9 Special Cloud Types

Question 1

Asperitas

Answer 1

Looks like a rough sea surface
Likely formed due to wind shear manipulating and moulding clouds into this shape (often associated with severe turbulence )
Often observed in strong northwest flow over southern alps developed after lenticularis and sometimes prior to thunderstorms
1 indication of severe turbulence
2 precursor to cb

Question 2

Mammatus

Answer 2

Supplementary (most be associated with one of ten main cloud types, usually on the underside of large cb anvils)
Form due to subsidence of cold air (last short periods 10 minutes to an hour)
1 Turbulence depends on cloud it is associated with, in cb anvil it indicates severe turbulence and wind shear, otherwise usually light- moderate turbulence
2 obviously if attached to cb other cb hazards exist

Question 3

Altocumulus lenticularis

Answer 3

Lenticularis is supplementary cloud feature
Stable air flowing over a barrier
Indicates significant winds aloft
Cloud doesn’t move as it continually forms at leading edge while dissipating at trailing edge

Question 4

Rotor cloud

Answer 4

Usually in strong northwest airflow over ranges
Fast moving air trapped in a vortex, with enough moisture the upgoing air will create ragged cloud, if dry no cloud will be present but rotor will still exist
Rotor streaming results from east or southeast winds over range, rotors not locked in place and so advect downstream and break up
1. If first wave is directly over the mountain the wind at ridge top is 20 knots
2. If first wave is downwind of the mountain the wind is stronger
3 if visible waves are increasing in frequency and height more moisture is being added and front is likely getting closer
4 flight within wave is smooth but downdrafting sections may be stronger than aircraft climb performance
5 between wave systems are counter rotating rotors
6 in clear air beneath crest of each wave is rotor zone with severe turbulence
7 eventually creates strong surface winds and possible turbulence across whole area downwind of ranges
8 large qnh differences require constant altimeter changes
9 temps east of divide will increase due to fohn effect reducing aircraft performance and creating dry climate

Question 5

Kelvin Helmholtz waves

Answer 5

Warm layer over cold layer moving in opposite directions or same direction at extremely different speeds
Cold air rises in billows while warm air pushes down and create wave motions which crest and break creating possible severe turbulence and destroying itself
Form on top layers of thin clouds ci, ac, sc, st and rarely cu
Smaller waves higher than 5000’ are most turbulent
Usually short lived

Question 6

Altocumulus castellanus

Answer 6

Mid level convective clouds that resemble a battle meant kind of Y shaped
Indicate unstable mid level of troposphere
Moderate turbulence sometimes worse
Possible cb or thunderstorms development in next 12-24 hours

Question 7

Banner cloud

Answer 7

Orographically induced on Lee side of sharp pointed mountain peaks
Wind flowing over peak creates low pressure in Lee which leads to cooling and condensation
Indicates wind direction and a moist atmosphere at mountain top
If size of banner increases or wisps of cloud form at lower levels moisture content in air is increasing. This is usually an indication of deteriorating weather especially when paired with falling pressures