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EAS 202 > 2: Violent Weather > Flashcards

2: Violent Weather Flashcards

Saturation, Pressure, Humidity

1
Q

What is fog

A

water in gas form

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2
Q

Hydrological Cycle

A

Water cycle
Condensation –> precipitation –> surface and snowmelt runoff –> evaporation –> transpiration (cyclic)

image 9

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3
Q

What is humidity and how can it be quantified or measured

A

atmosphere is a mixture of dry air and water vapor. Measured by:
* vapor pressure (e)
* mixing ratio

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4
Q

What is vapor pressure and mixing ratio

A
  • vapour pressure (e): partial pressure exerted by water vapour alone
  • Mixing ratio: mass of water vapour divided by mass of dry air
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5
Q

What is saturation

A

evaporation = condensation
* air has reached its saturation vapor pressure es (subscript) so vapor pressure cannot exceed this (besides supersaturation)
* vapor pressure = saturation vapor pressure
* any additional water vapor added to the air will immedietly be condensed out into liquid water (dew, fog, cloud) because air cannot hold any more water vapor

image 10

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6
Q

What does saturation vapor pressure depend on and relationship when increasing

A
  • depends only on temperature
  • increases exponentially with temperature
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7
Q

What does graph of es(T) look like and what is it. Explain relationship between e and es.

A
  • exponential graph of vapor pressure vs temperature called the saturation curve
  • along the curve, the air is saturated: e=es
  • to the right of the curve the air is not saturated: e<es
  • to the left of the curve the air is supersaturated: e>es

image 11

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8
Q

water vapor, saturation, and temperature relationship

A
  • if you decreasw T then you need little water vapor to reach saturation because cld air is compressed
  • if you increase the temperature then you need lots of water vapor to reach saturation

image 11

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9
Q

Pa, kPA, hPa, mb relationships

A

1000 Pa = 1kPa
100 Pa = 1hPa
1hPa = 1mb (millibar)

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10
Q

Ways to reach saturation

A
  • Saturation by mixing
  • Saturation by addition of water vapor
  • Saturation by isothermal compression
  • Saturation by lifting
  • Saturation by isobaric cooling

MAILI

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11
Q

What is an isobar

A

equal pressure

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12
Q

What is saturation by isobaric cooling? Which image?

A
  • Image 12
  • Lower the temperature to Td (dewpoint temperature) to reach the saturation vapour pressure
  • This is how ground fog forms at night: the surface cools isobarically through longwave radiation and the air above the ground cools to saturation
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13
Q

relationship between T and Td on a saturation curve

A

if the distance between T and Td is large then the air is very dry, if the distance is small then the air is humid

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14
Q

What is dewpoint temperature

A
  • Td
  • The temperature to which an air parcel must be isobarically cooled to reach saturation vapor pressure
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15
Q

Saturation by addition of water vapor and which image?

A
  • Image 13
  • Increase water vapor, which isothermally increases the vapor pressure, to reach saturation vapor pressure
  • temperature remains constant
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16
Q

Saturation by isothermal compression and which image

A
  • Compression of air parcel decreases the volume and increases the density –> vapor pressure increase which reaches saturation vapor pressure
  • image 13
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17
Q

Saturation by lifting and what image?

A
  • image 14
  • combo of temperature and pressure changes can result in an air parcel becoming saturated
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18
Q

Saturation by mixing and what image

A
  • if two unsaturated air masses, one warm and one very cold, are mixed together, the resulting mixture can be supersaturated so will condense into a mixing fog
  • image 15
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19
Q

Saturation below freezing and what picture

A
  • the saturation vapor pressure of air over water is higher than over ice
  • the difference arises because it takes less energy to evaporate than it does to sublimate (solid to gas)
  • image 16
  • tiny water droplets in the atmosphere can remain in liquid form to temperature and are said to be supercooled
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20
Q

What is mixing ratio and specific humidity

A

Mixing Ratio (w): the ratio of the mass of water vapour to the mass of dry air in a given volume of air
- Formula: w = mv/md
- The unit of mixing ratio is g/kg but is mostly dimensionless

Specific humidity (q): ratio of mass of water vapour to the total mass of air
- usually use relative humidity instead
- q = mv/(mv+md)

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21
Q

Saturation Mixing Ratio

A
  • when humidity is 100%
  • mixing ratio for the saturated air
  • w = mvs (saturated water vapor)/md
  • could also be 0.622*(saturation vapour pressure/total atmospheric pressure)
22
Q

What is relative humidity

A
  • ratio of mixing ratio (w) divided by saturation mixing ratio (ws) times 100%
  • more commonly: vapour pressure/saturation vapour pressure times 100–> RH= (VP/SVP)*100
  • cannot exceed 100%, if it does then that means the air parcel is saturated with fog in the atmosphere
23
Q

Relationships between temperature, vapour pressure, saturation vapour pressure, and relative humidity and which image

A
  • image 17
  • If cooling, VP→, T↓, SVP↓, RH↑
  • If warming, VP→, T↑, SVP↑, RH↓
24
Q

What is dewpoint

A
  • denoted by Td
  • the temperature at which air must be cooled at a constant pressure to reach the saturation
  • saturation vapour pressure evaluated at the dew point temperature is equal to the vapour pressure at that temperature of the air
  • RH = (SVP (Td)/SVP (T), Td is basically VP
25
Q

