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Meteorology: Atmosphere and Environement > condensation on a macro-scale causing phenomenons > Flashcards

condensation on a macro-scale causing phenomenons Flashcards

1
Q

at constant pressure, saturation can be achieved by either _________ or _________ of air

A
  • evaporation

- cooling

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2
Q

what is the optimal condition for forming dew?

A
  • forming on vegetation early morning after a clear and calm night
  • vegetation: cools quickly than road surface
  • clear: clouds can trap heat. clear sky means no clouds and cool night (cold air holds less water so more water v. can be released)
  • calm: no wind. warm air above doesn’t mix with coolest air near the ground
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3
Q

why is the dew point temp usually the minimum night time temp?

A

dew forms due to condensation, releases latent heat, so it reduces the rate on temperature cooling.

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4
Q

when does frost form

A

when dew point is below 0C- frost point

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5
Q

what is white frost?

A

water vapour changes directly to ice crystals via deposition

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6
Q

what is black frost?

A

temperature is below 0C but no ice formed due to low humidity. condensation can’t happen –> no latent heat released –> great damage to vegetation as they freezes internally
-black- colour of damaged tissue

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7
Q

what is frozen dew?

A
  • dew point is just above 0C so dew forms first then freezes
  • dew point then drops below 0C and dew freezes.
  • not via deposition
  • ice formed without crystal
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8
Q

list the phenomenons that reduce visibility according to their strength.

A

haze< mist < fog (reduces visibility the most)

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9
Q

compare dry and wet haze

A

dry- particles selectively allow some rays of sunlight to be scattered while allowing other rays to be penetrated. (yellowish colour)
wet- some water condensation found on the particles –> haze thickens as particles grow in size–> wet haze (grey white colour)

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10
Q

why does condensation form clouds

A

at LCL, RH= 100% which means a lot of H2O molecules are found–> greater collision forming bigger lump of H2O. appears white as sizes increase are big enough to scatter visible light.

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11
Q

what is mist?

A

suspended water droplets (not big enough to form raindrops)

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12
Q

what is fog

A

like mist with lower visibility; like clouds at the surface

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13
Q

how is fog formed

A
  • cooling of air (cold water holds less water so more water v. releases)
  • evaporation of water into the air (water v. added to the air)
  • by mixing of two air masses so the mixture is saturated (the graph)
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14
Q

3 types of fog?

A
  • radiation fog
  • valley and upslope fog
  • advection fog
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15
Q

what are the favourable conditions for forming radiation (ground) fog?

A
  • long night (cold)
  • clear sky (cold; no clouds trapping heat)
  • shallow layer of moist air near ground (eg. from rain)
  • light wind (no mixing of air)
  • common over land in late autumn and winter (cold air)
  • low lying areas (cold ir sinks downhill)
  • forms deepest around sunrise as air is the coolest
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16
Q

what is a brief mechanism of radiation fog?

A

surface cooling cools the air above, causing the air to release water vapour and fog fog (more moisture–> more favourable)

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17
Q

why does shallow fog dissipate by afternoon?

A

as sunlight penetrates the fog and warms the ground–> convection causes mixing –> fog droplets evaporates

18
Q

compare valley fog and upslope fog

A

valley- cold air sinks downhill (denser)–> collects at valley bottoms –> air cools further due to cold surface (hills can be clear all day); cold humid air are found at river valley
upslope- moist air flowed up the hill/mountains, cools adiabatically, expands and saturates –> form fog if sufficient moisture

19
Q

what causes advection fog?

A

when warm moist air (eg. tropical maritime) moves over cold surface (cold coastal water) –> air cools to dew point –> form fogs (like in hot showers)

20
Q

what are fog and dew important sources to plants and animals?

A

they bring water sources

21
Q

what is evaporation fog

A
  • obtained by mixing 2 unsaturated air masses of different temp. to produce a supersaturated one. (eg. moist air coming out form your mouth in winter)
  • temp. and mixing ratio of the resulting airmass would be an average of both air masses.
22
Q

signs used for mixing ratio?

A

w, r

23
Q

what is steam fog

A
  • when cold air meets warm water.
  • water is evaporated adding moisture to the cold air, making it saturated.
  • cold air is heated by warm water –> rises and become steam
  • seen in lakes in autumn/early winter, when air is cold and lake is still warm (from summer)
24
Q

compare advection fog with steam fog

A

advection-when warm, moist air meets cold surface (coast)

steam- when cold moist air meets warm water

25
Q

define clouds

A
  • visible aggregation of tiny water droplets or ice crystals suspended in the air.
  • can be found at high elevation or low ground
26
Q

what are the paths to saturation?

A
  • cool air directly (higher RH since water v. releases)
  • mix with colder air (to cool air)
  • reduce pressure (adiabatic expansion and cooling)
27
Q

how does cloud form briefly

A

air rises, expands, cools, saturates (more water v. released) –> more collision –> condensation (droplets aggregate)

28
Q

what are the 4 mechanisms for uplift?

A
  • surface heating causes convection
  • lifting along topography
  • convergence of air due to low pressure system
  • lifting along weather fronts
29
Q

what are rising plumes?

A
  • warm, buoyant air

- usually caused by convection

30
Q

describe convective clouds

A
  • localised, caused by surface heating
  • due to localised condensation, clouds are usually heaped, with domed tops and flat bases (Cu, Cb)
  • when clouds reaches the stable layer (resist vertical motion), it spreads out horizontally –> stratiform clouds (Sc)
31
Q

dew point drops by ____C/km. it drops because pressure decreases as air rises, hence easier to reach saturation. (pressure inside the parcel is lower than the environmental pressure = saturation + growth)

A

2C/km

32
Q

difference between T and Td reduces by ___C for each km increase.

A

8

33
Q

what is the equation used to find cloud base height

A

125( T-Td)

OG= (T-Td difference)/8 x 1000 (from km to m)

34
Q

what is the lifting condensation level

A

when T=Td

35
Q

what do the clouds dissipate at the leeward side of the mountain

A

leeward side- air get compressed downslope –> pressure increases in parcel greater than environment –> droplets evaporates –> clouds dissipate

36
Q

why is the initial temp at the windward side different form the final temp at the leeward side

A

windward- air temp decreases by both dry and wet adiabatically
leeward- air temp increases dry adiabatically only

37
Q

lenticular clouds

A

formed at leeward side under stable flow over mountains.

can extend for 100km

38
Q

rotor clouds

A
  • at the leeward side
  • cause turbulence and shear
  • hazard for aircrafts
39
Q

warm front develops -______-type clouds horizontally

A

stratus. as its is harder for warm air to replace cold air- less energy inspired - stratus

40
Q

cold front develops _______-type clouds vertically

A

cumulus. easier for cold air to replace warm air - more energy - larger clouds formed

41
Q

why are clouds usually associated with depressions and troughs?

A

convergence of air are found in low pressure system, forming clouds

42
Q

why are fine weather associated with high pressure system

A

high pressure system –> divergence of air at the surface –> sinking of air –> clouds dissipate –> clear sky

Meteorology: Atmosphere and Environement (15 decks)

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