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.

The EDFA» found te a function of the E-field are given on Fig.2 in a form of histogram. Note, for the values 20-25 gV/i we used data by Nielsen et al . (1987) for an adjacent time interval. Both Norway and Finnish SNRs were used. The smallest signal detected has been -8.8 dB; its absence was considered formally as the same signal (EDFA) value. As a consequence the averaged SNRs tend to be increased especially for the small E-fields. We devided the whole E- field band into four intervals to keep some balance in the event number for each box. From Fig.2 one can see the first very important fact - an existence of the irregularities when the E-field is well under the FB instability threshold. This is a crushual fact for understanding of the irregularity "living" condition. The second thing is change of the EDFA (effective) values when E-field becomes less than 18-20 mV/m. The total band of the EDFA change is 20-25 times. It is apparently strong though is not similar to some sharp "jump" which seems to be related to the instability onset in uniform plasma. We will futher name the found EDFA changing as a "soft" E-field threshold for the irregularity excitation. Note, the STARE data used in statistics have been averaged at the 20-sec integration time. As for the echo occurrence the SNRs exhibit a quick rising at E = 10-13 mV/m (it is not shown) and the occurrence keeps more than 60 per cent when E * 13 mV/m. After that the SNR/EDFA growth becomes smoother Another feature of Fig.2 is not essential changings of mean electron densities in the boxes 3. DISCUSSION. The data presented here strongly support the idea that for 1Л0 MHz radar aurora appearence a threshold electric field observed can be soft and lower than it was considered earlier. From the physical point of view it could be a result of the following. a Real property of the EDFA as a function of E-field. However the causes which could form such a dependence for the FB instability are not known at present. At the same time the role of the GD instability should be kept in mind (Fejer and Kelley, 1980) as well as the electron gas transport in a course of the hydrodynamic turbulence formation and mixing in neutral atmosphere. 22