| Title: |
Laboratory-numerical models of rapidly rotating convection in planetary cores |
| Authors: |
Cheng, JS; Stellmach, S; Ribeiro, A; Grannan, A; King, EM; Aurnou, JM |
| Source: |
Geophysical Journal International, vol 201, iss 1 |
| Publisher Information: |
eScholarship, University of California |
| Publication Year: |
2015 |
| Collection: |
University of California: eScholarship |
| Subject Terms: |
Dynamo: theories and simulations; Heat flow; Core; outer core and inner core; Planetary interiors; Geology; Geophysics; Geomatic Engineering; Geochemistry & Geophysics |
| Subject Geographic: |
1 - 17 |
| Description: |
We present laboratory and numerical models investigating the behavioural regimes of rapidly rotating convection in high-latitude planetary core-style settings. Our combined laboratorynumerical approach, utilizing simplified geometries, can access more extreme parameters (e.g. Rayleigh numbers Ra ≲ 1013; Nusselt numbers Nu ≲ 103; Ekman numbers E ≳ 3 × 10-8) than current global-scale dynamo simulations. Using flow visualizations and heat transfer measurements, we study the axialized flows that exist near the onset of rotating convection, as well as the 3-D flows that develop with stronger forcing. With water as the working fluid (Prandtl number Pr ≲ 7), we find a steep scaling trend for rapidly rotating convective heat transfer, Nu~(Ra/RaC)3.6, that is associated with the existence of coherent, axialized columns. This rapidly rotating trend is steeper than the trends found at moderate values of the Ekman number, and continues a trend of ever-steepening scalings as the rotation rate of the system is increased. In contrast, in more strongly forced or lower rotation rate cases, the heat transfer scaling consistently follows a shallower slope equivalent to that of non-rotating convection systems. The steep heat transfer scaling in the columnar convection regime, corroborated by our laboratory flow visualizations, imply that coherent, axial columns have a relatively narrow range of stability. Thus, we hypothesize that coherent convection columns are not stable in planetary core settings,where the Ekman number is estimated to be~10-15. As a consequence, convective motions in the core may not be related to the columnar motions found in presentday global-scale models. Instead, we hypothesize that turbulent rotating convection cascades energy upwards from 3-D motions to large-scale quasi-2-D flow structures that are capable of efficiently generating planetary-scale magnetic fields. We argue that the turbulent regimes of rapidly rotating convection are essential aspects of core dynamics and will be necessary components of ... |
| Document Type: |
article in journal/newspaper |
| File Description: |
application/pdf |
| Language: |
unknown |
| Relation: |
qt1zb249hs; https://escholarship.org/uc/item/1zb249hs; https://escholarship.org/content/qt1zb249hs/qt1zb249hs.pdf |
| DOI: |
10.1093/gji/ggu480 |
| Availability: |
https://escholarship.org/uc/item/1zb249hs; https://escholarship.org/content/qt1zb249hs/qt1zb249hs.pdf; https://doi.org/10.1093/gji/ggu480 |
| Rights: |
public |
| Accession Number: |
edsbas.8D8F8F12 |
| Database: |
BASE |