Weather Lesson Two Pressure and Wind

PRESSURE Force at which the weight of the atmosphere pushes down upon Earth’s surface. Measured with a barometer. Standard pressure at sea level is 29.92 inches of Mercury or 1013.2 millibars.

29.92 in of Hg or 1013.2 mb

Let’s enlarge one section! Millibars Scale: Go Up By 1’s Inches of Hg Scale: Go Up By 0.01’s 1003.0 1002.0 29.59 29.58 1001.0 29.57 29.56 29.55 29.54 29.53 29.52 29.51

What is the pressure 10 miles above Earth’s surface?

PRESSURE AFFECTED BY: 1) Temperature

As temperature INCREASES, density decreases, so hot air rises, therefore pressure _____________. HOT AIR RISES – LOW PRESSURE COLD AIR SINKS – HIGH PRESSURE

1) Temperature 2) Moisture Content PRESSURE AFFECTED BY: 1) Temperature 2) Moisture Content

As water in the air INCREASES, pressure _____________. DECREASES

1) Temperature 2) Moisture Content 3) Altitude PRESSURE AFFECTED BY: 1) Temperature 2) Moisture Content 3) Altitude

As altitude increases, pressure _________ decreases

WIND The horizontal movement of air parallel to Earth’s surface. Wind speed is measured with an anemometer. Wind direction is measured with a wind vane. Winds are named for the direction from which they come.

Anemometer Wind Vane

Winds always blow from HIGH to LOW pressure. Ground Surface Winds always blow from HIGH to LOW pressure.

WIND SPEED Depends on pressure difference between two points. The GREATER the pressure difference, the ___________ the wind speed. GREATER