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Astron. Astrophys. 358, 759-775 (2000)

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5. Effect of the magnetic field

We have seen in Sect. 3 that an HSS should have little effect on the brightness of the plasma tail unless it is accompanied by an enhancement of the magnetic field. The argument was based on the scaling law which neglects the influence of the magnetic field. We test it by a numerical model calculation.

This calculation is also started from model 'slow1'. At t=0 the solar wind condition was changed to 'fast1' while keeping the magnetic field constant (the values of 'fast1' in brackets).

Figs. 8 and 9 show that the situation resembles more the case of a simple direction change, treated in Sect. 4, than the situation of a full HSS as described in Sect. 3. The most striking difference to the HSS model is the lack of a clear second brightness maximum in the tail (see the middle panel of Fig. 9). Therefore, one cannot identify a tail disconnection or even a cloud. The ions per tail length (upper panel of Fig. 9) vary only very little with time. After 4 hours there is also a kink in the tail, but it is less pronounced than the kink in the corresponding Fig. 2.

[FIGURE] Fig. 8. The same as Fig. 2 for an HSS without field enhancement

[FIGURE] Fig. 9. The same as Fig. 3 for an HSS without field enhancement

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© European Southern Observatory (ESO) 2000

Online publication: June 8, 2000