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ATPL - BGS [Mod 1] Meteorology > 04. Moisture and Convection > Flashcards

04. Moisture and Convection Flashcards

1
Q

Moisture and Convection

“Water will continue to evaporate until the concentration of water vapour reaches a point where the water vapour pressure is high enough to push water molecules back at the same rate as they are escaping. The air is then said to be saturated with water vapour”

This is a definition of what

A

SATURATION VAPOUR PRESSURE
(SVP)

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2
Q

Moisture and Convection

The Saturation Vapour Pressure depends only on what 2 things

A
  1. TEMPERATURE
  2. EVAPORATING SURFACE

  • Evaporating surface meaning water or ice conditions

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3
Q

Moisture and Convection

SVP is slightly MORE or LESS over ice than over supercooled water at the same teperature

A

LESS

  • If unsaturated air is cooled below 0℃ the frost point is reached before the dew point when hoar frost forms
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4
Q

Moisture and Convection

Saturation levels will be reached faster in COLDER or WARMER air

A

COLDER

  • Air at low temperatures reaches saturation at very low concentrations of water vapour
  • 15℃ air saturates at a 2% concentration
  • 30℃ air saturates at about 4% concentration
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5
Q

Moisture and Convection

In what regions of the earth and altitude would we expect to find the highest levels of water vapour i.e. which areas will be the most humid

A

LOW DOWN IN THE TROPICS

  • Tropics are very hot
  • Hot air holds more water vapour
  • Temperature decreases as altitude increases, meaning it can hold less water vapour
  • Therefore, the low level layer in the tropics will hold the most water vapour

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6
Q

Moisture and Convection

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

This is a definition of what

A

VAPOUR PRESSURE

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7
Q

Moisture and Convection

“The mass of water vapour present per unit volume of space, usually expressed in grams per cubi metre. It may be thought of as the density of the water vapour”

This is a definition of what

A

ABSOLUTE HUMIDITY

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8
Q

Moisture and Convection

“Mass of water vapour divided by the mass of air ( g kg^-1)”

This is the definition of what

A

SPECIFIC HUMIDITY

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9
Q

Moisture and Convection

“Mass of water vapour divided by the mass of dry air (g kg^-1)”

This is the definition of what

A

MIXING RATIO

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10
Q

Moisture and Convection

“Air at any given temperature can hold only a certain amount of water vapour before it is saturated. The total amount of evaporate air can hold at any given temperature, by weight relationship, is referred to as…”

This is the definition of what

A

SATURATION MIXING RATION

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11
Q

Moisture and Convection

“The temperature to which air must be cooled (at constant pressure and vapour content) for saturation to occur. The forst point temperature is similar except for saturation relative to ice”

This is the definition of what

A

DEW POINT TEMPERATURE

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12
Q

Moisture and Convection

“Ratio of specific humiidty to saturation specific humidity. The amount of water vapour compared with the amount required for saturation (at a particular temperature and pressure)”

This is a definition of what

A

RELATIVE HUMIDITY (RH)

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13
Q

Moisture and Convection

“Condition of the atmosphere when the evaporation rate is equal to the condensation rate. The amount of water vapour the air can hold is maximum for the given temperature and pressure”

This is a definition of what

A

SATURATION

aka equilibrium

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14
Q

Moisture and Convection

What method do meteorologists use to measure the content of water vapour in the air

A

HUMIDITY MIXING RATION

  • Ratio of grams of water vapour to kilograms of dry air
  • As air gets warmer or colder, the mixing ratio remains constant but the relative humidty and the saturation mixing ratio will change
  • This is because the air is capable of holding more or less water vapour at different temperatures

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15
Q

Moisture and Convection

If there is more water vapour in the air, this means that there is the potential for more of what sort of heat

A

LATENT HEAT

  • As temperature coolds, realtive humidity level increases to a poitn of saturation
  • Once point of saturation is met, gas pressure foces some of the water vapour to condense back into water droplets (cloud)
  • The process fo desublimnation or condensing releases latent heat

