Role of environmental stratification and shear for moist convection

Question 1

Different types of storms

Answer 1

Multicell storms, ordinary cell storm (showers), supercell storms, squad-line (broad wall of thunderstorms)

Question 2

Evaporation requires

Answer 2

• Water available
• Energy for evaporation is available
• Air needs to be un-saturated

Question 3

Condensation requires

Answer 3

• High RH or saturation and cooling
• This is a release of heat
• Lower updraft than droplet size to remove water from volume

Question 4

Effects of vertical motion on humidity

Answer 4

• Water vapour convected throu PBL leads to increase in mass mixing ratio (q)
• Lowered q if moist air is dumped at near top of PBL due to capping inversion
  => q and dewpoint temperature increase
  LCL lowered

Question 5

Different types of convection

Answer 5

Miller types

Question 6

Miller type I

Answer 6

Loaded gun. Warm, moist, well mixed layer below, strong inversion capping it. Large CAPE. strong downdrafts from evaporation aloft. Fast updraft makes hail likely.

Question 7

Miller type II

Answer 7

Deep layer if moist air (RH>60%). Conditionally unstable. weak CAPE. No inversion. Widespread convection.

Question 8

Miller type III

Answer 8

Similar to II but colder. Basically to parallel lines. Convection less intense. Usually weak CAPE.

Question 9

Miller type IV

Answer 9

Deep, very dry layer below, RH increases with height. Moist maritime air above. High based convection. Vigorous downdrafts produce strong surface winds.

Question 10

Life-cycle of ordinary cell

Answer 10

Cumulus, mature and dissipating.

Question 11

Cumulus growth phase

Answer 11

Strong convection and up-draft. Cloud droplets and ice-crystals formed.

Question 12

Mature phase

Answer 12

Up-drafts and downdrafts in a mature storm, cloud particles grow to precipitation. Region of precipitation up to 100 km^2, up to 5 km high. Falling precipitation creates downdrafts due to evaporative cooling. If vertical shear is not too great the cold pool of downdraft air near the surface will destroy the updraft.

Question 13

Decay stage

Answer 13

Anvil of many ice-crystals aloft and cold pool remain

Question 14

Tilt of updraft may cause:

Answer 14

• Downdraft detached from updraft
• Cold pool does not interfere with warm-moist inflow that creates updraft
• Cell is longer lived

Question 15

What can cause a tilt in updraft?

Answer 15

Wind shear and cold pool.

Question 16

Creation of new cell in multi-cell storms

Answer 16

Wind gust from cold pool causes air to be lifted to LCL and LFC so a new cell is created. Just the right amount of shear is needed for this.

Question 17

Structure of super cell storm

Answer 17

Strong rotating updraft accelerated by perturbation-pressure gradient force. Tilted so updraft separate from downdraft. Vortex stretching causes rotation in updraft.