ns2 3.2 clouds and fog

CHAPTER 2

CLOUDS AND FOG

Tiny particles of dust, pollen from plants,

factory smoke, and salt particles from

oceans are always present in the air. These

fragments are called hygroscopic nuclei.

Tiny particles that absorb or attract

moisture from the air

Hygroscopic Nuclei

A mass of hygroscopic nuclei that

have soaked up moisture from the

water vapor in the air.

Cloud

Clouds form when:

• Water vapor rises

• Vapor condenses

• Droplets cling to hydroscopic nuclei

• Nuclei bunch together and form clouds

or fog

Three things may happen to the water

droplets:

• Reevaporate and rise

• Rise and freeze into ice crystals

• Collide with other nuclei and form

larger drops

Cloud formations give clues concerning

the forces at work in our atmosphere.

Fragments of matter that are always in

the air are called _________ nuclei.

a. hydroscopic

b. hygroscopic

c. psychroscopic

d. psychrodropic

Cirrus Stratus

Cumulus

There are three

basic cloud types.

A cloud of a class characterized by

thin white filaments or narrow bands

and a composition of ice crystals: of

high altitude, about 20,000 - 40,000

feet

Cirrus


dense individual elements in the form

of puffs, mounds, or towers, with flat

bases and tops that often resemble

cauliflower

Cumulus

A cloud of a class characterized by a

gray, horizontal layer with a uniform

base, found at a lower altitude than

altostratus, usually below 8,000 feet

Stratus

There are also other types of clouds

having names with combinations of

the following:

• Nimbus - rain

• Alto - high

• Fracto - fragmented or windblown

Clouds are sometimes classified by

altitudes at which they most frequently

occur:

• Low - surface - 7,000 feet

• Middle - 7,000 - 20,000 feet

• High - above 20,000 feet

• Towering - exceptionally high cloud

with its base in low-altitude

Middle clouds seldom attain heights

greater than 13,000 feet in polar regions

but may reach 23,000 - 45,000 feet in

temperate and tropical zones.

There are ten general types of clouds

grouped into low, middle, and high

categories.

Low Clouds

Stratus

Nimbostratus

Stratocumulus

Cumulus

Cumulonimbus

• Lowest cloud type

• Gray layer with uniform base

• May cause drizzle, but never rain

• Fog becomes stratus when it lifts

Stratus

• Dark, shapeless, rain-laden

• Often have streaks of rain extending

to ground

• Often seen in summer at base of

thunderheads

• Brings steady, heavy snow in winter

Nimbostratus

A cloud of a class characterized

by a formless layer that is almost

uniformly dark gray, a rain cloud

of the larger type, of low altitude,

usually below 8,000 feet

Nimbostratus

The upper portion of a cumulus

cloud characterized by dense,

sharply defined cauliflower-like

upper parts and sometimes of

great verticality

Thunderhead

Stratocumulus

• Irregular, rounded masses spread out

in puffy or rolling layers

• Usually gray with darker spots

• Do not produce rain

• Usually precede bad weather


by large dark, rounded masses,

usually in groups, lines, or

waves, the individual elements

being larger than those in

altocumulus and the whole being

at a lower altitude, usually below

8,000 feet

Stratocumulus

Cumulus

• Dense, puffy clouds with a beautiful,

cauliflower-like appearance

• They rise by day and disappear at night

• Fleecy cumulus clouds usually mean

fair weather ahead

Consisting of, or resembling a

fleece (soft, fluffy)

Fleecy

• Dense clouds of the towering variety

• The base is a dark nimbus rain cloud

• May produce severe thunderstorms

and tornadoes

Cumulonimbus

(Thunderheads)

A cloud of a class indicative of

thunderstorm conditions,

characterized by large, dense

towers that may reach altitudes

of 75,000 feet, uniform except

for the tops, which appear

fibrous because of the

presence of ice crystals

Cumulonimbus

Middle Clouds

Altocumulus

Altostratus

Altocumulus

• Gray or whitish layers, puffy, fleecy

• Made up of water droplets

• Sometimes produce a pale blue or

yellow corona

• Presence means rain is probable

within 24 hours


globular masses or rolls in layers or

patches, the individual elements

being larger and darker than those of

cirrocumulus and smaller than those

of stratocumulus: of medium

altitude, about 8,000 - 20,000 feet

Altocumulus

Altostratus

• Dense sheets of gray or blue

• Sun or Moon will show through but

without corona

• Light rain is likely within 24 hours


by a generally uniform gray sheet

or layer, lighter in color than

nimbostratus and darker than

cirrostratus: of medium altitude,

about 8,000 - 20,000 feet

Altostratus

High Clouds

Cirrus

Cirrostratus

Cirrocumulus

Cirrus

• Thin, wispy, made up of ice crystals

• Called “mare’s tails”

