Meteorology Flashcards
Composition of the Atmosphere:
Nitrogen - 78% Oxygen - 21% Water Vapour - 0 to 3% Carbon Dioxide - 0.03% Other Gases
What is Condensation Nuclei?
Tiny suspended particle, solid or liquid which water vapour condenses on
What is the most important component of the atmosphere in terms of weather?
Water Vapour
Know Changes of State for Water
Yes Sir
True or False: The ability of the atmosphere to hold moisture increases with temperature?
True
3 Principle Properties of the Atmosphere:
Expansion - As air rises, it expands and cools water vapour may condense
Compression - Sinking air contracts and is heated clouds dissipate
Mobility - Both horizontally and vertically
What is more dense cold air or warm air?
Cold air is denser and tends to sink, warm air rises
Explain what Dewpoint is:
Temperature at a given pressure to which air must be cooled to cause saturation
What happens when air becomes fully saturated?
Water vapour will condense into clouds/fog
What is the difference between the temperature and the dewpoint called?
The spread - provides information of how close the air is to saturation and the likelihood of fog forming
What is the Dewpoint Lapse Rate?
0.5 C / 1000’
What is Relative Humidity?
Water vapour content of the air as a percentage of the maximum possible at current temperature (saturation)
Facts about the Troposphere:
- Surface to 28,000’ (Poles) - 54,000’ (Equator)
- Weather occurs here
- Pressure, temperature, density decrease with altitude
- Temperature decrease stops and remains steady at -56 C
Facts about the Stratosphere:
- Up to 160,000’
- Temperature constant at -56 C in lower portions, and rises to -15 C (ozone)
- Clouds rare, visibility good
Facts about the Mesosphere:
- Temperature decreases to approx. 275,000’
- Point at which temperature increase is called mesopause
Facts about the Thermosphere:
- Temperature increases into thousands of degrees
- Aurora occurs in this layer
What kind of energy is emitted by the sun?
Short Wave UV radiation
Give the distribution of Solar Energy absorption
19% Absorbed by Ozone 6% Reflected by Atmosphere 20% Reflected by Cloud Tops 4% Reflected by Earth's Surface 51% Absorbed by Earth's Surface
Heating Processes
Conduction - Heating through contact (limited air is a poor conductor)
Convection - Air that is warmed tends to rise, rising tendency until density is equal to surrounding air
Turbulent Mixing - Friction causes eddies as air moves over surfaces, disruption is proportionate to terrain
Advection - Horizontal movement of air masses (over warm surface, it will be warmed)
Compression - Descending air increases in pressure, increasing temperature, along ridges of mountain ranges (adiabatic heating)
Release of Latent Heat - Changing state releases heat energy (down an energy level)
Cooling Processes
Expansion - Rising air decreases in temperature, adiabatic cooling, occurs at two different lapse rates depending on moisture (DLAR: 3C/1000’ & SLAR: 1.5C/1000’)
Orographic/Upslope Lift: Result of air flowing over topographical features causes air to rise
Frontal Lift: Expansion cooling when warm air is forced up along a frontal surface, Cold fronts: displaces warm air causes it to rise, Warm fronts: Can’t displace cold air rises up over cold air
Mechanical Turbulence: Same mechanism as heat distribution process
Convection: Rising air cools according to lapse rate
Convergence: Air at centre of a low rises, causes cooling
Advection: Air mass moving over cold surface will cool
Evaporation: Opposite of condensation, liquid to gas heat is absorbed
What does Atmospheric Stability refer to?
Resistance to vertical movements of air parcels
How is Stability determined?
Determined by the temperature difference between rising air parcel and surrounding air
What does a Steep and Shallow Lapse Rate indicate?
Steep Lapse Rate implies unstable air
Shallow Lapse Rate implies stable air
What is Inversion?
Temperature increase with height, indicated extremely stable air
What is Environmental Lapse Rate?
The actual change of temperature with an increase in altitude
What is a Low Pressure Area also known as?
A Cyclone/Depression, marked by an “L”, airflow tendency is counter-clockwise toward the centre
What is a High Pressure System also known as?
Anticyclone, marked by an “H”, typically larger than low pressure systems, airflow is clockwise and outward from centre
What is a Trough?