What is precipitable water

A
  • the total content of a vertical column of air from the surface to the top of the atmosphere
  • moisture in the atmosphere
  • condensation of all water vapour in the atmosphere would produce a uniform global wading pool
26
Q

Weight of cold and warm air, and what is stable and unstable

A

Warm air: light
Cold air: heavy

Stable: light air over heavy air
Unstable: heavy air over light air

27
Q

What is a capping lid

A

allows heavy layer to be on top of lighter layer, if broken it causes convection —> overturning of heavy layer to be bottom and light on top

28
Q

Ways to break capping lid

A
  1. Vigorous convection
  2. Mountain and topography
  3. Near surface convergence: different air masses converge
29
Q

What is Adiabatic lifting

A

a parcel of air is contained in a balloon skin that allows transfer of pressure but no mixing with ambient air. During lifting/ascent, the pressure of the air drops and the air expands —> adiabatic expansion results in cooling ( inc height, dec pressure, dec temperature). For dry mass:
- each 100m ascent is 1C temperature cooling
- each 100m descent is 1C temperature warming

30
Q

On a clear calm day, when does RH fall and why

A

between sunrise and early afternoon due to the increase of temperature due to increase in saturation vapour pressure

31
Q

What affects saturation vapour mixing ratio

A

only temperature and it is proportional. If T inc then so does saturation vapour mixing ratio

32
Q

what happens to air density as you ascend in the atmosphere

A

air density decreases as you go up bc pressure decreases

33
Q

Ex: a parcel at height z = 0m has temperature T = 15C. What is T at z = 2500m after adiabatic lifting?

A

-10C

34
Q

Ex: Air with t = -2C descends from 2800m to 800. What is the final T

A

18C

35
Q

Ex: A air parcel has a temperature of 25C and RH of 20%. What is the RH after the air has
cooled to 10C? What is the RH if the cooling continues to 0C. Look at image 18

A

51.6% (at 10C( and 103.66% (at 0C). Page 19

36
Q

Ex: Air of T = 20C has a vapour pressure = 15 mb. What is the relative humidity? Look at image 18

A

64%. Page 18

37
Q

Ex: What is the relative humidity of a air mass of temperature 20C and dew point
temperature of 15C?. Look at image 18

A

73%. Page 23

38
Q

Ex: What is the temperature of a air mass of relative humidity 20% and dew point
temperature of 5C? Image 18

A

around 31C

39
Q

The temperature of air outside is -20C and dew point temperature of -25C. What is the
relative humidity of the air? If this air gets heated to get a comfortable 20C temperature,
estimate the new dew point temperature and new relative humidity? Look at image 18

A

Outside: 64%
Inside after heating: 3%

40
Q

What is Lapse Rate

A

the temperature decrease with height

41
Q

What is DALR and ELR

A
  • DALR: Dry Adiabatic Lapse Rate. Any parcel of air with RH less than 100%, termed unsaturated, will cool as it rises at a constant rate = 1C/100m
  • ELR: Environmental Lapse Rate. The observed lapse of temperature of the environment with respect to height. Aka actual air temperature
42
Q

Displacements of unsaturated air and which picture

A
  • image 19
  • Stable air layer: displaced parcel is forced to return to its original altitude. Stable air inhibits vertical motion (left)
  • Unstable air layer: displace parcel accelerates away from its original altitude. Unstable air enhances vertical motion (right)
43
Q

Relationship of ELR and DALR with Unsaturated air

A

Stable: ELR < DALR if ELR &laquo_space;10C/km
Neutral: ELR = DALR
Unstable: ELR > DALR (ELR cools faster than DALR) if ELR&raquo_space; 10C/km

44
Q

When do unstable conditions in unsaturated air occur

A
  1. Strong winds from different directions, making different temperatures at different heights. This leads to Clear Air Turbulence (CAT) about 10km above ground. Aviation hazard
  2. on a clear summer day, heating of the dry ground can result in short live adiabatic lapse rate in the lowest 20m above ground —> results in mirage, rising thermals, and rotating dustdevils
45
Q

4 indications of stable atmospheric conditions

A
  • temperature inversion
  • isothermal condition
  • no change in temperature with altitude (isothermal condition)
  • increase in temperature with altitude (temperature inversion)
46
Q

stability in saturated, cloudy air

A

condensation of water vapour into liquid cloud releases heat of about 2500J/g. This release of latent heat changes the temperature and therefore the lapse rate of a rising parcel

47
Q

what is MALR

A
  • moist adiabatic lapse rate
  • when a parcel of saturated/cloudy air ascends, the cooling due to adiabatic expansion is partly reduced by the release of latent heat during condensation. Varies but average is 5-6C/1000m.
48
Q

What is conditional instability

A

air layer is unstable for saturated air parcels and stable for unsaturated air parcels
- lapse rate is greater than 6C but less than 10C

49
Q

Is RH of saturated parcels affected

A

no because its already at 100% humidity

50
Q

relationship between ELR, DALR, and MALR in regards to stability

A

ELR > DALR is absolutely unstable
MALR < ELR < DALR is conditionally unstable
ELR < MALR is absolutely stable

51
Q

How is the stability of a sounding determined

A

by comparing the ELR with the MALR and DALR

52
Q

What happens to the saturation mixing ratio when a saturated cloudy air flows up the windward slopes of a mountain range

A

saturation mixing ratio (water vapour/dry air) decreases due to decrease in temperature bc of decrease in pressure

EAS 202 (14 decks)

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