06. Geostrophic and Gradient Winds Flashcards
Geostrophic and Gradient Winds
Wind is the HORIZONTAL or VERTICAL movement of the atmosphere
HORIZONTAL
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Geostrophic and Gradient Winds
What is the name of the wind gauge used to measure wind
ANEMOMETER
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Geostrophic and Gradient Winds
Wind direction is measured TO or FROM the direction the wind is blowing
FROM
- wind of 045° means it is blowing towards you from 045°, in otherwords from the North East
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Geostrophic and Gradient Winds
Free stream wind is measured from what altitude, which is to say what is the thickness of the boundary layer
2000 ft
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Geostrophic and Gradient Winds
Air will try to move from areas of HIGH or LOW pressure to areas of HIGH or LOW pressure
HIGH to LOW
- If there is high pressure i.e. pressure being applied on it from above, it will try to diverge away and move to areas of least resistance, in other words areas of low pressure
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Geostrophic and Gradient Winds
The first force felt by air is what force
PRESSURE GRADIENT FORCE
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Geostrophic and Gradient Winds
The closer the isobars together, the STRONGER or WEAKER the pressure gradient wind
STRONGER
- isobar lines closer together are a-typical of a low pressure.
- We know wind will move from high to low
- Therefore, wind will be stronger at Low pressure areas, where lines are closer together
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Geostrophic and Gradient Winds
The name of the force that tries to move air from High pressure to Low pressure
PRESSURE GRADIENT FORCE
(PGF)
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Geostrophic and Gradient Winds
What angle does the PGF act to Isobars
PGF - Pressure Gradient Force
90°
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Geostrophic and Gradient Winds
The first thing that air will try to do when acted on by the PGF is to start to move ALONG or ACROSS the isobars from HIGH or LOW pressure to HIGH or LOW pressure
- ACROSS
- HIGH
- LOW
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Geostrophic and Gradient Winds
When air is acted on by the PGF, it starts to move across the isobars from high to low pressure. As it moves, what second force strats to act upon it
CORIOLIS FORCE
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Geostrophic and Gradient Winds
The sum of the pressure gradient force and the coriolis force makes air ACCELERATE or SLOW DOWN, and in the Northern Hemisphere, turn LEFT or RIGHT
- ACCELERATE
- RIGHT
Geostrophic and Gradient Winds
The Coriolis Force acts at right angles to what
DIRECTION OF AIR MOVEMENT
- If the air were moving exactly north, then coriolis would be acting at 90° to the East
- In the Northern Hemisphere, coriolis acts to the right, in the Southern hemisphere, to the left
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Geostrophic and Gradient Winds
When the Pressure Gradient Force and the Coriolis Force are equal, they will be equally opposed to each other. The resultant wind in this state of equilibrium is known as what
GEOSTROPHIC WIND
Geostrophic and Gradient Winds
When the PGF and CF forces are in equilibrum, this creates the geostrophic wind. This wind flows OPPOSED or PARALLEL to the isobar
Coriolis Force
Pressure Gradient Force
PARALLEL
Geostrophic and Gradient Winds
In the Northern Hemisphere, air will circulate CLOCKWISE or ANTI-CLOCKWISE around a Low Pressure System
ANTIC-CLOCKWISE
Geostrophic and Gradient Winds
In the Northern Hemisphere, air will circulate CLOCKWISE or ANTI-CLOCKWISE around a High Pressure System
CLOCKWISE
Geostrophic and Gradient Winds
Wind speed can be determined on a chart by looking at what line spacing
ISOBAR SPACING
- Closer the lines, stronger the wind
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Geostrophic and Gradient Winds
The Geostrophic Wind Scale IS or IS NOT linear
IS NOT
Geostrophic and Gradient Winds
The geostrophic wind scale does not work between what latitudes in reference to the equator
15° N and 15°S
- Between about 15° North and South the geostrophic wind scale does not work
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Geostrophic and Gradient Winds
What is significant about the coriolis force at the equator and low level latitude approximately 15° North and South
HAS NOT EFFECT / DOES NOT EXIST
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Geostrophic and Gradient Winds
Winds between 15° North and South, which have no coriolis force applied against them initially cannot develope into geostrophic winds as the only force acting upon the air initially is PGF. These winds are known as what
CYCLOSTROPHIC
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Geostrophic and Gradient Winds
In a tropical storm, the isobars are incredibly close together meaning that the PGF is incredibly high. This means that what other force becomes relatively insignificant
CORIOLIS FORCE
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Geostrophic and Gradient Winds
For a given isobar spacing, wind speed will INCREASE or DECREASE with a decrease in latitude i.e. closer to the equator
INCREASE
- To understand this relationship, we use the formula;
Isobar spacing (PGF) = 2ωρVSin(Lat°)
Where;
* ω = Earths rate of rotation (15° per hour)
* ρ = air density
* V = velocity
- If you are given an isobar spacing, this is a constant. Therefore, using this equation, in order to keep it balanced, if one part of the formula changes, another part must also change to keep it balanced.
- If the latitude is decreasing, this means that Sin(Lat°) is changing. If it is getting smaller, something else must get bigger
- ω is a constant, and we are given no information about altitude so assume ρ is constant
- This leaves only Velocity (V) as the other variable that can change, and since Sin(Lat°) is getting smaller, V must get bigger
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Geostrophic and Gradient Winds
For a given isobar spacing, wind speed will INCREASE or DECREASE with an increase in latitude i.e. closer to the pole
DECREASE
- To understand this relationship, we use the formula;
Isobar spacing (PGF) = 2ωρVSin(Lat°)
Where;
* ω = Earths rate of rotation (15° per hour)
* ρ = air density
* V = velocity
- If you are given an isobar spacing, this is a constant. Therefore, using this equation, in order to keep it balanced, if one part of the formula changes, another part must also change to keep it balanced.
