MET 2204METEOROLOGY

Presentation 3: Atmosphere

1Presented by Mohd Amirul for AMC

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• Variation in Atmosphere• Air Stability• Conclusion

Part 1

Part 2

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.

•

4Presented by Mohd Amirul for AMC

Introduction

• Earth view:– Altitude

• Vertical height from earth

surface.

– 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.

Cont.

Cont.• 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, Helium)

*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.

Cont.

Layers (Structure) of Atmosphere

• 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

Cont.

• 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)

Cont.

– 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).

Cont.

• Stratosphere– Very small increase in

temperature (almost constant) except at the top where temperature is zero at 50 kms.

Cont.

Variation in Atmosphere

• The earth’s atmosphere varies vertically and horizontally in

– Temperature– Pressure– Density

– Humidity

Temperature

Definition• What are the differences between heat and

temperature?

HEAT TEMPERATURE

•It is the energy of a material which is stored in the form of heat

•Heat is what you feel (Sensible Heat).

•Refer to measurement how hot a particular subtance is.high temperature indicate more heat energy than low temperature

•Temperature is a measure the level of heat content of a body

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

Cont.

Radiation

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

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

20

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

Cont.

21

Terrestrial Radiation (TR)

• Energy emitted from earth to atmosphere

Cont.

22

Solar and Terrestrial radiation

SOLAR RADIATION

TERRESTRIAL RADIATION

Cont.

23

Difference between Solar & Terrestrial Radiation on the Earth Surface

SUNRISE SUNSETNOON

RA

DIA

TIO

N

OUTGOING (TR)

INCOMING (SR)

INCOMING =OUTGOINGMIN TEMP

SUNRISE +1HR

INCOMING=OUTGOINGMAX TEMP

1300H-1500H

Cont.

Temperature Variations in Atmosphere

• Temperature will vary with:– Diurnal Variation (Time of Day)– Latitude– Season– Nature of Surface– Altitude.

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.

Cont.– 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

Cont.

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

• 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

• 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

• 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.

Cont.• 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• 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.

Cont.• 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

Definition

• Atmospheric Pressure:– The weight of air in the column above unit area of

earth surface.– Pressure is the force per unit area:

Cont.

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

Air Pressure Depends On:• The mass of the molecules (density)

• Temperature

• 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 Scale of Measurement

Cont.

Pressure Measurement Instrument• Device to measure

- Mercurical Barometer- Aneroid Barograph

Cont.• 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.

Cont.• 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.

Cont.• Barograph (weather instrument)

– Used for recording atmospheric pressure.– Barometer

• Allow us to measure pressure tendency.• Important forecasting tool.

Barograph Barometer

Pressure Variation in Atmosphere:

• Pressure will vary with:– Altitude– Temperature– Diurnal Variation

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.

• 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.

Pressure Variation with Temperature

Consider two columns of air

Ps Ps

Pressure is the weight of theair above you.

Ps Ps

Cool Warm

Warm one side and coolthe other side. Maintaina constant surface pressure.

• Horizontal Difference in Temperature:– Creates horizontal difference in pressure.

Cont.

Ps Ps

Cool Warm

Consider an airplane flying at aconstant height. What are thepressures?

Cont.

So we see a high pressure, at the altitude of the plane, in thewarm column and a low pressure in the cool air.

Ps Ps

Cool Warm

Low High

The horizontal difference in temperature createsa horizontal difference in pressure.

Cont.

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• 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.

Cont.

• Use of Isobar:– reveal surface pressure pattern– Deduce wind condition (e.g. Isobar closer, wind

will blow harder)

Cont.

Density

Definition

• 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 will vary with:– Altitude– Latitude

Density Variation in Atmosphere:

• Air near surface more dense than air at higher surface.

Density Variation with Altitude

• 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

Density Variation with Latitude

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

Definition

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

• Water vapor: water in its gaseous state

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 dryif 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.

Cont.

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• 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.

Cont.• 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.

Conclusion• 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.

66Presented by Mohd Amirul for AMC

Key Points

• What is the Atmosphere?• Composition of Atmosphere• Layers of Atmosphere• Variation in Atmosphere• Air stability

67Presented by Mohd Amirul for AMC

End of Presentation #25 Minutes for Q/A session

68Presented by Mohd Amirul for AMC

Quote of the Day

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

Franklin P. Jones

69Presented by Mohd Amirul for AMC