Wind! Horizontal movement of air across surface Pressure gradient force = pressure change over the distance it takes to change Air flows from high to low pressure due to pressure gradient Greater the pressure difference, stronger the wind The unequal heating of Earth’s surface generates pressure differences. Solar radiation is the ultimate energy source for most wind.

Wind Instruments Wind direction is measured with a wind vane Winds are named by where they come FROM Ex. “Westerly” comes FROM the west Wind speed is measured with an anemometer

Isobars Lines of equal pressure Fastest winds occur when lines are closest together (pressure gradient increases) High Pressure Gradient

Pressure Systems Winds blow TOWARD the center of a LOW pressure system (CONVERGENT) Winds blow AWAY from the center of a HIGH pressure system (DIVERGENT) Rising air (low pressure system) is associated with cloud formation and precipitation, whereas sinking air (high pressure system) produces clear skies.

DIVERGENT CONVERGENT

30.0 29.8 FASTEST SPEED 29.6 NE WIND N W E S

29.8 29.6 SW WIND 30.0 N W E FASTEST SPEED S

Pressure Systems L 29.8 FASTEST SPEED 29.6 30.0 Winds blow Toward The center S

Observe the Jet Stream

What do these paths have in common? You will remember these hurricanes from the Hurricane Tracking Lab that you completed back in September. What do these paths have in common?

Watch Sandy at about 3:30

Why did Sandy turn sharply towards the west?