Meteorology Part 2 Flashcards
Temperature
Standard temperature is 15 degrees C at sea level.
Temperature tends to decrease approximately 2 C / 1000 ft.
Advection
Air flowing from a cold area over a warm area experiences heating from below by the earth’s warmer surface.
Convection
Air over a warm surface rises rapidly, and cool air takes it’s place where it is also heated.
Mechanical Turbulence
Wind blowing over rough terrain breaks up into whirls and eddies, causing a mixing of air and spreading surface heat into the air aloft.
Compression
Air comes under increased atmospheric pressure resulting in the air being heated.
Thermals
Heated from below, these rising currents of air create “free lift,” allowing aircraft-like gliders to fly for extended periods of time without engine power.
–most noticeable in hotter conditions near mountainous terrain.
heating
Advection
Convection
Turbulent Mixing
Compression
cooling
Radiation
Advection
Expansion
Radiation
At night, air in contact with the cooler earth will also be cooled.
Advection
Air from a warm region moves over a cool region.
Expansion
When air is forced to rise, it encounters a lower pressure and expands. This causes the air temperature to decrease
Horizontal Temperature Differences
Land = heats readily & loses heat quickly.
Water = hard to heat up & longer to cool down.
Temperature Inversions
Inversion – An increase in temperature with an increase in height.
3 common scenarios that produce temperature inversions
1) Radiation Inversion
2) Subsidence Inversion
3) Frontal Inversion
Radiation Inversion
At night, air near the ground cools by radiation. Cold dense air lies along the ground and is covered by a warmer layer above. This situation consists of stable air, (little vertical movement), and light to no wind.
Subsidence Inversion
Subsiding air well above the earth’s surface (8000 ft or higher) descends and warms adiabatically.
Frontal Inversion
During the advance of a cold front, a mass of warm air may be lifted over top of a colder, denser air mass creating a warm layer of air aloft.
Isothermals
Lines joining areas of equal temperature.
Isotherms are like isobars, except they show temperature, not pressure.
Humidity
The amount of moisture in the air.
The amount of moisture a given volume of air can absorb depends on its temperature. (because cold the molecules are together = no space for moisture)
Relative Humidity
The actual amount of moisture in the air, compared to the amount that it could hold at that temperature.
Dew Point
The temperature to which air must be cooled at a constant pressure to reach a state where it can hold no more water vapor.
At this point, the air contains 100% of the moisture it can hold, and is said to be saturated.
Temperature / Dew Point Spread
The temperature difference
between air temperature & dew point temperature.
The smaller the dew point spread =
the higher the relative humidity, the closer to clouds, fog and precipitation forming.
This number is of critical importance when night flying
If the temperature-dew point spread is within 2 or 3 degrees, you may takeoff in clear skies and return to find fog.
Lapse Rate
The rate of temperature decrease with height.
ISA lapse rate = 1.98°C / 1000 ft. assumes standard conditions.
–usually between Dry & Saturated adiabatic lapse rate.
Dry Adiabatic Lapse Rate (DALR)
The rate of temperature decrease with height of dry or unsaturated air.
Dry air cools at a rate of 3°C/1000 ft
Saturated Adiabatic Lapse Rate (SALR)
The rate of temperature decrease with height of wet or saturated air.
Wet or Saturated air cools at a rate of 1.5°C/1000 ft
aka: moist adiabatic lapse rate (MALR)
Cloud height can be found using:
- Surface temp.
- Dew point
- DALR
Freezing level can be found using
- Cloud height
- SALR
The environmental lapse rate (ELR),
decrease of temperature with altitude at a given time and location.
Put simply, it is what is actually happening with the lapse rate.
This is a STABLE environment (air)
Air that is forced to rise and is cooler than the surrounding air will sink back down again because it is more dense.
ELR is less than the DALR = stable air
This is an UNSTABLE environment. (air)
Air forced to rise that is warmer than the surrounding air will continue to rise as it is warmer and less dense.
ELR is greater than the DALR = unstable air
Steep Lapse Rate:
The temperature decreases rapidly with height.
Implies unstable air.
Shallow Lapse Rate:
temperature decreases slowly with height.
Implies stable air.
Modification of Lapse Rates (Made U N S T A B L E )
Warming from Below:
1) Day time heating
2) Advection [Cold air moving over a warm surface is heated from below]
Cooling Above:
1) rapidly moving cold front - air moves up = unstable
Modification of Lapse Rates (Made S t a b l e )
Cooling from Below
1) Night time
2) Advection [Warm air moves over colder ground = cools down]
Heating Above
1) Warm Fronts - gradual heating = more stable.
Characteristics of Stable & Unstable Air
–Visibility
Stable = Poor visibility/ May be smog or smoke/ Mist or fog
UNstable = Typically Clear
Characteristics of Stable & Unstable Air
–Cloud
Stable = Layer type cloud/ Steady precipitation
UNstable = Heap type cloud/ Showery precipitation
Characteristics of Stable & Unstable Air
–Wind
Stable = Steady and light
UNstable = Potentially more gusty/ Stronger winds
Characteristics of Stable & Unstable Air
–Turbulence
Stable = Smooth
UNstable = more turbulent –> Convective turbulence/
Clear air turbulence
Five Lifting Processes (forming clouds)
1) Convection
2) Orographic lift
3) Frontal lift
4) Mechanical lift
5) Convergence
Orographic Lift (to form a cloud)
Wind or air that suddenly meets rising terrain will be deflected upward, and continue to rise if the air is unstable.