Lines of low pressure extending outwards from a low pressure area, produces convergence, cooling low ceilings and visibilities with sufficient moisture
What is a Ridge?
Line of high pressure extending outwards from a high, produces subsidence, results in compression heating and clear skies
What is a Col?
Neutral area exist between two highs and two lows, geographically small, rarely has significant impact on weather
What is the definition of Air Pressure?
Weight of imaginary column of air
What are the two main ways to measure Air Pressure? (Know the difference between them)
Mercury Barometer
Aneroid Barometer
What is Station Pressure?
Weight of a column of air lying above the reporting station
What is Mean Sea Level Pressure?
Station Pressure + Weight of Imaginary Column of air between station and seal level (weight of column of air is calculated using average temperature of last 12 hours)
What is the weight of the column of air based on when finding mean sea level pressure?
The standard ICAO lapse rate of 1.98C/1000’
When flying in colder than standard conditions what will the altimeter do?
Altimeter will over-read, ok though because every aircraft’s altimeter will over-read
Know the saying for flying between pressure systems
High to Low - Look out below (may be lower than expected)
Low to High - Clear blue sky (may be higher than expected)
What are Isobars, and how far apart are they spaced out from each other?
Lines joining places of equal barometric pressure, spaced 4 hectopascals apart
What is a Pressure Gradient Force (PGF)?
The tendency for air to flow from high to low pressure creating a force associated with it (wind)
What is the cause of the Coriolis Effect?
The Earth rotates underneath us, so therefore when something is thrown in a straight line, it will go to either the left or right depending on the hemisphere
What is Buys Ballot’s Law?
If you stand with your back to the wind, in the northern hemisphere, the low pressure will be on your left
What are the conditions for a Geostrophic Wind?
Pressure Gradient Force = Coriolis Force
What is Geostrophic Wind?
Wind that flows parallel to isobars
Where does the Friction Effect occur, that affects the movement of air, reducing wind speed?
Occurs up to 2000-3000’ AGL
Explain the Sea Breeze
Breeze blowing toward the land from the sea, during the day, because of the warmth of the land, causing a low pressure system
Explain the Land Breeze
Breeze blowing toward the sea from the land, at night, owing to relative warmth of the sea
What are Anabatic Winds?
Warm wind, blows up a steep slop/mountain side, driven by heating of the slope, occur during the day in calm sunny weather
What are Katabatic Winds?
Downslope/gravity winds, occur at night when highlands radiate heat and are cooled
Understand how there can be a combination of anabatic and katabatic winds depending on where the sun is shining
Yes Sir
What is a Frontal Low Level Jet Stream?
Narrow band of strong winds in warm air just ahead of cold air, 500 - 5000’ AGL, hundreds of feet wide, up to 100 kts
What are Nocturnal Low Level Jet Streams? And what do they require?
Requires inversion, and flat terrain, forms 700 - 2000’ AGL, can reach 60 kts, dissipates as sun rises
What is the definition of turbulence?
Unpredictable and irregular motion of air
What are the main causes of turbulence?
Wind shear, frontal air, hot air, or surface texture
Convective Turbulence
Hot air rising quickly, daytime heating, usually only within 2000’ AGL, different surfaces reflect different amounts of heat
Mechanical Turbulence
Air moving around obstructions on ground causes complicated eddies, greater the wind, greater the obstructions, greater the turbulence, affected by stability, stable air: eddies don’t grow, but dissipate slowly, unstable air: eddies grow, but dissipate quickly
Mountain Waves
Occurs because of air flow going up and then back down a mountain, sets up wave patterns downwind up to 500 km
What are the requirements for Mountain Waves to form?
> 30 kts wind, flowing at 30 degrees of perpendicular to ridge line, stable air above mountains, strongest during winter and early spring, can extend up to 6,000’ above height of mountain, cause severe turbulence, and up/downdrafts
Three types of clouds formed by mountain waves:
Cap Clouds: Forms on windward side as air flows up and cools, indicated strong downdraft on leeward side
Lenticular Clouds: Form downwind of mountain, form in wave crest, indicated high winds and CAT
Rotor Clouds: Line of stratocumulus a few miles downwind and parallel to mountain range, form at/below mountain top heights forms in vortex below wave crests
5 Different types of Wind Shear:
Low Level Wind Shear: Sudden change in temperature in vertical plane, associated with approaching frontal depression
Frontal Zone Wind Shear: Sudden wind shifts can occur across a front, greater temperature differences create greatest turbulence, turbulence will usually be found along slope of the front, usually fairly narrow band, may be passed through quickly
Wing Tip Vortices: Passage of wind through air, pressure differential on both sides of wings creates rotating flow near tip, can persist in stable conditions and move with air masses as they rotate out and down
Vertical Wind Shear: Turbulence occurs when wind changes by 5 knots or more per 1000’
Horizontal Wind Shear: When wind speed differs dramatically between two adjacent areas, form in vicinity of troughs and ridges, associated with CAT
When do clouds form?
