Meteorology Flashcards
What climate zone is the UK situated in?
Temperate
Characteristics of a temperate zone
Hot and warm summers, drier than other seasons
Where does the atmosphere extend further into space?
Around the equator
Two reasons for atmosphere being more extended at equator than poles?
Earth’s rotation
Greater heating at equator
Thickness of atmosphere is proportional to
Temperature
In ISA, what atltitude is the tropopause at?
30,000ft
Aircraft fly mostly in what atmosphere subdivision?
Troposphere
What lies between the Earth’s surface and the stratosphere?
Troposphere
The trophosphere’s relation to temperature?
Proportional
Temperature in the stratosphere is..?
Constant
Troposphere’s characteristics at the poles?
Colder and shallower
Approx. what temp is the stratosphere?
-57 degrees Celsius
What substance in the air is critical for life on earth?
Water Vapour
In ISA, temp decreases at what rate?
2 degrees celcius per 1000ft gained
Name of lines on pressure maps connecting areas of similar pressure
Isobars
Variation of pressure with horizontal distance is called…
Pressure gradient
Impact on aircraft performance on humid damp days is due to
Higher proportion of water molecules in air reduces overall air density
Regular pressure variations owing to daily heating and cooling effects of the sun is called
Semi-diurnal variation of pressure
What kind of barometer is used in aircraft altimeters?
Aneroid
Altimeter reading 0ft at sea level would read what altitude if the pressure drops 10hPa?
300ft
Sun’s radiation strikes polar regions at what kind of angle?
Oblique
Transfer of heat energy from one body to another is called..
Diabatic process
When heat is neither added or removed from a system, it is called..
Adiabatic process
Expansion and compression of gases experience what kind of heat process?
Adiabatic process
Relationship between temperature and radiation wavelength
The higher the temperature of the body, the shorter the wavelength of the radiation
Convection describes
Process by which warm air rises into the atmosphere and carries its heat energy with it
Why does warm air rise?
It is less dense than the surrounding air
Advection follows what other diabatic process?
Convection
Advection describes
Horizontal motion of air replacing air that has risen due to convection
What has a higher heat capacity? Water or land
Water
Because water has a higher heat capacity than land, land does what?
Heat and cool more quickly than water bodies
ELR stands for
Environmental Relapse Rate
What describes the process of temperature change from altitude increase in the real world?
ELR
What is the DALR?
Dry Adiabatic Lapse Rate
DALR equates to
3 degrees celcius reduction for each 1000ft climbed
If water vapour condenses in a discrete parcel of air, what will happen?
The parcel of air will cool at a lower rate
What is the SALR?
Saturated Adiabatic Lapse Rate
SALR occurs when?
Parcel of air cools at a lower rate than DALR due to water vapour condensing and latent energy being released
Stable atmosphere occurs when…
ELR is less than SALR and DALR
Stable atmosphere means air has what tendency?
To return back to its origianl position if displaced
Stable atmosphere’s typical weather
Clear skies, fog, stratus
Unstable atmosphere occurs when
ELR is greater than SALR and DALR
Unstable atmosphere means air has what tendency?
Rise if displaced
Unstable atmosphere’s typical weather
Cumulus and cumulonimbus cloud
Conditional instability occurs when
ELR is less than DALR but greater than SALR
Conditional instability means
Dry, unsaturated air is stable. Moist, saturated air is unstable
In what conditions do temperature inversions occur?
Low wind and clear nights
At night, cooling air not mixing with higher altitude warmer air results in…
Temperature inversion
Approximately what degrees is the Earth tilted at from the vertical?
23 degrees
Why does warm tropic air move towards higher latitudes?
The air cannot rise higher due to stratospheric isotherm
What generally happens to cool air over the poles?
It sinks
General circulation consists of how many main cells?
3
What is the equatorial trough?
A band of low pressure at the earth’s surface in the tropics
What is the process by which surface air will move towards an area of low pressure?
Convergence
What is the process by which surface air will move outwards from an area of high pressure?
Divergence
What temp is absolute zero?
-273 degrees celsius
The transfer of heat by the horizontal motion of an air mass is called?
Advection
The transfer of heat by the vertical motion of an air mass is called?
Convection
What is wind?
Horizontal flow of air across the Earth
Wind Velocity is the combination of what?
Wind direction and wind strength
A wind changing in a clockwise direction is doing what?
Veering
A wind changing in an anti-clockwise direction is doing what?
