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SUMMARY:Morphology in rapidly rotating planetary cores - Ben McDermott (CU
 ED\, University of Cambridge)
DTSTART:20190125T130000Z
DTEND:20190125T140000Z
UID:TALK117628@talks.cam.ac.uk
CONTACT:Amélie Lamarquette
DESCRIPTION:The morphology of the flow in Earth’s outer core and its mag
 netic field are thought to be intimately related. Columnar flow usually re
 sults in a predominantly dipolar magnetic field\, as evidenced from dynamo
  simulations. The convection columns assume the form of alternating cyclon
 es and anti-cyclones\, and carry a large degree of helicity. When the ther
 mal forcing is increased\, there is an abrupt transition to a disorganised
  flow\, and the dipole breaks down. The transition in these simulations is
  marked by a `local’ Rossby number of <span>&#126\;</span>0.1.  Similarl
 y\, in rotating turbulence experiments\, there is a sharp transition at a 
 Rossby number of <span>&#126\;</span>0.4. For smaller values of the Rossby
  number\, the flow is organised into helical columnar structures\, and for
  larger values the flow appears more three-dimensional. We perform six dir
 ect numerical simulations of the flow induced by a layer of buoyant anomal
 ies subject to rotation. As the rotation is weakened\, we identify a porti
 on of the flow which is more strongly three-dimensional. We show that the 
 flow in this region is turbulent\, and has a Rossby number above a critica
 l value <span>&#126\;</span>0.4\, consistent with previous findings. We su
 ggest that the discrepancy between the value found here (and in rotating t
 urbulence experiments)\, and that seen in dynamo simulations (<span>&#126\
 ;</span>0.1)\, is due to different definitions of the length scale used to
  define Ro. This in turn suggests that inertial waves\, continually launch
 ed by buoyant anomalies\, sustain the columnar structures in dynamo simula
 tions\, and that the transition documented in these simulations is due to 
 the inability of inertial waves to propagate for Ro>0.4.
LOCATION:JDB Seminar Room\, CUED
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