Dynamics: Nov. 11. Which are non-divergent, irrational ??

Dynamics: Nov. 11

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Which are non-divergent, irrational ??

Circulation:

Circulations often conserved.

=

Deformation:

Flow over mountains

Orthonormal to div, vort.

Flow can be broken down into divergent, rotational, anddeformation components

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Both deformationAnd shearStrengthen frontalzones

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Effective gravity g, includes centrifugal force

Motion introduces additional force : Coriolis

f=

Flow to right of motion =>CW in NH

2 examples:•land-sea breeze (Hsu, 1970, MWR)• mountain slope/valley circulation (Rocky Mountains/Plains)• katabatic flow ?

INERTIAL CIRCLES: less common in atmosphere (less inertia)

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Motion determined by balance between pressure gradientForce, Coriolis force, frictional force

Geostrophic wind = balanced pressure/coriolis flow

Fx,y =vertical gradient in horizonalmomentum

NH

*1/

Midlatitude horizontal velocities ~ 10 m/sDv/dt ~ 10-4 m s-2

Coriolis force ~fV~10-3 m s-2

In Boundary Layer, frictional drag in evidence

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Wind speed sub-geostrophic, drifts towards lower pressure

fV = |P|cos

Gradient Wind: in regions of high curvature, addthe centripetal acceleration to eqn of motion

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Sub-geostrophic Super-geostrophic

Thermal Wind: The vertical shear in geostrophic windIs related to the horizontal temperature gradient

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Barotropic atm => grad T =0 =>geostrophic wind constant

Equivalent barotropic

Again…

Explains why westerlies strongestAt top of troposphere

Do these plotsmake sense ??

30-yr Mean meridional Profile Of temp. and zonalWind, from Australia toEastern Siberia, January

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Cold advection Warm advection