MET 2204METEOROLOGY Presentation 3: Atmosphere Presented 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. Presented by Mohd Amirul for AMC
Introduction • Earth view: • Altitude • Vertical height from earth surface. • Longitude • Latitude
Cont. • 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. • 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)
Cont. *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. • 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.
Variation in Atmosphere • The earth’s atmosphere varies vertically and horizontally in • Temperature • Pressure • Density • Humidity
Definition • What are the differences between heat and temperature?
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
Radiation • Energy transmit in the form of rays, waves, or particles. • Solar = relating to the sun • Terrestrial = relating to the earth (e.g. land)
Cont. 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. Terrestrial Radiation (TR) • Energy emitted from earth to atmosphere
Cont. Solar and Terrestrial radiation SOLAR RADIATION TERRESTRIAL RADIATION
Cont. Difference between Solar & Terrestrial Radiation on the Earth Surface INCOMING=OUTGOING MAX TEMP 1300H-1500H RADIATION INCOMING (SR) OUTGOING (TR) SUNRISE NOON SUNSET INCOMING =OUTGOING MIN TEMP SUNRISE +1HR
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.
Cont. 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 • 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
Definition • Atmospheric Pressure: • The weight of air in the column above unit area of earth surface. • Pressure is the force per unit area: F P = A
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 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 • 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.
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.
Cont. • Horizontal Difference in Temperature: • Creates horizontal difference in pressure. Consider two columns of air Warm Cool Ps Ps Ps Ps Pressure is the weight of the air above you. Warm one side and cool the other side. Maintain a constant surface pressure.
Cont. Consider an airplane flying at a constant height. What are the pressures? Warm Cool Ps Ps
Cont. So we see a high pressure, at the altitude of the plane, in the warm column and a low pressure in the cool air. Low High Warm Cool Ps Ps The horizontal difference in temperature creates a horizontal difference in pressure.
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