C13 - Cloud Formation and Precipitation Flashcards
Define Advection?
Horizontal Movement of Air.
Describe an example of Advection?
Warm, moist air moves over a cooler surface is cooled from below.
During Advection what happens in the cloud when along the surface (2)?
- Cause Condensation.
- Low-Level Clouds.
During Advection, when the Visibility is less than 1,000m, what weather phenomenon occurs?
Advection Fog.
What two factors are required to lift Advection Fog to become Stratus Clouds?
- Wind.
- Rising Temperatures.
True or False. Continued cooling from Advection Fog can lead to a layer of Nimbostratus Clouds?
True.
Define Radiation?
Layer of Air in contact with the surface cools by Conduction.
During Radiation, if the Air cooled below its Dew Point, what weather phenomenon occurs?
Radiation Fog.
Radiation is a winter ‘____’ system?
High Pressure.
What conditions are needed to produce Radiation Fog (3)?
- Clear Skies.
- Winter Night.
- < 5kt of Wind.
What two factors are required to lift Radiation Fog to become Stratus Clouds?
- Wind.
- Rising Temperatures.
True or False. Uplift is the most significant cause of Cloud Formation? Why (2)?
- True.
- Air is forced to rise, expands and cools adiabatically.
Unsaturated Air cools at the rate of?
3°C per 1,000 ft.
The Dew Point of Air decreases at the rate of?
0.5°C per 1,000 ft.
Further reduction in Temperature caused by continuing Uplift, results in water condensing out into visible moisture droplets. This occurs at the ‘____’?
Condensation Level.
What is the formula to calculate Cloud Base?
(Temperature – Dew Point) x 400.
The lower the Dew Point, relative to the Temperature of the Air Parcel, the ‘____’ the Cloud Base?
Higher.
How can we calculate the Cloud Tops?
When Environmental Lapse Rate is equal to Saturated Adiabatic Lapse Rate.
Increased warming in Stable Atmospheric Conditions will cause Clouds to ‘____’?
Dissipate.
True or False. Cloud will not dissipate with general changes in the characteristics of an Air Mass?
False.
What are the most common factors which causes Air to Rise (5)?
- Turbulent Uplift/Mixing.
- Orographic Uplift.
- Convection.
- Frontal Uplift.
- Convergence.
Turbulence near the surface is caused by the disruption of smooth airflow by ‘____’ and ‘____’ effects. Either of these effects can produce a ‘____’ of air from the surface to a height of about ‘____’ (4)?
- Mechanical.
- Thermal.
- Turbulent Layer/Friction Layer.
- 2,000 ft.
When Wind meets a physical barrier such as hills or mountains the Air is forced to ‘____’ and thus begins to ‘____’. This is known as ‘____’ (3)?
- Rise.
- Cool Adiabatically.
- Orographic Uplift.
True or False. Hills and Mountains are prolific Cloud producers?
True.
Orographic Cloud in Unstable Conditions are cause what type of Clouds?
Rapid growth of Cumuliform Clouds.
True or False. Severe Storms can’t be generated by Mountains which can cause Severe Turbulence, Icing, Lighting and Hail?
False. It can.
Orographic Cloud in Stable Conditions are cause what type of Clouds?
Cap Clouds (Stratus).
Air is forced to ‘____’ on the Windward side of the Mountain and to ‘____’ on the Leeside of the Mountain?
- Rise.
- Sink.
On the Leeward side of a Mountain the Cloud eventually evaporates due to ‘____’?
Adiabatic Warming.
When the Wind is strong, Orographic effects in a Stable Atmosphere can produce what weather phenomenon (3)?
- Mountain Waves.
- Lenticularis.
- Rotor Clouds.
When Air at Low-Levels are warmed by the surface, it heats up and expands. The reduction in Density causes it to become buoyant and to rise. This is known as?
Convection Uplift.
Convection currents are strongest over land masses during which period?
Summer Afternoons.
What type of Cloud can form under Convection Uplift?
Cumuliform Clouds.
Define a Front?
Boundary between a large mass of Warm Air and a large mass of Cold Air.
When a cold mass of Air moves, the cold, denser Air slides underneath the warmer lighter Air. This is known as?
A Cold Front.
When a warm mass of Air moves, the warm Air rides up over the cold denser Air. This is known as?
A Warm Front.
Frontal Uplift is the most common form of Uplift found in the ‘____’ of the World?
Mid-Latitudes.
When Wind from one direction meets Wind coming from the opposite direction, this causes a general uplifting at the meeting point. This is known as?
Convergence Uplift.
Convergence Uplift is a common feature of ‘____’ and is often associated with ‘____’ conditions (2)?
- Low Pressure Troughs.
- Poor.
What is the name of the most famous Convergence in the World?
Intertropical Convergence Zone (ITCZ).
What type of Cloud are found in the ITCZ?
