Lesson 5 Reading Guide

Why Does the Wind Blow?

• What causes wind to blow? Wind is caused by the uneven heating of the earth’s surfaces.

• Meteorologists use the word convection to describe the movement of heat through air or water.

• This movement results from temperature differences; this cycle of temperature differences and circulation of air is referred to as a convection current.

• Draw and label sea breezes. Refer to the drawing on page 59.

• When do sea breezes occur? day

• Draw and label land breezes. Refer to the drawing on page 59.

• When do land breezes occur? night

• What are monsoons? Monsoons are very powerful land and sea breezes that change direction with the seasons.

• Name a factor that causes local winds. Refer to paragraph 1 under the grey box. One factor is color. Dark soils absorb heat faster than light green fields do.

• What are global winds? Winds that form over long distances and form between the equator and the poles.

• Global winds are the result of giant convection currents that circulate within the Northern and Southern Hemispheres of the earth.

• What are trade winds? Trade winds are global winds that form because of the earth’s rotation and the sun’s energy.

• What are 2 other names for trade winds?

Westerlies and Easterlies• Westerlies flow from the west to east.

• Easterlies flow from the east to west.• What happens when global winds meet?

Where the westerlies and easterlies meet, weather changes occur.

• What is the jet stream? Long, narrow “tubes” of air in the upper troposphere that contain strong winds

• How does the jet stream help high flying airplanes? Airplanes can follow their paths. It makes it easier to move from west to east.

Weather Fronts• Fronts bring changes in the weather.

They occur when air masses of different temperature, pressure, and humidity conditions collide.

• Fronts form along the boundary between different air masses.

• Cold fronts frequently move fast and cause abrupt changes in the weather including violent thunderstorms or tornadoes.

• Warm fronts typically move slowly, so rainy weather usually stays around for days.

• Stationary fronts, where two different air masses meet, but neither has enough force to move the other, the water vapor in the warm air condenses into rain, snow, fog, or clouds.

• At an occluded front both a cold and a cool air mass collide with a warm air mass, which becomes trapped in the center; the weather at this boundary may bring clouds and rain or snow.

• Label each type of front.

warm front cold front

occluded front

Trouble in Tornado Alley

• Tornado Alley, includes the Central Plains states of Kansas, Oklahoma, Texas, and Missouri.

• In Tornado Alley cool, dry air from the Rocky Mountains and Canada meets warm, moist air from the Gulf of Mexico. (Refer to map on p. 65)