• If scattered, indicate clear, cold

weather

• If in parallel lines, indicate violent

change in weather within 36 hours

Cirrostratus

• May nearly cover the sky with a filmy

cloud

• Curly appearance at their edges

• Form large halos around the Sun and

Moon

• Indicate clear and cold weather


by a composition of ice crystals

and often by the production of

halo phenomena and appearing as

a whitish and usually somewhat

fibrous veil, often covering the

whole sky and sometimes so thin

as to be hardly discernible: of high

altitude, 20,000 - 40,000 feet

Cirrostratus

Cirrocumulus

• Thin, patchy clouds that sometimes

form in wavelike patterns

• Do not leave shadows

• Precipitation usually follows within

24 hours


by thin, white patches, each of

which is composed of very small

granules or ripples: of high

altitude, 20,000 - 40,000 feet

Cirrocumulus

Thunderheads start at almost any

altitude and sometimes extend to

heights of as much as 75,000 feet. The

name given to these clouds is

__________.

a. nimbostratus

b. stratocumulus

c. cumulus

d. cumulonimbus

Clouds have been leading lost seamen,

navigators, and explorers to land since

the days of the earliest hardy sea

voyagers.

Stationary clouds on the horizon usually

indicate an island is close by.

In the tropics, clouds often reflect the

colors of the sandy beaches or coral

reefs below.

Precipitation (rain, snow, sleet, and hail)

cannot occur without clouds.

Temperature and presence of

hygroscopic nuclei or ice crystals

determine if there will be precipitation

and in what form it will take.

Raindrops form when moist air is

cooled to the point where the moisture

condenses into heavy drops.

Cloud moisture

droplets are

1/2,500 of an inch in

diameter. If the

droplet grows to

1/125 of an inch, it

will fall from the

cloud. The

combining of

moisture droplets is

called coalescence.

Large Raindrop

Small Raindrop

Not to Scale

To grow together into one body

Coalescence

Coalescence occurs in two known ways:

• Bigger droplets move about slowly,

bump into other droplets and combine

with them (low clouds).

Coalescence occurs in two known ways:

• Ice crystals and water droplets form

near each other, the droplets evaporate

and resulting vapor collides with ice

crystals and condenses into snow or

ice pellets. They melt into rain as they

pass through warmer air at lower

altitudes.

_________and the presence of

hygroscopic nuclei will determine

whether or not there will be precipitation

and what form it will take.

a. Humidity

b. Temperature

c. Altitude

d. Pressure

Rainmaking has been a concern of

humans since the most ancient times.

Rain dances, sacrifices, drums, cannons,

and smoke have all been used in an attempt

to make rain, especially during a drought.

A long period of dry weather that

is injurious to crops, animals, and

humans

Drought

Seeding a large cumulus cloud with one

pound of artificial nuclei made of dry-ice

or silver-iodide crystals can start a

shower.

Sowing or scattering clouds with

crystals or particles of silver iodide

or solid carbon dioxide to induce

precipitation

Seeding

A pale yellow, water-insoluble solid,

which darkens on exposure to light:

used chiefly in medicine, photography,

and artificial rain making

Silver-Iodide Crystals

Seeding can cause:

• Rain to fall sooner

• More rain to fall

• Rain to fall from a cloud that normally

would not produce rain

Seeding cannot cause:

• Rain to fall from fair skies or

fair-weather cumulus clouds

• Rain to fall over a large area

Sleet occurs when rain formed in relatively

warm air falls through a layer of freezing air.

Precipitation in the form of ice

pellets created by the freezing of

rain as it falls

Sleet

Hail usually occurs in the summertime. It

begins as raindrops, that updrafts take to

greater heights. They are coated with water

from lower clouds, lifted again and again until

too heavy to be lifted.

Showery precipitation in the form of

irregular pellets or balls of ice more

than 1/5 inch in diameter

Hail

Most hailstones are smaller than

marbles. Hailstones as large as

baseballs have killed people and

animals.

In wintertime, when the upper air is very

cold, water vapor will condense into ice

crystals. Snow is the result.

Dew is water vapor that condenses on

objects that have cooled below the

condensation point of the air around them.

Moisture condensed from the

atmosphere and deposited in

the form of small drops upon

any cool surface

Dew

Frost is similar to dew, but it forms

at temperatures below freezing.

A covering of minute ice needles,

formed from the atmosphere at

night upon the ground and other

exposed objects when they have

cooled by radiation below the

dew point, and when the dew

point is below the freezing point

Frost

Water vapor that has condensed on

objects that have cooled below the

freezing point is called ___________.

a. sleet

b. dew

c. hail

d. frost

Fog is really a low-lying cloud that is near

or touching the surface of the Earth.

A cloudlike mass or layer of minute

water droplets or ice crystals near

the surface of the Earth, appreciably

reducing visibility

Fog

Fog formation requires the presence of

moisture, a gentle breeze, and a combination

of warm and cold temperatures.

