1. Air Pressure

2. Air pressure at sea level:
14.7 pounds per square inch 1013 millibars 29.9 inches of Mercury 1 atmosphere

3. Pressure with Height Pressure decreases with increasing altitude
The number of air molecules above a surface changes as the height of the surface above the ground changes
Most of the atmosphere's molecules are held close to the earth's surface by gravity. Because of this, air pressure decreases rapidly at first, then more slowly at higher levels.

4. Increase Altitude Decrease Air Pressure

5. High Pressure Centers also known as anticyclones
A high pressure center is where the pressure has been measured to be the highest relative to its surroundings. That means, moving in any direction away from the "High" will result in a decrease in pressure.
A high pressure center also represents the center of an anticyclone and is indicated on a weather map by a blue "H".

6. Low Pressure Centers also known as cyclones
A low pressure center is indicated on a weather map by a red "L" and winds flow counterclockwise around a low in the northern hemisphere

7. Which column is more representative of the atmosphere above a high pressure center? Which one is more likely to be found over a low pressure?

8. Analysis of a Pressure Field:

9. H L Pressure ALWAYS goes HIGH to LOW HIGH PRESSURE CENTER
LOW PRESSURE CENTER
Pressure ALWAYS goes HIGH to LOW

10. Isobars lines of constant pressure
Isobars are drawn at intervals of every 4 mb

11. The rules for drawing isobars are: Isobar lines may never cross or touch. Isobar lines may only pass through pressures of or - 4. In other words, allowable lines are 992, 996, 1000, 1004, 1008, and so on.

12. Learning Lesson: Drawing Conclusions - Surface Air Pressure Map
                                                                                                    
Learning Lesson: Drawing Conclusions - Surface Air Pressure Map
                                                                                                    
Learning Lesson: Drawing Conclusions - Surface Air Pressure Map
                                                                                                    
Learning Lesson: Drawing Conclusions - Surface Air Pressure Map
                                                                                                    
Learning Lesson: Drawing Conclusions - Surface Air Pressure Map
                                                                                                    

14. Solution 4