Clouds and precipitation (weather and climate)

Cloud

Aggregation of tiny water droplets and ice crystals that are suspended in air.

Clouds form:

When the air becomes saturated and the water vapor condenses or deposits onto tiny particles

Warm clouds

Form in the tropics and only have cloud droplets

Cold clouds

Form in the midlatitudes and only have ice crystals

Mixed-phase clouds

Have both cloud droplets and ice crystals

Cloud classifications is based on:

Altitude and shape

Stratiform clouds

Flat and layered clouds with horizontal development

Cumuliform clouds

Puffy and globular clouds with vertical development

Cirroform clouds

Wispy clouds are usually high in altitude and made of ice crystals

Fog

Low-lying cloud, often in contact the ground

Fog results from:

Cooling or when air becomes saturated through the addition of water vapor.

Presence of fog means:

Air temperature and the dew point temperature at ground level are the same

Radiation fog

Forms at night when Earth’s surface cools, aided by clear skies and calm winds, usually dissipates by sunrise

Advection fog

Forms when warm, moist air moves over a cold surface, causing the air to cool and become saturated, can occur with windy conditions

Evaporation fog

Forms when cold air moves over a warmer body of water, resulting in evaporation and then condensation as fog. (aka stem fog)

Upslope fog

Occurs when relatively humid air moves up a gradually sloping landform or up a mountain

Frontal fog

Formed when rain evaporates as it falls through a layer of cool air below. (Aka precipitation fog)

Cloud condensation nuclei (CCN)

Microscopic particles (aerosols) on which condensation occurs, resulting in cloud droplets.

Ice nuclei (IN)

Microscopic particles (aerosols) on which deposition occurs, resulting in ice crystals

Cloud droplets

CCN + condensed water surrounding it

Water vapor needs a __ to condense or deposit on depending on the temperature

Surface

Ice nuclei needs:

Bacteria, particles of clay and other minerals, and other compounds that mimic the hexagonal crystalline structure of ice

Mixed phase clouds contain:

Some ice crystals and more cloud droplets

Temperatures are below freezing in mixed-phase clouds, the cloud droplets are:

Supercooled

Precipitation occurs when:

Cloud droplets or ice crystals grow large enough to fall with gravity

Collision-coalescence process

for raindrops in warm clouds

Bergeron process

for snowflakes in cold clouds

Two primary mechanisms form precipitaion

Collision-coalescence process and Bergeron process

Colision-coalescence process happens mostly:

Over regions in which air is very humid and relatively clean.

Aggregation

As snowflakes fall, collide with one another and merge in the process of:

Hail

Hard rounded pellets of ice only produced in large cumulonimbus clouds