BAK Met Review Flashcards
Composition of the Atmosphere
78.08% Nitrogen
20.95% Oxygen
0.93% Argon
0.04% Carbon Dioxide
Average percentage of water vapour in air.
1%
Avogadro’s Law
At a given temperature and pressure, the number of molecules present is constant for a particular volume. Hence the addition of water vapour to the air results in the reduction of the density of the air.
Layers of the Atmosphere.
Troposphere - <20km
Stratosphere - 20km - 50km
Mesosphere - 50km - 85km
Thermosphere - 85km - 690km
Exosphere - 690km - 10000km
Environmental Lapse Rate
The rate at which temperature falls as height increases.
Temperature above the tropopause.
Constant value of - 56 C above FL360
Tropical Tropopause
Approx 60,000ft.Temperatures recorded lower than - 90 C
Polar Tropopause
Approx 20000ft.Temp as low as -40 C
Jetstreams
Fast, narrow currents of air separating multiple overlapping areas of tropopause.
Stratosphere
Extends upwards from the tropopause until approx 120000ft.Temperature reasonable constant around -56C in lower layers.Temperature increases to near 0C at the top layer.
Which layer of the Atmosphere does the ozone layer sit in?
Stratosphere.
Aurora
A natural light display in the sky particularly in the high latitude, Arctic and Antarctic, regions, caused by the collision of highly charged particles with atoms in the Thermosphere.The charged particles originate in the magnetosphere from solar winds and are directed by the Earth’s magnetic field towards the atmosphere at the poles.
International Standard Atmosphere
Temperature - 15C
Pressure - 1013.25 hPa
Density - 1225 g/m3
Temperature Lapse Rate - 1.98C (2) per 1000ft until 36090 ft where it remains at -56.5C
Pressure Lapse Rate - 1 hPa per 30 ft
The air is dry.
What is the main absorber and conductor of solar energy?
The surface of the Earth
Conduction
The transfer of energy through contact.
Convection
The vertical transfer of energy through theatmosphere.
Advection
The horizontal transport of energy through the atmosphere or ocean.
Radiation
The transfer of energy through wave or particles.
Latent Heat
The amount of energy absorbed or released during a substance change of state or phase transition.
Pressure
The weight or force of a column of air due to gravity.
Density
Mass per unit volume; that is how many molecules are in a given sample within a column of air.
Temperature
A measurement of heat energy within asample.
Warmer air vs cold air (temp/pressure/density)
Higher Temperature
Higher Pressure
Lower Density
Rises due to lower density than surrounding air.
What is a radiosonde?
Battery powered instrument packages attached to weather balloons that are then released into the atmosphere. They are designed to send atmospheric telemetry to a ground receivers. This data is then plotted on a graph called an aerological diagram that then creates a snapshot of the present atmosphere.
Data relayed by radiosondes
Altitude
Pressure
Temperature
Relative humidity
Wind (speed and direction)
Geographical position
Density of the air at 25000 ft relative to that sea level
Approximately half
Why is air density important to pilots?
The lift force supporting the aircraft’s weight is generated by theflow of air around the wings.
Engine power is generated by burning fuel and air (oxygen).
Humans need to breathe air (oxygen) in order to live.
What units are used in aviation meteorology for Altitude, Pressure, Temperature, Horizontal Visibility and Horizontal Distance?
Altitude - Feet
Pressure - Hectopascals
Temperature - Degrees Celsius
Horizontal Visibility - Kilometres
Horizontal Distance - Nautical Miles
How does a change in pressure affect temperature?
An increase pressure will effectively force the molecules together; this creates friction and an increase in temperature.
Conversely a decrease in pressure effectively reduces friction and therefore temperature.
What is the adiabatic process?
The change in temperature due to a change in pressure.
What are the causes of vertical movements of air?
Thermal
Orographic uplift
Turbulence
Convergence and Divergence
Frontal
What is a thermal?
A rising mass of warm air. As the land heats up it conducts its heat energy to the air in contact with it. The vibrating air molecules begin to push harder on each other, forcing them apart. The pressure remains constant and the result is a change in density. The warmer air is less dense than the surrounding air and therefore rises.
What kind of areas produce good thermals?
Good conductors of heat energy such as cities, bitumen road, and darker areas.
What is orographic uplift?
Orographic uplift is a result of air flowing over mountains, following the contours and rising vertically. As the rising air is cooled adiabatically below its dewpoint, any water vapour will condense and clouds will form.
What is turbulence?
