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PPL Met > water vapour > Flashcards

water vapour Flashcards

1
Q

why is water vapour vital to earth?

A

Without water vapour in the Earth’s atmosphere, there would be no clouds or precipitation. Precipitation is vital to life on earth

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2
Q

how does water vapour enter the atmosphere?

A

through evaporation and transpiration

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3
Q

what is evaporation?

A

Evaporation is the
process by which water changes from a liquid to a gas or vapour. Water boils at 100 degrees
C, but it actually begins to evapourate at 0 degrees C. As the temperature increases, the rate of
evaporation also increases

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4
Q

what is transpiration?

A

Transpiration is the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to water vapour
and is released to the atmosphere.

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5
Q

where is water vapour normally found?

A

lower troposphere.

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6
Q

what are the properties of water vapour?

A

The water molecule is relatively light

and when it is present in large quantities, the total density of the air tends to be quite low.

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7
Q

where are the main sources for water in the atmosphere?

A

The greatest source of water in the atmosphere is rivers, lakes, and oceans

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8
Q

what is saturation?

A

Saturation is the maximum amount of water a parcel of air can hold, when its at maximum capacity its considered saturated.

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9
Q

what effect does temperature have on saturation?

A

the higher the temperature of the air, the more water vapour air can hold.

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10
Q

what happens if the air contains less that the max value of water?

A

it is unsaturated.

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11
Q

what happens if saturated is cooled?

A

it is supersaturated.

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12
Q

how can air be saturated?

A

by cooling or by the addition of moisture.

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13
Q

how does the addition of moisture saturate the air?

A

If liquid water comes into contact with unsaturated air, the water will slowly evaporate. The process will continue until no more moisture can be absorbed.

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14
Q

how does cooling saturate the air

A

Cooling is by far the most significant cause of condensation in the atmosphere. It occurs by radiation, contact with a cold surface, or by expansion of lifted air

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15
Q

what is dew point?

A

the temperature at which air would become saturated if cooled at a constant pressure.

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16
Q

what is frost point?

A

The frost point is the temperature at which the air is saturated with respect to water vapor over an ice surface.

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17
Q

how can dew point change?

A

it can only change with addition or subtraction of water vapour.

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18
Q

what will adding moisture do to relative humidity

A

it will increase relative humidity and if enough moisture is added, air may become saturated and cloud will form.

19
Q

what happens if you add moisture to a parcel of air that’s temperature is constant

A

the parcel of air will be saturated but outside temperature will remain unchanged and there’ll be a new dewpoint.

20
Q

The effects of temperature and relative humidity on dew point can be summarised as ?

A

when air temperature increases, Relative humidity goes down and dew point isn’t affected
When air temperature reduces, Relative humidity increases and dew point isn’t affected.
When water vapour content decreases, Relative humidity goes down and so does dew point
When water vapour content increases, relative humidity goes up and so does dew point.

21
Q

what are the three states of water?

A

gas as water vapour
liquid as water
solid as ice.

22
Q

what is condensation?

A

the change of gas to liquid

23
Q

what is the process of condensation?

A

air is cooled to dew point and moisture is formed.

24
Q

how is cloud or fog formed?

A

condensation

25
Q

what does the condensation process require?

A

it require the presence of condensation nuclei such as salt,carbon, soot. around which water can cling to become a liquid.

26
Q

what is evaporation?

A

opposite of condensation, the change from liquid to gas.

27
Q

what is the process of evaporation.

A

When water is heated it turns to gas. the warmer the air is the more water vapour it can hold. the rate of evaporation will be greater with warmer and dry air.

28
Q

what is deposition?

A

when water vapour will turn to ice by passing the liquid state.

29
Q

what is sublimation?

A

ice changes directly to water vapour.

30
Q

what is melting?

A

ice (solid) water changes to liquid

31
Q

what is freezing?

A

liquid water turns to a solid.

32
Q

what is latent heat?

A

the heat energy released or absorbed during the change from states.

33
Q

why is latent heat important?

A

latent heat is required to change the above states of matter. As stated, Laten heat is the energy required or given off to make the change; it does not affect the temperature of the substance during the change

34
Q

what is the rate of evaporation affected by?

A

Air temperature – the ability of the air to absorb water as a vapour depends mainly on the temperature of the air. The warmer the air the more vapour it can hold. Warmer air
will have a higher rate of evaporation.
• Moisture content of air – the rate of evaporation will increase with higher moisture content
• Atmospheric pressure – when the atmospheric pressure is low there is a higher rate of evaporation. With low-pressure, particles are freer to move around and absorb energy. There is less force keeping the particles on the ground.
• Wind – when wind is blowing, there is a high rate of evaporation which aids in mixing.

35
Q

what is humidity?

A

the amount of water vapour in the air.

36
Q

what is mixing ratio?

A

the quanitity of water in a given quantity in air expressed in grams per kg.

37
Q

how can the volume of air in water decrease the total mass?

A

the mass of a molecule of water vapour is less then a molecule of dry air

38
Q

what is relative humidity?

A

relative humidity indicates the amount of water vapour as a percentage of what It can actually hold.

39
Q

considering relative humidity what percentage would unsaturated air be

A

less than 100%

40
Q

considering relative humidity what percentage would saturated air be

A

100%

41
Q

what is relative humidity dependent on and why?

A

relative humidity is dependent on temperature, totally dry air has a relative humidity of 0%, meaning that relative humidity may change with no addition of water or condensation of moisture - just by changing temperature.
Relative humidity also vary with height as pressure varies and causes adiabatic cooling or heating

42
Q

what happens when moisture is added to air of a given temperature?

A

Relative humidity increases

43
Q

what happens to a given space of air when its temperature reduces?

A

Its ability to hold water reduces and relative humidity increases and 100% relative humidity is reached with less water content.

44
Q

why is dew point better then relative humidity for aviation purposes?

A

because relative humidity only measure the percentage of water in the air whereas dew point measures the temperature and water content needed to reach 100% relative humidity.

PPL Met (20 decks)

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