Basics of Environmental Science

58 / Basics of Environmental Science

momentum. These tend to exaggerate the undulations, which become extreme (3). Finally (4), the
wind pattern fragments into cells. After this, the jet stream disappears for a short time, then re-
establishes itself and the index cycle repeats. During 1, surface pressure systems and the weather
associated with them move steadily in an easterly direction, but during 2 and 3 the move-ment
becomes more irregular, with latitudinal deviations. In 4, the weather becomes almost stationary,

Figure 2.18 General circulation of the atmosphere

Note: ITCZ=intertropical convergence zone

Figure 2.19 The development of cells in jet streams and high-level westerlies