...
The temperature of the air in the atmosphere does not gradually warm from the poles to the equator, but instead there is a sharp gradient between the cold air at the poles and the warmer air just south:. As warmer air is less dense than cold air, the meeting of warm and cold air in the atmosphere produces a density interface like that seen in the lab. The whole system is rotating with the Earth, causing the formation of fronts.
.
Figure 6.1: Left: Air temperature at 500mb for the Northern hemisphere in January. The change in temperature between the cold air at the North pole and the warmer air near the equator occurs only in the midlatitudes; otherwise, there is essentially no temperature gradient. This is because of the same phenomenon driving what we saw in the lab; Coriolis forces due to Earth's rotation keeps the dense cold air at the poles in fronts. Right: Potential air temperature as a function of pressure and latitude. Potential temperature is preserved under adiabatic processes and is therefore a better indicator of heat transport than temperature. Between 20 and 60 degrees latitude, there is a sharp potential temperature gradient where the polar front and warm air from south latitudes meet, creating a slope similar to that seen in the lab experiment.
. 
Figure 6.2: Left: Where the temperature gradient is largest, the wind speeds are also greatest. At around 60 degrees latitude, this temperature gradient produces the polar jet stream, which consists of powerful westerly winds. Just as in the lab, the boundary of the dense air in the polar cell forms a sloped boundary with the less dense warm air from the Ferrel cell. Right: Wind speed as a function of pressure and latitude, showing how both powerful and contained the jet stream is.
7 Polar Oceanic Front