Waves and Instabilities at Midlatitudes - The Earth's Ionosphere: Plasma Physics and Electrodynamics - page 313

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21:50 21:55 22:00

May 7, 1983

22:05

Figure 6.30b Doppler spectrogram (measured from St. Croix with the CUPRI 50MHz
radar) for the event associated with Fig. 6.30a. The gray scale denotes intensity normal-
ized to the peak intensity in a given spectrum and the vertical axis gives the Doppler
shift in meters per second. The range is noted in kilometers. [After Riggin et al. (1986).
Reproduced with permission of the American Geophysical Union.]

and the typical electric fields are small. As we shall see following, equatorial-
like geometries may indeed occur at midlatitudes and lead to two-stream
conditions.
Many midlatitude events have been characterized as quasi-periodic or Q-P
echoes. An example from the Gadanki radar in India is illustrated in Fig. 6.32.
Typically, the echo slants downward in range as time goes by, as shown. Q-P
echoes have been reported frommany sites (Yamamoto et al., 1991, 1992; Huang
et al., 1995; Chau and Woodman, 1999; Tsunoda et al., 1999). Due to the high
aspect sensitivity of plasma scattering, the characteristic Q-P slants, which seem
to be altitude dependent, may in fact be related to a change in range as such a
blob moves into and out of the beam at a fixed height. For example, a structure
slanted from northwest to southeast and moving toward the west (which as we