Lecture panel 3 Flashcards

1
Q

Vapour pressure (e) and equilibrium

A

The partial pressure of air that is exerted by water vapour

equilibrium when the evaporation rate is equal to the condensation rate

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2
Q

how does temperature affect saturation vapour pressure?

A

increasing temp means increasing saturation vapour pressure

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3
Q

below freezing, is the saturation vapour pressure greater over water or ice?

A

water

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4
Q

Dew point

A

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

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5
Q

relative humidity (RH)

A

Ratio of vapour pressure to saturation vapour pressure. amount of water vapour compared with the amount required for saturation.
RH = e/es*100

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6
Q

Specific humidity

A

Mass of water vapour per unit mass of air (qv)
qv = 0.622e/P
where e is vapour pressure and P is air pressure
0.622 = ratio of the molecular weight of water vapour to the average molecular weight of dry air

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7
Q

What happens when an air parcel rises? falls?

A
  • it cools internally and expands as it rises

- compresses and warms as it falls

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8
Q

adiabatic process

A

temperature change that does not involve the removal or input of heat

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9
Q

lapse rate

A

rate at which an atmospheric variable (esp temp) changes with altitude

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10
Q

dry and wet adiabatic lapse rate

A

dry: -10C/1000m
wet: -6C/1000m
wet rate starts after dew point (from environmental lapse rate temp change of surrounding air)

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11
Q

Absolute stability

A

rising air packet always cooler than environmental rate

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12
Q

Absolute instability

A

air packet temp always higher than the surrounding air

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13
Q

conditional stability

A

rising air starts out cooler than environment, but then becomes warmer

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14
Q

What is the typical cloud-condensation nuclei diameter and what is the typical raindrop diameter?

A

nuclei are 2microns, raindrops are 2000 microns diameter.

moisture droplets in the cloud can be about 20 microns.

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15
Q

What happens if air contains vapour but no condensation nuclei?

A

air becomes super-saturated (>100% RH) because no droplets can form

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16
Q

condensation nuclei size range

A

10^-5mm to 10^-1 mm

17
Q

why is the wet adiabatic rate lower than the dry?

A

because condensation of water releases energy and warms the surrounding air

18
Q

What do ships do for clouds?

A

ship exhaust can be used as condensation nuclei, so clouds form behind the path of ships

19
Q

are continental or maritime droplets larger?

A

maritime are larger - there are more condensation nuclei over continents, and therefore more (and smaller) droplets. Droplets in maritime clouds are more likely to grow by collision and coalescence

20
Q

how can precipitation be inhibited or enhanced by condensation nuclei?

A

too many CCN can hinder precipitation, while very large CCN can enhance precipitation

21
Q

What droplet formation process dominates in warm clouds (>0C)

A

coalescence and collision are the primary mechanism for drop growth. Condensation dominates in the very initial stages of droplet formation.
-as the droplet falls, it creates a zone of negative pressure that pulls in other droplets

22
Q

cold cloud

A

below -40C, the cloud is glaciated and contains ice crystals

23
Q

mixed cloud

A

0 to -40C both liquid and ice crystals included in cloud

24
Q

how do crystals grow in mixed clouds?

A

(0 to -40C) crystals grow due to Bergeron-Findeisen process. Lower saturated vapour pressures over ice means that ice crystals grow at the expense of water droplets

25
What are the multiple zones that exist within a cloud (profile)
from warmest to coldest: 1. diffusional droplet zone (growth by condensation) 2. coalescence zone 3. rainout zone 4. mixed phase zone 5. glaciated zone
26
what occurs in the rainout zone?
growth by coalescence is balanced by loss of larger droplets
27
four lifting mechanisms
1. convergent 2. convectional 3. orographic 4. frontal
28
What is the ITCZ and its significance?
Inter-tropical convergence zone - trade winds converge here along equator, so there is lifting (convergence) and precipitation
29
conditions necessary for hurricane development
- warm ocean waters to depths of about 50m - thunderstorm development - light upper level winds - no hurricanes exactly at the equator due to the lack of Coriolis - hurricanes are convergent systems, so require air rising in low pressure zone
30
orographic precipitation mechanism
winds push air mass up mountain (from ocean), where it condenses and rains (on ocean side) -mechanism also works within continent but less moisture is in the water
31
frontal lifting mechanism
cold fronts -cold air forces warm air aloft - 400 km wide warm fronts -warm air moves up and over cold air gently -1000km wide
32
what type of clouds do warm fronts form?
grey and formless
33
What type of clouds do cold fronts form?
thunderstorm clouds
34
Major influences on precipitation distribution
- water vapour content (over oceans vs continents/ high elevation) - mechanisms for uplifting air - orographic effects - amount and type of cloud condensation nuclei (maritime aerosols enhance precipitation, and abundant microscopic aerosols over continents suppress precipitation)