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AVIA 101 - FM1 > Meteorology 1 > Flashcards

Meteorology 1 Flashcards

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1
Q

Atmosphere Composition

A
  • 78% Nitrogen
  • 21% Oxygen
  • 0-3% Water vapour
  • 0.03% carbon Dioxide
  • Argon, Helium, Neon, other rare gases
  • Condensation nuclei allows water vapour to condense
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2
Q

Water Vapour

A
  • Most important in context of weather
  • Only component of atmosphere that is found in all 3 states under normal conditions
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3
Q

Changes of State

A
  • Heat is released or absorbed when water changes state
  • Melting, Evaporation, Sublimation (Heat Absorbed)
  • Freezing, Condensation, Deposition (Heat Released)
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4
Q

Moisture Content

A
  • Ability for atmosphere to hold moisture increases with temperature
  • Weather occurs due to water vapour in the air and the changes of state it goes through
  • Main sources are evaporation from oceans and lakes and transpiration from vegetation
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5
Q

Properties of the Atmosphere - Expansion

A
  • As air rises, it expands and cools
  • Water Vapour may condense to form clouds or precipitation
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6
Q

Properties of the Atmosphere - Compression

A
  • Sinking air contracts and is heated
  • Clouds dissipate
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7
Q

Gas Law

A
  • Cold air is more dense and tends to sink
  • Warm air is less dense and tends to rise
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8
Q

Properties of the Atmosphere - Dewpoint

A
  • Temperature at a given pressure to which air must be cooled to cause saturation
  • When air is saturated, water vapour will condense to form clouds or fog
  • Difference between temperature and dewpoint is called the spread, provides likelihood of fog forming
  • Dewpoint lapse rate is 0.5º/1000 ft (increase in spread)
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9
Q

Properties of the Atmosphere - Relative Humidity

A
  • Expresses water vapour content of air as percentage of maximum possible at current temperature (saturation)
  • 60% relative humidity means the air is 60% saturated
  • At 100% water vapour will condense to water droplets and form clouds or fog
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10
Q

Divisions of the Atmosphere - Troposphere

A
  • Varies in height from ground to 28,000’ over poles or ground to 54,000’ over equator
  • Most weather occurs in troposphere
  • Pressure, temp, and density all decrease with altitude
  • Tropopause at top of troposphere
  • Temp decrease stops and remains steady at -56ºC
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11
Q

Divisions of the Atmosphere - Stratosphere

A
  • Up to 160,000’
  • Temperature remains constant at -56ºC in lower portion
  • Temperature rises to near -15ºC due to ozone
  • Clouds are rare and visibility is excellent
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12
Q

Divisions of the Atmosphere - Mesosphere

A
  • Temperature decreases to approx. 275,000’
  • The mesopause is the point where temp begins to increase again
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13
Q

Divisions of the Atmosphere - Thermosphere

A
  • Temperature Increases to the 1000’s of degrees
  • Aurora Occur in this layer, sun’s rays cause molecules of oxygen, hydrogen, and nitrogen to fluoresce
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14
Q

Heating of the Troposphere - Solar Radiation

A
  • Energy emitted from sun as short-wave UV radiation
  • Ozone layer acts as filter, approximately 19% of UV rays are absorbed
  • 30% of UV rays reflected by atmosphere, cloud tops, and the earth’s surface
  • 51% gets absorbed by the earth’s surface
  • Little direct heating of atmosphere once past ozone layer
  • Absorbed UV causes surface to warm
  • Air in contact with surface is warmed by conduction
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15
Q

Heating Processes - Conduction

A

Heating Through Contact

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16
Q

Heating Processes - Convection

A
  • Air that is warmed becomes less dense and tends to rise
  • Rising tendency continues until the density (temp) is equal to surrounding air
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17
Q

Heating Processes - Turbulent Mixing

A
  • Friction causes eddies to form as air moves over surfaces
  • Disruption is proportionate to terrain, rough terrain means more mixing
  • In combination with convection, air can rise quite high into the troposphere
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18
Q

Heating Processes - Advection

A
  • Horizontal Movement of Air Masses
  • If an air mass travels over a warmer surface, it will be warmed
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19
Q

Heating Processes - Compression

A
  • Descending (subsiding) air increases in pressure, in turn increasing temperature
  • Can occur along ridges of high pressure or over mountain ridges
  • Known as adiabatic heating
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20
Q

Heating Processes - Release of Latent Heat

A

Changing state (down and energy level) releases heat energy

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21
Q

Cooling Processes - Expansion Cooling

A
  • Rising air decreases in temp
  • Known as adiabatic cooling
  • Lapse Rate is the rate at which air warms or cools in response to altitude (pressure) changes
  • Adiabatic cooling occurs at two different rates depending on moisture content
  • Dry Adiabatic Lapse Rate (DLAR) is 3º/1000 ft and occurs with less than 100% relative humidity
  • Saturated Adiabatic Lapse Rate (SLAR) is 1.5º/1000 ft and occurs at 100% relative humidity
  • SHOULD KNOW LAPSE RATES
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22
Q

