Chapter 8.4 - Pressure Systems and Wind Flashcards
What number appears on the Isobars?
MSL Pressure (hPa).
What is a region of High Pressure called and it’s marking on synoptic charts (2)?
- Anticyclone.
- H or High.
What is a region of Low Pressure called and it’s marking on synoptic charts (2)?
- Cyclone/Depression.
- L or Low.
An elongated region of High Pressure extending outwards from an Anticyclone is called?
Ridge.
An elongated region of Low Pressure extending outwards from a Cyclone is called?
Trough.
In an Anticyclone, the central pressure is ‘x’ than the surrounding area?
Greater.
In which directions does airflow in High Pressure?
Anticlockwise.
Which inversion is associated with High Pressure?
Subsidence.
Which type of clouds (if any) form under High Pressure?
Stratiform
In a Cyclone, the central pressure is ‘x’ than the surrounding area?
Lower.
In which directions does airflow in Low Pressure?
Clockwise.
A Cyclone in the tropics is known as?
Tropical Depression.
A Tropical Cyclone is when the central pressure has fallen below ‘x’ hPa and the windspeed has increased to above ‘x’ knots?
- 1000 hPa.
- 34 kts.
Which type of clouds form under Low Pressure?
Cumuliform.
An area of Neutral Pressure between two Anticyclones and Cyclones is called?
Col.
Name three types of Col?
- Anticyclonic Col.
- Cyclonic Col.
- Neutral Col.
True or False. A Col will appear on the weather map with Isobars?
False.
Air in horizontal/vertical motion is called wind?
Horizontal.
Define Pressure Gradient Force?
The resulting force when there is a difference in pressure across a surface.
True or False. The steeper the pressure gradient, the larger the pressure gradient force?
True.
Wind tends to blow at right angles to/parallel to Isobars?
Parallel.
The spacing of Isobars indicate the size of what?
Pressure Gradient.
Describe the wind between Isobars being closer and further apart from each other (2)?
- Closer = Stronger Winds.
- Further = Lighter Winds.
Describe the pressure between Isobars being closer and further apart from each other (2)?
- Closer = Rapid changes in Pressure.
- Further = Slower changes in Pressure.
Wind is described (in maps, charts, ATC and ATIS) as coming from or going to?
Coming from.
Meteorologists will give wind direction from True North/Magnetic North?
True North.
ATC and ATIS will give wind direction from True North/Magnetic North?
Magnetic North.
Define Gradient Wind and its movement around Isobars (2)?
- The wind resulting in the combined forces of Pressure, Coriolis and Centripetal.
- Parallel to.
True or False. Isobars on a surface synoptic chart will indicate the direction and speed of the gradient wind?
True.
True or False. Latitude doesn’t have any effect on Isobars?
False.
Define Friction Layer?
The layer adjacent to the earth’s surface.
Define Surface Wind?
The result of surface friction changing/modifying the gradient wind.
The speed of the surface wind varies the gradient wind by how much percentage over the ocean?
60% to 75%.
The speed of the surface wind varies the gradient wind by how much percentage over land areas?
30% to 50%.
True or False. The friction layer affects the direction of surface wind?
True.
When will Pilots need to know the surface wind?
Takeoff and Landing.
In the southern hemisphere, the wind will always change in which direction?
Clockwise.
Define Gusts?
An increase in windspeed over the mean, lasting for more than a few seconds.
Define Lulls?
A decrease in windspeed below the mean, lasting for more than a few seconds.
Define Squall?
A sudden increase in windspeed lasting for a few minutes and then dissipating.
Define Gale?
Windspeed of 34 kt or more.
Define Veering?
Wind direction changes clockwise.
Define Backing?
Wind direction changes anticlockwise.
What is the average wind speed (kt) in the Wind Category Calm?
Less than 1.
What is the average wind speed (kt) in the Wind Category Light?
1 to 10.
What is the average wind speed (kt) in the Wind Category Moderate?
11 to 21.
What is the average wind speed (kt) in the Wind Category Strong?
22 to 33.
What is the average wind speed (kt) in the Wind Category Gale?
34 to 40.
Name one main cause of local winds?
The density difference between the air over areas of the earth’s surface.
What is a Sea Breeze?
A local wind occurring in coastal areas moving to land.
How are Sea Breezes caused?
Differential heating of the air above the land and sea.
Which times will a Sea Breeze start and will be at its strongest (2)?
- Weak = 0900 LMT.
- Strong = 1500 or 1600 LMT.
A Sea Breeze can last for a distance between?
8 to 16 kilometres inland.
What is a Land Breeze?
A local wind occurring over land moving to sea.
Which times will a Sea Breeze start and will be at its strongest (2)?
- Midnight.
- Just after sunrise.
A Land Breeze can last for a distance between?
5 to 8 kilometres out to sea.
What is Foehn Wind?
Warm and dry wind flowing down the lee side of a mountain.
Both Foehn and Karabatic winds produce which type of currents from high ground?
Down currents.
