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ATPL Theory - Module 1 > Meteorology - Moisture and Convection > Flashcards

Meteorology - Moisture and Convection Flashcards

1
Q

What happens to molecular activity and gas pressure as the temperature rises?

A

Rising temperature increases molecular activity, making molecules in the liquid more likely to escape to the gas state, while rising gas pressure above the liquid pushes the molecules back.

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2
Q

What is Saturation Vapour Pressure (SVP)?

A

SVP is when the concentration of water vapor reaches a point where the water vapor pressure is high enough to push water molecules back at the same rate they are escaping, causing the air to be saturated with water vapor.

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3
Q

What happens when the air subsequently cools?

A

The gas pressure will push some vapor back to the water state, visible as cloud fog or dew, until the concentration of water vapor decreases and temperature and gas pressure factors are in equilibrium.

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4
Q

On what does the saturation vapor pressure depend?

A

The saturation vapor pressure depends only on the temperature and the evaporating surface.

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5
Q

What is the SVP over water at -20°C?

A

1.25 hPa

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6
Q

What is the SVP over ice at -20°C?

A

1.03 hPa

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7
Q

What is the significance of the SVP being slightly less over ice than over supercooled water at the same temperature?

A

It means that if unsaturated air is cooled below 0°C, the frost point is reached before the dew point, causing hoar frost to form.

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8
Q

At what concentration does air at 15°C reach saturation?

A

At 2% concentration

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9
Q

At what concentration does air at 30°C reach saturation?

A

At about 4% concentration

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10
Q

Why is the average concentration of water vapor in the troposphere low?

A

Because at low temperatures, air reaches saturation at very low concentrations of water vapor, leading to an average concentration of less than 1%.

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11
Q

Where is the majority of water vapor found?

A

In areas where the air is warm - low down and in the tropics.

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12
Q

What is the term “humid” defined as?

A

Marked by a relatively high level of water vapor in the atmosphere.

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13
Q

What percentage of the total volume of the atmosphere does water vapor constitute?

A

0-4%

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14
Q

Why is water vapor important for weather and climate?

A

It determines weather and climate because it condenses to form precipitation, acts as an energy source for atmospheric motion and convective weather systems, and influences the rate of surface evaporation and transpiration.

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15
Q

What are the main sources of water vapor in the lower atmosphere?

A

Evaporation from the Earth’s surface and transpiration by plants. In the stratosphere, the breakdown of methane by sunlight is another source.

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16
Q

What is vapour pressure?

A

The partial pressure of air that is exerted by water vapour (hPa or mb).

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17
Q

What is absolute humidity?

A

The mass of water vapour present per unit volume of space, usually expressed in grams per cubic metre.

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18
Q

What is specific humidity?

A

Mass of water vapour divided by the mass of air (g/kg).

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19
Q

What is mixing ratio?

A

Mass of water vapour divided by the mass of dry air (g/kg).

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20
Q

What is saturation mixing ratio?

A

The total amount of evaporated air can hold at any given temperature before it is saturated, by weight relationship.

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21
Q

What is dew point temperature?

A

The temperature to which air must be cooled (at constant pressure and vapour content) for saturation to occur.

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22
Q

What is relative humidity (RH)?

A

The ratio of specific humidity to saturation specific humidity, indicating the amount of water vapour compared with the amount required for saturation at a particular temperature and pressure.

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23
Q

What is saturation or equilibrium in the atmosphere?

A

The condition when the evaporation rate is equal to the condensation rate, with the maximum amount of water vapour the air can hold at that temperature and pressure.

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24
Q

What do meteorologists measure using the Humidity Mixing Ratio?

A

The content of water vapour in the air.

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25
Q

What is the ratio in the Humidity Mixing Ratio?

A

The ratio in grams of water vapour to kilograms of dry air.

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26
Q

What is the value called that corresponds to saturation in humidity measurements?

A

The Saturation Mixing Ratio.

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27
Q

How does the Saturation Mixing Ratio change with temperature?

A

It remains constant, but relative humidity and the Saturation Mixing Ratio will change as the air can hold more or less water vapour at different temperatures.

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28
Q

What does absolute humidity measure?

A

The mass of water vapour per unit volume of air (grams per cubic metre).

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29
Q

How is specific humidity defined?

A

It is the same as mixing ratio: a measure of mass of water vapour per unit mass of air (grams per kilogram).

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30
Q

How does the specific humidity change with temperature?

A

It does not change with temperature.

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31
Q

What happens when there is more water vapour in the air?

A

It means more latent heat energy.

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32
Q

What does it mean if the air can’t hold any more water vapour?