Frontal Lift (to form a cloud)
A front is the boundary zone between a warmer air mass and colder air mass.
When met with colder denser air, a warm air mass will be lifted on top of the colder, denser air mass.
Mechanical Lift (to form a cloud)
Friction with larger terrain (mountains, hills, buildings, trees), will cause turbulent eddies, lifting air near the surface to higher levels.
Convergence (to form a cloud)
Winds blow toward the centre of a low pressure area.
Air in this convergent zone is forced to rise.
Convection (to form a cloud)
Air is heated through coming in contact with the earth and forms columns of rising air.
unequal heating of different surfaces = clouds in some spots with more moisture.
3 things must be present to form a cloud:
1) Water Vapor -Relative humidity near 100% (temperature equals dew point).
2) Condensation Nuclei: Water vapor must have something to attach to such as dust, smog particles, or smoke particles.
3) Cooling Process: Due to radiation, advection, expansion etc.
Cloud Categories
Cumuliform Cloud
Stratiform Cloud
Nimbus Clouds
Cumuliform Cloud
vertical development
heaped /puffy clouds
unstable air
The size = the instability of the air.
The greater the instability = higher the current rises = higher the cloud extends.
Stratiform Cloud
stable air is cooled below its saturation point.
There is little or no vertical motion.
Nimbus Clouds
precipitation falls.
Cloud Categories
Low cloud – Below 6,500’ AGL
Middle cloud – 6,500’-20,000’ AGL
High cloud – Above 20,000’ AGL
Vertical Development
Low cloud – Below 6,500’ AGL
Stratus (St)
Stratocumulus (Sc)
Nimbostratus (Ns)
Middle cloud – 6,500’-20,000’ AGL
Altocumulus (Ac)
Altostratus (As)
High cloud – Above 20,000’ AGL
Cirrus (Ci)
Cirrostratus (Cs)
Cirrocumulus (Cc)
Vertical Development - cloud types
Cumulus (Cu)
Cumulonimbus (Cb)
Altocumulus Castellanus (Acc)
Towering Cumulus (Tcu)
Cloud Types - Cirrostratus
often create a halo effect around the sun or moon.
Cloud Types - Cirrocumulus
high-level puffy cirrus clouds are rolled in appearance and
composed entirely of ice crystals.
Cloud Types - Cumulus
low level clouds are indicative of fair weather.
They are dense clouds of vertical development.
Cloud Types – Towering Cumulus
These are very large cumulus clouds that may produce significant turbulence or showers.
**TCUs are to be avoided.
Cloud Types – Altocumulus Castellanus
somewhat uncommon cumuliform clouds are named for their castle-like or turreted appearance.
Cloud Types – Cumulonimbus
largest of all cumuliform clouds
–produce virtually every meteorological hazard to aviation
–including thunderstorms.
Cloud Types – Mammatus Clouds
extremely rare clouds are characteristic of descending air masses
Cloud Types – Rotor Clouds
Part of a mountain wave, rotor clouds are indicative of severe turbulence
Cloud Types – Lens Clouds
Also part of a mountain wave, lens clouds are indicative of severe turbulence.
Cloud Types – Contrails
Technically clouds, contrails are frozen ice crystals formed as a bi-product of fuel combustion.
Precipitation
All moisture that falls from the sky is precipitation
100% humidity doesn’t guarantee precipitation –> Most clouds don’t precipitate ;)
Causes of Precipitation
Coalescence - Droplets collide to form a larger droplet.
Ice Crystal Process – Ice crystals grow from the water vapor given up by evaporating water droplets and eventually fall from clouds as snow.
Precipitation from clouds : Ns, As
Snow, rain, continuous
Precipitation from clouds: Sc, Ac
Snow, rain intermittent
Precipitation from clouds: Cb, TCu, Acc
Snow, rain showery
Precipitation from clouds: Cb , TCu
Snow pellets, ice pellets, hail
Precipitation from clouds: Clear sky
Ice crystals
Surface Based Layers (fog vs. mist)
ground based layer = FOG if visibility = < 5/8th of statute mile
ground based layer = MIST if visibility = > 5/8th of statute mile
Fog - cloud layer based on the ground
ideal conditions = (3)
1) High relative humidity
2) Abundance of condensation nuclei
3) Process to create condensation
Fog Types (6)
Radiation Fog
Advection Fog
Upslope Fog
Steam Fog
Ice Fog
Frontal Fog
Radiation Fog
Night = ground cools by radiation = cools air directly above it.
If the air is moist & temp decreases below dew point = fog
Conditions: On land, Light winds, Clear skies, Moist air
Advection Fog
cooling of moist air flowing over a surface colder than itself
Upslope Fog
forms (up mountains) orographically due to the cooling of moist air by expansion, as it moves up a slope
Steam Fog
Forms when water vapour is added to the air
Ice Fog
Formed of ice crystals.
Water vapour added through fuel combustion (ex: tailpipe)
Frontal Fog
Forms when rain falling from warm air evaporates and saturates the cooler air below.
