07. Topographic Effects and Sea Breezes Flashcards
Topographic Effects and Sea Breezes
Within the boundary layer at the surface, air will steadily INCREASE or DECREASE in speed with an increase in altitude
INCREASE
- Surface air suffers friction against the surface of the earth
- As it moves away from the earth, the friction force becomes less until such point that airflow is free flowing
- Similar principle in PoF lessons with air stream flow over an aerofoil
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Topographic Effects and Sea Breezes
How will the roughness of a surface impact on the boundary layer
MORE ROUGH MEANS MORE FRITCTON
MORE FRICTION MEANS SLOWER SPEED
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Topographic Effects and Sea Breezes
What are the 2 classes by which the boundary layer can be categorised
- TURBULENT
- LAMINAR
Topographic Effects and Sea Breezes
In the boundary layer, vertical mixing takes place if the airflow is LAMINAR or TURBULENT
TURBULENT
- Air streams are free to flow over each other
- In turbulent air flow, there is a degree of vertical mixing
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Topographic Effects and Sea Breezes
Air flow in the boundary layer will be FASTER or SLOWER in turbulent conditions compared to laminar conditions
FASTER
- vertical mixing means that lower air is mixed with higher free stream air, having a non linear reduction in speed down through the layers
- Compared to laminar flow as per the diagram in below link, the wind is faster at the same given level
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Topographic Effects and Sea Breezes
An anemometer measures wind speed typically at what height in meters above the ground, and in the best practical location on the airfield
10m
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Topographic Effects and Sea Breezes
The LAMINAR or TURBULENT boundary layer is the thicker of the 2.
TURBULENT
Topographic Effects and Sea Breezes
The turbulent boundary layer is how many feet thick
2000 ft
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Topographic Effects and Sea Breezes
The laminar boundary layer is between how many feet thick
1000 ft to 1500 ft
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Topographic Effects and Sea Breezes
- The average time an anemometer reading is taken for local routine and special reports is how many minutes
- The average time an aneomometer reading is taken for aerodrome routine reports (METARs) is how many minutes
- 2 MIN
- 10 MIN
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Topographic Effects and Sea Breezes
What are the dangers of a decreasing headwind with a constant airspeed on descent for an aircraft which is maintaining a 3° approach
INCREASING GROUNDSPEED
- WIth a decreasing headwind component, the airspeed will increase if the speed is maintained as constant
- If an aircraft is descending at a specific rate i.e. 750ft per min and airspeed increases, to maintain the same approach of 3°, the rate of descent must be increased with an increase in groundspeed
- A pilot must monitor the descent very carefully
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Topographic Effects and Sea Breezes
Whether the boundary layer is laminar or turbulent depends on what 2 things in relation to the topography of the land
- MECHANICAL MIXING
- THERMAL CONVECTION
- Mechanical mixing can happen around hills which forces air mixing
- Thermal convection from the surface can cause vertifcal lifting, which can lead to a depression
- It is accurate to summize with these conditions that we expect;
- Laminar airflow over cold flat surfaces
- Turbulent airflow over hot rough surfaces
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Topographic Effects and Sea Breezes
The boundary layer is either laminar or turblent based on mechanical mixing or thermal convection, where mechanical mixing happens over hills and rought surfaces, and thermal convection happens over very warm surfaces.
