ATOC 4720 class 38 1 Thermally driven circulation

ATOC 4720 class 38 1. Thermally driven circulation in the absence of rotation 2. Generation of kinetic energy

In the previous class: Primitive equations: ( )

1. Thermally driven circulation without rotation (f=0) Lab experiment 1: Energetics: available potential energy

Energetics for large scale atmospheric circulation (f=0) Available potential energy Kinetic energy; m=1 Fluid motion. Assume no friction, what will happen?

Oscillate forever because of E With friction: equilibrium state -- state of rest Random molecular motions Potential energy(PE) Kinetic energy internal energy Analagous to atmosphere: symmetric ITCZ; Question: Why do atmosphere is in quai-steady Motion, rather than a state of rest?

Answer: In real atmopshere, available potential energy is constantly replenished by diabatic heating Experiment 2: A steady-state HEAT Sink HEAT Source

N pole EQ S pole Minimum (net loose: sink) Solar radiation maximum (earth surfacenet gain: source) Minimum (net loose: sink)

Net+Latent heat EQ Pole Atmosphere: potential temperature rather than temperature Once motion starts: rate of available PE = dissipation Use primitive equations for explanation.

2. Generation of kinetic energy (f=0) Pressure surfaces PE -- KE(Kinetic energy) : work done by PGF

Ignore other horizontal forces and f=0 (CF=0): Work done for unit mass unit time Type (a): thermally direct; Type (b): thermally indirect

Convergence Divergence Z-coordinate: If