50 02 Local Winds Flashcards
(42 cards)
What device measures the wind strength and what measures the direction?
How high are these placed above the ground?
- Anetometer measures the wind strength
- Wind Vane measures the wind direction
- These are placed 10m off the ground to avoid interference from the ground
Conversions from kts to:
- Km/h
- m/s
- mph
- 1 kt = 1.85 Km/h
- 1 kt = 0.5 m/s
- 1 kt = 1.15 mph
Wind Speeds: Gust
- Sudden increase in wind speed of 10kts above the average
- lasts for less than 1 min
Wind Speeds: Squall
- A gust lasting more than 1 min
Wind Speeds: Lull
- A sudden drop in wind speeds
Wind Speeds: Calm
- Wind speeds of 1 kt or less
Wind Speeds: Gale
- Wind speeds of 34kts to 47kts
Wind Speeds: Storm
- Wind speeds of 48kts to 63kts
Wind Speeds: Hurricane
- Wind speeds of 64kts+
What is it called when wind changes direction in:
- Clockwise direction
- Anti-clockwise direction
- Clockwise: Veering
- Anti-clockwise: Backing
The Corilois effect bends the wind in what direction in:
- Northern Hemisphere
- Southern Hemisphere
- Northern: Right
- Southern: Left
Buys Ballot Law
Someone standing with their back to the wind, in the northern hemisphere, will have low pressure to their left.
What is Geostrophic wind and what are the forces involved?
When is it fastest?
- Geostrophic wind is wind moving along a straight line (i.e. straight isobars)
- It is when the Pressure Gradient force (PGF) and the Coriolis Force (or Geostrophic Force) are equal and opposite
- It is fastest when the CF is smallest (at the equator) as the CF slows Geostrophic wind down
What is Gradient wind and what are the forces involved?
- Gradient wind is curved wind which follows the curved isobars
- There are three forces involved in Gradient wind:
~ Pressure Gradient Force
~ Coriolis Force
~ Centripetal Force
Which pressure system (high or low), given the same spacing of isobars, would have the fastest winds?
A high pressure system will have faster winds since the the Centrifugal and Pressure Gradient Forces are working in the same direction.
At what height do the Geostrophic and Gradient winds sit at?
2000 to 3000 ft
What happens to winds below 2000 - 3000 ft with regards to the Coriolis effect and Pressure Gradient Force?
- As the wind is closer to the surface its spd drops (due to friction)
- This means that the Coriolis effect is smaller and PGF predominates
- In the Northern Hemisphere the wind Backs and Slacks
- Turns to the Left
For the following what are the degree of deflection, and speed reductions?
- Sea
- Land Day
- Land Night
- Sea: 10 degrees, 70% of original speed
- Land Day: 30 degrees, 50% of original speed
- Land Night: 45 degrees, 25% of original speed
Describe Anabatic Winds:
- What they are
- Speed
- What they cause
- Anabatic winds are caused when the sides of a valley or mountain are heated. This causes the air to rise up the side of the valley/mountain.
- About 5kts
- The resultant low pressure creates Vally Winds
Describe Katabatic Winds
- What they are
- Speed
- What they cause
- Katabatic winds are caused by cooling air sinking down the sides of a valley or mountain.
- Faster at 8 to 10kts
- The resultant High pressure creates Mountain winds (sometimes referred to as Valley winds)
What is the Head Land effect?
The head land effect is caused by an out crop of land which causes the streamlines across the sea to converge.
This increases the speed of the wind around the outcrop (or headland)
Describe what causes a Sea breeze and when it occurs?
- Sea breezes occur during the day
- When the sun warms the land it warms much faster than the sea. The air in contact with the surface warms (through Conduction). This air rises and diverges out. The portion which moves out to sea cools and sinks. The relatively high pressure out to sea and low pressure on land causes the air to move back towards land.
- The sea breeze brings moister with it and so clouds often form over land with precipitation.
- As the day goes on the sea breeze becomes stronger and goes further inland.
- About 10 kts.
- 5 to 10nm inland
Describe a Land Breeze and when it occurs?
- Land Breezes occur only at night.
- When the land cools much faster than the sea. They are the opposite of sea breezes
- Generally weaker then Sea Breezes
Describe the following regarding Mountain waves (aka Standing or Lee waves)
- Conditions needed
- Effects caused
- Types of cloud produced
Conditions:
- Winds increasing with speed with increasing altitude
- Minimum speeds of 15-20 kts
- Wind direction must within 30 degrees of the perpendicular
- A layer of stable air between unstable layers on the lee side
Effects:
- Creates ‘waves’ as the air rises and falls between the stable and unstable layers
- Waves can reach lengths of 5 to 10 nm and heights of 1500 ft
- Waves can reach 50 to 100 nm downwind from source
- Under waves an area of turbulence is generated in the ‘Roll Zone’
- Waves can go as high as the tropopause
Cloud produced:
- Lenticular cloud in the waves
- Roll cloud in the ‘Roll Zone’
- Cap cloud on the top of the mountain
