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Unformatted text preview: etrical convection, where heat
from the bottom is equal to loss off the top, viscosity is
constant, and both top and bottom boundaries are free-slip.
Cold downwelling will be the same difference from average as
the warm upwelling, And both top and bottom will have
symmetrical Thermal Boundary Layers. These are the
transition zones that are unstable, and are in contact with
either the heating or cooling source. Tectonic plates are the
upper boundary layer. Much of the rest of the fluid is
gravitationally stable. The upper boundary layer thickens and cools as it moves away
from the divergence zone and toward the downwelling zone,
forming a horizontal boundary current. It flows as far as it can
before cooling enough to sink, thus defining the size of a
tectonics plate in the simplest sense. An aspect ratio of 1 is
Gravity drives the vertical currents, but the horizontal currents
are driven by pressure gradients. High pressure forms as the
plumes reach the surface, and flow toward low pressure in the
more dense downwelling zones, s...
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- Winter '14