Air Pressure and Wind

5th Grade Science

Changes in Air Pressure• Volume• Elevation• Humidity

– Water vapor molecules weigh less than oxygen– Moist air has less pressure than dry air

• Temperature – Hot air molecules speed up and spread out– Hot air weighs less and has less pressure than cold air– WARM AIR RISES

High Pressure, Low Pressure, Isobars, oh my!

• Isobars: areas of equal air pressure on a weather map (white lines)

• High Pressure (H) center of the storm has a higher pressure, winds blow outward from the center in a clockwise pattern

• Low Pressure (L) the center of the storm has a lower pressure, winds blow toward the center in a counterclockwise pattern

Weather Station Model

• Temperature• Wind speed• Wind direction• Air pressure changes• Air pressure

What causes wind?• Wind is named for where it comes from• Air that moves horizontally is wind• Air that rises is an updraft• Air that sinks is a downdraft• Convection cell

– WARM AIR RISES– Unequal heating and cooling

DowndraftUpdraft

Land and Sea Breezes

• Land heats and cools faster than water• Wind that blows from the sea towards land is

called a sea breeze (Day)• Wind that blows from the land towards the

sea is called a land breeze (Night)• Valleys and Mountains: Valley breeze during

the day and mountain breeze at night

Coriolis Effect

• Earth’s rotation causes the wind to curve

• Northern hemisphere curves to the right

• Southern hemisphere curves to the left

Global Wind Patterns

• Coriolis Effect + convection cells = global wind patterns

• We live in the prevailing westerlies

• This means our weather moves from WEST to EAST across the U.S.