EXAMPLE

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16
Q

Moisture and Convection

In a standard atmosphere, the saturation mixing ratio i.e. the mass of water the air can hold, will INCREASE or DECREASE with altitude and why

A
  1. DECREASE
  2. TEMPERATURE DECREASES WITH INCREASE OF ALTITUDE

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17
Q

Moisture and Convection

Complete the following temperature/saturation table;

Temperature (℃) | -20 | -10 | 0 | +10 | +20| +30 |
Saturation (g/kg) | ?? | ?? | ?? | ?? | ?? | ?? |

A

Temperature (℃) | -20 | -10 | 0 | +10 | +20| +30 |
Saturation (g/kg) | 0.8 | 1.8 | 3.8 | 7.8 | 15 | 28 |

TABLE

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18
Q

Moisture and Convection

“tells us how much water vapour the air is holding compared to what it could hold”

This is a definition of what measurement

A

RELATIVE HUMIDITY

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19
Q

Moisture and Convection

If air is holding half the content of water vapour that it could hold under equaly temperature, what Relative Humidity would it have

A

50%

  • The parcel of air is holding half of what it could hold, so 50%
  • If the parcel of air is saturated, it is holding all that it can hold, so 100%

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20
Q

Moisture and Convection

If a parcel of air at a constant pressure decreases in temperature, the Saturation Vapour Pressure (SVP) and Saturation Mixing ration will INCREASE or DECREASE, and the Relative Humidity will INCREASE or DECREASE

A
  1. DECREASE
  2. INCREASE

RELATIVE HUMIDITY

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21
Q

Moisture and Convection

What is the Relative Humidty for a mass of air with a temperature of 10℃ and a Mixing Ratio of 1.8 g/kg

A

23%

  • Use the Saturation Water Vapour TABLE
  • Mixing Ration / Saturation Water Vapour x 100
  • (1.8 / 7.8) x 100
  • 23%

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22
Q

Moisture and Convection

What is the equation to determine the Relative Humidity if given the Temperature and Dew Point

A

RH = 100 - (5 x (TEMP - DEW POINT))

RH = 100 - (5 x (T - Td))

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23
Q

Moisture and Convection

The temperature at which cloud will form is known as what

A

DEW POINT

8

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24
Q

Moisture and Convection

Dew point temperatures can be measured directly using what tool

A

HYGROMETER

8

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25
Q

Moisture and Convection

If the OAT is MORE than the Dew Point, will the air be MORE or LESS saturated and therefore have a HIGHER or LOWER relative humidity

A
  1. LESS SATURATED
  2. LOWER RELATIVE HUMIDITY

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26
Q

Moisture and Convection

The different between the dew point and the OAT is referred to as what

A

DEW POINT SPREAD

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27
Q

Moisture and Convection

As SVP is less over water than it is ice, at temperatures of 0℃, what will form first before dew

A

FROST
(hoar frost)

8

28
Q

Moisture and Convection

What is the method (equipment) used for measuring humidity

A

PSYCHROMETER

WET BULB/DRY BULB THERMOMETERS

  • Thermometers are side by side
  • Difference between the Wet Bulb and Dry Bulb gives the relative humidity

9

29
Q

Moisture and Convection

If the OAT is 30℃ and the dew point is 21℃, what is the relative humidity

A

55%

  • Use the formula to determine relative humidity
  • RH = 100 - (5 x (T - Td))
  • 100 - (5 x (30 - 21)
  • 100 - (5 x 9)
  • 100 - 45
  • RH = 55%

10

30
Q

Moisture and Convection

“an instrument that measures humidity through the human ahirs ability to expand when moist and contract when dry”