A

It is saturated.

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33
Q

How does altitude affect temperature and humidity?

A

As altitude increases, temperature generally falls, and the Saturation Mixing Ratio decreases gently with height.

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34
Q

How does the Saturation Mixing Ratio at sea level vary with temperature?

A

Saturated tropical air at 30°C can hold nearly twice the total weight of water vapour that temperate climate air can hold at 20°C.

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35
Q

What does a decrease in temperature at constant pressure do to the relative humidity?

A

It reduces the Saturation Vapour Pressure (SVP) and the Saturation Mixing Ratio, increasing the Relative Humidity (RH).

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36
Q

How does an increase in temperature affect the relative humidity?

A

It reduces the RH.

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37
Q

What are the three indicators used in meteorology to measure humidity?

A

Relative humidity, dew point, and wet bulb temperature.

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38
Q

What does Relative Humidity (RH) tell us?

A

How much water vapour the air is holding compared to what it could hold under equal temperature and pressure conditions.

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39
Q

What is the RH if the air holds half the water vapour it could?

A

50%.

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40
Q

What happens to RH as the temperature rises during the morning?

A

RH decreases.

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41
Q

What happens to RH after the maximum daily temperature is reached at about 2PM?

A

RH increases as the air cools down.

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42
Q

What do meteorologists measure using the Humidity Mixing Ratio?

A

The content of water vapour in the air.

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43
Q

What is the ratio in the Humidity Mixing Ratio?

A

The ratio in grams of water vapour to kilograms of dry air.

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44
Q

What is the value called that corresponds to saturation in humidity measurements?

A

The Saturation Mixing Ratio.

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45
Q

How does the Saturation Mixing Ratio change with temperature?

A

It remains constant, but relative humidity and the Saturation Mixing Ratio will change as the air can hold more or less water vapour at different temperatures.

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46
Q

What does absolute humidity measure?

A

The mass of water vapour per unit volume of air (grams per cubic metre).

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47
Q

How is specific humidity defined?

A

It is the same as mixing ratio: a measure of mass of water vapour per unit mass of air (grams per kilogram).

48
Q

How does the specific humidity change with temperature?

A

It does not change with temperature.

49
Q

What happens when there is more water vapour in the air?

A

It means more latent heat energy.

50
Q

What does it mean if the air can’t hold any more water vapour?

A

It is saturated.

51
Q

How does altitude affect temperature and humidity?

A

As altitude increases, temperature generally falls, and the Saturation Mixing Ratio decreases gently with height.

52
Q

How does the Saturation Mixing Ratio at sea level vary with temperature?

A

Saturated tropical air at 30°C can hold nearly twice the total weight of water vapour that temperate climate air can hold at 20°C.

53
Q

What does a decrease in temperature at constant pressure do to the relative humidity?

A

It reduces the Saturation Vapour Pressure (SVP) and the Saturation Mixing Ratio, increasing the Relative Humidity (RH).

54
Q

How does an increase in temperature affect the relative humidity?

A

It reduces the RH.

55
Q

What are the three indicators used in meteorology to measure humidity?

A

Relative humidity, dew point, and wet bulb temperature.

56
Q

What does Relative Humidity (RH) tell us?

A

How much water vapour the air is holding compared to what it could hold under equal temperature and pressure conditions.

57
Q

What is the RH if the air holds half the water vapour it could?

A

50%.

58
Q

What happens to RH as the temperature rises during the morning?

A

RH decreases.

59
Q

What happens to RH after the maximum daily temperature is reached at about 2PM?

A

RH increases as the air cools down.

60
Q

What is the dry adiabatic lapse rate (DALR)?

A

3°C per thousand feet (1°C per 100 m).

61
Q

What does “adiabatic” mean in meteorology?

A

Without energy gain or loss.

62
Q

How does rising air behave in terms of energy exchange?

A

It does not exchange energy with the environment.

63
Q

What happens to a parcel of air as it rises?

A

It expands and cools due to lower atmospheric pressure.

64
Q

How does the dry adiabatic lapse rate apply to different starting temperatures and heights?

A

It is constant for all starting temperatures and heights.

65
Q

What happens when saturated air rises and the temperature goes down?

A

Water vapor condenses into water, releasing latent heat, preventing the temperature from falling at the full 3°C/1000 ft rate.

66
Q

What is the Saturated Adiabatic Lapse Rate (SALR)?

A

The lapse rate for saturated air, lower than the dry adiabatic lapse rate due to latent heat release.

67
Q

How does the SALR compare to the DALR?