Cooling Processes - Orographic and Upslope Lift

A
  • Result of air flowing over topographical features that cause the air to rise
  • Slope of rising terrain is not important
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23
Q

Cooling Processes - Frontal Lift

A
  • Expansion cooling occurs when warm air is forced up along a frontal surface
  • Cold Fronts are when advancing cold air displacing warmer air, causing it to rise quickly
  • Warm Fronts are when warm air cannot displace the cold air, so warm air gradually rises up and over cold air
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24
Q

Cooling Processes - Mechanical Turbulence

A

Same mechanism as the heat distribution process, can result in cooling

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25
Q

Cooling Processes - Convection

A

Rising air cools according to the appropriate lapse rate

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26
Q

Cooling Processes - Convergence

A
  • Air at the centre of a low pressure area rises, causing cooling
  • Air spins counter-clockwise inwards
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27
Q

Cooling Processes - Non-Expansional Cooling

A

Advection, an air mass moving over a cool surface will cause cooling of the air mass

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28
Q

Cooling Processes - Non-Expansional Cooling

A

Evaporation, opposite of condensation, as liquid turns to gas, heat is absorbed

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29
Q

Atmospheric Stability

A
  • Stability in the air refers to the resistance to vertical movements of air parcels
  • Stability is determined by temp difference between the rising air parcel and the surrounding air
  • An air parcel will continue to rise as long as its temp remains above the temp of the surrounding air
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30
Q

Stability Definitions - Steep Lapse Rate

A

Temperature decreases rapidly with altitude, this implies unstable air

31
Q

Stability Definitions - Shallow Lapse Rate

A

Temperature decreases little with altitude, this implies stable air

32
Q

Stability Definitions - Isothermal Layer

A
  • Temperature does not change with an increase in altitude
  • More stable than a shallow lapse rate
33
Q

Stability Definitions - Inversion

A

Temperature increases with height, this indicates extremely stable air

34
Q

Stability Definitions - Environmental Lapse Rate

A

The actual change of temperature with an increase in altitude

35
Q

Pressure Terminology - Low (L)

A
  • Area of pressure lower than that which surrounds it
  • Centre of low pressure area marked by an L
  • Scale ranges from 1 km to hundreds of km
  • Lower the pressure, deeper the L
  • Air flow tendency is counter-clockwise and toward the centre
36
Q

Pressure Terminology - High (H)

A
  • Area of pressure higher than that which surrounds it
  • Centre of high pressure area is marked by an H
  • Also known as an anticyclone
  • Typically larger than low pressure systems
  • Airflow tendency is clockwise and outward from centre
37
Q

Pressure Terminology - Trough

A
  • Line of low pressure extending outwards from a low pressure area
  • Produces convergence, resulting in cooling and promotes low ceilings and visibilities with sufficient moisture
38
Q

Pressure Terminology - Ridge

A
  • Line of high pressure extending outwards from a high pressure area
  • Produces subsidence, resulting in compression heating and clear skies
39
Q

Pressure Terminology - Col

A
  • Neutral areas that exist between two highs and two lows
  • Geographically small, rarely significant impact on the weather
40
Q

Air Pressure

A
  • Weight of an imaginary column of air
  • Two common methods of measurements, mercury barometer and aneroid barometer
41
Q

Air Pressure Measurements - Mercury Barometer

A
  • Consists of an open dish of mercury into which the open end of and evacuated glass tube is placed
  • Atmospheric pressure causes mercury to rise
42
Q

Air Pressure Measurements - Aneroid Barometer

A

Consists of a flexible metal cell that contracts with increasing pressure and expands with decreasing pressure

43
Q

Station Pressure

A

The Weight of a column of air lying above the reporting station

44
Q

Mean Sea Level Pressure

A
  • Station Pressure plus the weight of an imaginary column of air between the station and sea level
  • Weight of this column of air is calculated using the average temp over the previous 12 hours
45
Q

Altimeter Setting

A
  • Station Pressure plus the weight of an imaginary column of air between the station and sea level
  • Weight of this column of air is based on the ICAO Standard Lapse Rate of 1.98ºC /1000’
46
Q

Flying with Pressure Systems

A
  • Aircraft altimeters do not automatically detect changes in pressure
  • Altimeter settings must be adjusted in the cockpit to ensure accurate altitude indications
47
Q

Air Circulation - Isobars

A
  • Lines joining places of equal barometric pressure
  • Spaced 4 hectopascals apart
48
Q

Air Circulation - Pressure Tendency

A

The change of pressure over time

49
Q

Air Circulation - Pressure Gradient Force (PGF)

A
  • Air moves from areas of high pressure to areas of low pressure
  • Intensity of PGF can be determined by spacing between isobars (close together means strong winds)
50
Q

Coriolis Force

A
  • Earth’s Rotation plays a significant part in movement of air, particularly when moving north or south
  • Air moving from high pressure to low pressure does not flow directly from one to the other
  • The Earth rotating under the moving air creates an apparent deflection to the right (Fennel’s Law)
  • Coriolis force is deflecting force
  • Results in winds around a high pressure area to move clockwise around the centre of the high pressure area
  • Results in winds around a low pressure area to move counter-clockwise around the centre of the low pressure area
51
Q

