Кустов, А. В. О пороговом электрическом поле для возникновения авроральных неоднородностей с длиной волны около одного метра / А. Кустов, М. Успенский, И. Кангас ; Акад. Наук СССР, Кол. фил. им С. М. Кирова, Поляр. геофиз. ин-т. – Препр. ПГИ-87-06-60. - Апатиты : [б. и.], 1988.

(for details see the next paragraph). After 2221 UT electron density data were absent. The F and N radar echo intensities are shown on the bottom panel of Fig.l. At some moments the signal was observed on the F or N radar only, e.g. at 2203-2205 UT when it was the F one (the lowest signal/noise ratio -8.6 dB corresponds to instrumental sensitivity of radars) . When the electric field was more than 10 - 15 mV/m, then, as a rule, echoes were registered by the both radars. For a smaller E-field the echoes did not disappear totally although the echo amplitude and the echo occurrence Decarae apparently lower. During the whole event discussed the F radar aurora intensity was higher than the N one. Me suggest it to be a result of backscatter azimuth anisotropy, Andre (1983). 3. EXPERIMENTAL DATA ANALYSIS. From the data available, Fig.l, one can find the ‘’threshold” E-field (when the irregularities and echoes appear suddenly or persist during its low value though the electron density is noderate) covers a band from 10 mV/m at 2154 UT to 20 mV/m at 2203-2205 UT. The lowest E-field when any echo exists is around 5 mV/a, e.g. at 2159 UT. It seems an echo appearence is also a function of the E-field azimuth. Below we will try to find a quantitative characteristic for the echo E-field threshold properties utilizing formalism discussed by Uspensky (1985) and Oksman et al. (1986). The backscatter power is known to be a function of the radar parameters, of the scatter volume slant range as well as a function of the radar volume cross-section. The equation for the volume cross- section can be written in a fora (Farley et al., 1981; Uspensky et al., 1983; Okeman et al., 1986) 6 = const <N>2 <(^рГ> • F,(05 F,(<P) , ( 1 ) where <(4г-'Г>/7 - the electron density fluctuation amplitude (EDFA) or the ionospheric wave turbulence level, - mean electron density in the scatter volume, F^(0) and F ф - functions describing the azimuth and aspect anisotropies of auroral backscatter. For the STARE frequency band ( 140 MHz) those functions from the data statistics (Starkov et al., 1983: Oksman et al., 1986) are 20