Cloud Formation Dew, Fog, or Clouds form when air becomes ____________. This occurs when enough water vapor is added to the air or when air is cooled to the __________ ________

Air Compression & Expansion When energy is used to compress air, the motion of the gas molecules increases and the air temperature rises.

When air is allowed to E X P A N D, it ___________, And when air is COMPRESSED, it ___________. Cools Warms WHY ? Because Density is either decreased or increased.

Outline - what is a cloud? - cloud classifications - clouds and precipitation

Basic Cloud Genera Clouds are characterized by three properties 1. Basic shape or FORM 2. HEIGHT above ground 3. Does it produce precipitation

Problems with Classification Clouds are 1. Not always distinct 2. Change shape readily 3. Blend with other clouds 4. Evolve through a number of types

Classification by Height Clouds are 1. Low clouds 2. Middle clouds 3. High clouds 4. Vertically developed clouds

Introduction Previously, – We learned that when air is displaced vertically, it cools due to adiabatic processes – Discussed causes of vertical motion Convection Orographic lifting – We also discussed what happens once the temperature cools to the dew point temperature, namely, we expect clouds to form as water vapor changes to liquid Today, – We want to discuss what forms these clouds take Classify cloud formations Discuss characteristics that allow us to identify different types of clouds

Cloud Types By Height and Form 1. High Clouds Cirrus Thin, wispy clouds of ice Cirrostratus Layered, thin, wispy clouds of ice Cirrocumulus Thin, wispy clouds of ice with vertical development 2. Middle Clouds Altostratus Layered clouds Altocumulus Clouds with vertical development

Cloud Types (Con.) 3. Low Clouds Stratus Layered clouds Stratocumulus Layered clouds with vertical development Nimbostratus Rain-producing, layered Clouds 4. Extensive Vertical Development Cumulus Clouds having vertical development Cumulonimbus Rain-producing clouds with vertical development

Cloud Type by Form Clouds: – Optically thick mass of suspended water drops or ice crystals Cirrus: Thin wispy, feathery clouds That are High in the Sky!

Cirrus

Stratus: Layered clouds with fairly continuous coverage. (They seem to S T R E T C H over the entire sky!)

Individual clouds characterized by heaped, puffy appearance. Have vertical extent, from 1-3km up to tropopause Cumulus: cotton Ball, Cauliflower, puffy White Billowy Clouds LOOOOW in the Sky!

Cloud Type by Altitude-01 Can also classify them based on their altitude “Cirro” “Alto” “Strato” “Fog” Cirro High clouds (7-18) km Cold (<-25 C) with exclusively ice crystals Cirrocumulus: high, puffy clouds Cirrus: high, wispy clouds

Cloud Type by Altitude-02 Altostratus: thin, layered clouds Middle level in the sky! Altocumulus: individual or “rolls” of clouds Mid- Level in the sky Alto Middle level clouds (2-7 km) 0-25 C composed of both water and ice crystals

Cloud Type by Altitude-03 Stratus: Dense, uniform gray layers Stratocumulus: groups of dense, puffy clouds Strato Low level clouds (0 - 4 km) > 5 C composed of water

Cloud Type by Altitude-04 Fog Clouds at ground level Radiation fog: forms at night when cold ground cools the air above it (in valleys) Advection fog: forms when warm, moist air moves over colder surface and cools (in coastal areas)

Cloud Type by Rain Finally, we can classify them based on the presence of rain Nimbus: any cloud that rains Cumulonimbus: vertical clouds that produce heavy rain and sudden Downbursts ! Nimbostratus: low, flat clouds that drizzle

The 10 Cloud Genera

Thunderstorms Thunderstorms form when we have an unstable, moist atmosphere resulting in strong vertical motions Actually composed of many individual circulation “cells” Updraft region is where the upward motion is intense and where the rain typically falls Downdraft region is associated with downward motion which can also be intense -> leads to downbursts Can produce hail: this is when an ice particle is continuously cycled through the convection cell before becoming heavy enough to fall out Can also produce lightening: as water is moved within the cell, it develops a fictional charge; the discharge occurs through a spark, i.e. lightening

Clouds and Precipitation-01 Rain (or any precipitation) – Requires Vertical motions -> cooling Presence of condensation nuclei -> something for the rain drops to form on – Condensation does not necessarily mean rainfall; could just form clouds – In order to form precipitation, the drops must be large enough to fall against the upward motion of the air This requires that the aggregation (or coalescence) of lots of water molecules into drops Cloud droplets are typically micro-meters in diameter In contrast, rain drops are typically 500 micro-meters before they begin to fall (drizzle) At micro-meters, they are considered rain drops

Clouds and Precipitation-02 There are also other forms of precipitation Snow - crystallized water formed by the aggregation of frozen water Sleet - rain falling through a colder lower layer and freezing Hail - the aggregation of liquid water onto frozen water and subsequent freezing Note that precipitation does not necessarily fall straight to the ground - it might start to fall then get caught in an updraft and cycle through; during this process more aggregation occurs and we get very large rain or hail falling out (i.e. ‘golf-ball size hail’)