LEC.175 Atmosphere, weather, and climate Flashcards
(126 cards)
1
Q
What instrument is used to measure Temperature?
A
Thermometer
2
Q
Why is a Stevenson screen used for measuring temperature and what are some of the features?
A
To limit exposure. Naturally ventilated, shielded from solar and terrestrial radiation, shielded from rain, white to reflect sunlight.
3
Q
Where do temperatures get measured?
A
Standard screen level, grass surface, concrete surface, and at 5, 10, 20, 30, 50, 100cm depth in soil.
4
Q
What is the automatic measurement instrument for Temperature?
A
Thermistor (and thermocouples)
5
Q
How do thermocouples work?
A
Bimetallic strips, current flows through the strip, varies when there is a gradient in temperature across it, older variants use mechanical movement of the strip (due to thermal expansion) to move the arm
6
Q
How do thermistors work?
A
Mixtures of metallic oxides have a resistance to the flow of electrical current that varies greatly with temperature.
7
Q
Why does a Stevenson screen open on the poleward side?
A
So that direct sunlight does not enter during reading temperature.
8
Q
Pros and cons of automatic measurements?
A
Pros - no person needed to take the measurement
Cons - need calibration, degrade with time (meaning they need frequent calibration)
9
Q
What is the symbol and unit used for Relative Humidity?
A
RH, %
10
Q
What is humidity?
A
Water vapour content of air
11
Q
What is absolute humidity (pw)?
A
Units of concentration, partial pressure, or mass mixing ratio
12
Q
What is saturation vapour pressure (ew)
A
The maximum amount of water vapour that air, above liquid or solid water, can contain at equilibrium. Depends very sensitively on temperature.
13
Q
What is relative humidity (%RH)?
A
Ratio of the partial pressure to the vapour pressure of water (or ice). %RH = 100(pw/ew)
14
Q
If %RH < 100% what cannot form?
A
Clouds, and any remnants will rapidly evaporate
15
Q
What instruments can be used to measure Relative Humidity?
A
hair hygrometer, psychrometer
16
Q
How does a psychrometer work?
A
Ordinary thermometer ‘dry bulb’ matched with thermometer covered in a wet muslin cloth ‘wet bulb’. The difference in temperatures is related to relative humidity because heat has been used to evaporate water form the cloth.
17
Q
What is the automatic measurement instrument for Relative Humidity?
A
Capacitance
18
Q
How does a capacitance work?
A
By detecting changes in the capacitance of a hygroscopic dielectric material between two electrodes, which is directly proportional to the amount of water vapor absorbed.
19
Q
What is the symbol for Wind Speed?
A
U, V
20
Q
What units are used to measure Wind Speed?
A
m/s, kt
21
Q
What instrument is used to measure Wind Speed?
A
Anemometer
22
Q
What is the Beaufort scale?
A
Subjective scale used when instruments are not present e,.g. Force 8 = gale, impedes walking, small twigs breaking off
23
Q
What does conventional wind speed measure?
A
Horizontal component of the wind, usually 3-4 orders of magnitude bigger than the vertical component.
24
Q
What instrument is used to measure Wind Direction?
A
Wind vane
25
What is the symbol and unit used for Pressure?
p, mb,hPa
26
What instrument is used to measure Pressure?
Barometer
27
How does a mercury barometer work?
Reads station pressure, which is converter to mean sea level pressure using the stations altitude. A barometer balances the weight of the atmosphere against the weight of the liquid in it which tends to be mercury.
28
Why is an aneroid barometer more commonly used now?
Safer and more convenient, however does require calibration.
29
What unit is used to measure Precipitation?
mm/day
30
What instrument is used to measure Precipitation?
Rain gauge
31
What is the automatic measurement instrument for Precipitation?
Tipping bucket
32
What is the measurement for Cloud coverage?
okta
33
What 'instrument' is used to measure cloud cover?
(Observer)
34
What is the automatic measurement instrument for Cloud coverage?
Camera
35
What is the measurement for Visibility?
km
36
What 'instrument' is used to measure Visibility?
(Observer)
37
What is the measurement for Sunshine duration?
hours
38
What instrument is used to measure Sunshine duration?
Campbell-Stokes
39
What is the automatic measurement instrument for Sunshine duration?
Radiometer
40
What is the measurement for Evaporation?
mm/day
41
What instrument is used to measure Evaporation?
Evaporating pan
42
What time is meteorological observation data typically collected?
0900hrs GMT
43
Observation requirements for data quality:
Representative, accurate, consistent
44
What % of the atmospheres mass is below 5km?
50%
45
Atmospheric composition in dry air?
78% nitrogen, 21% oxygen, ~424ppm CO2, 1% argon, tiny amounts of Ne, He, Kr, H2
46
Importance of the atmosphere?