It is fair to summize therefore that;
- You can expect laminar airflow over HOT or COLD surfaces that are FLAT or ROUGH
- You can expect turbulent airflow over HOT or COLD surfaces that are FLAT or ROUGH
- COLD & FLAT
- HOT & ROUGH
- Mechanical mixing can happen around hills which forces air mixing
- Thermal convection from the surface can cause vertifcal lifting, which can lead to a depression
- It is accurate to summize with these conditions that we expect;
- Laminar airflow over cold flat surfaces
- Turbulent airflow over hot rough surfaces
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Topographic Effects and Sea Breezes
What are the 3 primary factors that determine the depth of the boundary layer
- STABILITY
- WIND SPEED
- SURFACE ROUGHNESS
- Air can be warmor cold, stable or unstable, but it is known that unstable air will have a deeper boundary layer than stable air as it will want to rise
- We know that orographic lifting can trigger unstable air rising, so rough surfaces in unstable air will have a deeper boundary layer than smooth surfaces with stable air
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Topographic Effects and Sea Breezes
As a result of surface frictiong slowing the air, this effects what force in terms of wind, PGF or CORIOLIS FORCE
CORIOLIS FORCE
- Pressure gradient force remains the same and unchanged
- Coriolis force will be slowed down
- This means that wind will turn towards low pressure areas
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Topographic Effects and Sea Breezes
We know that Low pressure is to the left in the Northern Hemisphere. Applying the knowledge that surface friction weakens the coriolis force, as you descent through the boundary layer, the wind speed will reduce and turn towards the LEFT or RIGHT
LEFT
- Pressure gradient force remains the same and unchanged
- Coriolis force will be slowed down
- This means that wind will turn towards low pressure areas
- In the Norther Hemisphere, the wind BACKS at the surface
- In the Southern Hemisphere, the wind VEERS at the surface
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Topographic Effects and Sea Breezes
We know that Low pressure is to the right in the Southern Hemisphere. Applying the knowledge that surface friction weakens the coriolis force, as you descent through the boundary layer, the wind speed will reduce and turn towards the LEFT or RIGHT
RIGHT
- Pressure gradient force remains the same and unchanged
- Coriolis force will be slowed down
- This means that wind will turn towards low pressure areas
- In the Norther Hemisphere, the wind BACKS at the surface
- In the Southern Hemisphere, the wind VEERS at the surface
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Topographic Effects and Sea Breezes
In the Northern Hemisphere, the closer to the surface you are, the wind VEERS or BACKS
BACKS
- Pressure gradient force remains the same and unchanged
- Coriolis force will be slowed down
- This means that wind will turn towards low pressure areas
- In the Norther Hemisphere, the wind BACKS at the surface
- In the Southern Hemisphere, the wind VEERS at the surface
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Topographic Effects and Sea Breezes
In the Southern Hemisphere, the closer to the surface you are, the wind VEERS or BACKS
VEERS
- Pressure gradient force remains the same and unchanged
- Coriolis force will be slowed down
- This means that wind will turn towards low pressure areas
- In the Norther Hemisphere, the wind BACKS at the surface
- In the Southern Hemisphere, the wind VEERS at the surface
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Topographic Effects and Sea Breezes
By what degree (°) does the wind back by day in the Northern Hemisphere over land, which is ____% of freestream airspeed
- 30°
- 50%
- Surface friction is greatest over land and night when the air is colder and thicker
- With more surface friction, this means the air is slowed more, having more adverse effect on coriolis
- This means that over land at night, the wind will back MORE than during the day
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Topographic Effects and Sea Breezes
By what degree (°) does the wind back by night in the Northern Hemisphere over land, which is ____% of freestream airspeed
- 40°
- 30%
- Surface friction is greatest over land and night when the air is colder and thicker
- With more surface friction, this means the air is slowed more, having more adverse effect on coriolis
- This means that over land at night, the wind will back MORE than during the day
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Topographic Effects and Sea Breezes
By what degree (°) does the wind back by day in the Northern Hemisphere over sea, which is ____% of freestream airspeed
