Department of Earth and Planetary Sciences People at EPS

Peter Olson - Examples of Recent Research

Numerical Models of the Geodynamo
Polar Vortex Motion in the Core
Zonal Winds generation on the Giant Planets
Rotating Convection
Rapid Decrease of the Dipole Moment

 

Numerical Models of the Geodynamo

 

Animation of 6000 years of geomagnetic secular variation on the core-mantle boundary from a numerical dynamo model. Red = magnetic flux out from the core; blue = magnetic flux into the core.  

Animation of a magnetic polarity reversal from a numerical dynamo model. Left: Time history of the colatitude of the axis of the main dipole field. Red lines indicate the time interval of the reversal, when the dipole axis is within 45 degrees of the equator. Shading indicates relative intensity of the dipole field (dark=high intensity; light=low intensity). Right: Evolution of radial component of the magnetic field on the core-mantle boundary during the same time. Blue indicates inward-pointing magnetic flux; red indicates outward-pointing magnetic flux. Calculations in collaboration with Johannes Wicht from Max-Plank Institute for Aeronomy.

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Polar Vortex in the Earth's Outer Core

 

Geomagnetic secular variation on the core-mantle boundary between 1870 and 1990, showing westward motion of a patch of reversed magnetic flux.  Yellow = magnetic flux out from the core; Blue magnetic flux into the core. Right: zonal velocity and vorticity inferred from the magnetic secular variation.  

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Zonal Winds on the Giant Planets  

The planets Jupiter and Saturn have strong zonal winds, in particular, strong eastward (prograde) equatorial jets. The origin of the equatorial jets remains enigmatic. Below is a numerical model of thermal convection in a rotating spherical shell, showing a) temperature near the outer boundary, b) temperature in the equatorial plane, c) azimuthal velocity (note the strongly eastward equatorial jet), and d) zonal sections of azimuthal velocity and meridional circulation. Red indicates positive and blue indicates negative values, respectively. 

 

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Rotating Convection

 

 

 

 

 

 

 

Side view (left) and equatorial plane view (right) of thermal convection in a rotating spherical shell of water with the geometry of the Earth's liquid outer core. The columnar structure of the convection is due to the strong constraint of Earth's rotation. 

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Rapid Decrease of the Dipole Moment

Rapid Decrease of the Dipole Moment

The geomagnetic dipole moment has decreased by nearly 6% per century since first measured by Gauss in the 1840s. This is 10-20 times faster than the Ohmic decay rate of the fundamental mode dipole field in the core (upper left). The causes of this rapid decrease are the proliferation of reverse magnetic field on the core-mantle boundary, especially beneath the South Atlantic  (upper right), and the advection of magnetic field from high to low latitudes by flow in the outer core (lower  left). The combination of advection of magnetic field on the core-mantle boundary  and radial diffusion of through the core-mantle boundary is weakening the dipole moment (lower right).

    

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