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BSc Environmental Science > LEC.175 Atmosphere, Weather, and Climate > Flashcards

LEC.175 Atmosphere, Weather, and Climate Flashcards

1
Q

How much cloud cover is there across the globe?

A

~1/2

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2
Q

What is the most abundant gas in the atmosphere (%)?

A

Nitrogen (78%)

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3
Q

What do units ppmm and ppmv mean?

A

ppmm = parts per million by mass
ppmv = parts per million by volume

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4
Q

By how much does CO2 increase per year in ppmv?

A

~20 ppmv/yr

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5
Q

What are 5 reasons why the atmosphere is important?

A
  1. Warms Earth’s surface by ~33°C
  2. Mixes heat vertically by convection
  3. Mixes heat meridionally (equator to pole) by advection
  4. Redistributes water via hydrological cycle
  5. Absorbs most energetic solar radiation (external UV shield)
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6
Q

What is the difference between convection and advection?

A

Convection is movement of air by heating whilst advection is movement of air by pressure differences

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7
Q

What are the 5 spheres in the atmosphere from closest to furthest from the Earth’s surface?

A

Troposphere –> stratosphere –> mesosphere –> thermosphere –> exosphere

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8
Q

Which sphere in the atmosphere do most weather systems occur in?

A

Troposphere

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9
Q

What is the homosphere and heterosphere?

A

Homosphere = troposphere –> mesosphere edge (homopause), homogeneous mixture of gases
Heterosphere = 100km –> 500km, heterogeneous mixture of gases

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10
Q

Does pressure increase or decrease with increasing altitude in the atmosphere?

A

Decrease

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11
Q

What is the mean free path in a gas?

A

Average distance travelled by a molecule between collisions with other molecules (dependant on T and P)

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12
Q

At homopause in the atmosphere, what is the mean free path of gases approximately equivalent to?

A

The average scale of turbulent motion (below = mixing by turbulence, above = mixing by diffusion)

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13
Q

Approximately at what altitude is the critical level in the atmosphere and what is mean free path approximately equal to at the critical level?

A

~500km, the distance to escape the Earth’s gravitational field

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14
Q

What causes overturning/mixing/an unstratified atmosphere?

A

Hot, less dense layers below cold, more dense layers (not stable)

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15
Q

Why does temperature increase in the stratosphere?

A

Due to the presence of ozone which absorbs solar radiation

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16
Q

Why is the stratosphere stratified?

A

Temperature increases throughout layer so no turbulence/overturning/mixing

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17
Q

What are 4 features of the troposphere?

A
  1. ‘Overturning sphere’
  2. Vertical motion
  3. Contains almost all atmospheric water
  4. Most weather systems occur in the troposphere
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18
Q

Why does overturning occur at the planetary boundary layer?

A

Wind velocity decreases to 0 at surface so friction causes overturning

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19
Q

What are 2 reasons why weather forecasting is difficult?

A
  1. Sun heats atmosphere but mostly indirectly by heating Earth’s surface
  2. Atmosphere is sensitive to change
    …So no simple cause and effect
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20
Q

What is used to collect and transmit weather data?

A

Radar/station data/satellite data/civil aircraft/sondes –> national meteorological centre –> regional meteorological centre

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21
Q

What are the 2 types of weather stations used to make observations in the UK?

A
  1. Synoptic stations (send data directly to Met Office) e.g manned Met Offices, part manned stations, automatic stations
  2. Daily climate stations e.g. voluntary climate observers
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22
Q

In which direction do winds move around high and low pressure systems?

A

High pressure systems: Clockwise
Low pressure systems: Anti-clockwise

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23
Q

What are cold and warm air fronts and how are they represented in a forecast?

A

Cold air front: Cold air mass, triangles
Warm air front: Warm air mass, semi-circles

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24
Q

What are 2 ways weather observations are made consistent?

A
  1. Every detail of station observation is regulated by Met Observer’s Handbook in UK
  2. Observations are referenced to mean sea level pressure as pressure differs with altitude
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25
Q

What are the 2 types of thermometer used to measure temperature manually and how do they work?

A

Mercury-in-glass or alcohol-in-glass thermometers, work via expansion + contraction of liquid

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26
Q

At what time is air temperature always measured and what other measurements are taken?

A

0900, maximum and minimum temperatures since previous observation

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27
Q

What is used to protect thermometers from external factors and how does it work?

A

Stevenson screen - naturally ventilated + shielded from solar/terrestrial radiation + rain

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28
Q

What are the units of absolute humidity and saturation vapour pressure?

A

Absolute humidity: pw
Saturation vapour pressure: ew

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29
Q

What is saturation vapour pressure?

A

The maximum amount of water vapour that air, above liquid/solid water, can contain at equilibrium (depends very sensitively on T)

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30
Q

What is relative humidity (%RH) and what is the equation for %RH?

A

Ratio of partial pressure to vapour pressure of water/ice, %RH = 100 (pw/ew)

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31
Q

How does a psychrometer measure relative humidity?

