Met General Flashcards
What part of the atmosphere contains all the elements of weather?
The Troposphere
What are the layers of our atmosphere?
- Troposphere
- Stratusphere
- Mesosphere
- Thermosphere
Colourless gass that absorbs ultraviolet radiation and is found at all altitudes?
Ozone
The earth’s surface is heated by?
Short wave solar radiation
Temps in the lower stratosphere approximate those of the ___.
Tropopause
Whenever air moves horizontally, it is influenced by the Coriolis force, which is caused by ___.
Rotation of the earth.
Atmospheric motions in the vertical direction?
Convection
Heat transfer from molecule to molecule without significant movement of the molecules?
Conduction
When surface temps rise due to daytime heating, this heating effect is transmitted aloft by…
Convection
What area experiences the least diurnal (day/night) range in temperature?
Termperate zone oceans
Lifting process that causes choppy turbulence below 3000’
Mechanical turbulence
List 3 lifting agents?
- Convection
- Convergence
- Mechanical Turbulence
Convergence describes air that is…
squishing into an area (converging)
What process can result in expansional cooling, condensation and cloud formation?
Overrunning
Characteristics of a Cyclone?
- low pressure
- left rotation (anti-clockwise)
- ascending air
- convergence (inward spiraling winds)
- warm air
Characteristics of an Anticyclone
- high pressure
- right rotation (clockwise)
- descending air
- good weather
- cold air
The term used when no heat is transferred. This could be used for a rising parcel of air that does not transfer any heat in or out as it ascends.
Adiabatic
Subsiding air warms at the ___ lapse rate?
dry adiabatic lapse rate
Air descending down the lee side of mountain slopes will warm at the ______ rate.
dry adiabatic lapse rate
When air subsides, the relative humidity ___
decreases.
What happens during the condensation process?
Latent heat is released to the surrounding air.
Dry adiabatic lapse rate
3°C / 1000’
Why does saturated air that’s rising cool less rapidly than if it were dry air?
Because heat is released during the condensation of water vapor.
What are the Dry, Saturdated and Environmental lapse rates?
- DALR - 3°/1000’
- SALR - 1.5°/1000’
- ELR - 1.98°/1000’
What lapse rate should you use when calculating cloud bases?
2.5°/1000’
The stability and instability of the atmosphere refers to the suppression or promotion of ____ movement.
vertical
The stability of warm, dry air depends on the relationship between…
the dry adiabatic lapse rate and the environmental lapse rate.
Stable air is associated with what type of visibility?
sustained low vis
Haze layers, drizzle and fog are features of what type of air?
Stable air
One weather condition that may affect visibility in unstable air is…
Snow showers
Stable air becomes unstable as a result of…
Heating from below
What are altocumulus castellanus?
Mid-level tower clouds.
Castellanus clouds are evidence of mid-atmospheric instability.
What process inhibits or blocks rising air?
An inversion
The vertical distance between two specific pressure levels is ___ in cold air than in warm air.
less
A trough is…
An elongated area of relatively low pressure.
A neutral area, not bonded by any one isobar, within which light winds are blowing and the weather is changing very slowly, exists between two high and two low pressure systems. The name given to this indefinite pressure area is…
A col
Port (left) drift = aircraft true altitude ____
incresing
Starboard (right) drift = aircraft true altitude ___
decreasing
What two factors are used to calculate density altitude?
The airport’s pressure altitude and air temp.
True altitude is greater than indicated in conditions of…
warm air and high pressure.
What is MSL pressure?
Station pressure reduced to MSL using the average surface temp for the last 12hrs.
What is altimeter setting?
Station pressure reduced to MSL assuming ISA conditions.
Terrain clearance must be monitored closely when pressures are ___ and temparatures are ___.
low, low
The relationship betwene the amound of water vapor in the air and the maximum possible vapor that could be held by the air at th that temp and pressure.
Relative humidity
What does relative humidity depend on?
Absolute humidity and temperature.
What will the temperatures be if measuring air with a 100% humidity using a dry bulb and a wet bulb thermometer?
The same temp if the relative humidity is 100%
An instrument that is used to measure air humidity?
Psychrometer
The height of the cloud base is most depended on?
The moisture content of the air.
Clouds and precip are most common in areas of ____ air?
Ascending
What type of cloud frequently forms as a result of evaporation from rain, rather than expansion cooling?
Stratus.
Wisps or streaks of water or ice particles that fall from the bottom of a cumuliform cloud and evaporate or sublimate before reaching the ground appear as?
virga
How does drizzle form?
by the coalescence of stratus cloud droplets.
