2_6 Flashcards
Clouds that can be associated with low ceilings and poor visibility are called:
Stratus
Explanation
Low-level clouds are found between the ground and 6,500 feet. They are composed of water droplets, possibly supercooled, and sometimes ice crystals. Low visibility can
be expected.
Those clouds include stratus (St), stratocumulus (Sc) and nimbostratus (Ns).
The temperature of the air that descends rapidly on the leeward side of a mountain after it has been forced upward on the wind-ward side when it was saturated will _____ at the _____ adiabatic lapse rate.
Increase; dry
Explanation
Orographic lift occurs when the wind blows against a mountain range. The air, forced upward, encounters a lower pressure: it expands and cools. When dew point is met,
condensation occurs, causing the formation of orographic clouds on the wind-ward side and on the upper side of the mountains. The rapid descending air on the leeward
side will not usually create a cloud formation as it has been dried up. Moreover, as it is compressed during the descent, the air warms up at the dry adiabatic lapse rate.
Clouds and precipitations than can be associated with moist and unstable air are:
Towering cumulus and showers.
Cumulus clouds develop in rising air currents and are a show of unstable air.
Convective clouds include cumulus (Cu), towering cumulus (TCu) and cumulonimbus (Cb). Convective clouds are created in unstable air. Flight conditions under those
clouds are turbulent because of vertical currents and turbulence. Precipitation under those clouds is showers.
________ type clouds are characteristic of mountain wave activity.
Lenticular.
Explanation
If the air mass related to orographic waves is moist, it will create particular clouds:
- cap clouds: these cover mountaintops, making them invisible to pilots;
- lenticular clouds: these appear lens-shaped on the ridges of waves, and can expand vertically over several thousands of feet;
- rotor clouds: these are formed in turbulence swirls and can develop to cumulonimbus stage. Their base lies below mountain peaks and their top may exceed the peaks. We find the most severe turbulence between the ground and these clouds.
Jet streams stronger than 110 kts at the core have areas of significant clear air turbulence near them in the sloping tropopause _____ the core, in the jet stream front_____the core and on the ______ pressure side of the core.
Above; below; low.
Explanation
AIM, AIR 2.10: These rules of thumb are given to assist pilots in avoiding clear air turbulence (CAT). They apply to westerly jet streams. The Air Command Weather Manual (TP 9352E) available from Transport Canada discusses this subject more thoroughly.
- Jet streams stronger than 110 kt (at the core) have areas of significant turbulence near them in the sloping tropopause above the core, in the jet stream front below the core and on the low-pressure side of the core.
On a 250 hPa chart, isotachs are close together. What should you expect?
Sufficient horizontal wind shear to cause CAT.
Explanation
AIM, AIR 2.10: These rules of thumb are given to assist pilots in avoiding clear air turbulence (CAT). They apply to westerly jet streams. The Air Command Weather Manual (TP 9352E) available from Transport Canada discusses this subject more thoroughly.
- On charts for standard isobaric surfaces such as the 250 mbs charts, 30 kt isotachs spaced closer than 90 NM indicate sufficient horizontal shear for CAT. This area is normally on the north (low-pressure) side of the jet stream axis, but in unusual cases may occur on the south side.
What type of clouds could be encountered near a mountain wave activity?
Cap clouds.
Rotor clouds.
Lenticular clouds..
Explanation
If the air mass related to orographic waves is moist, it will create particular clouds:
- cap clouds: these cover mountaintops, making them invisible to pilots;
- lenticular clouds: these appear lens-shaped on the ridges of waves, and can expand vertically over several thousands of feet;
- rotor clouds: these are formed in turbulence swirls and can develop to cumulonimbus stage. Their base lies below mountain peaks and their top may exceed the peaks. We find the most severe turbulence between the ground and these clouds.
Coriolis force is caused by:
The rotation of the Earth.
Explanation
Air always moves from high pressure to low pressure zones. The force creating this movement is called the “pressure gradient force.” The Coriolis force, created by Earth’s rotation, forces air in movement to deviate to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. As wind speed increases, the Coriolis force becomes more powerful.
The Coriolis force is nil at the equator and increases with latitude to be the strongest at the poles.
In the Northern Hemisphere, wind blows counterclockwise around the depression and moves away from high pressure deviating to the right (clockwise). The opposite occurs in the Southern Hemisphere.
To find the low-pressure zone, stand with the wind at your back, and low pressure will be on your left (see Buys Ballot’s law).
