[3] The distributions of
hmF2 in the belt of the invariant latitudes
between
40o and
65o according to the Intercosmos 19 data were
built. The data cover conditions of the local summer in the
Northern and Southern hemispheres during the solstices for the
period with high solar activity ( F10.7 200 ) since 1979 till 1981.
The data for very quiet conditions ( AE < 300 nT) were chosen in
order to minimize the influence of the electric fields and acoustic
gravity waves (AGW) and therefore to reduce the data scatter and
to increase the accuracy of the representation of the
hmF2 distribution. As a result, the stable background state of the quiet
ionosphere determined (as one of the factors) by the undisturbed
wind system was found. About 100 and more than 60 orbits were
chosen in the Northern and Southern hemispheres, respectively.
The satellite orbits in both hemispheres are oriented in such a way
that the local time increases with a latitude increase from
2300 LT (40o
L ) to
0100 LT (65o
L ).
The local time at the fixed
invariant latitude changes with the longitude also. In order to
eliminate this weaker dependence, the data were corrected taking
into account the diurnal variations in
hmF2 from the
International Reference Ionosphere
(IRI) model.
The correction was carried out to the nearest hour in local time:
2300 LT for 40o
L, 2330 LT for 50o
L,
2400 LT for 60o
L, and 0100
LT for 65o
L.
Thus the obtained distribution is not a LT map in a
literal sense; however, all data fall into a narrow interval of the
near-midnight hours, and this does not complicate strongly the
analysis. The other circumstance is more important: the auroral
ionosphere at 0100 LT at ~70% of longitudes is sunlit, so in the
period when at a latitude of 40o
L purely night conditions are
realized, some intermediate conditions are maintained at 65o
L,
that
should be taken into account in the calculations.
[4] The data on the electron temperature Te obtained from in situ measurements on board the Cosmos 900 satellite were also used in calculations. The measurements were conducted almost in the same conditions as the measurements of hmF2 at altitudes of ~370 km and ~470 km in the Northern and Southern hemispheres, respectively [Karpachev et al., 1997]. A correction of the Te values on the altitude using the IRI model was performed in the Southern Hemisphere. The Te distribution in the latitude belt from 40o L to 65o L was obtained by averaging of 70 and 100 satellite orbits in the Northern and Southern hemispheres, respectively.
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Figure 1 |
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