processes increase precipitation developement

Question 1

increase raindrop diameter ________ number of raindrops per m3 of air of the same diameter

Answer 1

decreases

Question 2

increase raindrop diameter ________ rain rate

Answer 2

increases

Question 3

define terminal velocity

Answer 3

gravitational force = air resistance (friction)

Question 4

what is the shape of a raindrop at terminal velocity

Answer 4

parachute like shape. the base is pushed up.

Question 5

define precipitation

Answer 5

any form of water (liquid of solid) falling from the sky

Question 6

other than condensation, droplets can also grow by collection (in warm clouds). define the terms collision and coalescence involved in collection

Answer 6

• collision: when larger droplets with higher velocity catch up with smaller droplets with lower velocity. they collide and become a larger droplet
• coalescence: droplets combine to become one due to opposite charges

Question 7

what is low collection efficiency?

Answer 7

Not all droplets will collide and stick

Question 8

what causes low collision efficiency

Answer 8

smaller droplets may be swept past the larger droplet

Question 9

what causes low coalescence efficiency

Answer 9

droplets can bounce or re-separate after collision (usually due to identical charges)

Question 10

the curve of growth by collection increases ___________

Answer 10

exponentially

Question 11

how come only condensation is involved initially with the growth of droplets?

Answer 11

• droplets have to grow to a certain size that it can have velocity before collection can happen.
• time is needed for droplets to fall and collide with other droplets, so it can’t start immediately

Question 12

define continuous collection

Answer 12

Droplets are uniformly distributed in space so can be collected uniformly at the same rate by all collector drops of a given size

Question 13

define Stochastic collection

Answer 13

droplets are not uniformly distributed in space, therefore collisions are individual events, distributed statistically in time and space

Question 14

what is the Cascade process of raindrops

Answer 14

continuous process where small droplet grows to be large droplets. large droplets then break and become small droplets again. this cycle continues

Question 15

why raindrops reaching the surface rarely exceed 5 mm in diameter?

Answer 15

• Collisions between large raindrops break them into smaller drops.
• surface tension is too weak to hold the larger drops together

Question 16

If RH below the cloud is high, then the droplets will arrive at the ground as ________

Answer 16

drizzle

Question 17

what would happen to the raindrop if the cloud base is high?

Answer 17

drops will evaporate before reaching the surface

Question 18

why do thicker clouds allow raindrops to grow to a greater size

Answer 18

Thicker clouds, formed by convective motion, can have stronger updrafts (due to convection motion )and can keep larger cloud droplets aloft, permitting them to join (coalesce) with more droplets and grow to greater sizes

Question 19

describe homogenous nucleation (pure water) of both deposition and freezing in cold clouds

Answer 19

• deposition (vapour to ice): very unlikely to happen, temp has to be lower than -60C so the molecules have very low energy and stick together to form ice crystals
• freezing (liquid to ice): water molecules within the droplet must gather rigidly to form an ice embryo, large enough to survive and grow
• both very improbable

Question 20

true or false:

water have a larger change to freeze at 0C if it is in a large volumn

Answer 20

true.
large volume means more water molecules –> higher chance a few of the molecules will line up properly to become crystal structure

Question 21

true or false
heterogenous freezing (ice nuclei involved) happens at a higher temperature compared to homogeneously

Answer 21

true. as ice nuclei aid the freezing process. Most effective ones have a crystal structure similar to ice hence ice can form around and on them easily

Question 22

define effective ice nuclei and give some examples.

Answer 22

• effective ice nuclei has a molecular geometry similar to the molecular structure of ice. This geometry helps water molecules in the surrounding air to align in the molecular structure for forming ice when they deposit on the surface of the nucleus
• Clay minerals
• some bacteria from decaying plants

Question 23

how come ice crystals and supercooled water can coexist at the same time when there is a relative sparseness of ice nuclei

Answer 23

• low ice nuclei population means not all supercooled water can form on the ice nuclei and be ice crystals. therefore they can coexist
• this allows Bergeron process to happen

Question 24

4 ways ice particles can be formed and describe them briefly

Answer 24

• Heterogeneous Deposition - vapour transformed to ice on a nucleus
• Condensation followed by Freezing - droplet forms on a nucleus which freezes
• Contact - nuclei makes contact with a droplet which then freezes (airplane wing)
• Immersion - nuclei becomes immersed in a droplet which then freezes

Question 25

true or false:
the saturation vapour pressure is lower in ice compared to supercooled water at same temperature ( for temperature below 0C)

Answer 25

true. this is because ice has larger volume and larger surface tension than water therefore ice has a lower pressure–> lower water vapour and saturation vapour pressure

Question 26

true or false:

vapour pressure difference between ice and supercooled water is greatest at -12C

Answer 26

true. it is where freezing and deposition happens most frequent

Question 27

what is the Bergeron process

Answer 27

• Bergeron process happens since the svp of supercooled water is higher than the svp of ice, which means that diffusion can happen due to the pressure gradient
• this diffusion allows the ice crystals to grow as the water molecules from the water moves to the ice
• this happens when ice and supercooled water both coexist together.

Question 28

Bergeron process explains how precipitation consisting single ice crystals can be formed. however, for larger precipitation to be formed, ice crystal have to grow by accretion or aggregation. define these two terms

Answer 28

• Accretion: ice particles collide with supercooled water droplets, which freeze upon contact. (forms snow pellets/ graupels)
• Aggregation: collisions and aggregations of ice particles falling at different speeds (forms snowflakes, may melt to become rain)

Question 29

Shape of snow crystals depends on _________ and ________

Answer 29

• temperature

- humidity

Question 30

true or false:

clouds can be a water/ice mixture

Answer 30

true

Question 31

what are the 4 types of precipitation and describe their formation from snow.

Answer 31

• snow: air temp is below 0C the whole time –> no ice melts
• sleet (ice pellet): the snow meets a shallow warm layer high above the surface –> ice partially melts, but the melted supercooled water refreezes afterwards.
• freezing rain: the snow meets a deep warm layer –> all ice melts completely. however near the surface, the supercooled water freezes again via contact
• rain: air temp is above 0C the whole time –> all ice melts.