Cloud FormationCloud 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 & Air Compression & ExpansionExpansion

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 GeneraBasic Cloud Genera

Clouds are characterized by three propertiesClouds are characterized by three properties

1.1. Basic shape or FORMBasic shape or FORM

2.2. HEIGHT above groundHEIGHT above ground

3.3. Does it produce precipitationDoes it produce precipitation

Problems with ClassificationProblems with Classification

Clouds areClouds are

1.1. Not always distinctNot always distinct

2.2. Change shape readilyChange shape readily

3.3. Blend with other cloudsBlend with other clouds

4.4. Evolve through a number of typesEvolve through a number of types

Classification by HeightClassification by Height

Clouds areClouds are

1.1. Low cloudsLow clouds

2.2. Middle cloudsMiddle clouds

3.3. High cloudsHigh clouds

4.4. Vertically developed cloudsVertically 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 HeightCloud Types By Heightand Formand Form

1. High CloudsCirrus Thin, wispy clouds of ice Cirrostratus Layered, thin, wispy

clouds of ice Cirrocumulus Thin, wispy clouds of ice

with vertical development

2. Middle CloudsAltostratus Layered clouds Altocumulus Clouds with vertical

development

Cloud Types (Con.)Cloud Types (Con.)

3. Low CloudsStratus Layered clouds Stratocumulus Layered clouds with vertical

development Nimbostratus Rain-producing, layered Clouds

4. Extensive Vertical DevelopmentCumulus 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 cloudsThat are High in the Sky!

CirrusCirrus

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, Individual clouds characterized by heaped, puffy appearance. Have vertical extent, puffy appearance. Have vertical extent,

from 1-3km up to tropopausefrom 1-3km up to tropopause

Cumulus: Cumulus: cotton cotton BallBall, , Cauliflower, puffyCauliflower, puffyWhite Billowy CloudsWhite Billowy CloudsLOOOOW in the Sky!LOOOOW in the Sky!

Cloud Type by Altitude-01 Can also classify them based on their altitude “Cirro” “Alto” “Strato” “Fog”

CirroHigh 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 cloudsMiddle level in the sky!

Altocumulus: individual or “rolls” of clouds Mid-Level in the sky

AltoMiddle 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

StratoLow level clouds (0 - 4

km)> 5 C composed of water

Cloud Type by Altitude-04Fog

Clouds at ground levelRadiation 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

ThunderstormsThunderstorms form when we have an unstable, moist atmosphere resulting in strong vertical motionsActually composed of many individual circulation “cells”

Updraft region is where the upward motion is intense and where the rain typically fallsDowndraft 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 outCan 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 50-100 micro-meters in diameter In contrast, rain drops are typically 500 micro-meters before

they begin to fall (drizzle) At 1000-2000 micro-meters, they are considered rain drops

Clouds and Precipitation-02There are also other forms of precipitation

Snow - crystallized water formed by the aggregation of frozen waterSleet - rain falling through a colder lower layer and freezingHail - the aggregation of liquid water onto frozen water and subsequent freezingNote 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’)