Balance of forces and different types of flows/weather phenomena in the northern hemisphere are given. Match the following:Balance of forcesFlow type/weather phenomenaPBalance between pressure gradient force, centrifugal force and Coriolis force in anticlockwise rotationXGeostrophic flowQBalance between pressure gradient force and centrifugal force in clockwise/ anticlockwise rotationYCyclonesRBalance between pressure gradient force and Coriolis force in a uniform flowZTornado

The correct matching is P - Y; Q - Z; R - X.A balance of pressure gradient, centrifugal and Coriolis forces in curved flow is the gradient wind; anticlockwise rotation in the Northern Hemisphere is cyclonic, so P describes cyclones (Y).A balance of pressure gradient and centrifugal force alone is cyclostrophic flow, found in small, intense vortices where the Coriolis force is negligible and either sense of rotation is possible: tornadoes (Q-Z).A balance of pressure gradient and Coriolis force in straight, uniform flow is geostrophic flow (R-X).The other options assign geostrophic flow to curved or cyclostrophic balances, or tornadoes to the gradient balance, which mismatch the forces involved.

Geostrophic and Gradient Wind Questions and Answers

Q: Which conclusion can be drawn if observed and geostrophic winds agree closely?

Agreement indicates that neither curvature nor friction is contributing appreciably, which means straight flow in the free atmosphere. The strength of the gradient does not affect whether the approximation holds, temperature is irrelevant on a pressure surface, and proximity to the equator would make the agreement worse rather than better. Using the comparison as a diagnostic of the flow regime is a good habit when examining observations. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.

Q: Which discrepancy suggests strong curvature rather than friction?

Curvature changes the speed required for balance without introducing any cross-contour component, so a subgeostrophic wind flowing along the contours indicates cyclonic curvature. Friction, by contrast, produces both a speed reduction and a cross-isobaric component towards low pressure. Distinguishing the two signatures allows the cause of a discrepancy to be identified from the observation alone.

Q: In the Ekman flow limit, directions of ocean surface current and the geostrophic wind are

In the Ekman limit the two directions are the same.Two Ekman layers act in turn (Northern Hemisphere). In the atmospheric boundary layer, friction slows the wind and the pressure gradient turns it, so in the Ekman limit the surface wind blows 45° to the left of the geostrophic wind above. In the ocean's surface Ekman layer, the wind stress drives a surface current 45° to the right of the surface wind.The two 45° turns cancel, so the ocean surface current flows parallel to, and in the same direction as, the geostrophic wind. The options with a single 45° turn count only one of the two layers, and 'exactly opposite' has no basis.

Q: The variation in geostrophic winds with height, in particular, at the atmospheric boundary layer, considering the variation in pressure gradient as a function of height, is referred to as __________.

This is the Thermal wind.The thermal wind is the vertical shear of the geostrophic wind: the difference between the geostrophic winds at two levels. It arises because horizontal temperature gradients make the pressure gradient change with height, and it blows parallel to the mean isotherms with cold air to the left in the Northern Hemisphere.The isallobaric wind is the ageostrophic part driven by pressure changing with time. The gradient wind adds curvature (centripetal) effects to the geostrophic balance, and the cyclostrophic wind is the balance of pressure gradient and centripetal force alone, as in tornadoes. None of these describes a change with height.

Q: What will happen to the speed of a balanced flow as one moves across the isobar along a particular latitude?

The key gives The speed remains constant for a geostrophic flow and changes for a cyclostrophic flow.In geostrophic balance the pressure gradient force is balanced by the Coriolis force:\[ V_{g} = \frac{1}{\rho f}\frac{\partial p}{\partial n} \]Along a fixed latitude the Coriolis parameter \(f\) is the same, so for a given pressure gradient the speed does not depend on the position across the isobars. In cyclostrophic balance the pressure gradient is balanced by the centripetal acceleration of curved flow:\[ \begin{aligned} \frac{V^{2}}{r} &= \frac{1}{\rho}\frac{\partial p}{\partial n} \\ \Rightarrow V &= \sqrt{\frac{r}{\rho}\frac{\partial p}{\partial n}} \end{aligned} \]The speed depends on the radius \(r\), which changes as one moves across the circular isobars, so the speed changes. The other options reverse this or treat both balances alike.