- If the latitude is increasing, this means that Sin(Lat°) is changing. If it is getting bigger, something else must get smaller
- ω is a constant, and we are given no information about altitude so assume ρ is constant
- This leaves only Velocity (V) as the other variable that can change, and since Sin(Lat°) is getting bigger, V must get smaller
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Geostrophic and Gradient Winds
For a given isobar spacing and latitude, what can be said about the geostrophic wind speed at high altitude compared to that at low altitude
HIGHER AT ALTITUDE
- To understand this relationship, we use the formula;
Isobar spacing (PGF) = 2ωρVSin(Lat°)
Where;
* ω = Earths rate of rotation (15° per hour)
* ρ = air density
* V = velocity
- We are given a latitude and isobar spacing, which means these are both constant - Sin(Lat°) will not change
- ω is a constant, which leaves air density ρ and velocity V as the variables that change
- We know that air density decreases with altitude, therefore, if air densitiy is getting smaller, velocity must get bigger to balance the equation
- Therefore, at higher altitudes wind speed is higher
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Geostrophic and Gradient Winds
In general at temperate latitudes;
- Wind speed is FASTER or SLOWER at high altitudes compared to low altitudes
- Wind speed is FASTER or SLOWER for a given PGF closer to the equator than the poles
- FASTER
- FASTER
- For a given PGF, as latitude decreases, wind speed increases
- Geostrophic wind speeds are higher at altitude
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Geostrophic and Gradient Winds
What is the formula to understand the relationship of Coriolis force and wind velocity
2ωρVSin(Lat°)
Where;
* ω = Earths rate of rotation (15° per hour)
* ρ = air density
* V = velocity
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Geostrophic and Gradient Winds
Isobars are rarely straight lines and on pressure charts always join up typically in circle type shapes around points of equal pressure - example.
As a result of the geostrophic wind blowing parallel to isobars, and the isobars being circular in nature, what addditional force is now applied to wind as it blows around the isobar lines
CENTRIFUGAL FORCE
- centrifugal force acts outwards from the center
- centripedal acts inwards towards the center
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Geostrophic and Gradient Winds
A low pressure system is considered a CYCLONE or ANTICYCLONE system
CYCLONE
- considered a cyclonic system
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Geostrophic and Gradient Winds
A high pressure system is considered a CYCLONE or ANTICYCLONE system
ANTI-CYCLONE
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Geostrophic and Gradient Winds
Geostrophic Winds as a result of centrifugal force are considered HIGHER or LOWER around a high pressure system compared to a low pressure system
HIGHER
- PGF is trying to move air from HIGH to LOW, meaning in a high pressure system this is outwards from the center
- The curved isobar line means centrifugual force is also trying to push air outwards from the center
- Combined, this means that PGF no longer equals Coriolis since it has additional force making it unbalanced
- We know the equation for coriolis is;
Coriolis = 2ωρVSin(Lat°)
- Therefore, in order for coriolis force to remain the same to balance PGF and Centrifugal, coriolis must be stronger
- The velocity of the wind speed is the only variable that we can change so wind speed must be stronger to maintain coriolis, ergo, coriolis force is stronger
- When PGF and Coriolis balance with stronger speeds, the Geostrophic resultant wind must also be stronger
- At low pressure systems, this is reversed in that centrifugal force acts outwards with coriolis
- PGF is strong since isobars are tightly packed, meaning the centrifugal force is greater acting outwards
- This combines with the coriolis force meaning that to keep coriolis adn PGF constant, velocity must decrease
- This means the Geostrophic wind is slower at low pressure systems than high pressure systems
REMEMBER
Gradient Wind = LOW around LOW, HIGH around HIGH
Gradient wind around a low is LESS than the geostrophic wind
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Geostrophic and Gradient Winds
Geostrophic Winds as a result of centrifugal force are considered HIGHER or LOWER around a low pressure system compared to a low pressure system
LOWER
- PGF is trying to move air from HIGH to LOW, meaning in a high pressure system this is outwards from the center
- The curved isobar line means centrifugual force is also trying to push air outwards from the center
- Combined, this means that PGF no longer equals Coriolis since it has additional force making it unbalanced
- We know the equation for coriolis is;
Coriolis = 2ωρVSin(Lat°)
- Therefore, in order for coriolis force to remain the same to balance PGF and Centrifugal, coriolis must be stronger
- The velocity of the wind speed is the only variable that we can change so wind speed must be stronger to maintain coriolis, ergo, coriolis force is stronger
- When PGF and Coriolis balance with stronger speeds, the Geostrophic resultant wind must also be stronger
- At low pressure systems, this is reversed in that centrifugal force acts outwards with coriolis
- PGF is strong since isobars are tightly packed, meaning the centrifugal force is greater acting outwards
- This combines with the coriolis force meaning that to keep coriolis adn PGF constant, velocity must decrease
- This means the Geostrophic wind is slower at low pressure systems than high pressure systems
REMEMBER
Gradient Wind = LOW around LOW, HIGH around HIGH
Gradient wind around a low is LESS than the geostrophic wind
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