Formation of Clouds Questions and Answers

Q: Steam fog and frontal fog, form as the :

Steam fog and frontal fog form as water evaporates and mixes with drier air.Both are evaporation (mixing) fogs. Steam fog forms when cold air moves over much warmer water: water evaporates from the surface and the vapour mixes with the cold air and condenses. Frontal fog forms when warm rain falling through cold air near a front evaporates and saturates the cooler air beneath.Fog formed by the air cooling, as in radiation and advection fog, belongs to the other main class. Air warming lowers the relative humidity and dissipates fog, and 'air circulating' does not describe a mechanism of saturation.

Q: The lifting condensation level is the height at which

Correct answer: a rising parcel first becomes saturatedA rising parcel cools at the dry adiabatic rate while its dew point falls only slowly, so the two converge; the height at which they meet is the lifting condensation level, and condensation begins there. It is the cloud base for any parcel lifted from the surface, which is what the next item is about.

Q: A surface parcel is at 25 degrees Celsius with a dew point of 15 degrees. The cloud base is at approximately

Correct answer: 1250 metresThe dry adiabatic rate is about 10 degrees per kilometre and the dew point falls about 2, so the two close at roughly 8 degrees per kilometre - giving the rule of thumb \[ h \approx 125\,(T - T_d) = 125 \times (25-15) = 1250\ \mathrm{m}. \] The 2500 m offered uses the temperature depression twice over, and 125 m drops a factor of ten.

Q: Match each lifting mechanism with its description.List IA. OrographicB. ConvectiveC. FrontalD. ConvergenceList II1. warm air ascending over a denser air mass2. air forced to rise over a mountain barrier3. air piling up horizontally and forced upward4. surface heating producing buoyant parcels

Correct answer: A-2, B-4, C-1, D-3Four ways of lifting air, and everything else about the cloud follows from which one is at work. Orographic lifting forces the air over a mountain barrier. Convective lifting comes from surface heating making a parcel buoyant. Frontal lifting has warm air ascending over a denser air mass along a boundary. And convergence piles air up horizontally so that it has nowhere to go but up.

Steam fog and frontal fog, form as the :

A.Water evaporates and mixes with drier air
B.Air cools and mixes with drier air
C.Air warms and mixes with drier air
D.Air circulate and mixes with drier air

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: A

Steam fog and frontal fog form as water evaporates and mixes with drier air.

Both are evaporation (mixing) fogs. Steam fog forms when cold air moves over much warmer water: water evaporates from the surface and the vapour mixes with the cold air and condenses. Frontal fog forms when warm rain falling through cold air near a front evaporates and saturates the cooler air beneath.

Fog formed by the air cooling, as in radiation and advection fog, belongs to the other main class. Air warming lowers the relative humidity and dissipates fog, and 'air circulating' does not describe a mechanism of saturation.

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A cloud forms when a parcel of air

A.is cooled until its water vapour begins to condense
B.is warmed until it can hold rather more water vapour
C.is compressed until its internal pressure rises sharply
D.loses the whole of the water vapour it was carrying

Answer: A

Cooling reduces the saturation vapour pressure until the air already holds more vapour than it can retain. The excess condenses onto available particles, and it is those droplets rather than the vapour itself that are visible.

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Assertion (A): Rising air cools even though no heat is removed from it.
Reason (R): It expands against the lower pressure aloft and does work at the expense of its own internal energy.

A.A is false but R is true
B.Both A and R are true, and R is the correct explanation of A
C.Both A and R are true, but R is not the correct explanation of A
D.A is true but R is false

Answer: B

Both are true and the reason gives the mechanism, and this adiabatic cooling is what makes ascent the dominant route to cloud formation in the atmosphere. No external refrigeration is involved at any point in the process.

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Unsaturated air rises 1 km. By approximately how much does it cool?