Q: A westerly wind is blowing in the Northern Hemisphere. What is the direction of net mass transport in the Ekman layer?

The net Ekman transport is southward.A westerly wind blows from the west towards the east. In the Northern Hemisphere the Coriolis effect deflects the depth-integrated Ekman transport 90 degrees to the right of the wind direction. Ninety degrees to the right of eastward is southward.Northward transport would be the Southern Hemisphere result, where deflection is to the left. North-eastward and south-westward correspond to 45-degree deflections, which describe the surface current, not the net transport over the Ekman layer.

Q: A rotating weather system has a tangential velocity of 100 m s-1, diameter of 1 km, and located at a latitude where the Coriolis parameter is 10−4 s-1. Which one of the following statements is true about this weather system?

The system is in cyclostrophic balance.Compare the centrifugal and Coriolis terms through the Rossby number, using the radius R = 0.5 km:\[ Ro = \frac{V}{fR} = \frac{100}{10^{-4} \times 500} = 2000 \]The centrifugal acceleration \(V^{2}/R\) is two thousand times the Coriolis acceleration \(fV\), so the Coriolis force is negligible and the pressure gradient force is balanced by the centrifugal force alone. That is cyclostrophic balance, typical of tornadoes and dust devils.Geostrophic balance needs \(Ro \ll 1\), and gradient wind balance matters when both terms are comparable. A cyclostrophic vortex always has low pressure at its centre, since the pressure gradient must point inward, so it cannot be a high-pressure system.

Q: Which of the following combinations of forces is/are balanced in a cyclostrophic motion?

In cyclostrophic motion the pressure gradient and centrifugal forces balance.Cyclostrophic balance applies to small, intense vortices such as tornadoes and dust devils, and to flow near the equator, where the Rossby number is large: the Coriolis force is negligible compared with the centrifugal force of the tight, fast rotation. The inward pressure gradient force is balanced by the outward centrifugal force alone.Including all three forces describes gradient wind balance; pressure gradient against Coriolis is geostrophic balance; and centrifugal against Coriolis without a pressure gradient describes inertial motion.

Q: Widely spaced isobars indicate a :

Widely spaced isobars indicate a weak pressure gradient and light winds.Isobars join places of equal pressure. When they are far apart, pressure changes little over distance, so the pressure gradient force is weak and the wind it drives is light. Closely packed isobars mean a steep gradient and strong winds, as around a cyclone.Options A and C pair wide spacing with a steep gradient, which reverses the relationship, and option D pairs a weak gradient with strong winds, which contradicts the gradient being what drives the wind.

101.

Which conclusion can be drawn if observed and geostrophic winds agree closely?

A.The flow is nearly straight and above the boundary layer
B.The pressure gradient must be unusually strong at that location compared with its surroundings
C.The air is very cold
D.The observation must have been taken close to the equator where the Coriolis parameter is small

Answer: A

Agreement indicates that neither curvature nor friction is contributing appreciably, which means straight flow in the free atmosphere. The strength of the gradient does not affect whether the approximation holds, temperature is irrelevant on a pressure surface, and proximity to the equator would make the agreement worse rather than better. Using the comparison as a diagnostic of the flow regime is a good habit when examining observations. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.

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102.

Which discrepancy suggests strong curvature rather than friction?

A.The observed wind matches the geostrophic value in speed but differs by ninety degrees in direction
B.The observed wind is slower than geostrophic but blows along the contours
C.The observed wind is slower than geostrophic and blows across the contours towards low pressure
D.The observed wind exceeds geostrophic and blows across the contours towards high pressure

Answer: B

Curvature changes the speed required for balance without introducing any cross-contour component, so a subgeostrophic wind flowing along the contours indicates cyclonic curvature. Friction, by contrast, produces both a speed reduction and a cross-isobaric component towards low pressure. Distinguishing the two signatures allows the cause of a discrepancy to be identified from the observation alone.

