Environmental Engineering Reference
In-Depth Information
rapid temperature gradient. Typically the westerly jets are connected with the zone of
maximum slope or fragmentation of the tropopause, which coincides with the maximum
poleward temperature gradient. They can lead to intense accelerations (and decelerations)
of air in their vicinity. As we shall see later, when air is forced to change its rate of flow,
tropospheric vertical motion may be started. In turn this may influence events at lower
levels. The tropical easterly jet forms in summer near the tropopause from southeast Asia,
India and into Africa. Its origins are probably related to the warmer atmosphere to the
north derived from heating over the Tibetan plateau and over the Sahara.
Aircraft navigation makes good use of the westerly jets by avoiding them when flying
east to west and flying within them in the reverse direction. Over the North Atlantic, the
journey from New York to Europe is about an hour less than from east to west.
Figure 6.17
(above) Mean 500 hPa contours in January for
the northern hemisphere. Units are decametres.
Source: Boville and Randel (1986).
