Электродинамические процессы в высоких широтах: материалы междунарордного симпозиума «Полярные геомагнитные явления», 25-31 мая 1986 г., Суздаль, СССР / Междунар. геодез. и геофиз. союз, Междунар. ассоц. геомагнетизма и аэрономии ; Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т ; [редкол.: О. М. Распопов (отв. ред.). и др.]. - Апатиты : Кольский филиал АН СССР, 1988.

nevertheless unequivocal. Figure 7 shows that using this formalism the ag r e e ment b et w e en auroral ra d ar velocities and incoherent scatter velocities is very good. A theoretical foundation of this ion-acoustic approach will be g iv e n in section XIX, F o r ma n y years only, the D o pp l e r velocities obtained f r o m auroral radar b ackscatter have b e e n q uantitatively used. Onl y ver y recen t l y also the other i nf o r ma t i on contained in the backsc a tt e r signal was studied (Timofeev and M i r o s h n i k o v , 1982.; Ogawa et al.,1983; Providakes et al.,1983; N i e l s e n et al., 1984). This i n fo r mation became available af t er sophisticated pulse tran s m is sion schemes wer e employed, pr oviding the complete spectr u m of the radar echo. O ne-of the most important findings of these studies was that there are a p pa rently two types of spectra: n a r r o w spectra w i t h a w i d t h of typical 400 m/s and b r oa d spectra w i t h a w i d t h of sometimes 1 0 0 0 m/s or more. Haldoupia et al.(1984) attributes the f ormer to true primary MTSI w av e s the l a tter to secondary waves created in the wav e field of the primaries by wave'-wave interaction. A n ot h e r important result w a s that the observed spectra are most f re q u en tly skewed, as shown in Figure 8 (Schlegel et al.,1986). This indicates a limitation of the "Double-Pulse" technique, w i d e l y employed in auroral radars, since this m e t h o d presupposes a symmetric spectrum. Other relevant resulta of spectral studies are - backs c at t e re d power is slightly pos i t iv e l y correlated w i t h the m ea s u r e d velocity - the w i d t h of the spectra q n d the b ac k s ca t t er e d power is on the average different for the eastward and the w e s t w a r d electrojet. The first result can prob a b ly only be ex plained by a no n - li n e ar theory w h i c h is still lacking. The second result is proba b l y due to the fact that eastward and w e s tw a r d electrojet occur i n different a ltitudes (e.g.Brekke and Rino,1978; Igarashi and S c h l e g e l , 1986) w h i c h me a ns a different influence of the col l i si o n freq u en c y o n the unstable wav e s (see above). C.I n situ rocket r e s u l t s . Some of the important parameters of the MTSI can only be m e a s u r e d in situ, like for instance the w a v el engths and the strength of the i r re g u larities created b y the instabilities. These i r r eg u l a r ities can occur as elec t ro n de n s it y f lu ctuations as wel l as electric field fluctuations. Several rocket experiments have bee n perfox-med in the past to m e a sure these fluctu at i o ns (e.g. T hrane and G r a n d a l ,1981; Pfaff et al.,1984). F igure 8 . Typical skewed spectrum reco r d ed w i t h the S AB R E radar. SABRE BAY 195 198 4r 12 4S 0 ш н I ЯАыве i2o к п інтееи is mm ACF 0 1 All -300 mcnostc ) SPtCTKUM (Vf‘ W4HZ) п о м е т Т6.Г X24.7 288.9 -S.S 84