This is a definition of what instrument

A

HAIR HYROMETER

10

31
Q

Moisture and Convection

What is the average Environmental Lapse Rate (ELR) per 1000m and per 1000 ft

A
  1. 6.5℃ per 1000 m
  2. 2℃ per 1000 ft

12

32
Q

Moisture and Convection

What tool is used to detect the actual ELR

Environmental Lapse Rate

A

RADIO SONDE

12

33
Q

Moisture and Convection

What is the Dry Adiabatic Lapse Rate (DALR) per 1000 ft and per 100m

A
  1. 3℃ per 1000 ft
  2. 1℃ per 100 m

DALR and SALR

13

34
Q

Moisture and Convection

What is the Saturated Adiabatic Lapse Rate (SALR) per 1000 ft and per 100m

A
  1. 1.8℃ per 1000 ft
  2. 0.6℃ per 100 m

DALR and SALR

14

35
Q

Moisture and Convection

Why does the cooling of the DARL suddenly slow down at the point of the SALR

A

LATENT HEAT RELEASED

  • Latent heat is released as water vapour is condensing into water and forming clouds
  • This warms the surrounding air, thus slowing down the cooling process

LATENT HEAT SALR

14

36
Q

Moisture and Convection

At higher altitudes and surface temperatures below -20℃ where the total water content at saturation is very low, the SALR is equivilant to what

A

DALR
3℃ per 1000ft

  • roughly the same, not exactly

14

37
Q

Moisture and Convection

The definition of a STABLE air mass is that the air will do what after it has risen

A

FALL AGAIN

  • Air will rise, i.e. because of an object such as a mountain forcing it orgraphically to lift, but then sinks back down again as it is more dense and colder than its surrounding air
  • Think about PoF lessons, Static stability, where the aircraft wants to return to its originaly point.

15

38
Q

Moisture and Convection

The definition of an UNSTABLE air mass is that the air will do what when rising

A

CONTINUES TO RISE

  • Air will continue to rise on its own
  • Think about PoF lessons, dynamic instability is aircraft moving away from its original point becoming increasingly unstable

15

39
Q

Moisture and Convection

If the ELR is unstable, the air mass will always be WARMER or COLDER than the DALR and WARMER or COLDER than the SALR for a given altitude

A
  1. WARMER (more)
  2. WARMER (more)

  • DALR and SALR will always be warmer than ELR in Unstable air
  • If the ELR is greater than the DALR, it is considered to be Absolutely Unstable
    UNSTABLE AIR

DALR and SALR

16

40
Q

If the ELR is stable, the air mass will always be WARMER or COLDER than the DALR and WARMER or COLDER than the SALR for a given altitude

A
  1. COLDER (less)
  2. COLDER (less)

  • ELR will always be colder, meaning it is stable and will always want to sink back down once it has risen
  • If the ELR is less than the SALR it is said to be Absolutely Stable

DALR and SALR

17

41
Q

Moisture and Convection

If the ELR is exactly the same as the DALR, the condition is said to be what

A

NEUTRAL STABILITY

17

42
Q

Moisture and Convection

An ELR that falls between the DALR and the SALR i.e. between a lapse rate of 1.8℃ and 3℃, is said to be what

A

CONDITIONALLY UNSTABLE

  • If ELR is between the DARL and the SALR the airmass is conditionally unstable - stable if the rising air is dry, and unstable if the rising air is saturated

CONDITIONALLY UNSTABLE

DALR and SALR

18

43
Q

Moisture and Convection

What type of air movement, warm or cold, can affect the stability of the atmosphere, both aloft and at the ground

Think of lateral movement

A

ADVECTION

19

44
Q

Moisture and Convection

Advection of air aloft will contribute to a more STABLE or UNSTABLE atmosphere

A

UNSTABLE

19

45
Q

Moisture and Convection

Advection of air near the surface will contribute to a more STABLE or UNSTABLE atmosphere

46
Q

Moisture and Convection

What are 2 conditions that enhance atmospheric instability

A
  1. WARMING OF SURFACE AIR
  2. COOLING OF AIR ALOFT (cold advection)

  • in both circumstances, the air will want to move to another position i.e. warmer air to rise and cooler air to sink

19

47
Q

Moisture and Convection

What are 4 conditions that contribute to a stable atmosphere

[ ] SOLAR HEATING OF THE GROUND
[ ] RADIATIVE COOLING OF SURFACE AT NIGHT
[ ] ADVECTION OF COLD AIR NEAR THE SURFACE
[ ] COLD ADVECTION ALOFT
[ ] AIR MOVING OVER A COLD SURFACE
[ ] AIR MOVING OVER A WARM SURFACE
[ ] ADIABATIC WARMING DUE TO COMPRESSION FROM SUBSIDENCE

