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MET 2204 METEOROLOGY. Presentation 3: Atmosphere. Recapitulate. Lets recap what we have done last week: Definition of Meteorology Different between Weather and Climate Importance of Meteorological in Aviation. Presentation Outline. Introduction Layers of Atmosphere

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Met 2204 meteorology


Presentation 3: Atmosphere

Presented by Mohd Amirul for AMC


  • Lets recap what we have done last week:

    • Definition of Meteorology

    • Different between Weather and Climate

    • Importance of Meteorological in Aviation

Presentation outline
Presentation Outline

  • Introduction

  • Layers of Atmosphere

  • Variation in Atmosphere

  • Air Stability

  • Conclusion

Part 1

Part 2

Learning outcomes
Learning Outcomes

  • At the end of this session, student should be able to:

    • Outline the composition and structure of earth atmosphere

    • Identify the temperature, humidity, pressure, and density variation vertically and horizontally in atmosphere.

    • Understand the concept of air stability.

Presented by Mohd Amirul for AMC


  • Earth view:

    • Altitude

      • Vertical height

        from earth


    • Longitude

    • Latitude


  • Air is one of the primary things that makes life on Earth possible. Air is a synonym for atmosphere. The Earth’s atmosphere or air is made up of a variety of gases and other particles.


  • What is the Atmosphere??

    • layer of gases surrounding the planet Earth that is retained by Earth's gravity.

  • Gases in atmosphere:

    • 78% - Nitrogen

    • 21% - Oxygen

    • 1% - Other gases (Argon,

      Carbon Dioxide, Neon,



*In fact the air never completely dry!! (it contains some water vapor 0-5% by volume)

*This proportion remains constant until at least 60 km – 70 km altitude.


  • Troposphere

    • Temperature will decrease with altitude.

    • 75% of weight of atmosphere.

    • Contains almost all weather

    • Altitude (height) vary with:

      • Latitude: lower at poles and higher at equatorial

      • Seasons: higher in summer than winter

    • Almost all clouds in this layer.

    • Most commercial aircraft flying in this altitude


  • Tropopause

    • Boundary between troposphere and stratosphere.

    • Temperature stop to decrease.

    • Not a continuous line

      (Usually a gap at 40° of latitude between polar and tropical)


  • Height vary with:

    • Latitude:

      • Thickest in tropic (20 km or 65000 ft from sea level)

      • Thinnest near poles (7km or 23000ft from sea level)

  • Height of tropopause is important because it marks:

    • Max. Height of Cloud.

    • Presence of Jetstream.

    • Presence of Clear Air Turbulence (CAT).


  • Stratosphere

    • Very small increase in temperature (almost constant) except at the top where temperature is zero at 50 kms.

Variation in atmosphere
Variation in Atmosphere

  • The earth’s atmosphere varies vertically and horizontally in

    • Temperature

    • Pressure

    • Density

    • Humidity


  • What are the differences between heat and temperature?

Temperature scale of measurement
Temperature Scale of Measurement

  • Fahrenheit scale: from -32 to 212 deg

  • Celcius(centigrade) scale: from 0 to 100 deg

  • Kelvin (absolute) scale: from -273 to 373 deg


  • Energy transmit in the form of rays, waves, or particles.

  • Solar = relating to the sun

  • Terrestrial = relating to the earth (e.g. land)

Solar radiation sr


Solar Radiation (SR)

  • The sun is a main source of heat for earth

  • Emitted from the sun to the earth.

  • Much of SR reflected back, absorbed by atmosphere upper layers

  • Only average 45% SR reach the earth surface

Terrestrial radiation tr


Terrestrial Radiation (TR)

  • Energy emitted from earth to atmosphere

Solar and terrestrial radiation


Solar and Terrestrial radiation



Difference between solar terrestrial radiation on the earth surface


Difference between Solar & Terrestrial Radiation on the Earth Surface













Temperature variations in atmosphere
Temperature Variations in Atmosphere

  • Temperature will vary with:

    • Diurnal Variation (Time of Day)

    • Latitude

    • Season

    • Nature of Surface

    • Altitude.

Temperature variation with diurnal
Temperature Variation with Diurnal

  • Change of temperature from day to night (brought by daily rotation of earth):

    • Day:

      • The earth receives heat during the day by solar radiation and losses heat by terrestrial radiation.

      • Warming and cooling depend on imbalance of solar and terrestrial radiation.

