CK12 Earth Science

Table 16.3: (continued)

F Scale (km/hr) (mph) Damage

F4 333-419 207-260 Devastating - houses

leveled, cars thrown

F5 420-512 261-318 Incredible - struc-

tures fly, cars be-

come missiles

F6 >512 >318 Maximum tornado

wind speed

Cyclones

AcycloneisasystemofwindsrotatingcounterclockwiseintheNorthernHemispherearound
a low pressure center. On the east side, winds come from the south and so are warmer than
those on the west side. The swirling air rises and cools, creating clouds and precipitation.
Cyclones can be the most intense storms on Earth. There are two types of cyclones: middle
latitude cyclones and tropical cyclones. Mid-latitude cyclones are the main cause of winter
storms in the middle latitudes. Tropical cyclones are also known as hurricanes.

Ananticyclone, as you might expect, is the opposite of a cyclone. An anticyclone’s winds
rotate around a center of high pressure. Air from above sinks to the ground to fill the space
left when the air moved away. High pressure centers generally have fair weather. Anticyclone
winds move clockwise in the Northern Hemisphere, exactly the opposite of a cyclone. Since
winds on the east side of the anticyclone come from the north and those on the west side
come from the south, the east side tends to be colder than the west side of the high.

Middle Latitude Cyclones

Middle latitude cyclones, sometimes called extratropical cyclones, form at the polar front
when the temperature difference between two air masses is large. These air masses blow past
each other in opposite directions. Winds are deflected by Coriolis Effect—to the right in the
Northern Hemisphere and to the left in the Southern Hemisphere. This causes the winds
to strike the polar front at an angle. Warm and cold fronts form next to each other. Most
winter storms in the middle latitudes, including most of the United States and Europe, are
caused by middle latitude cyclones (Figure16.30).

The warm air at the cold front rises and creates a low pressure cell. Winds rush into the
low pressure and create a rising column of air. The air twists, rotating counterclockwise in