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Figure 4. Differences in bow-shock position for $\gamma =5/3$ and $\gamma =2$. The magnetospheric boundary should be scaled to the planetary ionopause surface (from Spreiter et al., 1966).

DISCUSSION

This paper has reviewed a theoretical model for the obstacle presented by a planetary ionosphere to the solar wind. Basic features of this model include small flux penetration of the ionosphere by the solar wind and a weak magnetic field below the dayside ionosphere. The model also predicts that large asymmetries may be found in the ionopause height and shock height from pole to equatorial terminator. The variations in shock height due to these asymmetries are comparable to the variations reported by Gringauz et al. (1974) for Mars, although the variability could also be explained in terms of an asymmetric rotating planetary dipole

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