Gc. Hussey et al., E-REGION MIDLATITUDE DECAMETER IRREGULARITIES OBSERVED AT 4 RADAR FREQUENCIES - EXPERIMENT AND FIRST RESULTS, Annales geophysicae, 15(7), 1997, pp. 918-924
In this paper an experiment designed for multifrequency azimuthal Dopp
ler-spectrum investigations of decametre-scale plasma irregularities i
n the midlatitude E region is introduced and some preliminary results
are presented. The observations were made with the high-frequency Vale
nsole radar in the south of France. The radar operated in a multifrequ
ency mode that allowed simultaneous measurements of Doppler spectra at
the four frequencies of 9.23, 11.03, 12.71 and 16.09 MHz, which corre
spond to scatter from field-aligned irregularities with wavelengths of
16.2, 13.6, 11.8 and 9.3 m, respectively. In addition, a digital iono
sonde was operating beneath a small part of the radar viewing region.
The data show that lower-frequency echoes are stronger, more frequent
and more spatially extended than higher-frequency ones, in general agr
eement with theory and rocket measurements. On the other hand, the pre
liminary analysis shows no pronounced differences of the Doppler spect
rum with radar frequency. Some trends in the spectral moments do exist
, however, which can be understood as the result of temporal and/or sp
atial mixing of backscatter from directly generated (primary) plasma w
aves by the gradient drift instability and secondary low-velocity wave
s. Finally, a close relation of mid-latitude coherent backscatter with
patchy sporadic E-layers is present in the data, but the details of t
his relation remain unresolved.