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In order to visualize the Hadley Circulation, a rotating tank experiment was set up. We define Hadley Circulation as a "low rotation" experiment since the effect of Earth's rotation is small. Place a bucket of ice in the center of the tank, which will represent the cold poles. Make sure to measure the mass of the ice beforehand (Our mass of ice was 675 grams). The equator will be represented at the edge of the tank, since it is warmer than in the center of the tank. Then, place eight thermometers in the tank to get data on temperature gradient inside of the tank. The set-up is shown as below:
(Top-view of the tank set-up)
(Side-view of the tank and thermometers placement) (Christopoulos, 2014)
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Note that the tank moves in counterclockwise motion in the image below. The crystals move in clock-wise motion, opposite of the tank rotation, but the blue dye moves in the direction of the tank rotation. The crystals represent "Easterly wind" and the blue dye the "Westerly wind."
Note how the cold water would slowly move out from the center at the bottom (such as Blue #1, #2) and the eventually, the temperature of the outermost thermosisters would drop. The trend of the graph clearly decreases over time. There are minor "bumps" in the graph, which could be attributed to the rotation of the tank.
Then, we used the thermal wind equation for water, since water in the tank is an incompressible fluid:
where Ω = 0.1046 rad/sec, α = 207 * 10^-6^ K^-1, and dT/dr = 35.7 C/m. du/dz ended up to be 0.34 s^-1 from those values. The surface velocity was 0.054 m/s. The Hadley circulation is axisymmetric, especially in due to thermal wind balance with the radial temperature gradient.
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