Vertically Averaged Divergence in General Circulation

ATOC 4720 class37 1. The vertically averaged divergence • The primitive equations • The general circulation: description • Thermally driven circulation in the absence of rotation

1. Vertically averaged divergence Atmosphere: high degree of compensation: One level digergence -- the other level convergence.

Structure of external and internal waves There is vertically averaged divergence Complete Compensation Of divergence Internal External:

2. Primitive equations: ( )

3. General circulation: description Ultimate energy source: solar radiation

General circulation Two broad classes atmospheric motions: Driven by horizontal heating gradients in stably stratified atmosphere (98% kinetic Energy); large-scale: synoptic-planetary (gestrophy); sometimes convert to small-scale: instabilities (2) Driven by convective instability (2%); important for transport latent and sensible heat from earth’s surface upward;

General circualtion: description Usually, general circulation--indicates motion as type (1): Large scale Energy cycle: Large-scale horizontal heating gradients -- potential energy -- convert to Kinetic energy -- dissipation; General circulation is maintained by the horizontal heating gradients. (say Hadley cell)

Dynamical point of view: hotizontal heating gradients -- horizontal pressure gradients -- large-scale horizontal motion; Geostrophic adjustment process: PGF, Coriolis Force; In lower latitudes: most kinetic energy is quasi-steady, thermally driven circulation -- caused by uneven distribution of heat sources and sinks; Monsoon and ITCZ Mid-latitude: daily change is large: baroclinic waves Frictional dissipation in PBL

4. Thermally driven circulation without rotation

Convergence Divergence Z-coordinate: If

Vertically Averaged Divergence in General Circulation

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