A

Ordinary thermometer (‘dry bulb’) is matched with thermometer covered in wet muslin cloth (‘wet bulb’) and diff. in temp. is related to relative humidity e.g. when Twet < Tdry, heat has been used to evaporate water from cloth so T decreases

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32
Q

What meteorological instrument is used to measure wind speed and how does it work?

A

Calibrated cup anemometer, counts no. rotations per minute

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33
Q

What scale is used to subjectively measure wind speed when instruments aren’t available?

A

Beaufort scale (0-12, e.g. Force 8 = gale)

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34
Q

Why is wind speed measured at a standard height of 10m?

A

Friction reduces wind speed close to the ground

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35
Q

What are 2 ways of measuring wind direction?

A
  1. Wind vane (measures angle from north, clockwise, in °)
  2. Run of wind (cumulative wind measured by connecting anemometer to a mile-ometer, standard height = 2m)
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36
Q

What causes winds?

A

Pressure differences (winds travel from high –> low pressure

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37
Q

What instrument is used to measure atmospheric pressure and how does it work?

A

Barometer, reads station pressure and converts to mean sea level pressure using station altitude

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38
Q

What units are used for atmospheric pressure and how many Pa is this unit equivalent to?

A

mbar (requires accuracy to 0.1 mbar), = 100 Pa

39
Q

How does an aneroid barometer work and what is it used for?

A

On a barograph, pressure is recorded on a rotating chart, as pressure decreases sealed metal chamber expands, used to study pressure tendency (change in pressure over time)

40
Q

How does precipitation radar measure precipitation?

A

Raindrops reflect radio waves, strength of radar echo is proportional to rain intensity, gives info on mean size of raindrops + velocity of weather system

41
Q

What are the low, medium, and high cloud types?

A

Low: Cumulis, stratus, fog, stratocumulus, nimbostratus
Medium: Altostratus, altocumulus
High: Cirrus, cirrostratus, cirrocumulus, contrails
All 3: Cumulonimbus

42
Q

Why are less upper air measurements needed than surface measurements?

A

Weather changes on much larger scales

43
Q

What do weather satellites do?

A

Record intensity of EM radiation in particular wavelength regions –> data transmitted to ground base –> corrected for known instrument + re-transmitted to users

44
Q

What are the 2 types of weather satellite?

A
  1. Geostationary orbits (fixed position relative to Earth on equatorial plane, 35,000 km above)
  2. Polar orbiting (850 km above, return over same location twice a day, coverage better at poles than Equator)
45
Q

What is the width of a satellite view called?

A

Swath

46
Q

Why are weather satellite images taken in the infrared region where absorption by water vapour is very strong?

A

Atmosphere is transparent to some wavelengths but opaque to others

47
Q

What is the source of energy that drives climate?

A

The Sun

48
Q

What 2 equations are used to calculate energy from the Sun?

A
  1. Stefan-Boltzmann Law (W m^-2): F = σT^4
  2. Wien’s Law: λ = 3000 / T
49
Q

In which type of radiation is peak energy output of the Sun?

A

Visible radiation

50
Q

What are the 2 heat sources from Earth?

A
  1. Geothermal energy from Earth’s interior
  2. Gravitational energy (via tides)
51
Q

What do IR and far-IR absorption cause?

A

IR: Vibrational excitation e.g. CO2
Far IR: Rotational excitation e.g. water vapour

52
Q

Do molecules scatter more efficiently at shorter or longer wavelengths?

A

Shorter

53
Q

At what wavelength is the atmospheric ‘window’ where heat from Earth can escape but can be blocked by clouds?

A

10 µm

54
Q

What drives the meridonial heat flux (ocean and atmosphere carry heat poleward)?

A

Flux of solar energy is greatest at Equator + there is a larger atmospheric path length at high latitudes (so oblique solar irradiance) so there is a surface temp. gradient

55
Q

Which form of the Ideal Gas Law equation (pv = nRT) is more convenient for an unbounded gas with known composition e.g. the atmosphere?

A

p = mass / volume

56
Q

What is the atmospheric equation of state?

A

p = ρRT where R = specific gas constant for dry air (287 J K-1 kg-1)

57
Q

Define isobars

A

Contour lines of equal pressure, hPa (isobar spacing directly proportional to wind speed e.g. closer spacing = faster wind speed)

58
Q

What kind of trend is the decrease in pressure with increasing height?

A

Exponential

59
Q

What 3 things do gravitational forces vary with?

A
  1. Distance from centre of Earth
  2. Variations in Earth’s shape/composition
  3. Centrifugal acceleration due to Earth’s rotation
60
Q

What is geopotential height measured in and how many metres is this equal to?

A

Decameters, 1 dam = 10 metres

61
Q

What is thermodynamics?

A

Change in heat of a system is equal to change in energy of the system

62
Q

What is the first law of thermodynamics?

A

dq = C(p) dT - (1/ρ)dp = 0

63
Q

What is the equation for calculating the temperature of an air parcel at any pressure (as long as it moves adiabatically)?

A

T(2) / T(1) = (P(2) / P(1))^(R/C(p))

64
Q

What are adiabatic processes?