Form when saturation is reached, water vapour condenses into small droplets/ice crystals
What are the 4 families of clouds?
High “Cirro-“ - Bases >20,000’ ASL
Middle “Alto-“ - Bases between 6,500 and 20,000’ ASL
Low - Bases between surface and 6,500’ ASL
Clouds of Vertical Development “Cummul-“ - Bases usually below 6,500’ ASL, extending sometimes up to tropopause
What are the 3 main types of High Clouds?
Cirrus (CI) - Very high, thin wispy, no significant icing, minor turbulence
Cirrocumulus (CC) - Individual puffs, patchy, thin, cotton like, may have some icing and turbulence
Cirrostratus (CS) - Continuous appearance, thin (can see sun/moon through them), indicates approaching warm front or occlusion, little if any icing, no turbulence
What are the 4 main types of Middle Clouds?
Altocumulus (AC) - Series of patches of rounded cotton-ball clouds, formed in unstable air masses, do not indicate weather development, small amounts of icing, some turbulence Altocumulus Castellanus (ACC) - Altocumulus with turreted appearance, indicated instability, turbulence, and possibly showers, might develop into cumulonimbus, some icing Altostratus (AS) - Thick grey cloud, covers large area of the sky, indicates approaching warm front, light rain or snow, moderate icing, no turbulence, restricted sunlight Lenticular - Lens-shaped clouds, strong winds over mountainous areas, cause patterns of up and down waves, very strong turbulence
What is the main difference between High, Middle, and Low clouds?
High composed of ice crystals
Middle composed of ice crystals and water droplets
Low composed of water droplets mostly, some ice crystals
What are the 4 main types of Low Clouds?
Stratus (ST) - Uniform light to dark grey, blankets large area of sky, can be considered fog if base extends to ground, drizzle, little-no turbulence, hazardous icing if below freezing
Stratus Fractus (SF) - Small, unorganized layers form beneath nimbus clouds, called “scud”, bases near the ground
Stratocumulus (SC) - Irregular masses of cumulus merged together, may be in layers or patchy, common in high pressure areas, some turbulence, icing possible
Nimbostratus (NS) - Rain clouds, bottoms blurred due to precipitation, associated with warm fronts, very little turbulence, serious icing if below freezing
5 main types of Vertical Development Clouds
Cumulus (CU) - Thick, rounded cotton balls, during day, dissipate at night, flight bumpy near these clouds, no icing
Cumulus Fractus (CF) - Small, thin unorganized puffs form from larger cumulus clouds, called “scud”, low to ground
Towering Cumulus (TCU) - Unstable air causes strong vertical convection currents, cause clouds to grow really tall, early stage of thunderstorm, very strong turbulence, with some clear icing
Cumulonimbus (CB) - Thunderstorm, extend above freezing level, violent vertical currents in and near cloud, hail within cloud, line of them indicates cold front, could be embedded in stratus layers, should be avoided, violent turbulence, strong possibility of icing
Cumulus Mammatus - Cellular pattern of pouches underneath the base of a cloud, usually associated with cumulonimbus, indicate strong storm
How do you calculate Cloud Base?
1) Calculate spread (current temperature - dew point)
2) Divide spread by 2.5
3) Multiply by 1000
Give height in AGL, adjust if needed for ASL
What is the simplest description of fog?
Ground level cloud, happening when the visibility falls below 5/8 SM
What is Vertical Visibility vs Slant Range Visibility?
Vertical Visibility - Visibility looking straight up
Slant Range Visibility - Visibility as seen on approach
What are the 3 important factors that ultimately lead to fog?
