Sep 2012

Lesson 4.2

Meteorology

Clouds

Reference

From the Ground UpChapter 6.2:CloudsPages 124 - 127

Introduction• Clouds can form in different ways and,

as a result, come in many different types.

• Pilots should know the properties of different types of clouds, and what weather conditions come with them.

Outline• Classifications• Sky Condition• Cloud Formation

Classifications• By formation:

– Cumulus – Vertical clouds, formed by rising air, indicates Unstable Air

– Stratus – Horizontal layers, indicates Stable Air

• By height (families):– Low (Strato) Surface – 6 500 ft– Middle (Alto) 6 500 ft – 23 000 ft– High (Cirro) 16 500 ft – 45 000 ft– Vertical Development 1 500 ft and up

High Clouds• Cirrus (Ci)

– Thin wavy, delicate wisps

High Clouds• Cirrocumulus (Cc)

– Thin cotton ball or flake-like

High Clouds• Cirrostratus (Cs)

– Very thin, high sheets– Makes sky white, halo around sun or moon

Middle Clouds• Altocumulus (Ac)

– Layer or patches of rounded masses

Middle Clouds• Altocumulus Castellanus (Acc)

– Altocumulus with turrets

Middle Clouds• Altostratus (As)

– Thick grey layer– Sometimes light rain/snow

Low Clouds• Stratus (St)

– Uniform layer like fog, but not on ground,Sometimes has drizzle

– When broken, called Stratus Fractus (Sf)

Low Clouds• Statocumulus (Sc)

– Thin layer or patches of rounded masses

Low Clouds• Nimbostratos (Ns)

– Uniform thick, dark, grey layer– Continuous rain/snow

Vertical Development• Cumulus (Cu)

– Thick, rounded or lumpy individual clouds– When fragmented, called Cumulus Fractus (Cf)

Vertical Development• Towering Cumulus (TCu)

– Very high towering masses– Rough air underneath

Vertical Development• Cumulonimbus (Cb)

– High, heavy masses going above freezing level– Usually hail inside cloud, heavy rain/snow beneath– Very turbulent

Sky Condition• Cloud cover broken down into oktas (8ths):

– Clear 0– Few 1 - 2– Scattered 3 - 4– Broken 5 - 7– Overcast 8

• Broken and Overcast considered a Ceiling

Cloud Formation• Clouds form from condensation or sublimation

(water vapour to water droplets or ice). This requires:– High relative humidity– Condensation nuclei– Cooling air

• Formed in two ways:– Air cools to saturation point (most common, by

expansion)– Air absorbs water vapour to reach saturation point

Lifting Processes• Clouds created when air rises, expands,

cools, condenses. Following processes force air up:– Orographic Lift – Air forced up by hills/mountains– Convection – Sun heats ground, warm air rises– Frontal Lift – Warm air forced up over cold front– Turbulence – Wind blowing over rough ground

creates eddies, forcing up and down currents– Convergence – Air inside a low pressure area is

forced upwards

Next Lesson

4.3 – MeteorologyPressure

From the Ground UpChapter 6.3:PressurePages 127 - 130