Met Lesson 1 Flashcards
Composition of the Atmosphere
Nitrogen = 78% Oxygen = 21% CO2 = 0.03%
Gravity Associated with Pressure
There is a higher pressure closer to the Earth’s surface
There is the highest amount of water vapour closest to the Earth’s surface
Layers of the Atmosphere
Troposphere Tropopause Stratosphere Mesosphere Thermosphere Exosphere
Troposphere
Almost all of the weather occurs in the troposphere
Tropopause
Top of the troposphere
30,000ft at the poles and 60,000ft at the Equator
Convection weakens
Stratosphere
Isothermal layer
-56.5 degrees celcius
Stevenson Screen
Measures temperature and dew point
International standard atmosphere (ISA) at MSL
Temperature: +15 degrees celcius with a lapse rate of -1.98 degrees celcius/1000ft to 36 090ft
Pressure: 1013.25hPa/29.92 inch Hg with a lapse rate of - 1hPa/30ft increase in altitude
Density: 1.225kg/m³
Horizontal Pressure Gradient
Areas of unequal pressures attempt to equal out
Air will flow from a high to a low
Affects of Volume on Density
If volume decreases: pressure, temperature and density increase
If volume increases: pressure, temperature and density decrease
Heat in the Atmosphere
Due to electro-magnetic radiation
Air is warmest closer to the Earths surface
Types of Electro-Magnetic Radiation
Short wave solar radiation from the sun
Long wave terrestrial radiation from the heated Earth
Types of Heat Transfer
Radiation (eg. sun or our bodies)
Conduction (eg. pan on a hotplate)
Convection (rising air)
Advection (eg. sea breeze)
Factors Affecting Atmospheric Temperature
Diurnal temperature variations The seasons Specific heat capacity Reflection Clouds Wind Costal proximity
Diurnal Temperature Variations
3pm is the warmest time of the day
Just after sunrise is the coldest part of the day
Solar radiation only occurs during daylight hours
Biggest amplitude at in-land stations
The Seasons
The Earth revolves around the sun in 1 year
The tilt of the Earth gives rise to the 4 seasons
Equinox
Equal amounts night and day
Specific Heat Capacity
SHC of water is 1 calorie/gram
SHC of air is 0.3 cal/g
Takes 3x more energy to heat water than dry air
Reflection
Fresh snow reflects 90% of heat energy Old snow reflects 60% of heat energy Sand reflects 20-30% of heat energy Ground (soil) reflects 15% of heat energy Forest reflects 5-10% of heat energy
Effect of Cloud
Overcast days are cooler
Overcast nights are warmer (blanketing effect)
Cloudless nights are relatively cooler due to maximum terrestrial radiation
Effect of Wind
Mixing of different air masses moderates the overall temperature
Effect of Costal Proximity
The cool sea breeze will cool a hot summers day on the coast
The warm sea breeze will warm a cool day
Large Scale Atmospheric Circulation
Polar high Sub polar low Sub tropical high Equatorial trough/low Sub tropical high Sub polar low Polar high
Low Pressure Areas
Areas of convection
Eg. Mainly at the equator
High Pressure Areas
Areas of subsidence
Equatorial/Monsoonal Trough Weather
Complex low pressure systems
Sub-Tropical Ridge Weather
High pressure systems
Sub-Polar Low/Polar Front Weather
Complex and intense low pressure systems
Sublimation
Solid to vapour
Deposition
Vapour to solid
Latent Heat and Temperature
Latent heat needs to go in when melting and out whilst freezing
Water Vapour
Moisture in the air
Humidity
The amount of water vapour in the atmosphere
Becomes a liquid when it condensates to form visible moisture
Effect of Humidity on Air Density
Water vapour is less dense than air (5/8 the weight of dry air)
Therefore, humidity will reduce air density and the performance of the aircraft
Relative Humidity
The ability of the air to hold moisture
The amount of water vapour present in relation to the maximum amount of water the air can hold at a certain temperature
%RH = (actual water vapour)/(max water vapour it can hold) x 100
Saturation
100% relative humidity
Dew point
Visible moisture forms (cloud formation)
The Affects of Temperature on Relative Humidity
Cooler air holds less water vapour than warm air
The relative humidity increases when air cools
Temperature Inversions
When temperature increases with an increase in height
Colder air underneath the warmer air
Indicates a stable atmosphere
Types of Temperature Inversions
Radiation
Subsidence
Frontal
Radiation Inversions
Lower layers are cooled by the cool ground, which cools rapidly overnight
Maximum terrestrial radiation occurs due to the clear nights
Unlikely on cloudy or windy nights
Subsidence Inversions
Associated with high pressure systems
Cold air subsides and warms rapidly adiabatically (high pressure and high temperatures)
Air at the surface diverges, moving horizontally, and is not heated adiabatically
4,000 - 8,000ft AGL
Warm air above with colder air near the surface
Frontal Inversions
Cold dense air forces the warm air upwards
Effects of Inversions
Turbulence
Pollution/dust/salt may be trapped under the inversion layer resulting in reduced visibility
Reduced aircraft performance after take-off whilst passing through the warmer section
Turbulence
Causes the aircraft to roll, yaw and pitch simultaneously
Thermal Turbulence
Due to solar radiation, frontal activity and inversions
Temperature differences in the air masses cause thermals, thunderstorm activity, frontal lines and horizontal wind shear
May also display as a large temp vs dew point split (hot and dry conditions)
Mechanical and Frictional Turbulence
Friction over the ground surface due to strong winds
Up to 3,000ft AGL
Depends upon wind speed and type of obstruction
Beware of vortices around mountainous terrain and downwind of obstructions
Wake Turbulence
Generated by air moving from a high pressure (below wing) to a lower pressure (above the wing)
Rotate inwards towards the fuselage
Drops at 500fpm and linger 1000ft below the aircrafts flight track
Pilot Actions to Avoid Wake Turbulence
Climb and descend more steeply
Touchdown after the point of the larger aircraft
Takeoff before the takeoff point of the larger aircraft
Parallel Runway Operations
With a light crosswind, aircraft may be affected by the wake turbulence of other aircraft on adjacent runways
Turbulence Classifications
Light: small effect on altitude and attitude of aircraft
Moderate: significant effect on altitude and attitude and a variation in IAS
Severe: large abrupt changes in attitude and altitude and short periods of uncontrollability
Extreme: practically impossible to control with possible structural damage
Pilot Actions in Turbulence
Consider changing altitude of flight level
Change airspeed, if required, to the manufacturer’s recommended ‘best turbulence speed’ (VB)
Maintain aircraft attitude only (request clearance to fluctuate on altitude)
Divert if necessary
Windshear
A sudden change in wind speed and/or direction over a short distance resulting in a speed variation larger than 10kts
Can be vertical or horizontal
Low Level Windshear
Below 1, 600ft AGL
Overshoot Effect Due to Windshear
Aircraft flying above the intended flight path
The pilot lowers the nose of the aircraft to maintain the glide path
The airspeed begins to increase
Compensate by reducing the power setting
Undershoot Effect Due to Windshear
Aircraft flying below the intended flight path
The pilot raises the nose to maintain the glide path
The airspeed begins to decrease
Compensate by increasing the power setting
Pilot Actions in Windshear
Accurate airspeed control Increase the approach speed to increase control Consider a 'reduced flap' landing Use Vb or Va Find the shortest way out
