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
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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.
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.
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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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.
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).