3: Clouds, Precipitation, and Weather Radar

Question 1

What is cloudy air

Answer 1

• water vapour is invisible
  cloudy air is condense liquid water droplets or sublimated ice crystals
  contrails form when hot humid exhaust from jet engines mixes with cold, drier air

Question 2

what is utility classification

Answer 2

• all clouds consist of water substance
• there is a continuum of different cloud bae heights
• classified by: high, middle, low

Question 3

Types of clouds and their altitudes

Answer 3

High: 5000-13000
Cirrus
Cirrostratus
Cirrocumulus

Middle: 2000-7000
Altostratus
Altocumulus

Low: 2000-surface
Stratus
Nimbostratus
Stratocumulus

Clouds with vertical development: to 3000
Cumulus
Cumulonimbus

Question 4

Cirrus clouds

Answer 4

• when the sky is very clear, wispy and looks like cotton balls
• consist of ice crystals

Question 5

Cumuliform clouds

Answer 5

Cumulonimbus: indication of very violent weather
Cumulus: fair weather
Cumulus congestus: towering cumulus. Some precipitation

Question 6

Mountain waves or gravity waves

Answer 6

• North-south mountain range deflects west wind into an up down wave like pattern called lee waves
• clouds form in crests (tip) where ascending air expands and cools
• Clouds dissipate in wave troughs where descending air is compressed and warms. When this happens energy breaks which results in clear air turbulence (CAT0

Question 7

What are clouds

Answer 7

aggregate of tiny water droplets and/or ice crystals

Question 8

What are aerosols and their importance

Answer 8

Aerosols are solid and liquid particles suspended in the atmosphere that are key for cloud formation
- have radius > 1 micrometer and act as a nuclei vapouring condensation or deposition of water vapour to form cloud droplet —> called cloud condensation nuclei (CCN)

Question 9

What is CCN and IN

Answer 9

• CCN: Cloud condensation nuclei —> aerosols that favour condensation of water vapour to form cloud droplet. Natural sources are dust from volcanic eruptions, wind eroded soil particles, particles released from forest fires, ocean salt spray, vehicular emissions
• IN: Ice forming nuclei —> promote ice crystal formation under sub zero temperatures

Question 10

What is terminal velocity

Answer 10

• how fast the particles fall from the sky: the heavier the faster
  Ex (from small to large): cloud droplets, drizzle drops, rain drops, hail

Question 11

drag and gravitation force

Answer 11

Drag force: pulls everything up
Gravitation force: pulls everything down

balance between these two determine where particles are in the atmosphere

• this means that cloud droplet has to grow into a bigger size so it can fall

Question 12

terminal fall velocity of ice crystal

Answer 12

plate shaped ice crystal: uniform, about 1m/s

Question 13

two processes of precipitation formation

Answer 13

1. Collision-coalescence process: warm-cloud precipitation formation
2. Bergeron-Findeisen process: cold-cloud precipitation formation

Question 14

Collision-coalescence process

Answer 14

• warm cloud precipitation formation
• a large droplet falls through a cloud of smaller droplets and collides with them. They merge, increasing the size of the larger droplet

Question 15

Bergeron-Findeisen process

Answer 15

• cold-cloud precipitation formation
• precipitation falling in middle and high latitudes form in cold clouds
• ice crystals grow at the expense of supercooled water droplets because the SVP of ice is lower than the water at the same temperature
• These snowflakes/ice crystals may melt on their way down, producing rain
• few water droplets will freeze and whatever available supercooled water droplet will freeze over the surface of the crystal and make it bigger

Question 16

7 Precipitation types

Answer 16

Rain: water droplets
Drizzle: smaller water droplets
Snow: loose aggregates of ice crystals
Sleet: partly melted snowflakes
Grapple: soft hail (liquid inside)
Hail: balls of ice
Freezing Rain: super-cooled rain drops that freeze on contact with cold surfaces

Question 17

snowflake forms and types

Answer 17

• all snowflake forms are hexagonal (6 sided)
• snow forms depends on temperature
  4 types:
  Needles: 0C
  Dendrites: -10C
  Plates: -20C
  Columns: -30C

Question 18

what affects the look of a hailstone

Answer 18

depends on the environment they grow in

Question 19

largest hailstone, mass, dimension, shape

Answer 19

mass: 220g
max dimension: 9cm
oblate spheroid
rough surface prior to melting

Question 20

olds hailstorm

Answer 20

• August 11, 2003
• multiple supercells
• $10 million in hail damage

Question 21

what is weather radar

Answer 21

remote sensing tool that helps in determining location, movement, and intensity of precipitation
- radar emits microwave signals and receives reflected signals from the targets (precipitates)
- radar antenna sits on tower and rotates around, rotation at different angle allows measuring of 3D rain field
-modern weather radar can detect the movement of violent weather

Question 22

Mod of weather radar

Answer 22

1. reflectivity mode
2. velocity mode

Question 23

Reflectivity mode

Answer 23

radars emit pulses of microwave energy at wavelength between 10-11.1cm
- at this wavelength radar signals are reflected by rain, snow, or hail, and cannot properly detect cloud droplets or crystals
- reflected radar signals are processed as radar echo
- of above 40 db then that is heavy precipitation

Question 24

Velocity mode

Answer 24

• doppler radar: works on the principle of doppler effect
• velocity detection capabilities
• stationary sound wave sources generates acoustics waves with uniform frequency
• a moving wave source generates wave pattern, with a frequency higher ahead of the source than behind of the source

Question 25

how does doppler radar work

Answer 25

• captures the movement of precipitation particles moving towards and away from the radar
• the frequency oof radar signal shifts between emission and the return of the signal
• if the rain shower is stationary: frequency of returned echo = frequency of emitted signal
• if rain shower is approaching the radar: frequency of returned echo > frequency of emitted signal
• if rain shower is moving away: frequency of returned echo < frequency of emitted signal