Backing
Wind caused by rotation of the Earth is called
Coriolis force
Geostrophic wind results from what…
Balance between coriolis force and pressure gradient force
Increasing latitude does what to the relative motion of earth
Reduces the easterly motion of the earth
The Earth’s rotation has what effect on the relationship between the Earth and a parcel of air
It will lag behind the easterly motion of the parcel of air
Observer’s experience of the coriolis force
Wind is deflected to the right
Coriolis effect increases with
Airflow
Coriolis effect cannot occur without
Airflow
Why is the Coriolis effect greater away from the equator?
Changes in latitude cause more significant changes in the difference of easterly movement
In the northern hemisphere, the Coriolis effect deflects the wind to the..
Right
Leftward deflection of wind by Coriolis effect occurs where?
Southern hemisphere
Geostrophic wind’s relationship to isobars
It flows parallel to the isobars
Best sentence to describe the formation of geostrophic wind
The pressure gradient force gets the air moving and the Coriolis effect turns it to the right
Geostrophic wind parallel to isobars has the low pressure on what side?
Left
Buys Ballot’s Law is…
Standing with your back to the wind in the northern hemisphere, the low pressure will be on your left
Flying from high to low pressure (in Northern Hemisphere) is indicated by what?
Right starboard drift, as the wind is from the left
Right starboard drift (in Northern Hemisphere) indicates what?
Flying from high to low pressure
Flying from low to high pressure (in Northern Hemisphere) is indicated by what?
Left drift
Left drift (In Northern Hemisphere) indicates what?
Flying from low to high pressure
In the NH, wind flows in what direction round a high?
Clockwise
In the NH, wind flows in what direction round a low?
Anti-clockwise
In the NH, wind flowing clockwise indicates a what?
High pressure
In the NH, wind flowing anti-clockwise indicates a what?
Low pressure
Wind blowing around a low experiences what process?
Pressure gradient force is greater than the Coriolis force
Wind blowing around a high experiences what process?
Coriolis force is greater than the pressure gradient force
Surface wind is usually measured at what height
30 ft
Why is wind usually less strong at the surface compared to higher levels?
Earth’s surface exerts friction
Friction causes surface wind to what?
Weaken in strength and back in direction
In general, the more unstable atmospheric stability is results in what effect to surface wind
It backs less and is more similar to the 2000ft wind
Why is windspeed greater around a high compared to an equally-spaced-isobar low?
Coriolis force increases with wind speed
Diurnal can be thought of as another word for..?
Daily
Roughly speaking, what altitude does the top of the boundary layer occur? (And frictional/thermodynamic effects become negligible)
2000 to 3000 feet
What part of the day does mixing of wind layers reduce?
Night
What happens to wind at night?
Slacks and backs
Why does sea breeze occur on sunny days?
Land heats more quickly than the sea
Light winds + convection near water =
Sea breeze
Vertical extent of a sea breeze is usually what?
1000 to 2000 feet
Why does sea breeze cause visibility problems?
It may bring cool, moist air over land
When does sea breeze occur?
Day
When does land breeze occur?
Night
Basics of a land breeze?
Land cools quicker than the sea, cooler land air replaces rising warm sea air
What kind of heat transfer causes air to cool during clear, cloudless nights?
Conduction (due to ground becoming cool because of terrestrial radiation)
In what land type does katabatic wind occur?
Mountainous
What causes katabatic wind?
At night, cool air flows down mountain slopes creating wind blowing into valleys
What two kinds of wind occur exclusively in mountains/hills?
Katabatic and Anabatic
What causes anabatic wind?
Warm air rises up a mountain slope
Why is anabatic wind weaker than katabatic wind?
Air flowing upwards is opposed by gravity
Cumulonimbus clouds’s up/downdraughts can extend how far into clear air around them?
20nm
High pressure systems do what to temp inversions?
Detach them from the surface
What cloud formation occurs in the lower lee side of a mountain during mountain wave?
Rotor cloud
In the tropics, pressure gradients are usually…
Weak
Why is the Coriolis force very weak in the tropics?
The distance of isobars from the earth’s axis remains constant
What wind system dominates in the tropics?
Pressure gradient force
What are used instead of isobars in the tropic systems?
Streamlines and isotachs
What do streamlines indicate?
Wind direction
What do isotachs indicate?
Areas of equal wind strength
Outdraughts in a tropic area come from where?
High pressure areas
Indraughts in a tropic area come from where?
Low pressure areas
What do vertical gusts do to an aircraft’s performance?
Increase its angle of atttack
During turbulence, why is it good practice to hold the attitude, not the altitude?
Avoid using the elevator excessively to not over-stress the airframe
Mountain wave occurs during what system?
High pressure
ATC wind reports are relative to..?