      • During day, solar radiation will be more than terrestrial radiation. Therefore surface becomes warmer.


  • Night:

    • Solar radiation stop. But terrestrial radiation continues and cool the surface. Thus temperature will drop.

    • Cooling continues after sunrise until solar radiation exceeds terrestrial radiation.


Diurnal variation of surface temperature

The warmest time about 1500h & coldest at 0500h

At both of these times the incoming SR & outgoing TR are roughly balance

Temperature variation with season
Temperature Variation with Season

  • The earth revolves in a complete orbit around the sun

  • Northern Hemisphere is warmer in June, July and August because it receives more solar energy

  • Southern Hemisphere is colder in December, January and February because it receives less solar energy.

Temperature variation with latitude
Temperature Variation with Latitude

  • The sun is nearly overheaded in equatorial regions at latitude.

  • Therefore, equatorial regions will receive more radiant energy and are warmest.

  • Poles will receive less radiant energy.

Temperature variation with topography
Temperature Variation with Topography

  • Different earth surfaces have different capabilities in absorption and radiation of energy.

  • Major difference applies between land & water

  • Land -heats & cools quickly

  • Sea/water surfaces- heats & cools longer

  • Thus, water absorb and radiates energy with less temperature change than land.


  • Land surface – bare rock, sand and concrete attain higher temperature.

  • Wet soil and grassland – attain lower temperature.

  • Snow-

    • reflect solar radiation (colder)

    • However snow doesn’t prevent the earth from radiating its heat and therefore the air over snow will become colder day by day.

Temperature variation with altitude
Temperature Variation with Altitude

  • When the altitude increase the temperature will decrease (mostly in troposphere).

  • We define this as lapse rate.

  • Average lapse rate = 2°C per 1000 ft.


  • But in fact, temperature increase with height sometimes.

  • We call this as inversion (lapse rate are inverted)

    • E.g. The ground radiates and cools much faster than air in the cool night. Air contact with ground becomes cold while temperature a few hundred feet above change a little. So this time, temperature increase with altitude.

      *Notes: Inversion are common in stratosphere


  • Atmospheric Pressure:

    • The weight of air in the column above unit area of earth surface.

    • Pressure is the force per unit area:


P =



  • Pressure is the cumulative effect of air molecules colliding with a surface.

  • Air Pressure Depends On:

  • The mass of the molecules

  • (density)

  • Temperature

Pressure scale of measurement
Pressure Scale of Measurement

  • Pressure can be in the unit of millimeter mercury (mmHg), atmosphere (atm), Pascal (Pa) , milibar (mb), Inch of mercury etc.

  • In meteorology we us the units millibars(mb) / hectopascal (hp)

  • “Typical” sea-level pressure (reference standard) is approximately 1013 mb or 29.92 inch. Of mercury.

Pressure measurement instrument
Pressure Measurement Instrument

  • Device to measure

    - Mercurical Barometer

    - Aneroid Barograph


  • Mercurical Barometer

    • Pressure is determine by balancing air pressure against weight of a column of mercury in evacuated glass tube.

    • Greater air pressure will increase the rise of mercury within tube.

    • Always be vertical

      • Mount in the aircraft using gimbals. So it keep vertical despite rolling/pitching.


  • Aneroid Barometer

    • Consist of thin walled metal box. It contracts and expands depend on the pressure.

    • Connect to the dial by lever (rigid bar pinned) system.


  • Barograph (weather instrument)

    • Used for recording atmospheric pressure.

    • Barometer

      • Allow us to measure pressure tendency.

      • Important forecasting tool.



Pressure variation in atmosphere
Pressure Variation in Atmosphere:

  • Pressure will vary with:

    • Altitude

    • Temperature

    • Diurnal Variation

Pressure variation with altitude
Pressure Variation with Altitude

  • Weight are less when increase in altitude.

  • At troposphere (pressure decrease 1 inch for each 1000 ft increase in altitude)

  • Higher altitude, slower rate of decrease.

Pressure variation with temperature
Pressure Variation with Temperature

  • Rate of decrease of pressure with height in warm air is LESS than standard.

  • Rate of decrease of pressure with height in cold air is GREATER than standard.


  • Horizontal Difference in Temperature:

    • Creates horizontal difference in pressure.

Consider two columns of air







Pressure is the weight of the

air above you.