A

The SALR is lower than the DALR due to the release of latent heat during condensation.

68
Q

What is the typical SALR at sea level in temperate climates?

A

1.8°C/1000 ft (0.6°C per 100 m).

69
Q

How low can the SALR be in the tropics at sea level?

A

As low as 1°C/1000 ft.

70
Q

What happens to the SALR at surface temperatures below -20°C?

A

It is near to the DALR at 3°C/1000 ft due to very low total water content at saturation.

71
Q

What happens to the SALR at height?

A

It comes very close to 3°C/1000 ft.

72
Q

What are the three lapse rates to compare?

A

The Environmental Lapse Rate (ELR), Dry Adiabatic Lapse Rate (DALR), and Saturated Adiabatic Lapse Rate (SALR).

73
Q

What is the condition of unstable air?

A

When the ELR is greater than both the DALR and the SALR, the rising air is warmer than the environment and continues to rise, making the air mass absolutely unstable.

74
Q

What defines absolutely unstable air?

A

If the ELR is greater than the DALR.

75
Q

What is the condition of stable air?

A

When the ELR is very low or negative, causing the rising parcels of air to be colder and more dense than the environment, making the air mass absolutely stable.

76
Q

What happens to rising air in a stable air mass?

A

It sinks back down because it is colder and more dense than the environment.

77
Q

What is indifferent (neutral) stability?

A

An atmospheric condition where the environmental lapse rate is equal to the dry adiabatic rate.

78
Q

What happens when the ELR falls between the DALR and the SALR?

A

The air mass is conditionally unstable: stable if the rising air is dry, unstable if the rising air is saturated.

79
Q

What is the conditionally unstable air?

A

When the ELR is between the DALR and the SALR, making the air mass stable if dry and unstable if saturated.

80
Q

What is the typical ELR for the troposphere?

A

About 2°C/1000 ft.

81
Q

How does air mass stability vary in the troposphere?

A

It varies widely from place to place, with the average condition being conditional instability.

82
Q

What is “super-instability”?

A

An environmental lapse rate well above the DALR, which does not occur often.

83
Q

How can advection of air affect atmospheric stability?

A

Warm air advection at the surface and/or cool air advection aloft enhances instability; cold air advection at the surface contributes to stability.

84
Q

What are the conditions that enhance atmospheric instability?

A

Warming of surface air by solar heating of ground, warm advection near the surface, and air moving over a warm surface. Cooling of air aloft by cold advection aloft and radiative cooling of air/clouds aloft.

85
Q

What are the conditions that contribute to a stable atmosphere?

A

Radiative cooling of the surface at night, advection of cold air near the surface, air moving over a cold surface, and adiabatic warming due to compression from subsidence.

86
Q

What is the WMO definition of a cloud?

A

“A cloud is a hydrometeor consisting of minute particles of liquid water or ice, or both, suspended in the atmosphere and usually not touching the ground. It may also include larger particles of liquid water or ice, as well as non-aqueous liquid or solid particles such as those present in fumes, smoke or dust.”

87
Q

What is the condition of air at the surface normally regarding saturation?

A

It is normally not saturated, with a relative humidity (RH) of less than 100%, and has a dew point and wet bulb temperature lower than the outside air temperature (OAT).

88
Q

What happens to air as it rises and cools at the DALR?

A

It will continue to cool until it reaches dew point, at which height a cloud will form.

89
Q

What are typical figures for an air mass on an average summer day in temperate latitudes?

A

Surface OAT of 20°C, dew point of 13°C, and wet bulb temperature of 16.4°C.

90
Q

What happens to the air parcel’s temperatures as it rises?

A

The dry bulb temperature will fall at the DALR (3°C/1000 ft), and the wet bulb temperature will fall at the SALR (1.8°C/1000 ft).

91
Q

How does the dew point lapse rate work out?

A

About 0.7°C/1000 ft.

92
Q

What happens to the wet bulb and dry bulb temperatures as the air rises?

A

They converge at the rate of the DALR minus the SALR, which is 1.2°C/1000 ft.

93
Q

What happens to the dew point during the rise of the air parcel?

A

The dew point falls a little, and all three temperatures (OAT, wet bulb, and dew point) will coincide at cloud base.

94
Q

How do you calculate the cloud base height if the starting OAT is 20°C and the gap between OAT and wet bulb temperature is 3.6°C?

A

Cloud base will be at 3.6 ÷ 1.2 = 3 thousand ft.

95
Q

What effect does increasing relative humidity have on cloud base?

A

It reduces the gap between OAT and wet bulb temperature, thus lowering the cloud base.

