CHAPTER 2CLOUDS AND FOG

CHAPTER 2CLOUDS AND FOG

Tiny particles of dust, pollen from plants, factory smoke, and salt particles fromoceans are always present in the air. These fragments are called hygroscopic nuclei.

Tiny particles of dust, pollen from plants, factory smoke, and salt particles fromoceans are always present in the air. These fragments are called hygroscopic nuclei.

Tiny particles that absorb or attract moisture from the airTiny particles that absorb or attract moisture from the air

Hygroscopic NucleiHygroscopic Nuclei

Clouds form when:

• Water vapor rises• Vapor condenses• Droplets cling to hygroscopic nuclei• Nuclei bunch together and form clouds or fog

Clouds form when:

• Water vapor rises• Vapor condenses• Droplets cling to hygroscopic 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

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.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. hydroscopicb. hygroscopicc. psychroscopicd. psychrodropic

Fragments of matter that are always in the air are called _________ nuclei.

a. hydroscopicb. hygroscopicc. psychroscopicd. psychrodropic

CirrusCirrus StratusStratus

CumulusCumulus

There are three basic cloud types.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

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

CirrusCirrus

A cloud of a class characterized by dense individual elements in the form of puffs, mounds, or towers, with flat bases and tops that often resemble cauliflower

A cloud of a class characterized by dense individual elements in the form of puffs, mounds, or towers, with flat bases and tops that often resemble cauliflower

CumulusCumulus

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

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

StratusStratus

There are also other types of clouds having names with combinations of the following:

There are also other types of clouds having names with combinations of the following:

• Nimbus - rain

• Alto - high

• Fracto - fragmented or windblown

• Nimbus - rain

• Alto - high

• Fracto - fragmented or windblown

Clouds are sometimes classified by altitudes at which they most frequently occur:

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

• 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

There are ten general types of clouds grouped into low, middle, and high categories.

There are ten general types of clouds grouped into low, middle, and high categories.

Low CloudsLow Clouds

StratusNimbostratus

StratocumulusCumulus

Cumulonimbus

StratusNimbostratus

StratocumulusCumulus

Cumulonimbus

• Lowest cloud type

• Gray layer with uniform base

• May cause drizzle, but never rain

• Fog becomes stratus when it lifts

• Lowest cloud type

• Gray layer with uniform base

• May cause drizzle, but never rain

• Fog becomes stratus when it lifts

StratusStratus

• 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

• 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

NimbostratusNimbostratus

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

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

NimbostratusNimbostratus

StratocumulusStratocumulus

• Irregular, rounded masses spread out in puffy or rolling layers

• Usually gray with darker spots

• Do not produce rain

• Usually precede bad weather

• Irregular, rounded masses spread out in puffy or rolling layers

• Usually gray with darker spots

• Do not produce rain

• Usually precede bad weather

A cloud of a class characterized 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

A cloud of a class characterized 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

StratocumulusStratocumulus

CumulusCumulus

• 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

• 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

• Dense clouds of the towering variety

• The base is a dark nimbus rain cloud

• May produce severe thunderstorms and tornadoes

• Dense clouds of the towering variety

• The base is a dark nimbus rain cloud

• May produce severe thunderstorms and tornadoes

CumulonimbusCumulonimbus(Thunderheads)(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

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

CumulonimbusCumulonimbus

The upper portion of a cumulus cloud characterized by dense, sharply defined cauliflower-like upper parts and sometimes of great verticality

The upper portion of a cumulus cloud characterized by dense, sharply defined cauliflower-like upper parts and sometimes of great verticality

ThunderheadThunderhead

Middle CloudsMiddle Clouds

Altocumulus

Altostratus

Altocumulus

Altostratus

AltocumulusAltocumulus

• 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

• 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

A cloud of a class characterized by 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

A cloud of a class characterized by 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

AltocumulusAltocumulus

AltostratusAltostratus

• Dense sheets of gray or blue

• Sun or Moon will show through but without corona

• Light rain is likely within 24 hours

• Dense sheets of gray or blue

• Sun or Moon will show through but without corona

• Light rain is likely within 24 hours

A cloud of a class characterized 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

A cloud of a class characterized 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

AltostratusAltostratus

High CloudsHigh Clouds

Cirrus

Cirrostratus

Cirrocumulus

Cirrus

Cirrostratus

Cirrocumulus

CirrusCirrus

• 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

• 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

CirrostratusCirrostratus

• 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

• 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

A cloud of a class characterized 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

