Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmdi43a1772g&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #DI43A-1772
Physics
1510 Dynamo: Theories And Simulations, 2721 Field-Aligned Currents And Current Systems (2409), 4255 Numerical Modeling (0545, 0560), 5440 Magnetic Fields And Magnetism, 6235 Mercury
Scientific paper
As a general rule, planetary dynamos in the solar systems are not affected by external currents or electromagnetic forces. These sources are too far from the dynamo region and currents too weak to have a significant effect in the magnetic field generation. Mercury, with its large core and small magnetosphere, may be an exception to the rule. Interaction between the interplanetary solar wind with Mercury's internally generated magnetic field, gives rise to Chapman-Ferraro currents and an associated secondary magnetic field that can significantly modify the operation of Mercury's dynamo. To study the influence of Chapman-Ferraro curents we modeled the effect of an external constant field on solutions of self-sustained numerical dynamos. We explored three regimes where the self-sustained solutions yield: stable dipolar; stable dipolar with a significant multipolar component; and reversing dipolar dominated dynamos. The external field was chosen to oppose the direction of the original axial dipole, and its strength was varied in order to find the minimum necessary to affect the original dynamo magnetic field. We find the most dramatic effect on the overall magnetic energy in cases where the external field acts on the most stable dipolar regime. In those cases, the external magnetic field can cause a polarity reversal if its magnitude is at least 3% of the original dynamo field magnitude at the core-mantle boundary (CMB). A stable dipolar solution with a significant multipolar component requires less than 1% of the time-averaged (CMB) surface field in order to be affected by the external field. For the reversing regime studied, the external field does not affect the total magnetic energy significantly. However, an external field with a magnitude of about 1% of the original field magnitude reverses the polarity rapidly and changes the reversal rate of the solution, causing the field to be preferentially aligned with the external field. In order to have a better understanding of Mercury's magnetic field, it is important to understand the feedback mechanism between internal and external fields. Thanks to spacecraft measurements from MESSENGER and Mariner 10 we will have better measurements of averaged internal and external magnetic fields as well as accurate estimates of the magnetospheric currents, which are critical in order to determine the dynamo regime of Mercury and thus unravel its magnetic field generation dynamics.
Gomez-Perez Natalia
Heimpel Moritz
Wicht Johannes
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