for so long that they would run out of water and food for their livestock. Sailors would
toss horses and other animals over the side of the ship after they died. Sailors sometimes
didn’t make it either. On land, these high pressure regions mark the locations of many of
the world’s great deserts, including the Sahara in Africa and the Sonora in North America.
The other low pressure zone is between the Ferrell and Polar Cells at around 50-60o. This
is the usual location of the polar jet stream, where cold air from the poles meets warmer air
from the tropics and storms are common. As the Earth orbits the Sun, the angle of the Sun
shifts between 23.5oN and 23.5oS; in turn, this shift causes the polar jet stream to move. Like
the ITCZ, the position of the polar jet stream moves seasonally, creating seasonal weather
changes in the mid-latitudes.
The direction of the prevailing winds greatly influences the climate of a region. These
winds form the bases of the Hadley, Ferrell and Polar Cells. Winds often bring the weather
from the locations they come from. For example, in California, the predominant winds are
the westerlies. These winds blow in from the Pacific Ocean. The stability of the ocean’s
temperatures moderates California temperatures, so that summers are cooler and winters
are warmer. In the middle of the continent, the winds bring more variable conditions. Local
winds also influence local climate. For example, land breezes and sea breezes moderate
coastal temperatures.
Continental Position
When a particular location is near an ocean or large lake, the body of water plays an
extremely important role in affecting the region’s climate. When a location has amaritime
climateits climate is strongly influenced by the nearby sea: summers are not too hot and
winters are not too cold. Temperatures also do not vary much between day and night. For a
location to have a true maritime climate, the winds must most frequently come off the sea.
Acontinental climateis more extreme, with greater temperature differences between day
and night and between summer and winter.
The ocean’s influence in moderating climate can be seen in the following temperature com-
parisons. Each of these cities is located at 37°N latitude, within the westerly winds. San
Francisco is on the Pacific coast; Wichita, Kansas is in the middle of the North American
continent; and Virginia Beach, Virginia is on the Atlantic coast. San Francisco is cooler in
July and warmer in January than either of the other two cities. This is typical of a maritime
climate; not too hot, not too cold. Wichita has the greatest range of temperatures; the
hottest temperatures in July and coldest in January, which is typical for a continental cli-
mate. Although Virginia Beach is located on the Atlantic Ocean, it has a mostly continental
climate since the westerly winds come off the continent (Table17.1).