1. Weather Lesson Two
Pressure and Wind

2. 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 inches of Mercury or millibars.

3. 29.92 in of Hg or mb

6. 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

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

10. PRESSURE AFFECTED BY:
1) Temperature

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

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

14. As water in the air INCREASES, pressure _____________.
DECREASES

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

16. As altitude increases, pressure _________
decreases

17. 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.

18. Anemometer
Wind Vane

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

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