1) High Relative Humidity
2) Condensation Nuclei
3) Process to cause temperature/dew point spread to (cooling air to dew point or adding moisture to raise dew point)
What are the 6 different types of Fog?
Radiation Fog - Forms at night with clear skies, light winds, and stable air, caused by radiation cooling (air mass cools from the ground up), dissipated by the rising sun, surface warms, fog burns off, if cloud layer moves in dissipation is much more gradual
Advection Fog - Warm, moist air over cooler land or water, doesn’t burn off, wind speeds of 15 kts provide maximum thickness, occurs mostly in maritimes, sometimes on warm front approaching on very cold air mass
Upslope Fog - Light winds push warm, moist air upslope, cools and condenses into fog
Steam Fog - Cold air over warm water, evaporation increases dew point and cools air, fog forms
Frontal (Precipitation) Fog - Rain adds moisture to air, evaporation cools air, associated with warm fronts
Ice Fog - Moist air on extremely cold day, addition of water vapour increases dew point, sublimation of water vapour forms ice crystals, vapour trails in sky
Valley Fog is a form of what type of Fog?
Radiation Fog - cold air down mountainside, cools air to dew point
What is haze and how is it formed?
Microscopic water droplets, dust or salt particles suspended in air, stable air only
What are the rating systems for the oktas sky coverage?
Clear (0/8) Few (1-2/8) Scattered (3-4/8) Broken (5-7/8) Overcast (8/8)
What are the minimum visibility requirements for VFR flight?
3 miles
When does visibility tend to be reduced?
In stable air
What is VMC & IMC?
Visual Meteorological Conditions (VMC) - Conditions are good for VFR flight
Instrument Meteorological Conditions (IMC) - Flights must be IFR in these conditions
How is precipitation formed?
In clouds above freezing temperatures water droplets combing and become heavy and fall to Earth?
What is Coalescence?
Vertical movement causes droplets to collide
What does heavy precipitation indicate?
Indicates significant vertical development to above the freezing level
What is the difference between drizzle and rain?
Drizzle is raindrops with a maximum diameter of 0.5 mm, and rain is everything above that
What is the process of hail forming?
In the middle layer of vertical development clouds, super-cooled water droplets collide with ice crystals forming soft ice balls
What does larger hail indicate?
Larger hail indicates greater vertical currents in the cloud
Why is snow formed sometimes instead of hail?
If water region is not thick, the hard shell won’t freeze on the pellet and it will fall as snow
What precipitation types come from what cloud types?
Drizzle, freezing drizzle, granular snow - Stratus, Stratocumulus
Snow, rain (steady or intermittent) - Nimbostratus, Thick Altostratus, Altocumulus, Stratocumulus
Snow flurries, rain showers - Cumulonimbus, Cumulus Congestus, Altocumulus Castellanus
Snow pellets, sleet showers - Cumulonimbus, Cumulus Congestus
Steady sleet - Nimbostratus, Altostratus, Altocumulus, Stratocumulus
Hail - Cumulonimbus
Ice Prisms - Clear Sky
What are the 6 North American Air Masses?
Continental Arctic - Cold dry from far north
Continental Polar - Cool dry from not as far north
Maritime Arctic - Cold wet, formed over arctic, moves south in winter
Maritime Polar - Moves south and picks up moisture and warms
Maritime Tropical - Warm, moist sections of North America
Continental Tropical - Formed over warm, dry section of North America, only in summer
What is a Front?
Boundary between air masses
Where is the Frontal Zone located?
50-100 mile wide area between air masses
How is a Cold, Warm and Stationary Front symbolized?
Cold Front - Blue triangles
Warm Front - Red semi-circles
Stationary Front - Alternating symbols
What is the Polar Front?
Where cold air from the polar regions mixes with the warm air from the equatorial regions
What two air masses form the Polar Front?
Maritime Polar and Maritime Tropical
What is a Frontal Wave?
Opposite directed flow of air at a front, causes a counter-clockwise circulation to develop when there is a disturbance, there will be one cold front, and one warm front, and a low pressure area forms, the cold front moves faster than the warm and occlusion begins, eventually closing together and dissipating
How does warm air overtake cold air?
Sliding up and over a cold front, as warm air is lifted it cools and forms clouds
What are the clouds and weather during a moist stable warm front?
