Zonally (east/west) averaged horizontal and vertical winds

• Shading is zonal wind (positive means westerly, moving out of screen) and arrows denote meridional (north/south) and vertical winds.
• Recall vertical winds are ~100 times slower than horizontal. Also the vertical scale is greatly stretched: 90°S to 90°N is ~20,000km while 1000mb up to 200mb is less than 20km
• The only very obvious meridional circulation cell is the winter-hemisphere Hadley cell. The Ferrel cells and polar cells are not clearly apparent.
• The subtropical jet streams are obvious but the polar jets are not. The polar jets tend to meander more north/south so that their winds are smeared out more in the zonal average compared to the subtropical jets.
• Depending on the season the jets and the Hadley circulations migrate north/south. The maximum surface convergence and rising motion of the ITCZ is around 7-10° into the summer hemisphere.
• Both the Hadley cell and the jet in the winter hemisphere are stronger in the winter hemisphere because of the greater temperature contrast between low and high latitudes there. The greater temperature gradient leads to greater pressure gradients aloft, which cause the jet to be stronger. The Hadley cells exist to transport heat poleward, thus they are stronger when the temperature gradient is greater.