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.

C.-U.WAGNER, A.RANTA, H.RANTA HIG H E N E R G Y E L E C TR O N P R E CIPITATION D URING ISOLATED S UBSTORMS EMBE D DE D IN LO N G QUI E T PERIODS 1 I N T R O D UC T I ON . Cosmic noise a bs orption measurements have bee n used, since m or e than 2 5 years to study the precipitation of hig h energy electrons (aaome 10 keV) and especially to m o n itor their precipitation in auroral latitudes. N umerous studies have use d these m e asurements to investigate the morphology a nd dynamics of auroral absorption events (AA-eventa) see e.g. Hargreaves, 1969; B e r k le y et al.,1974). D ur i n g disturbed periods there occur long inter vals w i t h variable a b so rption caused b y superimposed AA-events, so that it becomes difficult to recognize the signatures of one special event. For s implifying the investigations, often isolated, clear pronounced substorms have b e e n studied (see e.g.Collie a n d Korth,1983, 1985, 1986). Ha v i ng in mind the great variab il i t y of the A A - s u bs t o rm signatures fr o m event to event, this seems to be the b e tt e r approach. But i n addition, the question arises, w h et h e r the reactions of the inner parts of the m ag n etosphere and, therefore, the auroral a b s orption substorm signatures depend o n the state of the magnetosphere, i.e. on w h e t h e r the magnetosphere w as in a stable, " quiet 11 state or w h ether it still feels the influences of recent storms, es p e cially of recent injections of h i g h energy electrons into the inner magnetosphere. To investigate this p r oblem we intend to study AA-ev e n ts r e l at e d to isolated substorms embedded in long quiet periods. 2. Selection rules f or global l y "stable", "quiet" periods: Whereas it is still a n u n s o lv e d pr o blem to define a "quiet" or "stable" state for the whole magnetosphere, this p ro b l e m seems to be m u c h easier f or the inner magnetosphere and e s pe cially f or problems connected w i t h the preci p i t ation of energetic particles. The inner m ag n etosphere including the r a d ia t i on belts is ve r y stable for periods w i t h Вг(1МР)> 0. F or an i n v estigation of h i g h energy elect r on precipitation, therefore, it seems to be reasonable to assume that the situation is quiet if m a n y days have passed af t e r the last great injection of particles into the inner magnetosphere. T aking into consi deration that great injections of energetic electrons are gen e ra l l y a s s oc i a ted w i t h great injections of ions b u il d i ng up the (asymmetric) r i n g current, concerning h i g h energetic particles such a "quiet" state m a y be characterized b y Dst > 0 for at least some days. Therefore, i n this inves ti g a ti o n time periods have b e e n taken for w h i oh the daily m e a n value of Dst is positive for at least 4 days w h e reas A p < 10 and I K p is low. 3. Da t a sets, selection of events and pr esentation of data: R e cords of the u n if o r m F i nn i s h riome t e r n e tw o r k covering L-ahells fr om 6.0 to 3.3 have b e e n used to iden t i fy AA -events w i t h amplitudes of at least 1 dB 90