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.

period from 01.06.1965 to 28.Q 6 . 1968. Then a stationary examination was made w h i c h gave positive results. The results obtained are ahown i n F i g . ? . where the distribution of the spectral density is gi v e n for the frequencies corres ponding to periods fr o m 32.0 to 25.3 days. Here it is clearly seen expressed periods of 27 days and slightly expressed ones of 29.6 days. The data were filtered in order tc eliminate the influence of the frequency corresponding to a period of 30.6 days. A low frequency fi l t e r was used for this purpose. T h e n the data obtained were filtered to eliminate the determinal component (27-day solar variation). This was done by using a determinal filter. The I data filtered this w a y were allowed to pass through the FFT and the spectral density was determined (Pig.8) and then the smoothed estimation wa s obtained (Pig.9). I n the latter figure the result is averaged b y three points. This leads to a n enhancement of the stability of the spectral density estimatibn. Fi n ally it is n ec e s s a r y to determine the interval of confidence of the estimation obtained for the spectral density. We take a confidential pr o b a b i l ity r » 0 . 5 0 and for the interval of confidence 50 per oent we receive 0.525x 1 0"e < f *x < 1.019хП0“8 . Fr o m the 50 per cent of oonfidence a conclu sion m a y be drawn that there exists a n effect of the lunar wake but it is c omparatively slight. Theoretical m o d e l . In the model of Spreiter, Marsh and Summers /17/ the M o o n is considered a n o n c o n ducting sphere w h i c h fully absorbs falling particles. The equations of the ideal magnetic hydrodynamics under assumption of V В are reduced to the effective gas-dynamical equations. The problem is solved in a n axis symmetrical approach. The cavity or vo i d formed behind the M o o n is limited by the tangential discontinuity» v m “0 - b m =° - (P + B ? /8?] - 0 Pig, 7. Spectral density d i s t r ibution fo r frequencies corresponding to periods of 25.28 to 32.00 days. D i s tinctly expressed 27 days of solar va r iat ion an d more w e a k lunar ones are seen. I09