Cumuliform Clouds.
What Hazards associated with Precipitation (6)?
- Reduced Visibility.
- Airframe Icing.
- Malfunction of Aircraft Sensors.
- Flame-out of Gas Turbine Engines.
- Structural Damage.
- Degrade Take-off and Landings performance.
The type of Precipitation depends on what two factors?
- Cloud Structure.
- Speed of Ascending Air.
When ascending air cools below its ‘____’, ‘____’ or ‘____’ takes place and Water Vapour changes state either to Liquid Water or Ice Crystals (3)?
- Dew Point.
- Condensation.
- Sublimation.
Intense ‘____’ produces the heaviest Water Droplets and the largest Hailstones?
Cumulonimbus.
The process of Ice Crystal growth occurs in Clouds which are below ‘____’ and which contain a mixture of Supercooled Water and Ice?
0°C.
True or False. Water Droplets are easier to form that Ice Crystals?
False. Ice Crystals are easier.
As Ice Crystals grow and fall, they pass through the Cloud Base, if this is above ‘____’ the Ice Crystals will ‘____’ and fall as ‘____’ (3)?
- Freezing.
- Melt.
- Rain.
If there is a sub-zero layer of Air below the Cloud, the rain may ‘____’ in the form of ‘____’ (2)?
- Refreeze.
- Ice Pellets.
If the layer of Freezing Air is at the surface the Precipitation will fall as ‘____’?
Freezing Rain.
How can a Pilot avoid Freezing Rain?
By climbing above the Cloud.
Define Coalescence Theory?
Formation of Precipitation in Clouds warmer that 0°C.
During Condensation/Sublimation, what is the size of Water Droplets/Ice Crystals?
0.02mm.
What size of Water Droplets can be found in Updraughts of Air (2)?
- Strong Updraught = Large Droplets.
- Weak Updraught = Small Droplets.
What is the Abbreviation, Water Droplet size and Cloud type association for Drizzle (3)?
- DZ.
- 0.5mm.
- Stratiform Clouds.
What is the Abbreviation, Water Droplet size and Cloud type association for Rain (3)?
- RA.
- 0.5 to 5.5mm.
- Cumuliform Clouds.
What happens to Water Droplets bigger than 5.5mm?
They break apart during descent.
Unbranched ‘____’ fall as needles, columns or plates of Ice. What am I?
Ice Crystals.
Ice Crystals which are branched, star-shaped or mixed with unbranched crystals. What am I and my abbreviation code (2)?
- Snow.
- SN.
Larger Snowflakes are produced ‘____’ -5°C and smaller Snowflakes are produced ‘____’ -5°C (2)?
- Above.
- Below.
Precipitation can fall as Snow as long as the Surface Temperature does not exceed ‘____’?
+4°C.
Very small, white, opaque grains of Ice with a diameter less than 1mm. What am I?
Snow Grains.
White and often called soft hail with a diameter between 2 to 5mm. What am I?
Snow Pellets.
Larger than Snow Pellets and comprise clear Ice. What am I and my abbreviation code (2)?
- Ice Pellets.
- PL.
Rain and Snow falling together, or Snow Melting as it falls. What am I?
Sleet.
White or opaque and vary greatly in Size. What am I and my abbreviation code (2)?
- Hail.
- GR/GS.
Hail of less than ‘____’ is called Small Hail and the abbreviation code is ‘____’. Hail which is larger the abbreviation code is ‘____’ (3)?
- 5mm.
- GS.
- GR.
Hailstones can only form deep in which type of Clouds?
Cumulonimbus Clouds.
What is the Intensity of Precipitation for Rain and Snow (3)?
- Slight = < 0.5.
- Moderate = 0.5 to 4.
- Heavy = > 4.
What is the Intensity of Precipitation for Rain/Hail Showers (4)?
- Slight = < 2.
- Moderate = 2 to 10.
- Heavy = 10 to 50.
- Violent = > 50.
Name three types of Continuity of Precipitation?
- Continuous.
- Intermittent.
- Showers.
Define Continuous Precipitation?
No breaks for more than 60 minutes.
Define Intermittent Precipitation?
No breaks for less than 60 minutes.
Define Showers?
Associated with Rain, Snow, Sleet or Hail.
Name two types of Clouds where Drizzle can be found?
- Stratus (St).
- Stratocumulus (Sc).
Name two types of Clouds where Continuous Rain and Snow can be found?
- Thick Altostratus (As).
- Nimbostratus (Ns).
Which type of Cloud can Hail be found?
Cumulonimbus (Cb).
Name two types of Clouds where Intermittent Rain and Snow can be found?
- Thick Altostratus (As).
- Stratocumulus (Sc).
Name two types of Clouds where Rain and Snow Showers can be found?
- Heavy Cumulus (Cu).
- Heavy Cumulonimbus (Cb).
