Ohmic dissipation and power requirements for dynamo generation on Mercury
Abstract
To sustain a convectively-driven planetary core dynamo, the rate at which mechanical energy is delivered to the process of magnetic field production must exceed the rate at which this energy is lost through ohmic dissipation. The amount and importance of ohmic dissipation depends on the magnetic field strength in the core and the physical length scale over which this dissipation occurs (Lcrit) — two highly uncertain parameters within planetary cores . Here, we describe a novel approach to calculate ohmic dissipation and apply it to Mercury's core. Mercury has an internally-generated magnetic field at present and crustal magnetic field signatures indicate that an ancient dynamo was active between 4 - 3.5 Ga. We revisit the entropy budget for Mercury's core and illustrate the importance of including ohmic dissipation. We assume core flow conditions are described to first order by a quasi-geostrophic balance, consistent with a recent consensus between experiments and numerical simulations (see Aurnou and King, 2017; Aubert, 2019). Accordingly, we take Lcrit to be proportional to the Ekman number E1/3, which depends on spin rate.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMDI010..05P
- Keywords:
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- 1507 Core processes;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1510 Dynamo: theories and simulations;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 7207 Core;
- SEISMOLOGY;
- 8115 Core processes;
- TECTONOPHYSICS