Buys Ballot’s Law

A

“If you stand with your back to the wind in the northern hemisphere, low pressure will be on your left”

52
Q

Geostrophic Wind

A
  • Occurs when Pressure Gradient Force equals Coriolis Force
53
Q

Friction Effect

A

Topographical features affect the movement of air, reducing wind speeds at low level
- This occurs between the surface and 2000’-3000’ AGL

54
Q

Localized Effects - Sea Breeze

A

A breeze blowing toward the land from the sea, especially during the day owing to the relative warmth of the the land

55
Q

Land Breeze

A

A breeze blowing toward the sea from the land, especially during the night owing to the relative warmth of the the sea

56
Q

Anabatic Wind

A
  • Warm Wind which blows up a steep slope or mountain side
  • Driven by heating of the slope through insolation
  • Also known as an upslope flow
  • These winds typically occur during daytime in calm sunny weather
57
Q

Katabatic Wind

A
  • Also called downslope wind or gravity wind
  • Blows down a slope because of gravity
  • Occurs at night, when highlands radiate heat and are cooled
58
Q

Low Lovel Jet Stream (LLJ) - Frontal

A
  • Narrow band of strong winds in warm air just ahead of a cold front
  • 500’-5000’ AGL, hundreds of feet wide, up to 100 knots
  • Wind shear is primary risk
59
Q

Low Level Jet Stream (LLJ) - Nocturnal

A
  • Requires inversion and flat terrain, no barriers to wind speed
  • inversion is a very stable condition typically found after sunset
  • 700’-2000’ AGL, can reach 60 knots
  • Dissipates as sun rises
60
Q

Turbulence Definition

A
  • Unpredictable and irregular motion of air
  • Can be caused by wind shear, frontal air, hot air, or surface texture
61
Q

Convective Turbuelnce

A
  • Hot air rising quickly
  • Caused by daytime heating
  • Different surfaces reflect different amounts of heat
  • Generally only within 2000’ of ground
62
Q

Mechanical Turbulence

A
  • Air moving around obstructions is broken up into a series of complicated and chaotic eddies
  • Stronger the wind and the more severe the obstructions, the stronger the turbulence
  • Turbulence carried downwind and is affected by stability
  • Eddies do not grow in stable air, but dissipate slowly
  • Eddies can grow in unstable air, but dissipate quickly
63
Q

Mountain Waves

A
  • Also known as lee waves
  • Can be very dangerous
  • Occurs as airflow is forced up the windward side of a mountain, crossing over the top and dropping back down the leeward side
  • This sets up a wave pattern extending downwind up to 500 km
  • Occur with lots of wind flowing 30º off perpendicular to ridge line, and stable air above mountaintops
  • Can break if strength is great enough
  • Strongest during winter and early spring
  • Can extend 6000’ above height of mountain with wavelength ranges of 3-15 miles
  • Risk is severe turbulence with up and downdrafts up to 4500 ft/min
64
Q

Mountain Wave Clouds - Cap Clouds

A
  • Forms on the windward side as air flows up and cools
  • Usually indicates strong downdraft on the leeward side
65
Q

Mountain Wave Clouds - Lenticular Clouds

A
  • Form downwind of mountain range
  • Clouds form in the wave crest
  • Indicates high wind speeds and clear air turbulence (CAT)
66
Q

Mountain Wave Clouds - Rotor Clouds

A
  • A line of stratocumulus a few miles downwind and parallel to mountain range
  • Form at and below mountaintop heights
  • Forms in vortex below the wave crests
67
Q

Low Level Wind Shear

A
  • Created when there is a sudden change in temp in the vertical plane
  • Often associated with approaching frontal depression
68
Q

Low Level Wind Shear Alerts

A
  • Surface to 500’ AGL with wind vector changes by 25 knots or more
  • Surface to 1000’ AGL with wind vector changes by 40 knots or more
  • Surface to 1500’ AGL with wind vector changes by 50 knots or more, PIREP’s report airspeed fluctuation of 20 knots or more
69
Q

Frontal Zone Wind Shear

A
  • Sudden wind shifts can occur across a front
  • Turbulence will usually be found along the slope of the front
  • Usually fairly narrow band, so it may be passed through quickly
70
Q

Wing Tip Vortices

A
  • Created by the passage of a wing through air
  • Pressure differential on upper and lower
71
Q

Vertical Wind Shear

A

Moderate or greater turbulence can occur when the wind changes by 5 knots or more per 1000 feet of altitude

72
Q

Horizontal Wind Shear

A
  • Occur when wind speed differs dramatically between two adjacent areas
  • Can form in the vicinity of troughs and ridges
  • Same effect as a river flowing rapidly around a corner
73
Q

Clear-Air Turbulence (CAT)

A
  • Turbulent movement of air masses in the absence of any visual clues
  • Caused by when bodies of air moving at widely different speeds meet
  • Cirrus clouds can also indicate high probability of CAT

AVIA 101 - FM1 (17 decks)

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