The General Circulation of the Atmosphere

Introduction

The circulation of the atmosphere across the globe is complex and long-term weather prediction is impossible in such a chaotic system. However, large-scale structures in atmospheric circulation are stable over time and can be predicted from a basic ideas about energy balance in the Earth system. 

These constraints are developed in three other tank experiments described on this wiki: Balanced Motion, Fronts and Convection. Bringing these concepts together into a general circulation model explains the existence of some persistent features of the atmosphere, including the subtropical and polar jet streams, the trade winds, and the midlatitude bands in which rotating weather systems can be observed.

Tank Experiment

Two rotating tank experiments were set up. Tank rotation speed was the important parameter varied: one tank rotated at a speed of 1 

LaTeX Unit
body rad s^{-1}

 and the other at 0.1 

LaTeX Unit
body rad s^{-1}

. 

Slow Rotation Experiment

A metal canister of radius 12

LaTeX Unit
body cm

 was placed in the center of a tank of radius 22 

LaTeX Unit
body cm

. Six HOBO temperature sensors were taped to the tank in the arrangement shown in the figure below. The thermometer cables were taped along the bottom and edge of the tank to minimize interference with water flow. The tank was filled with still water to a height of 12.6 

LaTeX Unit
body cm

.

...

The surface speed of the water was measured by tracking black paper dots in the Particle Tracker application. The speed on the tank floor was measured by tracking the purple pigment trails from granules of potassium permanganate using timecoded screenshots in the Particle Tracker.  Water speed shear between the top and bottom of the tank was measured with drops of blue food dye. 

 

Fast Rotation Experiment

A metal canister of radius 18 

LaTeX Unit
body cm

 was placed in the center of a tank of radius 31

LaTeX Unit
body cm

. Again six HOBO temperature sensors were taped to the tank in the arrangement shown in the figure below. The  This arrangement differs from the first experiment: thermometers 1 through 5 were placed in a line radially from the tank center; thermometer 6 was placed between 3 and 4, on the bottom of the tank but 10

LaTeX Unit
body cm

 further in the clockwise direction. This arrangement was devised to capture thermal signatures of the eddies that were hypothesized to form.  Thermometer 1 was placed at a height of 11 

LaTeX Unit
body cm

 and thermometer 5 at a height of 9 

LaTeX Unit
body cm

. The tank was filled with still water to a height of 14

LaTeX Unit
body cm

 with water

The rotating table was spun up to 1 

LaTeX Unit
body rad s^{-1}

 and allowed to spin until a paper dot placed on the surface of the water appeared motionless to the overhead corotating camera. In this setup, the speed The speed of the corotating camera was synced electronically with the table rotation speed through a computer interface. The canister was filled with 521.6

LaTeX Unit
body g

 of ice and then with water.

Surface speed, bottom speed and shear were measured as in the previous experiment: paper dots, permanganate granules and food dye, respectively. Two colors of food dye were used to illustrate eddy formation: blue dropped in the colder water near the canister and red in the warmer water near the outside edge.  

Results

Slow Rotation Experiment

Image AddedImage Added

Fast Rotation Experiment

Image AddedImage Added

 

Bibliography