Observations and Modelling of Fronts and Frontogenesis
Observations and Modelling of Fronts and Frontogenesis
Observations and Modelling of Fronts and Frontogenesis
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polynomials in z.) The vertical momentum balance is<br />
hydrostatic. The alongshore geostrophic velocity in the<br />
mixed layer is accelerated inertially <strong>and</strong> by the wind stress<br />
rX <strong>and</strong> decelerated by the entrainment stress Te<br />
A small<br />
layer immediately below the mixed layer, in which fluid being<br />
entrained from the interior is accelerated <strong>and</strong> through which<br />
the stress falls smoothly to zero, has been neglected (see<br />
Niiler, 1975). The interior geostrophic velocities are<br />
accelerated inertially.<br />
The variable upper layer density satisfies the<br />
thermodynamic equation,<br />
Plt + viPly = [-aQ/c + (i P1)weI/hl (3)<br />
where Q is net heating, c is specific heat, <strong>and</strong> a is thermal<br />
expansibility. The subscript I indicates an interior layer<br />
variable that is evaluated immediately below the base <strong>of</strong> the<br />
mixed layer. (Under certain conditions layer 3 may come in<br />
contact with the mixed layer, so that i will not always be<br />
p2) The effect <strong>of</strong> salinity on density could easily be<br />
included also, but we neglect it for simplicity.<br />
The entrainment velocity We 15 obtained by the energy<br />
argument <strong>of</strong> Kraus <strong>and</strong> Turner (1967). This balances the<br />
energy input from the wind, minus the potential energy<br />
removed by surface heating, with the potential energy created<br />
by entrainment <strong>of</strong> dense interior fluid into the mixed layer:<br />
m0p0u*3 (l/2)gh1aQ/c = (l/2)wg(p - p1)h1. (4)<br />
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