1. Atmospheric Pressure and Density4 3 .
Atmospheric Pressure and Density

2. Mercury Barometer
The pressure of the atmosphere at any point is due to the weight of overlying air. Pressure at the surface of the earth is normally measured by the mercury barometer and is expressed in inches of mercury. The mercury barometer consists of an open dish of mercury into which the open end of an evacuated glass tube is placed. Atmospheric pressure forces the mercury to rise in the tube. The great the pressure the higher the column rises.
Mercury Dish
Glass Tube
Atmospheric Pressure
Vacuum

3. Unit of Measure Pressure Inches of Mercury Millibars Kilopascals
Force per unit area
Inches of Mercury
The unit used to measure the length of a column of mercury in the barometer ("Hg).
Millibars
The pressure exerted on an area of 1 square cm by a force of 1000 Dynes (mb).
Kilopascals
Equals 10 hectopascals
One hectopascal equals one millibars (hPa).

4. ICAO - International Civil Aviation Organization
The ICAO standard atmosphere consists of:
a) Mean sea level pressure
29.92”Hg mb
101.3 kPa
b) Mean sea level temperature
15°C
c) Air is a perfectly
dry gas
d) Lapse rate is
1.98°C/1000ft

5. Density Pressure and Density Density is mass per unit volume.
Pressure and Density are directly proportional. As density increases so does pressure.

6. NOTE: You must use the buttons in the Confirmation Stage

7. Meteorology Atmospheric Pressure and Density
Let's try a few review questions on Meteorology:
Question #1 - Describe the ICAO mean sea level temperature? A
15oC B
1.98oC C
2.0oC D
29.92oC

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12. Meteorology Atmospheric Pressure and Density
Let's try a few review questions on Meteorology:
Question #2 - What are the units of measure of pressure? A
Inches of Mercury B
Isobar C
kilopascals D
Both A and C

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17. Altimeter Setting
The barometric pressure reading is used to adjust the altimeter for variations in existing atmospheric pressure or to the standard altimeter setting.
If set to the existing pressure it will read the true elevation of the airport above sea level.
It is measured in inches of mercury.

18. HIGH TO A LOW, LOOK OUT BELOW
Meteorological Aspects of the Altimeter
When flying from an area of high pressure to an area of low pressure the altimeter will read higher than what the aircraft is actually flying. H L
Intended Path
Actual Path
HIGH TO A LOW, LOOK OUT BELOW

19. LOW TO A HIGH, CLEAR BLUE SKY
Meteorological Aspects of the Altimeter
When flying from an area of low pressure to an area of high pressure the altimeter will read lower than what the aircraft is actually flying. H L
Intended Path
Actual Path
LOW TO A HIGH, CLEAR BLUE SKY

20. NOTE: You must use the buttons in the Confirmation Stage

21. Meteorology Atmospheric Pressure and Density
Let's try a few review questions on Meteorology:
Question #3 - The altimeter reads the altitude above level. A
Aerodrome B
Area C
Sea D
Ground

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26. Meteorology Atmospheric Pressure and Density
Let's try a few review questions on Meteorology:
Question #4 - What unit of measure is the altimeter expressed in? A
Inches of Mercury B
Isobar C
kilopascals D
Both A and C

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31. Meteorology Atmospheric Pressure and Density Congratulations!!
You have now completed the Atmosphere Pressure and Density lesson of the Meteorology Module. Of course, this lesson is always available to you for future reference if required.
You are now ready to move along to the next Meteorology lesson you have not completed or to any other module you wish. You can advance to the Self Test Module if you feel ready to challenge the final exam.
Good Luck!