Radius Ratio Effects on Rotating Convection and Dynamo Action

Details Radius Ratio Effects on Rotating Convection and Dynamo Action Radius Ratio Effects on Rotating Convection and Dynamo Action

May 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusmgp33a..08a&link_type=abstract

American Geophysical Union, Spring Meeting 2004, abstract #GP33A-08

Other

1213 Earth'S Interior: Dynamics (8115, 8120), 1507 Core Processes (8115), 3005 Geomagnetism (1550), 5440 Magnetic Fields And Magnetism, 5734 Magnetic Fields And Magnetism

Scientific paper

We present the results of numerical simulations of thermally-driven rotating convection and dynamo action in spherical shells with varying radius ratios, χ = ri/r_o, where ri and ro are the inner and outer shell radii, respectively. We have determined the critical Rayleigh number, RaC, over the range 0.10 ≤ χ ≤ 0.92 and at Ekman numbers Ek = 10-3, 3 x 10-4 and 10-4 for Prandtl number Pr=1.0 in cases with mechanically rigid, isothermal boundary conditions. We find the following fit to our critical Rayleigh number determinations: RaC Ek1.16= 0.21/χ2 + 22.4[(1-χ)/(1+χ)]1/2. This fit shows good agreement with the analytical results of Jones, Soward and Mussa (2000). Dynamo calculations have been carried out at weakly supercritical Rayleigh numbers to determine if similar scaling laws can be found for dynamo action. In these calculations 0.10 ≤ χ ≤ 0.75, Ek = 10-3 and 3 × 10-4, Pr=1.0, and the magnetic Prandtl number is fixed at Pm =5.0. The boundary conditions are mechanically rigid and isothermal and a strong dipolar seed magnetic field initiates each calculation. The onset of dynamo action occurs at roughly 5-10 x RaC for χ ≤ 0.15. However as χ increases, dynamo action onsets at Ra values increasingly closer to RaC. For Rayleigh numbers less than twice the value at which dynamo action onsets, columnar convection produces strong axially-aligned dipole dominant magnetic fields. In this weakly supercritical dynamo regime, the ratio of quadrupolar to dipolar Gauss coefficients g20/g_1^0 are fairly insensitive to the value of the radius ratio. However, the octopole-dipole ratio g30/g_1^0 does show a more substantial, although non-monotonic, variation with χ. These results suggest that it may prove difficult to estimate planetary core radius ratio values using satellite determinations of g20/g_1^0.

Affiliated with

Also associated with

No associations

Rating

Radius Ratio Effects on Rotating Convection and Dynamo Action does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Radius Ratio Effects on Rotating Convection and Dynamo Action, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Radius Ratio Effects on Rotating Convection and Dynamo Action will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1178233