... and top is still 500 mb, the vertical pressure gradient is smaller Fig 4- 7 4. 4 The distribution of pressure (cont.) Fig 4- 8 The gradual poleward decrease in mean temperature results in denser ... greater than the Coriolis force and the air turns to its left in the Northern Hemisphere Fig 4- 14 4.7 Near-surface wind • Geostrophic flow cannot exist near the surface • Friction slows the wind, ... SH (c) and (d) Fig 4- 17 4. 8 Cyclones, anti-cyclones, troughs, and ridges (cont.) Elongated zones of high and low pressure are called ridges (a) and troughs (b), respectively 4. 8 Cyclones, anti-cyclones,...