GES 121 - Clouds

About Clouds

made up of water droplets and/or ice crystals, in between this is generally 100% relative humidity - saturation within a cloud

• equilibrium between water vapour/liquid

forms when air is nearly saturated AND contains particles (condensation nuclei needed to induce condensation)

cloud nights are warmer than clear nights because clouds continue to radiate depending on temperature

10 types of clouds

Supercooled

Water can remain in liquid state much below freezing in a clean atmosphere

water vapour needs particles to condense upon

Cloud Classification

10 (11-ish) types generally classed by:

• altitude:

  • low (stratus, cumulus)

    • composed of water droplets

  • middle (alto-)

    • composed of both ice crystals and water droplets

  • high (cirro-, cirrus)

    • all ice crystals, often wispy

  • clouds can transcend levels

    • cumulonimbus has vertical development - anvils out because can’t extend into stratosphere

• and shape:

  • heaped up (-cumulus)

    • piled up clouds, lumpy appearence

  • layered (-stratum)

  • whether they’re producing rain (nimbus)

    • usually at least 2k of thickness before precipitation, dark

Types of Clouds

low:

• stratus

• statocumulus

mid:

• altocumulus

• altostratus

high:

• cirrostratus

• cirrus

• cirrocumulus (extra!)

cumuliform:

• cumulus

• cumulinimbus

• mamatus

• funnel clouds

Low Level Clouds

Stratus:

• uniform grey tone

Stratocumulus

• alternating dark/light, not a lot of vertical development, unlikely for precipitation

Mid Level Clouds

Altocumulus:

• heaped up, rows across sky, appear larger because they’re closer to the ground, may/may not have dark base (can get reflection off of the surface or lower clouds)

  • 3-5 fingers in size

Altostratus:

• like the sun is dimly visible through the cloud, because of likely water vapour, will not form halo, fairly uniform gray

High Level Clouds

Cirrostratus:

• forms veil, light tone, made up of ice crystals

  • sun shining through will form a halo around the sun, maybe moon

    • sundogs are a similar phenomenon, internal reflection of ice crystals; crystals close to the surface form false suns

Cirrus:

• “hooked”, fibrous, happens when precipitating, snow carried by high altitude winds to create “fall streaks”

Cirrocumulus:

• ice crystals, heaped up in atmosphere, some precipitation but never reaches ground, appear small because high up

• a finger held at arm’s length = 1° of angle (if same size, probbaly cirrus)

• never cover the whole sky

Cumuliform Clouds

Cumulus:

• fluffy, flat bases

  • towering cumulus can give showers, but not severe precipitation

Cumulonimbus:

• often but not always “animal top”, considerable vertical development, big!

Mammatus:

• often on the base/side of a cumulonimbus, look kinda creepy, most thunderstorms have them, signify unstable conditions in the atmosphere

• often can’t see them without specific lighting from the side-ish, like oblique sun angle, or lightning

Funnel Clouds:

• cold core, fairly high up in the atmosphere, very rarely touches ground unless large and lots of circulation around it

• if you see spinning and it reaches the surface, then tornado or small land spout

Fog

Cloud layer close/at the surface, essentially a stratus cloud close to the ground

Two types:

1. Radiation/ground fog

   • forms overnight when temperature is close to the dew point, high humidity (clouds have high relative humidity)

   • no wind! must be clear and calm because wind is turbulent and mixes the air

   • sun warms the ground through fog, warming and circulating the air, so fog then disperses or lifts to become a stratus cloud

2. Advection fog

   • wind! warm moist air blowing over cold surface

   • contact causes temperature to fall to dew point