Snow falling from a layer of stratocumulus cloud would indicate that?
The liquid water content in the cloud is decreasing.
An airport weather observer reports snow grains; this type of precip would imply?
that freezing drizzle is present aloft.
A large area of land or ocean of relatively uniform characteristics and above which an air mass can form is known as a…
source region
How are air masses classified?
According to their moisture content
What weather would you expect when Continental Arctic (cA) air moves south over the Great Lakes during the winter?
snow showers just south of the south shoreline.
Review the air masses.
Maritime Polar (mP)
cool, moist
Continental Arctic (cA)
very cold, dry
Continental Polar (cP)
cold, dry
Continental Tropical (cT)
hot, dry
Maritime Tropical (mT)
warm, moist
What weather would you expect when Maritime Tropical (mT) air moves north over the Great Lakes in the spring and early summer?
Low stratus, drizzle and fog over the north shores.
What would initially happen when Continental Arctic (cA) air moves southbound over the Great Lakes in the early autumn?
Steam fog over the northern portions of the lakes.
Fronts are named according to…
the direction of movement of the colder air mass
Which two weather fronts would most likely be present on Canadian weather charts during the winter?
Continental Arctic and Maritime Arctic
What is the sequence of clouds you would expect to encounter as you fly in cold air towards an approaching warm front?
Cirrus (CI), Cirrostratus (CS), Altostratus (AS), Nimbostratus (NS)
The extensive stratiform cloud decks commonly associated with warm fronts are caused by…
overrunning warm air that expands and cools.
4 factors that determine cold frontal weather.
- the stability of the warm air
- moisture content of the warm air
- speed of the font
- steepness of frontal surface
How do the clouds and precip associated with a cold front develop?
by warm air lifting on the frontal surface, then expanding and cooling.
A cold front with a steep frontal surface that is advancing with great rapidity upon moist, unstable air produces a suitable environment for…
a squall line thunderstorm
A combo cold / warm front is most likely associated with…
a trowal
Future movement of the centre of a frontal depression in the Northern Hemisphere tends to be parallel to the…
warm sector isobars
You fly westbound through a trowel, what happens to the temperature?
tremp rises, then falls.
At a stationary front, the cold air moves…
parallel to the front
What’s an occluded front?
When a cold front overtakes a warm front. Warm air is separated (occluded) from the center of the low pressure system at the ground.
What’s a stationary front?
It’s a pair of air masses, neither of which is strong enough to replace the other.
What’s a col?
A col or trough is an elongated region of relatively low pressure
A condition favorable for the development of strong katabatic winds is…
a glacier region
What’s a warm katabatic wind called?
A chinook
What do you call the distance to the farthest point on the ground that can be seen from an aircraft?
slant vis
What’s steam fog?
fog which is formed when very cold air moves over warmer water.
What is radiation fog?
Fog formed when the land cools after sunset on a calm clear evening. The cool ground produces condensation in the nearby air by heat conduction.
What doesn’t radiation fog form over the ocean?
because the ocean doesn’t cool by radiation at night
Does industrial smoke aid in the development of radiation fog?
Yes
Advection fog forms over both ___ and ___ while radiation fog forms only over ___.
land, water, land
What type of fog is caused by adiabatic cooling?
upslope fog
What happens to moist air moving west across the Prairies?
creates widespread upslope fog as it approaches the Rocky Mountains.
Ice fog forms by ___
sublimation
Large supercooled water droplets are most likely found in the ___ levels of cloud formed in ___ air where temps are ___
lower, unstable, just below freezing.
How is Rime ice formed?
- When small supercooled water droplets freeze on contact with a surface which is below zero.
- low catch rate, small droplets
- droplets freeze immediately without spreading
How is clear ice formed?
- forms when temperatures are around 2C to -10C
- large water droplets that spread and freeze
- freezing drizzle or freezing rain.
A cloud formed in stable air will have ___ supercooled water with height when temperatures are ___ freezing
more, just below
Icing in freezing drizzle is the worst at the ___ of the cloud.
bottom
Flying through what type of weather can cause rime ice?
freezing fog
Supercooled rain that freezes while falling through a sub-freezing layer becomes…
ice pellets
When the dewpoint temp is below -0.5°C, it’s sometimes referred to as?
frost point
The term used to describe the growth of a descending ice particle as it collides with nearby water droplets which then freeze onto the particle
Riming
What is hoar frost?
- Occurs when a sub-zero surface comes into contact with moist air.
- Water vapour turns directly into ice by sublimation
Besides a lifting force or triggering action, what other two conditions are necessary for the formation of a thunderstorm?
