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Regional Gliding School
The pressure of the atmosphere at any The pressure of the atmosphere at any point is due to the weight of overlying point is due to the weight of overlying air. Pressure at the surface of the earth is air. Pressure at the surface of the earth is normally measured by the mercury normally measured by the mercury barometer and is expressed in inches of barometer and is expressed in inches of mercury. The mercury barometer mercury. The mercury barometer consists of an open dish of mercury into consists of an open dish of mercury into which the open end of an evacuated which the open end of an evacuated glass tube is placed. Atmospheric glass tube is placed. Atmospheric pressure forces the mercury to rise in the pressure forces the mercury to rise in the
tube. The great the pressure thetube. The great the pressure the higher higher the column rises.the column rises.
Mercury Barometer
Mercury Dish
Glass Tube
Atmospheric Pressure
Vacuum
Regional Gliding School
PressurePressureForce per unit areaForce per unit area
Inches of MercuryInches of MercuryThe unit used to measure the length of a column of mercury The unit used to measure the length of a column of mercury in the barometer ("Hg).in the barometer ("Hg).
MillibarsMillibarsThe pressure exerted on an area of 1 square cm by a force The pressure exerted on an area of 1 square cm by a force of 1000 Dynes (mb). of 1000 Dynes (mb).
KilopascalsKilopascalsEquals 10 hectopascalsEquals 10 hectopascalsOne hectopascal equals one millibars (hPa).One hectopascal equals one millibars (hPa).
Unit of Measure
Regional Gliding School
ICAO - International Civil Aviation Organization
a)a) Mean sea level pressureMean sea level pressure
29.92”Hg29.92”Hg
1013.2 mb1013.2 mb
101.3 kPa101.3 kPa
c)c) Air is a perfectly Air is a perfectly
dry gasdry gas d)d) Lapse rate isLapse rate is
1.98°C/1000ft1.98°C/1000ft
b)b) Mean sea level Mean sea level temperaturetemperature
15°C15°C
Regional Gliding School
Density is mass per unit volume.
Pressure and Density are directly proportional. As density increases so does pressure.
Regional Gliding School
A
B
C
D
15oC
1.98oC
2.0oC
29.92oC
Let's try a few review questions on Meteorology:
Question #1 - Describe the ICAO mean sea level temperature?
MeteorologyMeteorologyAtmospheric Pressure and DensityAtmospheric Pressure and Density
Flying Scholarship Program
That answer is correct.
Let's move on...
Regional Gliding School
ICAO - International Civil Aviation Organization
a)a) Mean sea level pressureMean sea level pressure
29.92”Hg29.92”Hg
1013.2 1013.2 mbmb
101.3 101.3 kPakPa
c)c) Air is a perfectly Air is a perfectly
dry gasdry gas
d)d) Lapse rate isLapse rate is
1.98°C/1000ft 1.98°C/1000ft
b)b) Mean sea level temperatureMean sea level temperature
15°C15°C
Regional Gliding School
A
B
C
D
Inches of Mercury
Isobar
kilopascals
Both A and C
Let's try a few review questions on Meteorology:
Question #2 - What are the units of measure of pressure?
MeteorologyMeteorologyAtmospheric Pressure and DensityAtmospheric Pressure and Density
Flying Scholarship Program
That answer is correct.
Let's move on...
Regional Gliding School
PressurePressureForce per unit areaForce per unit area
InchesInchesof of MercuryMercuryThe unit used to measure theThe unit used to measure thelength of a column of length of a column of mercury in the barometermercury in the barometer("Hg).("Hg).
MillibarsMillibarsThe pressure exerted on an area of 1 square cm by a The pressure exerted on an area of 1 square cm by a force of 1000 Dynes (mb). force of 1000 Dynes (mb).
KilopascalsKilopascalsEquals 10 hectopascalsEquals 10 hectopascals
One hectopascal equals one millibars (hPa).One hectopascal equals one millibars (hPa).
Unit of Measure
Regional Gliding School
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.
Regional Gliding School
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.
HLIntended Path
Actual Path
HIGH TO A LOW, LOOK OUT BELOW
Regional Gliding School
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.
LOW TO A HIGH, CLEAR BLUE SKY
HL
Intended Path
Actual Path
Regional Gliding School
A
B
C
D
Aerodrome
Area
Sea
Ground
Let's try a few review questions on Meteorology:
Question #3 - The altimeter reads the altitude above level.
MeteorologyMeteorologyAtmospheric Pressure and DensityAtmospheric Pressure and Density
Flying Scholarship Program
That answer is correct.
Let's move on...
Regional Gliding School
Altimeter Setting
The barometric pressure reading is used to adjustthe altimeter for variations in existing atmosphericpressure or to the standard altimeter setting.
If set to the existing pressure it will read the trueelevation of the airport above sea level.
It is measured in inches of mercury.
Regional Gliding School
Let's try a few review questions on Meteorology:
Question #4 - What unit of measure is the altimeter expressed in?
MeteorologyMeteorologyAtmospheric Pressure and DensityAtmospheric Pressure and Density
A
B
C
D
Inches of Mercury
Isobar
kilopascals
Both A and C
Flying Scholarship Program
That answer is correct.
Let's move on...
Regional Gliding School
Altimeter Setting
The barometric pressure reading is used to adjustthe altimeter for variations in existing atmosphericpressure or to the standard altimeter setting.
If set to the existing pressure it will read the trueelevation of the airport above sea level.
It is measured in inches of mercury.
Regional Gliding School
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!
MeteorologyMeteorologyAtmospheric Pressure and DensityAtmospheric Pressure and Density