- 10°
- 70%
- Surface friction is greatest over land and night when the air is colder and thicker
- With more surface friction, this means the air is slowed more, having more adverse effect on coriolis
- This means that over land at night, the wind will back MORE than during the day
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Topographic Effects and Sea Breezes
By what degree (°) does the wind back by night in the Northern Hemisphere over sea, which is ____% of freestream airspeed
- 10°
- 70%
- Surface friction is greatest over land and night when the air is colder and thicker
- With more surface friction, this means the air is slowed more, having more adverse effect on coriolis
- This means that over land at night, the wind will back MORE than during the day
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Topographic Effects and Sea Breezes
When the pressure pattern is changing rapidly this causes air to blow across isobars in order to flow into low pressure areas. Flow across the isobars can be calculated by measuring the rate of change of pressure. This is done by drawing lines of equal rate of change of pressure. These are known as what
ISALLOBARS
- ISALLOBARIC EFFECT is Modification to the gradient and geostrophic wind caused by air blowing across isobars when pressure is changing rapidly
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Topographic Effects and Sea Breezes
When the pressure pattern is changing rapidly this causes air to blow across isobars in order to flow into low pressure areas. Flow across the isobars can be calculated by measuring the rate of change of pressure by drawing lines of equal rate of change of pressure called isallobars. The effect of the wind blowing over the isobars is known as what
ISALLOBARIC EFFECT
- ISALLOBARIC EFFECT is Modification to the gradient and geostrophic wind caused by air blowing across isobars when pressure is changing rapidly
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Topographic Effects and Sea Breezes
Why does converging wind in a valley increase in speed
VENTURI EFFECT
- The valley acts like a venturi tube
- When the streamlines are forced to converge due to the walls of the valley, this reduces static pressure and increases dynamic pressure to keep total pressure equal
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Topographic Effects and Sea Breezes
“During the day, the thin air above a high mountain sides warm quickly. The warm air rises and creates a local low pressure along the slope. Air from the lower valley moves in to replace the air that has warmed and risen, creating an upslope breeze.”
This is a definition of what sort of breeze
VALLEY BREEZE
- the valley air replaces the warm air that has risen, hence Valley breeze
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Topographic Effects and Sea Breezes
“At night, high mountain slopes cool very quickly. This cold, dnese air forms a local high pressure area. The pressure gradient drives a gentl breeze down the slope into the valley that is strongest just before sunrise”
This is a definition of what sort of breeze
MOUNTAIN BREEZE
- The air is flowing FROM the mountain into the valley, hence mountain breeze
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Topographic Effects and Sea Breezes
“warm dry winds that blow on the lee side of mountains. Named after the valley in Switzerland where they were first identified”
This is known as what sort of wind
FOHN WIND
- Moist stable air will be orographically lifted
- As it rises, it will be cooled at the DALR until it reaches the dew point
- Onc ethe dew point is reached, cloud forms, percipitation falls, and the air cools at the SALR until it reaches the mountain top
- As the air is stable, it will start to descend on the leeside however, since water content has been lost, the cloud base is higher than on the windward side
- The air will cool at the SALR until the cloud base is reached, then it will warm at the DALR until the surface
- As a result, the air on the leeside will be warmer at the foot of the mountain than on the windward side
- Fohn winds will be WARM and DRY on the LEEDWARD side of the mountain
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Topographic Effects and Sea Breezes
As a result of the Fohn effect, moist stable air orographically lifting over a mountain will GAIN or LOSE water vapour content, and will be WARMER or COLDER on the leeside than windward
- LOSE WATER VAPOUR
- WARMER
- Moist stable air will be orographically lifted
- As it rises, it will be cooled at the DALR until it reaches the dew point
- Onc ethe dew point is reached, cloud forms, percipitation falls, and the air cools at the SALR until it reaches the mountain top