A cloud of a class characterized 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

CirrostratusCirrostratus

CirrocumulusCirrocumulus

• Thin, patchy clouds that sometimes form in wavelike patterns

• Do not leave shadows

• Precipitation usually follows within 24 hours

• Thin, patchy clouds that sometimes form in wavelike patterns

• Do not leave shadows

• Precipitation usually follows within 24 hours

A cloud of a class characterized by thin, white patches, each of which is composed of very small granules or ripples: of high altitude, 20,000 - 40,000 feet

A cloud of a class characterized by thin, white patches, each of which is composed of very small granules or ripples: of high altitude, 20,000 - 40,000 feet

CirrocumulusCirrocumulus

Clouds have been leading lost seamen, navigators, and explorers to land since the days of the earliest hardy sea voyagers.

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 usuallyindicate an island is close by.Stationary clouds on the horizon usuallyindicate an island is close by.

In the tropics, clouds often reflect the colors of the sandy beaches or coral reefs below.

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.Precipitation (rain, snow, sleet, and hail) cannot occur without clouds.

Temperature and presence of hygroscopic nuclei or ice crystals determine if there will be precipitationand in what form it will take.

Temperature and presence of hygroscopic nuclei or ice crystals determine if there will be precipitationand in what form it will take.

Raindrops form when moist air iscooled to the point where the moisturecondenses into heavy drops.

Raindrops form when moist air iscooled to the point where the moisturecondenses into heavy drops.

Cloud moisturedroplets are1/2,500 of an inch indiameter. If thedroplet grows to1/125 of an inch, it will fall from thecloud. Thecombining ofmoisture droplets iscalled coalescence.

Cloud moisturedroplets are1/2,500 of an inch indiameter. If thedroplet grows to1/125 of an inch, it will fall from thecloud. Thecombining ofmoisture droplets iscalled coalescence.

Large Raindrop

Small Raindrop

Not to Scale

To grow together into one bodyTo grow together into one body

CoalescenceCoalescence

Coalescence occurs in two known ways:Coalescence occurs in two known ways:

• Bigger droplets move about slowly, bump into other droplets and combine with them (low clouds).

• Bigger droplets move about slowly, bump into other droplets and combine with them (low clouds).

Coalescence occurs in two known ways: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.

• 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.

Rainmaking has been a concern of humans since the most ancient times. 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.

Rain dances, sacrifices, drums, cannons, and smoke have all been used in an attempt to make rain, especially during a drought.

Seeding a large cumulus cloud with onepound of artificial nuclei made of dry-ice or silver-iodide crystals can start a shower.

Seeding a large cumulus cloud with onepound of artificial nuclei made of dry-ice or silver-iodide crystals can start a shower.

Seeding can cause:

• Rain to fall sooner• More rain to fall• Rain to fall from a cloud that normally would not produce rain

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:Seeding cannot cause:

• Rain to fall from fair skies or fair-weather cumulus clouds

• Rain to fall over a large area

• 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.Sleet occurs when rain formed in relatively warm air falls through a layer of freezing air.

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.

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.

Most hailstones are smaller than marbles. Hailstones as large as baseballs have killed people and animals.

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.

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.

Dew is water vapor that condenses on objects that have cooled below the condensation point of the air around them.

Frost is similar to dew, but it formsat temperatures below freezing.Frost is similar to dew, but it formsat 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

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

FrostFrost

Fog is really a low-lying cloud that is near or touching the surface of the Earth.Fog is really a low-lying cloud that is near or touching the surface of the Earth.

Fog formation requires the presence of moisture, a gentle breeze, and a combination of warm and cold temperatures.

Fog formation requires the presence of moisture, a gentle breeze, and a combination of warm and cold temperatures.

Fog is hazardous to aviation becauseit limits both ceiling (height above ground level of lowest layer of clouds that cover more than half the sky) and visibility (distance an object can be Seen with the unaided eye).

Fog is hazardous to aviation becauseit limits both ceiling (height above ground level of lowest layer of clouds that cover more than half the sky) and visibility (distance an object can be Seen with the unaided eye).

Fog at sea is a continual hazardto safe navigation.Fog at sea is a continual hazardto safe navigation.

Fog at SeaFog at Sea

The nautical "Rules of the Road" require that extra lookouts be stationed aboardship in foggy conditions.

