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.

APATITY, 24.02.5/ Pig. 1. H-component of the geomagnetic field, at A patity station, February 24, 1981. 19Hi 50 UT APATITY 24.02.81 Fig. 2. Example of a curl-like black band against the diffuse b a c k ground. TV camera field of view is about 20°. The study of i ntensity luminosity changes in black auroras have shown that the luminosity inside black auroras is not only lower than that in the visual auroral region but can be m u c h lower than the luminosity where auroras are absent. Fig. 3 gives a n example of a n auroral luminosity intensity о record taken b y a narrow-angle zenith photometer in 5577 A emission during the black aurora drifting along the photometer field of view. As was discov ered the intensity of black auroras, i.e, their blackness or lowering of their luminosity intensity relatively to the background, is not usually cons tant i n time an d extension for every band. The width of black bands varies from hundreds of meters to several dozens of kilometers. Several types of black auroras can be distinguished regarding the way of their formation and drifting. First type bands are unmoving as well as drifting. Drifting black bands move transverse to the formation's extension with the velocity of several hundred kilometers; their life-time is 30-120 seconds. A spicific feature of the second type bands is a streaming-like movement along the formation. In this case a black area appears i n the diffuse lumin osity forming a black r unning stream. Then the region of the stream's origin is filled wi t h diffuse luminosity. This process reoccurs many times and looks like alteraction between "black" and "white" streams along the same bed. This may be supposed to be a specific type of temporal-spatial pulsations. The velocity of the streams is about 1-3 km/s assuming their altitude being 110 km; the life-time is 30-60 s and the width from a f e w h undred meters to several kilometers. Fig. 3. Fragment of recordings of the auroral l u m inosity0 intensity i n 5577 A. The arrow marks the interval w i t h the black arc i n view of the zenith photometer; the arc crossed the geographical zenith. 92