- As the air is stable, it will start to descend on the leeside however, since water content has been lost, the cloud base is higher than on the windward side
- The air will cool at the SALR until the cloud base is reached, then it will warm at the DALR until the surface
- As a result, the air on the leeside will be warmer at the foot of the mountain than on the windward side
- Fohn winds will be WARM and DRY on the LEEDWARD side of the mountain
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Topographic Effects and Sea Breezes
A Fohn wind will be COLD & WET or WARM & DRY on the leeside of a mountain
WARM & DRY
- Moist stable air will be orographically lifted
- As it rises, it will be cooled at the DALR until it reaches the dew point
- Onc ethe dew point is reached, cloud forms, percipitation falls, and the air cools at the SALR until it reaches the mountain top
- As the air is stable, it will start to descend on the leeside however, since water content has been lost, the cloud base is higher than on the windward side
- The air will cool at the SALR until the cloud base is reached, then it will warm at the DALR until the surface
- As a result, the air on the leeside will be warmer at the foot of the mountain than on the windward side
- Fohn winds will be WARM and DRY on the LEEDWARD side of the mountain
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Topographic Effects and Sea Breezes
“A wind that flows down the sides of hills and mountains at night or very cold days when there is no strong gradient wind to hide the effect. The cold surface cools the air in contact by conduction, and the colder and more dense air begins to slide down the mountaing”
This is what type of wind
Katabatic or Anabatic
KATABATIC
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Topographic Effects and Sea Breezes
A Fohn wind effect is most notable around mountain areas where ANABATIC or KATABATIC winds occur
KATABATIC
- Katabatic winds take cold air down to pool inthe valley at night
- At dawn, the fohn wind effect produces a marked temperature inversion i.e. warming air over the leeside will sit on the low level valley cold air
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Topographic Effects and Sea Breezes
A location over the Canadian prairies where the Fohn wind is known to be very prolific
CHINOOK
Topographic Effects and Sea Breezes
What is the formula to calculate the rise in temperature at MSL on the leeside of a mountain due to the effects of a Fohn wind
TEMPERATURE RISE = (LEE CLOUDBASE - WINDWARD CLOUDBASE) x 1.2
EXAMPLE:
* A moist stable airmass is blowing over a range of hills 6000 ft high. The windward cloudbase is 1000 ft AMSL, the lee cloudbase 4000 ft AMSL. If the MSL temperature on the windward side is +15℃, what is the MSL temperature on the lee side
APPLY FORMULA
* TEMPERATURE RISE = (LEE CLOUDBASE - WINDWARD CLOUDBASE) x 1.2
* (4 - 1) x 1.2
* 3 x 1.2
* ** 3.6℃**
DETERMINE TEMPERATURE
* The MSL temperature on the windward side is +15℃
* The leeside is +3.6℃ warmer
* 15 + 3.6 = 18.6
* ** 18.6℃**
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Topographic Effects and Sea Breezes
A moist stable airmass is blowing over a range of hills 6000 ft high. The windward cloudbase is 1000 ft AMSL, the lee cloudbase 4000 ft AMSL. If the MSL temperature on the windward side is +15℃, what is the MSL temperature on the lee side
+18.6℃
APPLY FORMULA
* TEMPERATURE RISE = (LEE CLOUDBASE - WINDWARD CLOUDBASE) x 1.2
* (4 - 1) x 1.2
* 3 x 1.2
* ** 3.6℃**
DETERMINE TEMPERATURE
* The MSL temperature on the windward side is +15℃
* The leeside is +3.6℃ warmer
* 15 + 3.6 = 18.6
* ** 18.6℃**
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Topographic Effects and Sea Breezes
A famous wind in France that is known due to its katabatic effects as it passes down the Rhone Valley
MISTRAL WIND
- The bora that flows off the alsp into the North Adriatic is a katabatic wind that reaches peeds of up to 70 kts at low levels
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Topographic Effects and Sea Breezes
“A wind that flows up the side of mountains when the surface is hot, during the day. The air in contact with the surface is heated by conduction, and the less dense air slides up the hill. The heated air will tend to convect straight up rather than follow the slipe of the mountain so only really show when there is a gentle gradient wind flowing onto the slope”
Katabatic or Anabatic
ANABATIC
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Topographic Effects and Sea Breezes
“Air rising up the hill and cooling at the adiabatic lapse rate will rbing the zero degree isotherm lower on the windward side of a hill. This, combined with the updraft may produce ____ and ____ on the windward side”
