06. Geostrophic and Gradient Winds

Question 1

Geostrophic and Gradient Winds

Wind is the HORIZONTAL or VERTICAL movement of the atmosphere

Answer 1

HORIZONTAL

1

Question 2

Geostrophic and Gradient Winds

What is the name of the wind gauge used to measure wind

Answer 2

ANEMOMETER

1

Question 3

Geostrophic and Gradient Winds

Wind direction is measured TO or FROM the direction the wind is blowing

Answer 3

FROM

• wind of 045° means it is blowing towards you from 045°, in otherwords from the North East

1

Question 4

Geostrophic and Gradient Winds

Free stream wind is measured from what altitude, which is to say what is the thickness of the boundary layer

Answer 4

2000 ft

2

Question 5

Geostrophic and Gradient Winds

Air will try to move from areas of HIGH or LOW pressure to areas of HIGH or LOW pressure

Answer 5

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

2

Question 6

Geostrophic and Gradient Winds

The first force felt by air is what force

Answer 6

PRESSURE GRADIENT FORCE

3

Question 7

Geostrophic and Gradient Winds

The closer the isobars together, the STRONGER or WEAKER the pressure gradient wind

Answer 7

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

3

Question 8

Geostrophic and Gradient Winds

The name of the force that tries to move air from High pressure to Low pressure

Answer 8

PRESSURE GRADIENT FORCE
(PGF)

3

Question 9

Geostrophic and Gradient Winds

What angle does the PGF act to Isobars

PGF - Pressure Gradient Force

Answer 9

90°

3

Question 10

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

Answer 10

1. ACROSS
2. HIGH
3. LOW

3

Question 11

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

Answer 11

CORIOLIS FORCE

3

Question 12

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

Answer 12

1. ACCELERATE
2. RIGHT

GEOSTROPHIOC WIND

5

Question 13

Geostrophic and Gradient Winds

The Coriolis Force acts at right angles to what

Answer 13

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

GEOSTROPHIOC WIND

5

Question 14

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

Answer 14

GEOSTROPHIC WIND

GEOSTROPHIOC WIND

5

Question 15

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

Answer 15

PARALLEL

GEOSTROPHIOC WIND

5

Question 16

Geostrophic and Gradient Winds

In the Northern Hemisphere, air will circulate CLOCKWISE or ANTI-CLOCKWISE around a Low Pressure System

Answer 16

ANTIC-CLOCKWISE

• REMEMER Buys Ballots Law
• In the NH, wind in your back, Low to the Left

NH WIND DIRECTION

6

Question 17

Geostrophic and Gradient Winds

In the Northern Hemisphere, air will circulate CLOCKWISE or ANTI-CLOCKWISE around a High Pressure System

Answer 17

CLOCKWISE

• REMEMER Buys Ballots Law
• In the NH, wind in your back, Low to the Left

NH WIND DIRECTION

6

Question 18

Geostrophic and Gradient Winds

Wind speed can be determined on a chart by looking at what line spacing

Answer 18

ISOBAR SPACING

• Closer the lines, stronger the wind

6

Question 19

Geostrophic and Gradient Winds

The Geostrophic Wind Scale IS or IS NOT linear

Answer 19

IS NOT

WIND SCALE 1
WIND SCALE 2

7

Question 20

Geostrophic and Gradient Winds

The geostrophic wind scale does not work between what latitudes in reference to the equator

Answer 20

15° N and 15°S

• Between about 15° North and South the geostrophic wind scale does not work

8

Question 21

Geostrophic and Gradient Winds

What is significant about the coriolis force at the equator and low level latitude approximately 15° North and South

Answer 21

HAS NOT EFFECT / DOES NOT EXIST

8

Question 22

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

Answer 22

CYCLOSTROPHIC

8

Question 23

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

Answer 23

CORIOLIS FORCE

8

Question 24

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

Answer 24

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

9

Question 25

# 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

Answer 25

DECREASE ## Footnote * 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 9

Question 26

# 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

Answer 26

HIGHER AT ALTITUDE ## Footnote * 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 9

Question 27

# Geostrophic and Gradient Winds In general at temperate latitudes; 1. Wind speed is *FASTER or SLOWER* at high altitudes compared to low altitudes 2. Wind speed is *FASTER or SLOWER* for a given PGF closer to the equator than the poles

Answer 27

1. FASTER 2. FASTER ## Footnote * For a given PGF, as latitude decreases, wind speed increases * Geostrophic wind speeds are higher at altitude 9

Question 28

# Geostrophic and Gradient Winds What is the formula to understand the relationship of Coriolis force and wind velocity

Answer 28

2ωρVSin(Lat°) ## Footnote Where; * ω = Earths rate of rotation (15° per hour) * ρ = air density * V = velocity 4

Question 29

# 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](https://drive.google.com/file/d/1auf0PjnR5aYGAH8TRK0aCOO4spzqERBY/view?usp=drive_link). 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

Answer 29

CENTRIFUGAL FORCE ## Footnote * centrifugal force acts outwards from the center * centripedal acts inwards towards the center [CENTRIFUGUAL FORCE](https://drive.google.com/file/d/1axh7LZjarrer7tiPTvWmYZeCIGNvZBZY/view?usp=drive_link) 10

Question 30

# Geostrophic and Gradient Winds A low pressure system is considered a *CYCLONE or ANTICYCLONE* system

Answer 30

CYCLONE ## Footnote * considered a cyclonic system 11

Question 31

# Geostrophic and Gradient Winds A high pressure system is considered a *CYCLONE or ANTICYCLONE* system

Answer 31

ANTI-CYCLONE ## Footnote 11

Question 32

# 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

Answer 32

HIGHER ## Footnote * 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 [GEOSTROPHIC WINDS](https://drive.google.com/file/d/1axh7LZjarrer7tiPTvWmYZeCIGNvZBZY/view?usp=drive_link) 10/11

Question 33

# 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

Answer 33

LOWER ## Footnote * 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 [GEOSTROPHIC WINDS](https://drive.google.com/file/d/1axh7LZjarrer7tiPTvWmYZeCIGNvZBZY/view?usp=drive_link) 10/11