Полярные геомагнитные возмущения и связанные с ними явления : материалы международного симпозиума «Полярные геомагнитные явления», 25-31 мая 1986 г., Суздаль / Междунар. геодез. и геофиз. союз, междунар. ассоциация геомагнетизма и аэрономии, АН СССР, КНЦ, ПГИ. – Апатиты : [б. и.], 1989.

the rest of cases we observed the eeriea of almost parallel black bands accom panied by inhomogeneities mo v i n g f r o m w est to east southward of the arc simi lar to the cases discussed above. Moreover, the clockwise r o tation of the curls (when s e e n antiparallel to If ) demonstrated that the electric field related wi t h the v o r t e x structure of the bl a c k aurora is directed to the Earth. Thus, the experimental data indicated the existence of an intensive v o r tex movement (rot V ? 0) in the vicinity of black aurora wh i c h is related w i t h availability of the positive charge in the region of the b l a c k band i t self. The absence of inhomogeneity movement in the re g i o n n o rthward of the arc m a y occur due to b o t h general longitudinal eastward drift of auroral eleo' trons and large scale electric fields wh i c h are not directly connected wi t h the aro. I n the v i cinity of the b l a c k ba n d at the ionospheric level the elec tric field can be evaluated by the average velocity of the inhomogeneities movement and is equal to (Vno r th - V s o u t h ) B 2X105. 0.5-300 E - --- ----------- aoutn--- --- --------- ----- . 50 m v/m. 2 0 2x3 *10 If the general wi d t h of the aro :ls of the order of 5 k m then the potential difference across the arc is proved to be 0.25 kv. Apparently, the aame po t e ntial difference occurs along the magnetic field lines. In this case the electric field is directed downwards and it should decelerate the electrons. Similar estimations of the electric field values in the v i oinity of the arc on the ionospheric level have be e n made for the b l a c k arcs n e a r active auroras. As stated earlier the v e l ocities of the inhomogeneities movement around such arcs are about 10 km/s and the wi d t h of the black arc is several kilometers. W h e n the total wi d t h of the arc is 5 k m (an average value) the potential difference across the aro is equal to 2 .5 kv. The value of the fi e l d aligned potential difference for the considered event turned to be r e l a t i v e l y small though it fits the range of the potential difference detected by other techniques (see, /7/). Thus, the evaluations of the electric fields in the vioinity of the arc (from single experimental data) and the potential difference along the m a g n etic field demonstrate that 'in case of bl a c k auroras against the diffuse ba o k ground the double layer model could, ha r d l y fit the observed parameters of black auroras. For other types of bl a o k auroras (black bands n e a r active dis crete forms) the double layer model is in good accordance wi t h the parameters of black auroras. C o n c l u s i o n s . The m a i n results of the present paper m a y be formulated as follows. 1. Blaok auroras observed b y TV me t h o d s are described, thair similarity to usual auroras of the seme type is shown. 2. Some types of b l a c k auroras (black bands l ocated near discrete active auroras) are shown to be w e l l explained b y the double layer model w i t h the earthward eleotric field. At the same time there are certain auroral types (black auroras a g a i n s t ,the diffuse background) wh i c h cannot be explained wi t h i n the scope of this model a n d ne e d some other mec h a n i s m for their in t e r pretation. A p p l i c a t i o n of this model to account for pulsating bl a c k bands and spots requires fu r ther study a n d foremoat the study of distribution of p r e c i pitating ele c t r o n a n d p r o t o n fluxes and the velocity of auroral i n h o mogene ity movement in the a uroral vicinity. 94