Warms the surface, mixes heat vertically, mixes heat meridionally (quarter to pole), redistributes water via hydrological cycle, eternal UV shield for the biosphere
47
What is the atmospheric region below the homopause known as?
The turbopause - The homopause is sometimes referred to as the turbopause.
48
What process dominates atmospheric mixing below the homopause?
Turbulent motions
## Footnote
Below the homopause, the atmosphere is efficiently mixed by turbulent motions.
49
Above the homopause, what process becomes dominant?
Molecular diffusion
50
What factor influences molecular diffusion rates in the atmosphere?
Molecular mass. Molecular diffusion rates depend on the mass of the molecules.
51
What happens to the main components of the atmosphere above the homopause?
They become separated by mass. Above the homopause, lighter and heavier gases separate due to differences in molecular mass.
52
What is the significance of the Critical Level in the atmosphere?
Molecules have a significant chance of escaping to space
53
Which type of molecules are more likely to escape to space?
Light molecules (e.g., hydrogen)
54
What is the only region where the mass of a molecule matters in the atmosphere?
Above the Critical Level
55
What determines the composition of the atmosphere everywhere, apart from above the Critical Level?
Mixing - In regions below the Critical Level, mixing is the primary factor determining atmospheric composition.
56
How do CFCs reach the stratosphere?
By mixing across the tropopause. CFCs do not reach the stratosphere because they are lighter than air; they mix to get there.
57
What is stability in the context of the atmosphere?
Likelihood of overturning a layer in the atmosphere.
58
What would make the atmosphere unstable (stratification and stability context)
Hot less dense layers beneath cold more dense layers - leads to overturning and mixing.
59
Describe the stratosphere
The 'layered' sphere. Vertical transport damped. Contains the ozone layer which is an important atmospheric heat source. Very dry. Almost no clouds
60
Describe the troposphere
The 'overturning' sphere. Vertical motion on small and large scales. Almost all atmospheric water contained within. Most weather systems capped by the tropopause
61
Describe the planetary boundary layer
Wind velocity decreases to zero at the surface. Resultant friction causes much overturning of air. Part of atmosphere in contact with the terrestrial heat source.
62
What sort of measurement do satellites provide, and what do they supplement?
Indirect passive measurements, they are supplementary to surface readings
63
What are geostationary orbits?
Fixed position relative to Earth, equatorial plane, ~35,000km above surface
64
Pro and con of geostationary orbits
Pro - continuity
Con - views towards the higher latitudes/poles gets skewed
65
What is often done with satellite data to aid interpretation?
Displayed as images
66
What is visible detecting?
Reflected light/albedo
67
What is infrared detecting?
Emitted heat
68
Stefan-Boltzmann law?
F = (sigma)T^4
69
Wien's law?
lambda(peak) = 3000/T (in Kelvin)
70
Stefan-Botlzmann constant?
5.67 x10^-8 Wm^-2 K^-4
71
What wavelength is the suns energy?
Visible
72
Inverse square law?
Fse += Fs (rs^2/rse^2)
73
~what % of incoming radiation is reflected?
30%
74
What affects how wavelengths interact with the atmosphere?
The wavelength/type of wavelength 9UV/IR/etc)
75
Shortest wavelengths - UV and blue light in the atmosphere?
High enough energy to break up molecules in the atmosphere. UV and bluelight absorbed by some gases -> bond breaking. e.g. photolysis of ozone
76
Near-IR interactions in atmosphere?
Vibrational excitation. Molecules absorb IR, stretchier bonds, not enough to break. Diff molecules absorb particular wavelengths and vibrate in diff ways.
77
Which two gases don't interact directly with Near-IR explaining why they don't contribute to the GHG effect?
O and N
78
Far-IR interactions in the atmosphere?
Absorbed causing rotations, e.g. water vapour at 12micrometres (um).
79
Why does the sky look blue and setting sun look red?
Molecules scatter much more efficiently at shorter wavelengths. Blue scatters further out the beams of sun so when look away from sun more blue, and towards, more red.
80
What happens to absorption moving into the visible part of the spectrum?
Drops. At higher wavelengths chunks are taken out, specific gases for specific wavelengths.
81
What role does N2 have in absorption of solar or terrestrial radiation?
It doesnt
82
When does O2 (molecular oxygen) filter out short UV?
at altitudes above 60km
83
What part of IR to clouds absorb?
They absorb efficiently across the entire IR
84
Clouds and the visible part of the spectrum?
Block sunshine, can scatter some of it, absorb a tiny bit
85
Greenhouse forcing?
The radiative forcing from changes to GHG concentrations is small, but can have a significant effect on climate - through the water vapour feedback.
86
Water vapour feedback?