At night, a ______ may go down slopes when the earth’s surface is cooled by .
Katabatic; radiation.
Explanation
Mountain winds are caused by a slope heating process du
A slope not covered with ice or snow warms up during the day, and warms the air with which it is in contact. This air becomes less dense and moves up the slope to the
mountaintop. This phenomenon is called “anabatic wind.”
The Continental Arctic air mass is:
Dry and cold.
Explanation Continental arctic (cA) and continental polar (cP) air masses both consist of dry and cold air. They arise from extremely cold surfaces (covered by ice and snow) of the
extreme north.
While in flight in the overcast layer of a warm front, precipitation changes from steady rain to heavy showers. This is an indication that:
The warm air is moist and unstable.
An inversion will probably occur if a _____ air mass is over _____
mT; North Atlantic in spring.
Explanation
Inversion is when the Troposphere air temperature is increasing with altitude instead of decreasing.
An inversion can occur at night, when the ground cools down air with which it is in contact. Sometimes this happens when a cold air mass slips under a warm air mass. A tropical maritime air mass (mT) is warm and moist.
A Trowal forms:
During an occlusion.
Explana
A trowal (TROugh of Warm air Aloft) is a trough of warm air in altitude. It is found in warm or cold occlusion, or, in other words, when there are three air masses: a cool air mass moving over a cold air mass or a cold air mass moving over a cool air mass, and a third air mass, of warm air, that creates a trough above those two colder air masses.
What is the cause of the stratus cloud deck common to most warm fronts?
The adiabatic cooling of the climbing warm air.
Explanation
As air rises, it encounters a lower pressure: it expands and cools. This process is called “adiabatic cooling.”
Non-saturated air is cooled by approximately 3°C for each 1,000 feet. This phenomenon is called the “dry adiabatic lapse rate.”
If the air is cooled until the dew point, condensation is formed and clouds appear.
It is easy to see a warm active front approaching. The first clue is high cirrus clouds. Immediately afterward, you can see cirrostratus. It keeps growing until it becomes a solid altostratus and altocumulus mass. Low nimbostratus join altostratus to create a bench of compact clouds with their base close to the surface and their top up to 25,000 feet (sometimes more), which covers the whole area. Precipitation, usually abundant, will create precipitation fog (or frontal fog) and will develop because of extra humidity.
Warm air mass is usually pretty stable, air is calm, which helps the creation of stratus clouds.
During a flight inside stratus type clouds, you would expect _____ ice when the temperature is between _____ and _____
Rime; -10°C; -20°C.
Explanation
Supercooled water droplets in stratus clouds are small. When the temperature of the skin of an aircraft passing through these clouds is below the freezing point, rime ice
will appear. The ideal outside temperature for this type of icing is between -10 and -20°C.
During a navigation flight, you begin to fly at an altitude where the temperature is well below the freezing point. A few nautical miles before your arrival, you decide to start your descent to an altitude where the temperature is back over the freezing point and where it is raining. After a few minutes at this altitude, you notice that a layer of barely visible ice has formed on the aeroplane’s wings, just over the fuel tanks. What is the likely cause of this phenomenon?
The fuel temperature remained below the freezing point, cooling the wings and causing the formation of ice due to rain freezing on the surface.
Explanation
AIM, AIR 2.12.2: (e) The Cold-Soaking Phenomenon: Where fuel tanks are located in the wings of aircraft, the temperature of the fuel greatly affects the temperature of the wing surface above and below these tanks. After a flight, the temperature of an aircraft and the fuel carried in the wing tanks may be considerably colder than the ambient temperature. An aircraft’s cold-soaked wings conduct heat away from precipitation so that, depending on a number of factors, clear ice may form on some aircraft, particularly on wing areas above the fuel tanks. Such ice is difficult to see and, in many instances, cannot be detected other than by touch with the bare hand or by means of a special purpose ice detector.
As well, cold-soaking can cause frost to form on the upper and lower wing under conditions of high relative humidity. This is one type of contamination that can occur in above freezing weather at airports where there is normally no need for de-icing equipment, or where the equipment is deactivated for the summer. This contamination typically occurs where the fuel in the wing tanks becomes cold-soaked to below-freezing temperatures because of low temperature fuel uplifted during the previous stop, or cruising at altitudes where low temperatures are encountered, or both, and a normal descent is made into a region of high humidity. In such instances, frost will form on the under and upper sides of the fuel tank region during the ground turn-around time, and tends to re-form quickly even when removed.
Freezing drizzle:
Causes a severe clear icing just below the cloud it falls from.
