 |
| Titel |
Double diffusive dynamo action in Mercury's core |
| VerfasserIn |
A. Manglik, J. Wicht, U. R. Christensen |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250040668
|
|
|
|
|
|
| Zusammenfassung |
| Recent numerical dynamo simulations which model a stably stratified layer at the top part of
Mercury’s liquid iron core where successful in reproducing the planets observed weak
magnetic field. Assuming a sub-adiabatic temperature gradient at the core-mantle boundary
convection was mainly driven by the effects of inner-core solidification in the deeper layers.
In order to simplify matters, these models adopted a co-density approach which
effectively assumes equal diffusivities for both heat and the lighter core elements,
notably sulfur. In order to overcome this limitation, we have modified our dynamo
code to include two separate transport equations that allow to model differences in
diffusivities. To explore the potential effects of double diffusive convection on Mercury’s
dynamo we assume that sulfur diffuses ten times slower than heat and use an Ekman
number of 3 Ã 10-4. When adopting 2Â wght% of sulfur, the double diffusive case
exhibits a strong toroidal magnetic field within the stably stratified core region which
is missing in the co-density model. As a consequence, the magnetic field at the
planetary surface is two orders of magnitude stronger in the double-diffusive case
and thus not compatible with the observations. However, the surface field strength
becomes realistic again when the sulfur fraction is reduced below 0.2 whgt%. These
results therefore imply that Mercury’s core may be poor in sulphur and other light
constituents. |
|
|
|
|
|
|