Topic 2b: Cloud Microphysics

Question 1

Describe Homogeneous Nucleation

Answer 1

Condensation of small droplets without aerosols. minimum droplet size defined by a balance between surface tension and latent heat

Question 2

What is needed to form a droplet?

Answer 2

energy to create surface tension (work done to create interface water vapour/liquid water. if latent energy is smaller than the energy needed to overcome surface tension no droplets will form

Question 3

What are aerosols? give examples.

Answer 3

suspensions of small solid/liquid particles (not water). examples include seeds, pollen, bacteria, salts, solid earth, fuel combustion

Question 4

What are Cloud Condensation Nuclei?

Answer 4

small subset of aerosols that serve as particles upon which water vapor condenses

Question 5

What is heterogeneous nucleation?

Answer 5

Condensation of water vapor on foreign object (CCN)

Question 6

Marine clouds have ____ whereas Continental clouds have____

Answer 6

fewer larger droplets…numerous smaller droplets

Question 7

What are the properties of warm clouds?

Answer 7

clouds where the temperature us above 0 degrees everywhere. initially cloud is made up of small drops only. Droplets grow through condensation and collision

Question 8

For small spherical drops what are the acting forces?

Answer 8

Downward forces: gravity (-mg)

Upward forces: total friction

Question 9

What is collision/coalescence growth?

Answer 9

large rain drops falling through a cloud will collide with smaller drops and coalesce together.

Question 10

What are the properties of cold clouds?

Answer 10

mostly below 0 degrees. above freezing level there will be a mixture of supercooled water and ice (Bergeron effect)

Question 11

What is homogeneous freezing?

Answer 11

freezing of supercooled drops without nuclei

Question 12

What is heterogeneous freezing?

Answer 12

supercooled drops freeze in the presence of a foreign particle.

Question 13

What is another ice deposition mechanism?

Answer 13

directly from vapor

Question 14

What are the three main mechanisms for the formation of ice particle growth?

Answer 14

1. simple growth from vapour phase (deposition)
2. growth by riming or freezing of supercooled water onto ice. forms hail
3. growth by aggregation - collision of ice particles

Question 15

Describe Nowcast

Answer 15

Data driven, Real time, High impact, Rapid warning generation

Question 16

What is cloud seeding?

Answer 16

introduction of large particles to act as CCNs to stimulate growth of large drops. goal is to enhance precipitation

Question 17

What are the three types of polarimetric radar?

Answer 17

Standard radar - emits single beam. can see horizontal cross section

Polarimetric radar - emits two beams. one vertical and one horizontal

Doppler radar - measures the speed of movement of the reflecting particle as well