- lots of moisture
- a steep lapse rate
What indicates the arrival of the mature stage of a thunderstorm?
precip at the surface
What indicates the dissipating stage of a storm cell?
downdrafts through the majority of the cell
At what stage of development of a thunderstorm cell would the most serious icing problem be present?
just before the mature stage
Lightning strikes are at the highest probability at altitudes where the temperature is between…
-5°C and +5°C
Mammatus clouds are associated with…
violent thunderstorms and tornadoes
The name given to a low-level, tube-shaped, detached cloud seen at the leading edge of a cumulonimbus, which is part of a line of thunderstorms?
Roll cloud
Mesocyclonic movement detected by high-resolution Doppler radars is a sign of…
tornado development
What’s the recommend procedure if you accidently enter a thunderstorm?
- slow down to Va
- don’t try to maintain a specific alt or speed.
- maintain present heading
The shaft of a microburst at the surface is normally about ___ wide
2.2nm or less
A condition associated with potentially dangerous wind shear, especially during takeoff and landing is…
- a low level temperature inversion
- with strong winds above the inversion
These are 3 characteristics of ____.
- occur mostly in summer
- form over flat terrain during the presence of southwest winds
- usually associated with temperature inversions
Nocturnal Jet Streams
Before takeoff, you notice rain falling from a convective cloud with a base of around 15,000’ and the rain is evaporating before it reaches the ground. This could signal the presence of…
a dry microburst
These are 3 characteristics of ___.
- the presence of virga
- linked to cumulus clouds with a high base
- evaporative cooling
a dry microburst
Downdrafts associated with a microburst can be as strong as…
6000 feet/min
What types of winds can cause intense wind shear at arctic airports or at airports close to mountains?
valley, katabatic or funnel winds
Altocumulus standing lenticular clouds are a sign of…
a mountain wave
The lowest group of stationary clouds associated with a mountain wave is…
a rotor cloud
Where is the most powerful rotor cloud located when it’s associated with the presence of a mountain wave?
under the first wave crest
The part of the mountain wave system that usually presents the most severe turbulence is located…
between the ground and the top of the rotor cloud
A high-level jet stream oriented perpendicular to the axis of the mountain range can mean what danger?
severe turbulence at high altitude associated with the mountain wave system.
How can a mountain wave affect the altimeter?
It can falsely read high when flying through the crest of a mountain.
On a constant pressure, upper air chart the altitude gradient can be considered as the ___ of the pressure surface.
slope
On upper air contour charts, the wind blows ___ the contours in the same way that the 2000ft wind blows ___
along, along the surface isobars
Upper Air Contour Charts
- wind blows parallel to the height contours
- if the height contours are curved then centrifugal force acts on the wind
- the closer the contours, the stronger the wind
If the ___kt isotachs are spaced closer together than ___nm on the 250 hPa upper-air chart, you can expect sufficient horizontal shear from the occurrence of clear air fight.
30kt, 90nm
isotach = a line on a map connecting points of equal wind speed.
The tropopause can be identified during a climb in the upper troposphere by the occurrence of…
an abrupt change in the temp and lapse rate.
There is an abrupt change in the height of the tropopause over each…
frontal surface
Over a warm air mass the Tropopause is ___ and ___
higher and colder
In ISA conditions the height and temp of the tropopause is…
36,090 ft and -56.5°C
Steep pressure gradients and ___ constitute a major factor in the formation of jet streams.
the Coriolis force
Jetstreams usually occur in an area of intensified temperature gradients that normally exist across upper fronts and with their jet cores positioned just under the warm air tropopause, adjacent to the tropopause break.
North to South jet streams occur when the air beneath the jet stream is colder to the ___ than to the ___.
east, west
List 3 factors of clear air turbulence (CAT) in relation to jet streams.
- curving jet streams are more likely to have turbulent edges especially when they curve around a deep pressure trough
- Wind shear and CAT adjacent to jet streams are more intense above and to the lee side of mountain ranges.
- when two jet streams merge it can produce CAT
Turbulence associated with upper-level troughs is usually more ___ than with ridges.
severe
The jet stream core has the worst vertical extent of clear air turbulence on the side with ___ pressure and the ___ temperature air mass.
low, cold
If you’re flying across the jet stream in North America and experience clear air turbulence and notice the OAT is increasing, you should ___
climb
The polar jet stream moves ___ in the winter, has ___ core speeds and stays at a ___ lower altitude.
south, slower, lower
Flying near the jet stream with a crosswind, you encounter moderate clear air turbulence and notice the OAT is constant. You should…
climb or descend