96
Q

How can you work back the temperature at the cloud base using the OAT?

A

By reducing the temperature at 3°C/1000 ft for 3000 ft, which gives a reduction of 9°C, so the temperature at the cloud base is 20°C - 9°C = 11°C.

97
Q

What is the example calculation for cloud base if the surface OAT is 15°C and the wet bulb temperature is 9°C?

A

The difference is 6°C. Converging at 1.2°C/1000 ft, they will coincide at 5000 ft. At this height, the dry bulb temperature will be 0°C, and the wet bulb temperature, falling at the SALR, will also be 0°C.

98
Q

Why was there no reference to the dew point in the example calculation?

A

Because there is no accurate way to calculate it; however, the dew point at cloud base is the same as the dry bulb and wet bulb temperatures, 0°C.

99
Q

How do you work down from the cloudbase to the surface to find the OAT, wet bulb, and dew point?

A

You assume the air has arrived at the cloudbase from the surface cooling at the DALR. For a cloudbase at 3000 ft and OAT of 5°C, the OAT started at 14°C, the wet bulb started at 10.4°C, and the dew point is slightly higher than 5°C but lower than 10.4°C.

100
Q

What is the multiple choice answer for the OAT, wet bulb, and dew point at the surface when the cloudbase is 3000 ft with an OAT of 5°C?

A

Option (b): OAT = 14°C, wet bulb = 10.4°C, dew point = 8°C.

101
Q

Why don’t you need to accurately assess the dew point for the surface calculation example?

A

Because the syllabus does not require it; you only need to remember the general relation of dew point temperatures to height and to the wet bulb and dry bulb temperatures.

102
Q

What are thermodynamic diagrams used for in meteorology?

A

They are accurate graphs of temperature and pressure height used to analyze the actual state of the atmosphere from measurements transmitted by radiosondes, usually suspended below weather balloons.

103
Q

What is the main feature of thermodynamic diagrams?

A

The equivalence between the area in the diagram and energy, with the area enclosed by a closed curve within the diagram being proportional to the energy gained or released by the air.

104
Q

What are the three main types of thermodynamic diagrams used in weather services?

A

Tephigram (used primarily in the UK and Canada), Skew-T log-P diagram (used primarily in the USA), and Emagram (used primarily in European countries).

105
Q

What does a simplified thermodynamic diagram show?

A

How the saturated and dry adiabatic lapse rates vary with temperature and pressure, and shows the saturation mixing ratio lines overlaid.

106
Q

What are the five sets of lines or curves in a complete thermodynamic diagram?

A
  1. Pressure (isobars), 2. Temperature (isotherms)
107
Q

What do the pressure and temperature lines in a thermodynamic diagram represent?

A

They uniquely define the thermodynamic state of an air parcel. The horizontal lines represent isobars, and the vertical lines describe isotherms.

108
Q

How can you locate a parcel’s position on a thermodynamic chart?

A

By using the temperature and pressure lines. A point (P,T) does not necessarily have to fall on these reference lines; you can interpolate and draw these lines through any point as long as you keep them parallel to the reference lines.

109
Q

How do the values of pressure change from bottom to top on a thermodynamic diagram?

A

The values of pressure decrease from bottom to top, and the non-uniform spacing reflects how the pressure changes with height in the real atmosphere.

110
Q

What can be plotted upon the diagram at the same pressure level for completeness?

A

The dewpoint temperature of the parcel (Td).

111
Q

What are dry adiabatic lapse rates?

A

The straight, solid, green lines sloping upward to the left on the diagram, representing the temperature change that an unsaturated air parcel undergoes if moved up and down in the atmosphere and allowed to expand or compress without any addition or removal of heat.

112
Q

What are saturated adiabatic lapse rates?

A

The set of solid light blue curves, called “saturation adiabats,” that portray the temperature changes that occur upon a saturated air parcel when vertically displaced.

113
Q

How do saturation adiabats appear on the thermodynamic diagram?

A

As a set of curves with slopes ranging from 0.2°C/100 m in warm air near the surface to approaching the dry adiabats (1°C/100 m) in cold air aloft.

114
Q

What are saturation mixing ratios?

A

The dotted light blue lines on the diagram, representing the theoretical maximum amount of water vapor that air at a specific temperature and pressure can hold.

115
Q

What happens to the saturation mixing ratio value as temperature reduces at constant pressure?

A

The value reduces.

116
Q

What can be plotted on a thermodynamic chart knowing the OAT and wet bulb temperature and assuming instability?

A

The theoretical cloud base and dew point.

ATPL Theory - Module 1 (17 decks)

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