1. Circulation in the Atmosphere

2. Wind
Wind is the horizontal movement of air and it drives circulation in the atmosphere
Air moves from areas with higher pressure to areas with lower pressure
This is caused by uneven heating of the Earth’s surface and is what creates wind

3. Mapping Wind and Pressure
Wind and pressure are represented on maps using isobars
These maps work just like topographic maps with isobars that are closer together = steep pressure gradients and faster winds
The direction of the wind is indicated by flags on the map

4. The Coriolis Effect
Wind doesn’t move at a right angle to the gradient created by pressure
Due to the rotation of the Earth, wind moves in a curving path = Coriolis effect (Fig 13.4)

5. The Coriolis Effect
The Coriolis effect only changes wind direction, not wind speed
However, the faster the wind, the more it will curve
It is also strongest at the poles and weakest at the equator

6. Global Circulation
Distinct patterns form around the Earth due to a combination of low and high pressure bands and the Coriolis effect
The bands are caused by convection currents on a large scale within the atmosphere
Each “bubble” of circulating air is called a cell

7. Global Circulation
Near the equator there is a band of low pressure called the equatorial low that causes all the rain around the equator
At 30° north and south of the equator there are bands of high pressure called subtropical highs that create the deserts in Africa and Australia

8. Global Circulation
Winds deflected due to the Coriolis effect from the tropics and the poles meet in a region low pressure region called the subpolar low causing storms
There is a polar high at each of the poles, which produces the winds that travel to the subpolar low
See Fig 13.12

9. Global Circulation
The cells of air around the poles are called Polar cells
The cells of air in the mid-latitudes are called Ferrell cells
The cells of air near the equator are called Hadley cells