4. Addition of the 1990-1999 Period and of Other Stations
[21] The results obtained by
Vanina and Danilov [2003]
and
Vanina-Dart and Danilov [2006],
as well as the results presented above in this
paper, are based on the Russian midlatitude stations and the period
1979-1989. It is important to compare these results with other stations
and the next solar cycle (1990-1999).
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Figure 7
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[22] Figure 7 shows the seasonal behavior of
r(foF2) for Kiev and
Juliusruh stations for 1980 and 1991 (the years with approximately equal
solar activity) at
Ap < 16. One can see in Figure 7 that on the whole the
seasonal behavior of
r(foF2) in the 1990-1999 cycle stays the same as in
the 1979-1989 cycle studied earlier. The principal feature discussed, that
is, the presence of the maximum in the absolute value of negative
r(foF2) in spring is pronounced both, in 1980 and in 1991. That makes the
results obtained earlier in the detailed study of the 1979-1989 cycle even
more reliable.
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Figure 8
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[23] The western stations added to the list behave in a way similar to
the Russian stations. Figure 8 shows a comparison of the
r(foF2) seasonal behavior between two pairs of station (Juliusruh-Kaliningrad
and Kiev-Rome, each pair being located at nearly the same latitude).
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Figure 9
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[24] Figure 9 shows the
r(foF2) max dependence on the boundary
values of
Ap (similar to Figure 5) for six western stations for 1980. The
same tendency of
r(foF2) max decrease with the
Ap increase is seen in
Figure 9 for the midlatitude stations (Juliusruh, Slough, Rome, and
Kiev). For the auroral stations Sodankylä
and Kiruna the picture differs
from that for the midlatitude stations. Except the point
Ap < 8, which is
usually poorly provided by the data, the increase in the magnitude of the
negative correlation coefficient from
Ap < 8 to
Ap < 30 is relatively
small (about 0.05 in
r ), whereas for the midlatitude stations it may be as
high as 0.4-0.5 (see Figures 5 and 9a). We will consider this problem in
the section 6.
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