What is the associated hazard to the definition above
- MODERATE ICING
- TURBULENCE
- If the zero degree isotherm is lower, this means icing will occur lower
- Updraft of air, warm or cold, stable or unstable, will cause turbulence
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Topographic Effects and Sea Breezes
“airflow over a hill summit may induce lower pressures”
What is the associated hazard with this definition in relation to altitude
ALTIMETER OVERREAD
- REMEMBER HIGH to LOW, watching out BELOW
- If pressure drops over a mountain, your altimeter will read higher than it really is
- This is particularly hazardous when passing over a mountain/hill top as the pilot will want to know confidently what their clearance level is
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Topographic Effects and Sea Breezes
“On lee side of hills, the warm Fohn wind may generate a temperature inversion. Cold katabatic flow undercutting warmer air will have a smilar effect. The inversion will bring ____, ____ and ____ at the top of the cold layer”
What are the associated hazards with this definition
- WINDHSEAR
- TURBULENCE
- PERFORMACE DEGRADATION
- If taking off in a valley, colder, dense air at the bottom will increase performance
- As the aircraft breaks through the cold layer, the air will be less dense
- For a given airspeed, this means performance will drop off, so rate of climb will decrease and airspeed will decrease. More thrust will therefore be required
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Topographic Effects and Sea Breezes
The breeze will typically blow from sea to land during the DAY or NIGHT and is known as a SEA or LAND breeze
- DAY
- SEA BREEZE
- During the day land warms up air in contact by conduction and radiation
- Air parcles warm and expands
- This creates a pressure differential as the same pressure over land is now higher than over sea
- At night, land will cool faster than the sea from loss of heat through radiation.
- The air over sea will therefore have a higher pressure for a given level meaning air will want to flow from land to see
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Topographic Effects and Sea Breezes
The breeze will typically blow from land to sea during the DAY or NIGHT and is known as a SEA or LAND breeze
- NIGHT
- LAND BREEZE
- During the day land warms up air in contact by conduction and radiation
- Air parcles warm and expands
- This creates a pressure differential as the same pressure over land is now higher than over sea
- At night, land will cool faster than the sea from loss of heat through radiation.
- The air over sea will therefore have a higher pressure for a given level meaning air will want to flow from land to see
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Topographic Effects and Sea Breezes
The air flowing in to land from a sea breeze is typically WARM or COLD and DRY or DAMP
COLD & DAMP
- During the day land warms up air in contact by conduction and radiation
- Air parcles warm and expands
- This creates a pressure differential as the same pressure over land is now higher than over sea
- At night, land will cool faster than the sea from loss of heat through radiation.
- The air over sea will therefore have a higher pressure for a given level meaning air will want to flow from land to see
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Topographic Effects and Sea Breezes
During the day as land warms up, the sea breeze will become STRONGER or WEAKER and as a result penetrate FURTHER or SHORTER inland
- STRONGER
- FURTHER
- During the day land warms up air in contact by conduction and radiation
- Air parcles warm and expands
- This creates a pressure differential as the same pressure over land is now higher than over sea
- At night, land will cool faster than the sea from loss of heat through radiation.
- The air over sea will therefore have a higher pressure for a given level meaning air will want to flow from land to see
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Topographic Effects and Sea Breezes
During the day as land warms up, the sea breeze will become stronger and penetrate further inland. In the Northern Hemisphere, as a result the wind will BACK or VEER as a result of the strengthened coriolis force
VEER
- stronger wind means that it can overcome friction more easily
- As a result, the wind will back less
- An example is a beach that runs from North to South in the Northern Hemisphere i.e. beach is on my right and sea on my left if I stood facing north
- The wind may start at 5 kts from 270° and as the day progresses, this would change to 15 kts from 300°
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