A.about 2 degrees Celsius
B.about 20 degrees Celsius
C.about 10 degrees Celsius
D.about 6 degrees Celsius

Answer: C

The dry adiabatic lapse rate is close to 9.8 degrees Celsius per kilometre and applies to any unsaturated parcel regardless of how much vapour it carries. It is a consequence of expansion alone rather than of the humidity of the air.

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The saturated adiabatic lapse rate is smaller than the dry rate because

A.saturated air expands less rapidly as it ascends
B.saturated air is markedly denser than unsaturated air
C.condensation removes heat from the rising parcel itself
D.latent heat released by condensation warms the parcel

Answer: D

Once condensation begins, the latent heat released partly offsets the cooling from expansion. The saturated rate is therefore variable, being near 4 degrees per kilometre in warm moist air and approaching the dry rate in very cold air.

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Assertion (A): The saturated adiabatic lapse rate is not a single fixed number.
Reason (R): The amount of latent heat released depends on how much vapour the air holds at that temperature.

A.Both A and R are true, and R is the correct explanation of A
B.Both A and R are true, but R is not the correct explanation of A
C.A is true but R is false
D.A is false but R is true

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the cause. The saturated rate is the dry rate offset by the latent heat released as vapour condenses, and warm saturated air holds far more vapour than cold, so it releases far more heat per unit of lifting. The rate is therefore about 4 degrees per kilometre in warm tropical air and approaches the dry 9.8 in very cold air, where there is almost nothing left to condense.

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The lifting condensation level is the height at which

A.the parcel becomes warmer than its surroundings
B.a rising parcel first becomes saturated
C.a rising parcel stops rising altogether
D.the temperature of the parcel reaches zero degrees

Answer: B

Correct answer: a rising parcel first becomes saturated

A rising parcel cools at the dry adiabatic rate while its dew point falls only slowly, so the two converge; the height at which they meet is the lifting condensation level, and condensation begins there. It is the cloud base for any parcel lifted from the surface, which is what the next item is about.

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Assertion (A): Cumulus clouds over flat terrain tend to share a flat and common base.
Reason (R): Parcels lifted from a surface of similar temperature and humidity reach saturation at the same height.

A.A is true but R is false
B.A is false but R is true
C.Both A and R are true, and R is the correct explanation of A
D.Both A and R are true, but R is not the correct explanation of A

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the mechanism. Over uniform terrain the parcels rising from different points start with much the same temperature and dew point, so they all reach saturation at the same height and every cloud base forms at that level. The flat common base of a field of fair-weather cumulus is therefore a direct reading of the lifting condensation level.

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A surface parcel is at 25 degrees Celsius with a dew point of 15 degrees. The cloud base is at approximately

A.2500 metres
B.600 metres
C.125 metres
D.1250 metres

Answer: D

Correct answer: 1250 metres

The dry adiabatic rate is about 10 degrees per kilometre and the dew point falls about 2, so the two close at roughly 8 degrees per kilometre - giving the rule of thumb \[ h \approx 125\,(T - T_d) = 125 \times (25-15) = 1250\ \mathrm{m}. \] The 2500 m offered uses the temperature depression twice over, and 125 m drops a factor of ten.

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10.

Match each lifting mechanism with its description.
List I
A. Orographic
B. Convective
C. Frontal
D. Convergence
List II
1. warm air ascending over a denser air mass
2. air forced to rise over a mountain barrier
3. air piling up horizontally and forced upward
4. surface heating producing buoyant parcels

A.A-2, B-4, C-1, D-3
B.A-4, B-2, C-1, D-3
C.A-2, B-4, C-3, D-1
D.A-3, B-1, C-4, D-2

Answer: A

Correct answer: A-2, B-4, C-1, D-3

Four ways of lifting air, and everything else about the cloud follows from which one is at work. Orographic lifting forces the air over a mountain barrier. Convective lifting comes from surface heating making a parcel buoyant. Frontal lifting has warm air ascending over a denser air mass along a boundary. And convergence piles air up horizontally so that it has nowhere to go but up.

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