Explanation Freezing drizzle (FZDZ) falls from low stratus clouds (but can be found up to 15,000 feet at -10°C) that have a high water content. When leaving the cloud, the drizzle droplet
evaporates: it becomes smaller and smaller as it falls down to the ground. It is why the most severe icing (clear type) will occur just below the cloud, where the droplets are
the largest.
In flight, an aircraft encounters ______ precipitations. You may conclude that freezing rain precipitations will be present at higher altitudes.
Ice pellets.
Explanation
Here are the precipitations you should expect from high to low when crossing a warm front frontal surface in winter:
- snow in the higher cloud part of the warm air mass in which the temperature is below freezing point;
- rain in the cloud part of the air mass in which the temperature is above freezing point;
- freezing rain, caused by the rain going through cold air (usually under warm air), becoming supercooled and freezing upon contact of cold objects (like an aircraft flying at this frontal surface level);
- ice pellets in the area preceding freezing rain, which result from rain freezing when passing through cold air.
If you fly at high altitude, you will only encounter snow. However, if you are at a relatively low altitude and pass from cold air frontal surface to warm air, you will first encounter snow, followed by ice pellets and freezing rain.
What characterizes the dissipating stage of a thunderstorm?
The presence of downdrafts only, in the entire area of the cloud.
Explanation
Thunderstorms start dissipating after precipitation has reached the ground. This cold precipitation cools down the lower part of the cloud, causing a loss of energy in the
thunderstorm cell. The descending current, created by precipitation, extends more and more through the entire cell. Only a thin zone of the summit still has ascending
currents. Precipitation decreases gradually and the summit extends in an anvil shape.
In a tornado, wind circulation is _____ in the Southern Hemisphere.
Clockwise.
Explanation
A low pressure area is called “cyclone.” “depression” or “low pressure.” A depression is a zone where che pressure is relatively low and minimum value is in the centre.
A tornado is an extremely hollow depression, slightly extended, but very concentrated.
Air always moves from high pressure to low pressure zones. The force creating this movement is called che “pressure gradient force.” The Coriolis force, created by Earth’s rotation, forces air in movement to deviate to che right in the Northern Hemisphere and to the left in the Southern Hemisphere. As wind speed increases, the Coriolis force becomes more powerful.
The Coriolis force is nil at the equator and increases with latitude to be che strongest at the poles.
In che Northern Hemisphere, wind blows counterclockwise around the depression and moves away from high pressure deviating to the right (clockwise). The opposite occurs in the Southern hemisphere.
To find che low-pressure zone, stand with the wind at your back, and low pressure will be on your left (see Buys Ballot’s law).
The downdrafts associated with microbursts can reach a vertical speed of feet per minute.
6,000
Explanation
Downdrafts associated with microbursts can reach a vertical speed of 6,000 feet per minute. When arriving close to the ground, they spread out in all directions in
horizontal winds moving as fast as 80 knots. They cause strong wind shears and change direction fast. Microbursts can be found as far as 10 miles from the thunderstorm
cell and can remain for an hour.
Attempting to land below a thunderstorm, even if ceiling and visibility are favourable, is not recommended. This is because of:
The risk of strong irregular winds and gusts.
Explanation
Thunderstorms are responsible for strong winds (downbursts and wind shears), severe turbulence, gusts (up to 80 knots) and squalls. These conditions can be found under the thunderstorm, but also up to a distance of 15 nautical miles away from it. These changes in wind direction are particularly dangerous for aircraft taking off or landing at low altitude and low airspeed.
Low-level wind shear, when associated with a thunderstorm, is caused by a gust front and a strong downburst.
What type of fog is associated with a warm front?
Frontal fog.
Explanation
Precipitation fog, also called frontal fog, can usually be found at the warm front. Drizzle or rain falling down from the warm air evaporates in cold air and saturates it in humidity, which creates fog.
Arctic sea smoke is:
A type of fog that forms when Arctic cold air comes over a relatively warmer body of water.
Explanation
Steam fog occurs when cold air moves over a warm water surface. Water evaporation saturates cold air. Condensation forms and creates this fog which occurs most of the time in fall over lakes and rivers.
Arctic sea smoke is a kind of steam fog.
Radiation fog is caused by:
Air with high relative humidity cooling down during a clear night.
Explanation
Radiation fog occurs during clear nights: the ground cools down and cools the air with which it is in contact.