Magentic north at the airfield
Metereological reports on wind direction use what relative indication?
True North
A parcel of air moving in line with the pressure gradient force will experience Coriolis acting at what angle to its motion?
Perpendicular
Wind that flows around curved isobars is called the..?
Gradient wind
In the northern hemisphere, the mean surface wind direction compared to the gradient wind direction will…
Back
In what pressure system is vertical motion more upward?
Low pressure because the atmosphere is unstable
Lenticular cloud is a good indication of..?
Mountain wave and severe turbulence
What are the four forms of cloud?
Cirriform
Cumuliform
Stratiform
Nimbus
High-level cloud has what minimum base?
20,000 feet
Why does high-level cloud look fine and spideery?
Usually formed in coldest region of troposphere asice crystals rather than water particles
Description of cirriform
Fibrous
Description of cumuliform
Heaped
Description of stratiform
Layered
Description of nimbus
Rain-bearing
Clouds: cirru/cirro denotes what kind of cloud?
High-level
Stratus means what?
Layer
Cirrus means what?
High
Middle-level cloud occurs in what altitude range?
6,500ft to 20,000ft AMSL
What is virga?
Rain that does not reach the ground
Virga occurs in what kind of air?
Dry or warm air
Why does virga not reach the ground?
It evaporates or sublimes first
Alto- denotes what?
Middle-level cloud
Clouds: fractus denotes what?
Stratus or cumulus shreds below nimbo/alto-stratus
Clouds: castellanus is what?
Cumuliform clouds that are turret-shaped
Castellanus indicates what?
Unstable atmosphere
When water changes state, its transferred heat energy is known as..
Latent Heat
What does humidity measure?
The amount of water vapour present in the air
A saturated parcel of air means it has __% humidity?
100%
Relative Humidity Equation
RH = Vapour Pressure/Saturation Vapour Pressure
What factor determines how much water a particular parcel of air can support, regarding humidity?
Air temperature
Air temperature is proportional to how much water that air can support?
True
Relation between air temperature and saturation
The higher the air temperature, the more water it can support
How much water a parcel of air can support is formally known as?
Saturation Vapour Pressure
What is the Humidity Mixing Ratio?
Ratio of the mass of watter vapour in a parcel of air to the mass of dry air in the same parcel
What happens to the relative humidity of a rising unsaturated parcel of air?
It increases because temperature decreases and cooler air cannot hold as much water vapour
Why does rising unsaturated air increase in relative humidity?
Cooler air cannot hold as much water vapour
What remains constant in a rising parcel of unsaturated air?
Humidity Mixing Ratio
What is the dewpoint?
Temperature at which a parcel of air becomes saturated if it cools
What happens to a dewpoint related to moisture?
The moisture in the air, the higher its dewpoint temperature
What happens if a parcel of air is cooler than its dewpoint?
Excess wateer vapour will condense as water droplets
Two adiabatic ways in which cloud is formed
Mass uplift
Convection
Two diabatic ways in which cloud is formed
Advection
Radiation
What is the DALR?
3 degrees per 1000ft
Why is cooling not as great for saturated air as it continues to rise?
Latent heat is released due to condensation, so cooling is not as great
What is the SALR?
Saturated Adiabatic Lapse Rate
SALR’s relation to DALR?
Approximately half
Approximately, what rate is SALR?
1.5 degrees per 1000ft
What primary factor determines the type of cloud formed?
Stability of the atmosphere
What are the three kinds of atmopsheric stability when it comes to ELR/DALR/SALR and cloud formation?
Unstable, neutral and stable
ELR stuff: when does unstable air occur?
ELR is greater than DALR or SALR
ELR stuff: when does stable air occur?
ELR is less than DALR or SALR
ELR stuff: when does neutral air occur?
ELR is equal to DALR or SALR
In unstable air, clouds and air do what?
Continue to move verticaally after displacement
What clouds are typically formed in unstable air?
Cumuliform
What clouds are typically formed in neutral air?
Stratiform clouds
In neutral air, what happens to the air?
Remains in the position to which it was vertically displaced
In stable air, what happens to the air?
Returns to the position from which it was displaced
What clouds are typically formed in stable air?
Stratiform clouds or fog
When a parcel of air cools to the same temperature of its surrounding environment, it does what?
Stops rising
Air flowing over mountains cools and rises in what way?
Adiabatically
Why does cloud formed over mountains cease to exist as it descends on the lee side?
Temperature exceeds dewpoints and therefore water vapour vapourises
A cloud that forms as a ‘cap’ over the top of a mountain is known as what..?
Lenticular