A

[ ] SOLAR HEATING OF THE GROUND
[X] RADIATIVE COOLING OF SURFACE AT NIGHT
[X] ADVECTION OF COLD AIR NEAR THE SURFACE
[ ] COLD ADVECTION ALOFT
[X] AIR MOVING OVER A COLD SURFACE
[ ] AIR MOVING OVER A WARM SURFACE
[X] ADIABATIC WARMING DUE TO COMPRESSION FROM SUBSIDENCE

19

48
Q

Moisture and Convection

What is the equation to determine the cloud base when given the temperature and dew point

A

CLOUD BASE (ft) = (TEMPERATURE - DEW POINT) x 400

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49
Q

Moisture and Convection

Air will rise by the DALR initially until it reaches which point, which is when clouds will form. Air will then cool at the SALR

50
Q

Moisture and Convection

If the OAT is 20℃ and the dew point is 13℃, what is the cloud base likely to be

A

APPROX 2,800 FT

  • Use the formula DP = (T - Td) x 400
  • (20 - 13) x 400
  • 7 x 400
  • 2800 ft

CLOUD FORMATION

21

51
Q

Moisture and Convection

At what lapse rate does the wet bulb thermometer fall at

52
Q

Moisture and Convection

At what lapse rate does the dry bulb thermometer fall at

53
Q

Moisture and Convection

Given that the dry bulb thermometer is decreasing at the DALR and the wet bulb thermometer is decrease at the SALR, the 2 are converging as altitude increases. The same is said about the dew point temperature. When drawn on a graph all 3 lines converge which is the point where clouds will form.

What is the the formula to determine the convergence lapse rate between DALR and SALR, and what is it per 1000 ft

A
  1. DALR - SALR
  2. 1.2℃ per 1000 ft

  • This method can be used as an alternative to determing the cloud base
  • If at ground the OAT is 20℃, which will initially fall at the DALR, and you are given the SALR of 16.4℃, you can determine the cloud base
  • The starting DALR temperature is the same as the OAT, so 20℃
  • SALR is 16.4℃
  • 20 - 16.4℃ = 3.6℃
  • We know the Convergency lapse rate is 1.2℃ per 1000 ft
  • 3.6 / 1.2 = 3
  • 3,000 ft

CLOUD FORMATION

22

54
Q

Moisture and Convection

If given an OAT of 20℃ at the surface and a cloud base of 3,000 ft, what is the temperature of the cloud base

A

11℃

  • It is possible to work backwards when you know the lapse rates
  • The cloud base represents a point where the SALR and DALR and the DP cross
  • This means the air is cooling at the DALR until it crosses with the SALR and we know the DARL is 3℃ per 1000 ft
  • If the OAT at ground is 20℃ and the cloud base is 3,000 ft, this is 20 - (3 x 3)
  • 20 - 9
  • 11℃

CLOUD FORMATION

22

55
Q

Moisture and Convection

OAT at the surface is 15℃. The wet bulb temperature is 9℃. What would the height and temperature at cloudbase be

A

5,000 ft @ 0℃

DETERMINE TEMPERATURE DIFFERENCE
* Work out the difference between the OAT and the Wet bulb temperature i.e. DALR - SALR
* 15 - 9 = 6℃

DETERMINE ALTITUDE
* Apply the convergence lapse rate rate of 1.2℃ per 1000 ft
* We know we have 6℃ difference
* 6 / 1.2 to give us how many feet before the DALR and SALR converge
* 6 / 1.2 = 5
* 5 x per 1000 ft = 5000 ft

DETERMINE TEMPERATURE
* We now know how high the cloud base is formed and we can apply the DALR to the given OAT to determine the temperature
* DALR is 3℃ per 1000 ft
* 5 (as in 5000 ft) x 3℃ ⋉ 5 x 3 = 15℃
* Deduct this from our starting OAT
* 15 - 15 = 0
* 0℃

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ATPL - BGS [Mod 1] Meteorology (27 decks)

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