Increasing CO2 increases surface temperatures. This increases evaporation from the surface and so increases water vapour in the atmosphere. Increased water vapour causes increased temperature, because it too is a greenhouse gas.
87
Ideal gas?
pV=nRT
88
Atmospheric eqn of state?
p =rhoRT
89
what is pA and daltons law?
pA= partial pressure of substance A
Dalton's law - the pressure exerted by a mixture of ideal gases is the sum of the pressures exerted by the individual gases occupying the same volume alone.
90
Pressure decreases with increasing?
Altitude
91
Eqn for column of air at rest?
(p2-p1/z2-z1)=-rhog
92
The decrease of pressure with height is?
exponential
93
What does the hydrostatic relation do?
- Encapsulates the major physical difference between the ocean and the atmosphere
- Explains why you need oxygen to climb Mt. Everest
- Allows calculation of heights of pressure surfaces from temperature soundings, e.g., for radiosondes
- Applies for all but the most vigorous vertical accelerations
94
Largest pressure gradient?
In the vertical, and balanced by gravitational acceleration
95
Horizontal pressure gradient?
Tiny compared to vertical, but causes wind due to no gravitational difference.
96
What type of wind is the wind related to isobar spacing?
Geostrophic wind
97
Why are winds at the surface slower than geostrophic winds?
Surface friction (buildings, trees, mountains, etc)
98
What do gravitational forces vary with?
- distance from the centre of the Earth
- variations in the Earth;s shape and composition
- centrifugal acceleration due to Earth’s rotation
- as the inverse of the square of the distance between objects
99
Due to gravitational variations what is used instead of geometric height?
Surfaces of equal potential energy - geopotential height, constant g0
100
Mechanic behaviours of the atmosphere?
Pressure gradients, geostrophic balance
101
What does thermodynamics link?
Heat input (dq) to a system, to the change in temperature (dT) of the system, and the work done (often dp) by the system
102
First law of thermodynamics?
dq = CpdT - (1/rho)dp
103
Adiabatic conditions?
change in heat (dq) = 0, no heating, no cooling. Therefore fractional temp change = fractional pressure change
104
If you push air around on a horiztonal surface what happens to the temperature? (adiabatic)
Nothing
105
If air is forced to lift over e.g. mountain, what happens to pressure and temp? (adiabatic)
pressure decrease, temp decrease
106
On a global scale whats the relationship between evaporation and precipitation?
Roughly equal
107
if e>pw ?
sub-saturated conditions
108
if e = pw?
saturated conditions (equilibrium)
109
if e
super-saturated conditions
110
what is 'e' (not the number)
fixed saturation vapour pressure
111
what is 'pw'
partial pressure
112
What do saturated vapour pressures depend on?
Temperature - approx double every 10°C increase
113
When air is supersaturated what happens?
The excess water vapour is condensed to form droplets - clouds or fog
114
What is the effect on aerosol particles in the air?
makes cloud droplet production more efficient (CCN)
115
Radiation fog?
For dew, when the surface and air cool by long-wave emission to the point where the vapour pressure at that temperature is less than the partial pressure of water vapour in the air, then the excess vapour condenses on to aerosol particles, called cloud condensation nuclei (CCN). Such fogs are usually no more than a few metres deep.
116
Advection fog?
When warm air is transported over a colder surface, the air is cooled by conduction, and can super-saturate. Can be 10-100m deep
117
How are fogs dissipated?
Solar heating at the top of the fog layer. Air warms, saturated vapour pressure increases to > available water in vapour and condensed phases, fog droplets evaporate.
118
Is cloud formation adiabatic or diabatic?
Diabatic
119
How much of Earth's energy budget goes into evaporation/cloud formation?
approx 1/3, but condensation and rain releases energy again. Exo/endo
120
Describe the process of convective cloud formation?
- tends to be cumulus clouds
- heat ground surface, heat air above, air rise
- adiabatic lifting, cools air
- pw>e so cloud forms
- latent heat from cloud formation changes profile of temp
- e decreases as air rises expands and cools
- assume pw is constant below cloud
121
Why are the bases of clouds flat especially in the higher atmosphere?
At some point they have to reach condensation level.
122
Coriolis effect?
Motion in a rotating frame of reference. N1L - absence of forces body will continue at rest or moving in straight line. But Earth curved so viewpoint also curved. Perceived effect not an actual force.
123
Where is the Coriolis force at the greatest and least?
Greatest - pole Least - equator (technically 0)
124
How does speed influence the coriolis effect?
The faster the speed of the object the greater the coriolis effect
125
What way are air parcels deflected in N and S hemisphere?
N - right S - left
126
Geostrophic balance?
Pressure differences drive winds. The strength of the wind is proportional to the horiztonal pressure gradient. Strong pressure gradient - strong winds. Air moves parallel to isobars, moves along the pressure gradient not across it.
