Circulation in the Atmosphere

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

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

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)

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

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

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

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

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