Disturbed air. As the wind blows over the earth’s surface, variations in the terrain (natural or man-made) can disrupt the smooth flow and create eddies. The depth of turbulence depends on the nature of the surface and wind strength. It is the vertical component of turbulence that can have an impact on weather.
What are convergence and divergence?
Convergence is the horizontal inflow of air and subsequent lifting. The air is forced together and has nowhere to go but up (lifting). As the air rises it is cooled adiabatically. Unable to rise any further the air diverges and the cooler air sinks. As it descends it warms adiabatically (subsidence).
What is a frontal?
When two air masses interact the boundary between them is referred to as a front. An example of frontal lifting would be a cooler denser air mass undercutting a warmer less dense air mass. The result is the warmer air mass sliding on top of the cooler air mass. There is a wide area uplift along the boundary and based on temperature and pressure differences, can result in spectacular weather.
What is DALR?
Dry Adiabatic Lapse Rate is the rate of temperature decrease with altitude for a parcel of dry or unsaturated air rising under adiabatic conditions.Unsaturated air will cool adiabatically at 3°C every 1,000 feet as it rises and expands.
What is SALR?
Saturated Adiabatic Lapse Rate (SALR).As air cools, the humidity increases. After reaching Dew Point (100% humidity) further cooling will result in condensation; clouds will form. If the air mass continues upwards, cooling continues but not at 3°C/1,000 feet above the condensation level, the now-saturated air will continue to cool as it rises, but because latent heat is given off as the water vapour condenses into the lower-energy liquid state, the cooling will not be as great.If continued, upwards cooling continues at 1.5°C every 1,000 feet
ELR
Environmental Lapse Rate is the actual rate of change of temperature as altitude is gained in the surrounding atmosphere (air not moving vertically).In the real atmosphere, the actual ELR may vary from the ISA value - it might be less than 1°C/ 1,000 feet, or it might be as high as 4°C/ 1,000 feet.The actual ELR is not uniform and varies from location to location and from day to day.
What does the structure and type of cloud depend on?
The stability of the air and its water vapour content.
Explain an unstable atmosphere
If an air mass rises and cools at the DALR, and the ELR of the surrounding air is higher i.e. the rate of cooling is more, the air mass will always be warmer than its surroundings and will, therefore continue to rise; this is referred to as an Unstable Atmosphere and results in cumuliform clouds with vertical development.
Explain a stable atmosphere
If an air mass rises and cools at the DALR, and the ELR of the surrounding air is less, the surrounding air will be warmer and this tends to resist any vertical motion; this is referred to as a Stable Atmosphere and results in stratiform cloud with little or no vertical development.
What drives weather?
The movement of heat by the oceans, combined with differential heating from the land.
Consequences of cloud cover during the day.
Reflects solar radiation away from the Earth’s surface, resulting in less heating of the earth and lower temperatures on cloudy days.
Consequences of cloud cover at night.
Reflects terrestrial radiation back to earth resulting in less heat escaping and warmer nights. The Earth is always radiating heat energy.
Diurnal temperature variation
The Earth heats up during the day and reaches its maximum temperature about 2.00 pm and cools by night, reaching its minimum temperature approximately one hour after sunrise.
Name the tropics and their latitudes.
Tropic of Cancer - 23.5 degrees north Tropic of Capricorn - 23.5 degrees south
What are the three types of atmospheric cell?
Hadley cell
Polar cell
Mid-latitude or Ferrel Cell
What is wind?
Wind is essentially the horizontal movement of air over the earth’s surface. Only a very small percentage is vertical flow. Vertical movement of air can lead to cloud formation and other factors affecting aviation. It is the difference in pressure within the atmosphere as a result of temperature change that causes wind.
What is wind direction measured with?
Wind vane
What is wind speed measured with?
Anemometer
When, in Aviation Meteorology, is degrees magnetic used?
When reported by one of the following:
by the TOWER or CA/GRS;
on an ATIS, WATIR;
by an AWIS in place of an ATIS outside tower hours
What is a CA/GRS?
Certified Ground Radio Service
What is an ATIS?
Automatic Terminal Information Service
What is a WATIR?
Weather and Terminal Information Radar (ATIS at a CA/GRS Airport)
What is an AWIS?
Aerodrome Weather Information Service
What is backing?
When the direction changes anticlockwise.
What is veering?
When the direction changes clockwise
What is a gust?
A momentary increase in speed from the average as reported, lasting only a few seconds before dying away. When wind gust values are forecast or reported to exceed 10kt above the average they are displayed as 35025G40 (Wind direction 350° at 25 knots gusting to 40 knots).
What is a lull?
A momentary decrease in speed from the average as reported, lasting only a few seconds before returning to the average.The opposite of a gust