A

Processes that involve no heat exchange with the surroundings

65
Q

What is the equation for potential temperature?

A

θ = T (p(0) / p)^(R/C(p))

66
Q

What are 3 sources of climatic heating?

A
  1. Conduction of heat from surface
  2. Frictional heating at surface
  3. Latent heating from condensation of water vapour into clouds
67
Q

What is the value of dry adiabatic lapse rate (DALR)?

A

9.8 K km-1

68
Q

When (-dT/dz) = DALR, is the air column neutral, stable, or unstable?

A

Neutral (air requires no extra energy to move along adiabats so any small mechanical perturbation will allow air parcels to swap places spontaneously)

69
Q

When (-dT/dz) < DALR, is the air column neutral, stable, or unstable?

A

Stable (air above has higher θ than air below so mixing is suppressed)

70
Q

When (-dT/dz) > DALR, is the air column neutral, stable, or unstable?

A

Unstable (air above has lower θ than air below so lower air has excess heat + air column spontaneously overturns)

71
Q

What are the heat capacities (C(p)) of dry air, water, and land?

A

Dry air = 1004 J kg-1 K-1
Water = 4200 J kg-1 K-1
Land = 800 J kg-1 K-1

72
Q

What is heat capacity numerically equal to?

A

The amount of heat required to increase 1kg of a substance to 1K

73
Q

How do evaporation + condensation occur?

A

Molecules on liquid surface with sufficient energy evaporate, molecules in air collide with surface and condense if they stick (energy released when condensation occurs)

74
Q

When will a warm puddle evporate?

A

If air is sub-saturated relative to vapour pressure of warm puddle

75
Q

When is air supersaturated and what happens when it is supersaturated?

A

When partial pressure > vapour pressure that would exist over a surface of water at equilibrium, excess water vapour is condensed to form droplets (cloud/fog)

76
Q

What kind of particles make cloud droplet production more efficient?

A

Aerosol particles

77
Q

What is the specific heat of vaporisation of water and specific heat of fusion of ice?

A

Specific heat of vaporisation of water = 2500 kJ kg-1
Specific heat of fusion of ice = 334 kJ kg-1

78
Q

What is the form of energy used for phase change e.g. condensation?

A

Latent heat

79
Q

Describe convective cloud formation

A

Air lifted adiabatically causes cooling –> eventually Pw (partial pressure of water) > e (saturation vapour pressure) –> clouds form (releases latent heat)

80
Q

What Law shows motion relative to air (balance of gravitational acceleration + frictional drag)?

A

Stoke’s Law (velocity, v = 1.2x10^8 r^2)

81
Q

What are the different motions relative to ground for the cloud types: stratus, cumulus, lenticular, and cumulonimbus (depends on Stoke’s Law and updraft velocity)?

A

Stratus: ~10 cm s-1
Cumulus: ~1 m s-1
Lenticular: ~1 m s-1
Cumulonimbus: ~10 m s-1

82
Q

What are the equations for the terminal velocity of rain and hail with radius >30m and with >1000m and why are they different?

A

> 30m: v = 8x10^3 r
1000m: v = 250√r
Turbulence and drag behind drop change terminal velocity

83
Q

Cloud droplets don’t freeze at 0°C, so what temperature are they supercooled at?

A

T(f) < -40°C

84
Q

What does freezing give out to the air in a cloud?

A

Heat

85
Q

What happens when e(ice) < e(supercooled liquid)?

A

Initial rapid growth of ice particles by condensation

86
Q

How are snowflakes formed?

A

Deposition of vapour onto ice (hexagonal symmetry, v. efficient coalescence)

87
Q

How is hail formed?

A

Impaction of liquid drops on ice T 0°C, liquid spreads over surface clear (high density ice particle)

88
Q

How is graupel (soft hail) formed?

A

Impaction of liquid drops on ice T &laquo_space;0°C, liquid doesn’t spread much + air trapped in some ice layers (opaque, low density ice particle)

89
Q

How does the temperature decrease of an air parcel lifted adiabatically change while water is condensing?

A

Temp. decreases more slowly

90
Q

Where in the atmosphere is the difference between DALR and SALR greatest?

A

At high temperatures (low altitudes in troposphere) where the saturated water vapour mixing ratio changes rapidly

91
Q

What is horizontal position given relative to?

A

The centre of the Earth, the Equator, and the Greenwich Medium (frame of reference rotates with Earth - looked at from North Pole, rotation is anti-clockwise)

92
Q

What is the difference between centrifugal and Coriolis force?

A

Centrifugal force acts continuously on any object on Earth whilst Coriolis force acts on moving objects only

93
Q

What does horizontal deflection of the require?

A

A force acting in the horizontal (greatest at poles and zero at Equator)

94
Q

In which direction are N.hemisphere air parcels deflected from their direction of movement and what does the magnitude of deflection depend on?

A

Right, depends on velocity of air (Coriolis force deflects an air parcel but doesn’t affect its velocity)

BSc Environmental Science (11 decks)

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