Atmospheric Pressure and Density 4 3 . Atmospheric Pressure and Density

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.

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

ICAO - International Civil Aviation Organization The ICAO standard atmosphere consists of: a) Mean sea level pressure 29.92”Hg 1013.2 mb 1013.2 hPa b) Mean sea level temperature 15°C c) Air is a perfectly dry gas d) Lapse rate is 1.98°C/1000ft

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

NOTE: You must use the buttons in the Confirmation Stage

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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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.

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

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

NOTE: You must use the buttons in the Confirmation Stage

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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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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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!