| Autor: |
Xie, Lianghai, Lee, Lou-Chuang, Li, Lei, Zhang, Yiteng |
| Předmět: |
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| Zdroj: |
Astrophysical Journal; 7/1/2021, Vol. 915 Issue 1, p1-10, 10p |
| Abstrakt: |
We use a multifluid MHD model to study the formation of the small-scale magnetic flux rope (MFR) in the ionosphere of Mars. It is found that a straight flux tube can turn into a twisted MFR during its sinking into the lower ionosphere, caused by the differential compression at different parts of the tube. Further studies show that the MFR is not a force-free structure, in which there is always a pressure gradient force to balance the magnetic force. Moreover, we find that the ionospheric ions inside the MFR can be squeezed out from the two ends of the MFR, with an outflow flux of about 3.5 × 107 cm−2 s−1, which can play an important role for the ion escape from Mars. In addition, we find that both the sinking speed and the ratio of the ion gyroradius to the tube radius can affect the characteristics of MFR. An MFR can be more quickly formed for a larger sinking speed, but it can be also more quickly filled by the ambient ions. Oppositely, the MFR is more difficult to be filled when the ratio of the ion gyroradius to the tube radius is smaller. Once the MFR is filled, the compression is prevented by an outward pressure gradient force, and both the field strength and the rope helicity begin to decrease. Our results can explain the different altitude dependences of MFRs observed at Mars and Venus. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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