condensation on a macro-scale causing phenomenons

Question 1

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

Answer 1

• evaporation

- cooling

Question 2

what is the optimal condition for forming dew?

Answer 2

• 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

Question 3

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

Answer 3

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

Question 4

when does frost form

Answer 4

when dew point is below 0C- frost point

Question 5

what is white frost?

Answer 5

water vapour changes directly to ice crystals via deposition

Question 6

what is black frost?

Answer 6

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

Question 7

what is frozen dew?

Answer 7

• 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

Question 8

list the phenomenons that reduce visibility according to their strength.

Answer 8

haze< mist < fog (reduces visibility the most)

Question 9

compare dry and wet haze

Answer 9

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)

Question 10

why does condensation form clouds

Answer 10

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.

Question 11

what is mist?

Answer 11

suspended water droplets (not big enough to form raindrops)

Question 12

what is fog

Answer 12

like mist with lower visibility; like clouds at the surface

Question 13

how is fog formed

Answer 13

• 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)

Question 14

3 types of fog?

Answer 14

• radiation fog
• valley and upslope fog
• advection fog

Question 15

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

Answer 15

• 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

Question 16

what is a brief mechanism of radiation fog?

Answer 16

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

Question 17

why does shallow fog dissipate by afternoon?

Answer 17

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

Question 18

compare valley fog and upslope fog

Answer 18

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

Question 19

what causes advection fog?

Answer 19

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)

Question 20

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

Answer 20

they bring water sources

Question 21

what is evaporation fog

Answer 21

• 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.

Question 22

signs used for mixing ratio?

Answer 22

w, r

Question 23

what is steam fog

Answer 23

• 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)

Question 24

compare advection fog with steam fog

Answer 24

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

steam- when cold moist air meets warm water

Question 25

define clouds

Answer 25

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

Question 26

what are the paths to saturation?

Answer 26

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

Question 27

how does cloud form briefly

Answer 27

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

Question 28

what are the 4 mechanisms for uplift?

Answer 28

- surface heating causes convection - lifting along topography - convergence of air due to low pressure system - lifting along weather fronts

Question 29

what are rising plumes?

Answer 29

- warm, buoyant air | - usually caused by convection

Question 30

describe convective clouds

Answer 30

- 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)

Question 31

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)

Answer 31

2C/km

Question 32

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

Answer 32

8

Question 33

what is the equation used to find cloud base height

Answer 33

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

Question 34

what is the lifting condensation level

Answer 34

when T=Td

Question 35

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

Answer 35

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

Question 36

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

Answer 36

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

Question 37

lenticular clouds

Answer 37

formed at leeward side under stable flow over mountains. | can extend for 100km

Question 38

rotor clouds

Answer 38

- at the leeward side - cause turbulence and shear - hazard for aircrafts

Question 39

warm front develops -______-type clouds horizontally

Answer 39

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

Question 40

cold front develops _______-type clouds vertically

Answer 40

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

Question 41

why are clouds usually associated with depressions and troughs?

Answer 41

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

Question 42

why are fine weather associated with high pressure system

Answer 42

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