreted as representing the projection of ( E B 2 )on

the radar line of sight. This interpretation agrees with linear theory, since (see
Chapter 4) that theory predicts

× B /

ω = ·

V D /(

+ )

k 1 (10.19)

but disagrees with the equatorial electrojet observations, which show that
ω/ C s at any angle to the current. In view of recent equatorial data showing

that Doppler shift velocities match the nonisothermal ionacoustic speed rather
than the isothermal (Chapter 4), an application of these equatorial results to high
latitudes is now in progress with added consideration for elevated electron and
ion temperatures and electron heat flows (L. M. Kagan, personal communica-
tion). On the other hand, E

k =

B 2 drifts as large as 2000m/s are not uncommon
at high latitudes, so it was not unreasonable to assume that the coherent scatter
Doppler shift yields the projection of the E

× B /

B velocity.
Some of the first evidence that E-region temperatures might be very high came
from incoherent scatter observations in Alaska (Schlegel and St.-Maurice, 1981).
An example is shown in Fig. 10.29, where T e near 110 km is about three times
the neutral gas temperature. The dc electric field in this event was measured by
the same radar to be 85mV/m, which clearly must have been driving very intense

×

150

T i

140

T e

130

120

110

85 MV/M
1421 UT

100

90

0 400 800 1200

TEMP (K)

1600 2000 2400 2800

Figure 10.29 Typical electron (solid line) and ion (dashed line) temperature profiles in
the polar E region in the presence of a high electric field (southward, 85mV/m in this
example) measured at 1421 UT on November 13, 1979. [After Schlegel and St.-Maurice
(1981). Reproduced with permission of the American Geophysical Union.]