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103.

In the Ekman flow limit, directions of ocean surface current and the geostrophic wind are

A.the same
B.surface current is 45° to the left of the geostrophic wind
C.surface current is 45° to the right of the geostrophic wind
D.exactly opposite to each other

Exam Year(s)

GATE XE - 2018,

Answer: A

In the Ekman limit the two directions are the same.

Two Ekman layers act in turn (Northern Hemisphere). In the atmospheric boundary layer, friction slows the wind and the pressure gradient turns it, so in the Ekman limit the surface wind blows 45° to the left of the geostrophic wind above. In the ocean's surface Ekman layer, the wind stress drives a surface current 45° to the right of the surface wind.

The two 45° turns cancel, so the ocean surface current flows parallel to, and in the same direction as, the geostrophic wind. The options with a single 45° turn count only one of the two layers, and 'exactly opposite' has no basis.

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104.

The variation in geostrophic winds with height, in particular, at the atmospheric boundary layer, considering the variation in pressure gradient as a function of height, is referred to as __________.

A.Isallobaric winds
B.Gradient winds
C.Thermal winds
D.Cyclostrophic winds

Exam Year(s)

GATE XE - 2023,

Answer: C

This is the Thermal wind.

The thermal wind is the vertical shear of the geostrophic wind: the difference between the geostrophic winds at two levels. It arises because horizontal temperature gradients make the pressure gradient change with height, and it blows parallel to the mean isotherms with cold air to the left in the Northern Hemisphere.

The isallobaric wind is the ageostrophic part driven by pressure changing with time. The gradient wind adds curvature (centripetal) effects to the geostrophic balance, and the cyclostrophic wind is the balance of pressure gradient and centripetal force alone, as in tornadoes. None of these describes a change with height.

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105.

What will happen to the speed of a balanced flow as one moves across the isobar along a particular latitude?

A.The speed changes for a geostrophic flow and remains constant for a cyclostrophic flow
B.The speed remains constant for a geostrophic flow and changes for a cyclostrophic flow
C.The speed remains constant for both (geostrophic and cyclostrophic) types of flow
D.The speed changes for both (geostrophic and cyclostrophic) types of flow

Exam Year(s)

GATE XE - 2023,

Answer: B

The key gives The speed remains constant for a geostrophic flow and changes for a cyclostrophic flow.

In geostrophic balance the pressure gradient force is balanced by the Coriolis force:

\[ V_{g} = \frac{1}{\rho f}\frac{\partial p}{\partial n} \]

Along a fixed latitude the Coriolis parameter \(f\) is the same, so for a given pressure gradient the speed does not depend on the position across the isobars. In cyclostrophic balance the pressure gradient is balanced by the centripetal acceleration of curved flow:

\[ \begin{aligned} \frac{V^{2}}{r} &= \frac{1}{\rho}\frac{\partial p}{\partial n} \\ \Rightarrow V &= \sqrt{\frac{r}{\rho}\frac{\partial p}{\partial n}} \end{aligned} \]

The speed depends on the radius \(r\), which changes as one moves across the circular isobars, so the speed changes. The other options reverse this or treat both balances alike.

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106.

A westerly wind is blowing in the Northern Hemisphere. What is the direction of net mass transport in the Ekman layer?

A.Southward
B.Northward
C.North-Eastward
D.South-Westward

Exam Year(s)

GATE XE - 2024,

Answer: A

The net Ekman transport is southward.

A westerly wind blows from the west towards the east. In the Northern Hemisphere the Coriolis effect deflects the depth-integrated Ekman transport 90 degrees to the right of the wind direction. Ninety degrees to the right of eastward is southward.

Northward transport would be the Southern Hemisphere result, where deflection is to the left. North-eastward and south-westward correspond to 45-degree deflections, which describe the surface current, not the net transport over the Ekman layer.

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107.

