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.

intermediate range 67-72 km. They also found that during the sunrise and sun set periods wh e n oLe changes very rapidly (effects usually attributed to electron attachment to 0 2 and pho'todetachment from Og and to variations of the 0 /C >2 ratio) there was a marked asymmetry between the values at given solar z enith angle between sunrise and sunset. This asymmetry a n d the gradual change of и during the day ma y well have the same underlying cause, presum ably a progressive change in the D region chemistry governing electron and ion recombination. The PCA of February 1986 was much less intense than that o f August 1972. At the respective event maxiraa production rates differed by a factor of 25 at 60 km, and at the same times the electron densities at 70 k m diffe red by a factor of 8. It is therefore of interest to compare the profiles obtained for these two events b y essentially the same method. I n doing so, we have of course to assume that there are no major systematic difference between the respective particle or radar measurements, atmospheric models or computational techniques. Reagan and Watt's profiles from the PCA of August 1972 showed a marked local ma x i m u m at 80 km, a distant mi n i m u m betweai 65 and 75 km, and a strong increase of _ w i t h decreasing height below —7 —6 *4 —1 that level. At 90 km, values ranged between 4.5x10“' and 1.2x10” cnrs“ ; -5 -5 3 -1 at 60 k m most lay be t ween 10 J and 2x10 cnrs . The range of values has been superimposed for several heights o n Figure 10. The present measurements give similar values around 80 k m but are considerably smaller above 80 km and larger below. They do not show a peak at 80 km, but there is a n inflec tion between 70 and 75 k m and at some times a max i m u m at that level, where oC is considerably larger than Reagan and Watt's value. This value (10~'i спЗв- ^ ) is equivalent to the recombination coefficient for hydrated ions H + (Ho0) w i t h n ~ 6 (McEwan and P h illips,1975). The increase of о e below u XX ® 70 km, w h i c h is a marked feature of Rea g a n an d Watt's m easurements and is also indicated by the present 65 k m measurement, m a y be caused b y an increa sing concentration of negative ions or b y a n increasing proportion of the larger cluster ions, or both. Re a g a n and Watt discussed the second explana tion, but the first cannot be ruled out. The measurements of February 1984 do not go to low enough heights to delineate the behaviour i n the lower r e gion. The value of effective recombination determined at 90 km is closer to the theo retical value for Og than for N 0 + recombination. If the steady increase below that level down to 75 km-is attributed to a n increase, in the ratio (f) of hydrated to simple ions, for which the individual recombination coefficients are reapective- ly oth an d a ( g , then the effective values can be equated to о { e = (ois + U h ) / ( 1 + f ) Н.Ьы SIMPLE HYDRATED A (CH3S~‘) Figure 10. Height profiles of effective recombination coefficient for 1030,1200 and 1330 UT. Reagan and Watt's (1976) values are indicated for comparison. II3