Fog is hazardous to aviation because

it limits both ceiling and visibility.

The height above ground level of

the lowest layer of clouds that cover

more than one half the sky

Ceiling

The distance at which a given standard

object can be seen and identified with

the unaided eye

Visibility

Fog at sea is a continual hazard

to safe navigation.

Fog at Sea

The nautical "Rules of the Road" require

that extra lookouts be stationed aboard

ship in foggy conditions.

Any of the regulations concerning

the safe handling of vessels with

respect to one another, imposed by

a government on ships in its own

waters or upon its own ships on the

high seas

Rules of the Road

Fog at sea is frequently formed through a

process known as advection. Fog is likely

to develop when warm air that has passed

over warm water moves to an area of colder

water.

The horizontal transport of atmospheric

properties

The horizontal flow of air, water, etc.

Advection

When warm moist air comes in contact

with colder water, advection fog forms.

Advection fog is the name given to

air-mass fog produced by air in motion,

or to fog formed in one place and

transported by wind to another. It will

usually dissipate when the Sun rises.

To scatter in various directions;

disperse; dispel

Dissipate

Every Sailor is aware of the fogs that

blanket the harbors and coastlines

near these areas.

Puget Sound

San Francisco

Los Angeles

San Diego

Newport

New York

Norfolk

Steam fog is a type of advection fog

formed by air saturation.

A condition in the atmosphere

corresponding to 100 percent

relative humidity

Saturation

In the far north, "sea smoke" can be seen

in the late fall or winter when a river or

pond "steams" as frigid air cools the water

until it begins to form ice.

Fog caused by cold air flowing over

a body of comparatively warm water,

the vapor condensing in small

convective columns near the water

surface and giving the appearance of

smoke or steam

Sea Smoke

The heat that the Earth radiates causes

radiation fog. It forms only at night,

over a land surface. The Sun usually

burns the fog away.

Fog produced by the nocturnal

cooling of the surface boundary

layer to a temperature at which

its content of water vapor

condenses

Radiation Fog

The movement of cold air masses

causes frontal fog. It is common in

the upper Midwest.

A fog caused by the movement of two

dissimilar air masses

Frontal Fog

A type of fog formed by air saturation is

called ______ fog.

a. steam

b. frontal

c. radiation

d. advection

Q.1. What does the term

hygroscopic nuclei mean?

Q.1. What does the term

hygroscopic nuclei mean?

A.1. Particles that readily absorb

moisture

Q.2. What are examples of

hygroscopic nuclei?

A.2. Particles that are present in the

air, such as dust, smoke, and

pollen

Q.2. What are examples of

hygroscopic nuclei?

Q.3. How are raindrops formed?

A.3. Raindrops are formed when

moist air is cooled to the point

where the moisture condenses

into heavy drops.

Q.3. How are raindrops formed?

Q.4. What are the three basic types

of clouds?

A.4. Cirrus, cumulus, and stratus

Q.4. What are the three basic types

of clouds?

Q.5. What does the prefix “fracto”

mean?

A.5. Fragmented or wind-blown

Q.5. What does the prefix “fracto”

mean?

Q.6. What clouds are made of water

droplets, sometimes laid out in

parallel bands?

A.6. Altocumulus clouds

Q.6. What clouds are made of water

droplets, sometimes laid out in

parallel bands?

Q.7. What accounts for the different

shapes and altitudes of clouds?

A.7. Changes in the atmospheric

conditions

Q.7. What accounts for the different

shapes and altitudes of clouds?

Q.8. What clouds are often called

“mares’ tails?”

A.8. Cirrus clouds

Q.8. What clouds are often called

“mares’ tails?”

Q.9. What altitudes are associated

with high, middle, and low

clouds?

A.9. High: above 20,000 ft.

Middle: 7,000 to 20,000 ft.

Low: surface to 7,000 ft.

Q.9. What altitudes are associated

with high, middle, and low

clouds?

Q.10. How are clouds generally

named?

A.10. According to their appearance

and altitude

Q.10. How are clouds generally

named?

Q.11. What are the main types of

low clouds?

A.11. Stratus, nimbostratus, and

stratocumulus


low clouds?


middle clouds?

A.12. Altocumulus and altostratus


middle clouds?


high clouds?

A.13. Cirrus, cirrostratus, and

cirrocumulus


high clouds?

Q.14. What type of weather is

associated with

cumulonimbus clouds?

A.14. Thunderstorms and

tornadoes

Q.14. What type of weather is

associated with

cumulonimbus clouds?

Q.15. What weather condition

follows cirrocumulus

clouds?

Q.15. What weather condition

follows cirrocumulus

clouds?

A.15. Precipitation

ns2 3.2 clouds and fog

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