Balance of forces and different types of flows/weather phenomena in the northern hemisphere are given. Match the following:

Balance of forces		Flow type/weather phenomena
P	Balance between pressure gradient force, centrifugal force and Coriolis force in anticlockwise rotation	X	Geostrophic flow
Q	Balance between pressure gradient force and centrifugal force in clockwise/ anticlockwise rotation	Y	Cyclones
R	Balance between pressure gradient force and Coriolis force in a uniform flow	Z	Tornado

A.P - Z; Q - X; R - Y
B.P - X; Q - Y; R - Z
C.P - Y; Q - Z; R - X
D.P - Y; Q - X; R - Z

Exam Year(s)

GATE XE - 2024,

Answer: C

The correct matching is P - Y; Q - Z; R - X.

A balance of pressure gradient, centrifugal and Coriolis forces in curved flow is the gradient wind; anticlockwise rotation in the Northern Hemisphere is cyclonic, so P describes cyclones (Y).
A balance of pressure gradient and centrifugal force alone is cyclostrophic flow, found in small, intense vortices where the Coriolis force is negligible and either sense of rotation is possible: tornadoes (Q-Z).
A balance of pressure gradient and Coriolis force in straight, uniform flow is geostrophic flow (R-X).

The other options assign geostrophic flow to curved or cyclostrophic balances, or tornadoes to the gradient balance, which mismatch the forces involved.

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108.

A rotating weather system has a tangential velocity of 100 m s^-1, diameter of 1 km, and located at a latitude where the Coriolis parameter is 10⁻⁴ s^-1. Which one of the following statements is true about this weather system?

A.It is in geostrophic balance.
B.It is in gradient wind balance.
C.It is a high-pressure system.
D.It is in cyclostrophic balance.

Exam Year(s)

GATE XE - 2025,

Answer: D

The system is in cyclostrophic balance.

Compare the centrifugal and Coriolis terms through the Rossby number, using the radius R = 0.5 km:

\[ Ro = \frac{V}{fR} = \frac{100}{10^{-4} \times 500} = 2000 \]

The centrifugal acceleration \(V^{2}/R\) is two thousand times the Coriolis acceleration \(fV\), so the Coriolis force is negligible and the pressure gradient force is balanced by the centrifugal force alone. That is cyclostrophic balance, typical of tornadoes and dust devils.

Geostrophic balance needs \(Ro \ll 1\), and gradient wind balance matters when both terms are comparable. A cyclostrophic vortex always has low pressure at its centre, since the pressure gradient must point inward, so it cannot be a high-pressure system.

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109.

Which of the following combinations of forces is/are balanced in a cyclostrophic motion?

A.Pressure Gradient, Coriolis, and Centrifugal
B.Pressure Gradient and Centrifugal
C.Centrifugal and Coriolis
D.Pressure Gradient and Coriolis

Exam Year(s)

GATE XE - 2026,

Answer: B

In cyclostrophic motion the pressure gradient and centrifugal forces balance.

Cyclostrophic balance applies to small, intense vortices such as tornadoes and dust devils, and to flow near the equator, where the Rossby number is large: the Coriolis force is negligible compared with the centrifugal force of the tight, fast rotation. The inward pressure gradient force is balanced by the outward centrifugal force alone.

Including all three forces describes gradient wind balance; pressure gradient against Coriolis is geostrophic balance; and centrifugal against Coriolis without a pressure gradient describes inertial motion.

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110.

Widely spaced isobars indicate a :

A.Steap pressure gradient and strong winds
B.Weak pressure gradient and light winds
C.Steap pressure gradient and light winds
D.Weak pressure gradient and strong winds

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: B

Widely spaced isobars indicate a weak pressure gradient and light winds.

Isobars join places of equal pressure. When they are far apart, pressure changes little over distance, so the pressure gradient force is weak and the wind it drives is light. Closely packed isobars mean a steep gradient and strong winds, as around a cyclone.

Options A and C pair wide spacing with a steep gradient, which reverses the relationship, and option D pairs a weak gradient with strong winds, which contradicts the gradient being what drives the wind.

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