Warm one side and cool

the other side. Maintain

a constant surface pressure.


Consider an airplane flying at a

constant height. What are the







So we see a high pressure, at the altitude of the plane, in the

warm column and a low pressure in the cool air.







The horizontal difference in temperature creates

a horizontal difference in pressure.

Pressure variation with diurnal
Pressure Variation with Diurnal

  • Change of pressure during DAY

    • 1mb-3mb (max. 3mb usually in tropics)

      So what about change in pressure during NIGHT??

      -Ans: It’ll be lower than change of pressure during day.

Pressure analysis
Pressure Analysis

  • There is two types of pressure considered in aviation:

    • QFE: barometric pressure at the level of airfield

    • QFF: barometric pressure at stated place based on Mean Sea Level (MSL). (QFE converted to MSL).

      *Mean sea level (MSL) is a measure of the average height of the ocean's surface


  • Isobars

    • A line joining places of the same atmospheric pressure.


  • Use of Isobar:

    • reveal surface pressure pattern

    • Deduce wind condition (e.g. Isobar closer, wind will blow harder)


  • Density : mass per unit volume (m/v)

  • Density directly proportional to pressure

  • Density inversely proportional to temperature.

    • When air heated (temperature increase), the volume of air will expand. Therefore the mass of air decreases and lead to density decreases.

Density variation in atmosphere
Density Variation in Atmosphere:

  • Density will vary with:

    • Altitude

    • Latitude

Density variation with altitude
Density Variation with Altitude

  • Air near surfacemore dense than air at higher surface.

Density variation with latitude
Density Variation with Latitude

  • At surface: density increase with increase in latitude

  • At 26000 ft (7.9 km): density constant with increase in latitude

  • Above 26000 ft (7.9 km): : density decrease with increase in latitude

Change of density affect the a c operation
Change of Density affect the a/c operation

  • A/C and engine performance

    • Low density will reduce lift, increase take off run, and reduce maximum takeoff weight.

    • Most likely to occur at hot airfields (e.g. Africa, South East Asia)


  • Humidity is the amount of water vapor in the air.

  • Water vapor: water in its gaseous state

Measurement of humidity
Measurement of Humidity

  • Humidity can be measured in the following ways:

    • Absolute humidity

      • The weight of water vapor in unit volume of air usually expressed in grammes per cubic metre.

    • Relative Humidity

      • The amount of water vapor in a volume of air divided by the maximum amount of which that volume can hold at that temperature and expressed as a percentage. 100% relative humidity equals saturation.

        (If rel. humidity is less than 100%: air dry

        if rel. humidity is 100%: air wet)


  • Humidity Mixing Ratio

    • The weight of water vapor in unit mass of dry air, usually expressed in grammes per kg.

Diurnal variation with humidity
Diurnal Variation with Humidity

  • During day, relative humidity decrease as temperature decrease.

  • When temperature falls after 3.00 pm, the relative humidity will increase.

  • At night, relative humidity higher than day (formation of mist and fog especially in autumn and winter)

Air stability
Air Stability

  • Idea:

    • Stable: When put a disturbance it can go back to original position.

    • Unstable: Continues to move away from a normal position.

  • Stable air : resist any upward or downward displacement

  • Unstable air: Allows upward or downward disturbance to grow into vertical or circulation flow.


  • When cool air mass moves over warm region/surface, it will create an air mass less stable as temperature change quite rapidly.

  • If warm air mass moves over a cold region/surface, air becomes more stable (as convective (transfer of heat through a fluid) process slow)

    *air mass: large volume of air where the humidity and temperature are more/less constant.


  • The Earth’s atmosphere or air is made up of a variety of gases, other particles and in form of several layers.

  • The physical condition of atmosphere different for each layer.

  • The earth’s atmosphere varies vertically and horizontally in temperature, pressure, density and humidity.

Presented by MohdAmirul for AMC

Key points
Key Points

  • What is the Atmosphere?

  • Composition of Atmosphere

  • Layers of Atmosphere

  • Variation in Atmosphere

  • Air stability

Presented by Mohd Amirul for AMC

End of presentation 2
End of Presentation #2

5 Minutes for Q/A session

Presented by Mohd Amirul for AMC

Quote of the day
Quote of the Day

  • Experience is that marvelous thing that enables you to recognize a mistake when you make it again.

    Franklin P. Jones

Presented by Mohd Amirul for AMC