Ideal conditions for this type of fog include:
- moist air;
- temperature slightly below dew point;
- condensation nuclei;
- light wind increasing cooling in low levels;
- clear sky. allowing faster cooling.
Which of the following situations could lead to advection fog?
An air mass coming from the south shore and moving inward of northern lands during winter.
Explanation
Advection fog is created by warm moist air cooling that moves over a colder surface. It can occur when the air comes from warm land or a warm water surface and goes over a cold water surface. It also can appear when cooled down air is moving from the south to the north.
This fog can persist for many days and covers a wide area. It frequently occurs on the coasts.
Winds provided on _____ are expressed in magnetic degrees.
ATIS
Explanation
To determine if wind direction is being expressed in true or magnetic degrees, remember that “everything written is true.” The ATIS is a spoken message: therefore, the wind direction is in magnetic degrees.
On the other hand, the METAR is a written message: therefore, the wind direction is in true degrees.
Which of the following is true regarding VOLMETs?
The VOLMET is a meteorological information particularly for aircraft over the high seas.
Information on the content, issue times and transmitter frequencies for NAT VOLMET broadcasts is given in the CFS.
The VOLMET contains METARs and TAFs for selected aerodromes and may be provided either by data link (D-VOLMET) or by voice broadcasts on designated frequencies, normally HF.
Explanation
AIM, MET 1.4.1: The VOLMET is meteorological information for aircraft in flight, particularly those over the high seas. The VOLMET contains METARs and aerodrome forecasts (TAF) for selected aerodromes and may be provided either by data link (D-VOLMET) or by voice broadcasts on designated frequencies, normally high frequency (HF).
Information on the content, issue times and transmitter frequencies for NAT VOLMET broadcasts is given in the CFS, Section “D”, Radio Navigation and Communications.
Question 29
METAR CYCB 251900Z 02011KT 1SM BR BKN002 OVC020 01/01 A3000 RMK FG1SF6SC1 VIS SE1/4 S-W 3 SLP163= SPECI CYCB 251852Z 03009KT 1SM BR OVC002 RMK FG1SF7 VIS SE 1/4 W 3=
SPECI CYCB 251813Z 03009KT 1/2SM FG OVC002 RMK FG2ST6 VIS VRB 1/4-3/4=
TAF CYCB 251838Z 2519/2607 04012KT 1/2SM FG OVC002 TEMPO 2519/2521 5SM -DZ BR OVC005 FM252100 02012KT 2 1/2SM -DZ BR OVC005 TEMPO 2521/2607 P6SM NSW
BKN008 OVC015 RMK NXT FCST BY 260100Z=
According to the information above, the difference between the lowest cloud ceiling reported at 1900Z and the one forecasted for the same time is feet.
300.
AIM, MET 7.0: See explanations.
AIM, MET 7.4: “TEMPO” is only used when the modified forecast condition is expected to last less than one hour in each instance, and if expected to recur, the total period of the modified condition will not cover more than half of the total forecast period. The total period of the modified condition is the time period during which the actual modified weather condition is expected to occur, and not the total time stated for the ‘TEMPO” time period. When the modified forecast condition is expected to last more than one hour, either “FM” or “BECMG” must be used.
AIM, MET 8.0: See explanations.
An urgent PIREP will have the following code:
UACN01.
Explanation
AIM, MET 1.1.6.1: PIREPs are also transmitted under the headings “UACN10” for normal PIREPs and “UACN01” or “UUA” for urgent PIREPs.
On a Clouds and Weather GFA chart, a scalloped border, depicted in brown when shown in colour, encloses organized areas of clouds where the sky condition is:
BKN or OVC.
Explanation
AIM, MET 4.11: (b) Clouds: A scalloped border, depicted in brown when shown in colour, encloses organized areas of clouds where the sky condition is either broken (BKN) or overcast (OVC).
Where organized areas of clouds are not forecast and visibility is expected to be greater than 6 SM, a scalloped border is not used. In these areas, the sky condition is stated using the terms SKC. FEW or SCT.
When are winds indicated in GFAs?
When they blow at 20 knots or more.
Explanation
AIM, MET 4.11: (g) Surface winds—The speed and direction of forecast surface winds with a sustained speed of at least 20 kt are indicated by wind barbs and an associated windspeed value. When accompanied by strong gusts, mean sustained winds of less than 20 kt may also be included, at the forecaster’s discretion, if moderate mechanical turbulence is expected to occur as a result of the wind gusts. Wind gusts are indicated by the letter “G,” followed by the peak gust speed in knots (KT).
