Clouds and Precipitation

Clouds Visible masses of tiny water droplets or ice particles suspended in the atmosphere. 3 variables must be present for clouds to form. Water vapor: air must be saturated. Cool temperatures: air must be cooled to the dew point. Condensation nuclei: provides a surface for condensation to occur. Ex. : dust, salt, smoke.

Cloud formation As warm air rises and expands, it cools. When air reaches a level where its temperature is lower than dew point, condensation occurs to form a cloud. The level where condensation forms is called the condensation level. The base of the cloud forms here

What causes air to rise? Mountains(Orographic Lifting) - Air hits mountains and is forced up If one side gets all rain, what happens to other?

What causes air to rise? Frontal Wedging- cool air acts as barrier over which warmer, less dense air rises

What causes air to rise? Convergence- as air of the same density collides since it cannot be forced down, so it is forced up Localized Convection- unequal heating of the Earth causes differences in density

Stability Rising moving air = Unstable Air Warm air rises into cold air. Non- moving air = Stable Air Warm air above cold air Called inversion

Cloud Types

Cloud Types Clouds are classified on the basis of their form and height. Form Cirrus – “hair like”, high altitude, wispy Cumulus – “pile/pillow”, rounded Stratus – “ layer”, sheets or layered, no distinction between individual clouds

Cloud Types Height High Clouds- Cirrus, Cirrostratus, Cirrocumulus What do you notice? Middle Clouds- Altostratus, altocumulus Low Clouds- Stratus, stratocumulus, nimbostratus, nimbus = “rainy cloud” ????????????????????

High Clouds Cirrus Cirrostratus Cirrocumulus

Middle Clouds Altocumulus Altostratus

Low Clouds Stratus Stratocumulus Nimbostratus

Vertical Clouds Some clouds do not fit into one layer, these cloud can build to towering heights. Cumulus – puffy cloud usually found at low cloud levels Cumulonimbus- formed from rising of unstable air Often associated with thunder, lightning, and hail

Cumulonimbus

Mammatus Cloud – Occasionally found with cumulonimbus clouds

3 4 5 12 2 6 7 1 8 9 10 11

Fog Fog – a cloud at the surface of the Earth

Precipitation Any moisture that falls from the air to the earth’s surface.

How rain forms Collision-Coalescence Step 1: Large water drop falls Step 2: More drops are added Step 3: Splat

Types of Precipitation What kind of precipitation you receive depends upon if the water that falls freezes or melts during descent. Drizzle: smaller water droplets Rain: water is melted when it hits ground Snow: water is frozen and stays frozen Sleet: water freezes in mid-fall Freezing Rain(glaze): water freezes upon impact Hail: water is frozen as pellets and pellets grow in clouds.

Cloud Seeding Method used to cause or increase precipitation. Achieved by adding condensation nuclei to clouds