Nimbostratus Altostratus Cirrostratus Cirrus Precipitation will fall ahead of front
What are the clouds and weather at a moist unstable warm front?
Cumulonimbus embedded in clouds, heavy showers ahead of surface front
Which way does the wind change direction at the warm front?
Wind will change direction to the right
What is the typical temperature at the warm front?
Temperature will gradually rise
Visibility will be poor with low ceilings
Turbulence minimal (except if cumulonimbus present)
Precipitation will begin ahead of the front and get heavier as front approaches
What is the progression of weather when approaching a winter warm front?
Snow Sleet (Turn Around) Freezing Rain Rain
How does a cold front replace a warm air mass?
Leading edge of cold front pushes warm air up and over it very steeply, forms narrow band of cumulus clouds
What is the typical weather at a Cold Front?
Wind - Veers, and gusty
Temp - Drops slowly
Visibility - Improves after cold front passes
Pressure - Decreases as front approaches, and rises quickly after passage
Turbulence - Present if convective activity
Precipitation - Narrow band of showers
At a Stationary Front what is the weather like?
Weather is like a warm front
Which way do the winds flow at a Stationary Front?
Parallel to the front
What is an Occluded Front?
As a cold front overtakes warm air, it eventually catches up to itself as it flows around the low pressure area, weather is similar to warm front, may be thunderstorms
What is a TROWAL
Trough of Warm Air Aloft
When all the warm air is lifted up at an occluded front, usually has some precipitation
When is an Upper Cold Front formed?
Advancing cold front meets other colder air and rises up over the colder air
Why does icing form?
Super-cooled water hits an aircraft, it freezes and sticks to plane
Name the 3 different types of Icing:
Clear Ice - Large drops that freeze slowly, clear, glassy, hard, forms on leading edge and spreads backwards over wing, forms in - clouds and precipitation temperatures just below freezing
Rime Ice - Small droplets freeze rapidly, opaque, brittle, granular, weighs less than clear, disrupts flow more, forms in - cloud, on leading edge but does not spread back
Mixed Ice - combination of the two, severe icing in cumulus cloud, less severe in stratus cloud
Name 3 pieces of De-Icing Equipment
De-icing Boots - Expand to break ice
Heated wings, props, windshield
Fluid released through leading edge or onto prop
What constitutes Severe Icing?
De-icing equipment cannot keep up
Know what to do when you encounter icing
Turn Around
Descend to Warmer Air
Climb
File a PIREP
What are 3 things that must be present for a thunderstorm to form?
1) High moisture content
2) Unstable (steep) lapse rate
3) Lifting action
What are the 3 stages of a thunderstorm?
1) Cumulus Stage - Cumulus cloud needs strong updraft to fully develop into thunderstorm (unstable air), lasts 10 minutes
2) Mature Stage - Appearance of precipitation, updrafts and downdrafts, violent turbulence, top forms anvil shape, lasts 15-20 minutes
3) Dissipating Stage - As rain falls, cloud cools and loses energy, big downdrafts, rain ceases
3 Types of Thunderstorms
1) Air Mass - Convective lift, singly or in clusters on hot, humid summer day, tend to be scattered
2) Frontal - Usually cold front, form line hundreds of miles long, embedded in other clouds often
3) Orographic - Air forced upward by hills or mountains
Thunderstorm Weather Characteristics
Wind Shear
Gust Front - Downdrafts spread out ahead of storm, similar to mini cold front
Downburst - strong downdraft of cold air, often in dissipating
Macroburst - Downburst at least 2.5 NM diameter, lasting 5 - 20 minutes
Microburst - Downburst smaller than macroburst, may contain virga
Shelf Cloud - Area of strong downdraft wind and outflow, moving away from main precipitation area
Wall Cloud - Signifies area of strongest updraft
Tornado
Funnel Cloud
Hail
Lightning
Thunder
Icing
Pressure Change
Thunderstorm Dangers
Turbulence - Up to 20 miles away from cloud
Lightning - Radio interference, blindness, strikes, damage
Hail - Structural damage
Icing
Pressure Change - Performance of altimeter
Rain - May contaminate wing surfaces, reduce/distort visibility, hydroplaning
Strong Winds - Abrupt changes in speed and direction
How far away should you stay from Thunderstorms?
20 Miles - to the right