The nautical "Rules of the Road" require that extra lookouts be stationed aboardship in foggy conditions.

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.

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.

The horizontal transport of atmospheric properties

The horizontal flow of air, water, etc.

AdvectionAdvection

When warm moist air comes in contactwith colder water, advection fog forms.When warm moist air comes in contactwith 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 willusually dissipate when the Sun rises.

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 willusually dissipate when the Sun rises.

Every Sailor is aware of the fogs that blanket the harbors and coastlines near these areas.

Every Sailor is aware of the fogs that blanket the harbors and coastlines near these areas.

Puget SoundPuget Sound

San FranciscoSan Francisco

Los Angeles Los Angeles

San DiegoSan Diego

NewportNewportNew YorkNew York

NorfolkNorfolk

Steam fog is a type of advection fog formed by air saturation.Steam fog is a type of advection fog formed by air saturation.

A condition in the atmosphere corresponding to 100 percent relative humidity

A condition in the atmosphere corresponding to 100 percent relative humidity

SaturationSaturation

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.

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 overa body of comparatively warm water,the vapor condensing in smallconvective columns near the watersurface and giving the appearance of smoke or steam

Fog caused by cold air flowing overa body of comparatively warm water,the vapor condensing in smallconvective columns near the watersurface and giving the appearance of smoke or steam

Sea SmokeSea 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.

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

Fog produced by the nocturnal cooling of the surface boundary layer to a temperature at which its content of water vapor condenses

Radiation FogRadiation Fog

The movement of cold air massescauses frontal fog. It is common inthe upper Midwest.

The movement of cold air massescauses frontal fog. It is common inthe upper Midwest.

A fog caused by the movement of two dissimilar air massesA fog caused by the movement of two dissimilar air masses

Frontal FogFrontal Fog

Q.1. What does the term hygroscopic nuclei mean?Q.1. What does the term hygroscopic nuclei mean?

A.1. Particles that readily absorb moistureA.1. Particles that readily absorb moisture

A.2. Particles that are present in the air, such as dust, smoke, and pollen

A.2. Particles that are present in the air, such as dust, smoke, and pollen

Q.2. What are examples of hygroscopic nuclei?Q.2. What are examples of hygroscopic nuclei?

A.3. Raindrops are formed when moist air is cooled to the point where the moisture condenses into heavy drops.

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.3. How are raindrops formed?

A.4. Cirrus, cumulus, and stratusA.4. Cirrus, cumulus, and stratus

Q.4. What are the three basic types of clouds?Q.4. What are the three basic types of clouds?

A.5. Fragmented or wind-blownA.5. Fragmented or wind-blown

Q.5. What does the prefix “fracto” mean?Q.5. What does the prefix “fracto” mean?

A.6. Altocumulus cloudsA.6. Altocumulus clouds

Q.6. What clouds are made of water droplets, sometimes laid out in parallel bands?

Q.6. What clouds are made of water droplets, sometimes laid out in parallel bands?

A.7. Changes in the atmospheric conditionsA.7. Changes in the atmospheric conditions

Q.7. What accounts for the different shapes and altitudes of clouds?Q.7. What accounts for the different shapes and altitudes of clouds?

A.8. Cirrus cloudsA.8. Cirrus clouds

Q.8. What clouds are often called “mares’ tails?”Q.8. What clouds are often called “mares’ tails?”

A.9. High: above 20,000 ft. Middle: 7,000 to 20,000 ft. Low: surface to 7,000 ft.

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.9. What altitudes are associated with high, middle, and low clouds?

A.10. According to their appearance and altitudeA.10. According to their appearance and altitude

Q.10. How are clouds generally named?Q.10. How are clouds generally named?

A.11. Stratus, nimbostratus, and stratocumulusA.11. Stratus, nimbostratus, and stratocumulus

Q.11. What are the main types of low clouds?Q.11. What are the main types of low clouds?

A.12. Altocumulus and altostratusA.12. Altocumulus and altostratus

Q.12. What are the main types of middle clouds?Q.12. What are the main types of middle clouds?

A.13. Cirrus, cirrostratus, and cirrocumulusA.13. Cirrus, cirrostratus, and cirrocumulus

Q.13. What are the main types of high clouds?Q.13. What are the main types of high clouds?

A.14. Thunderstorms and tornadoesA.14. Thunderstorms and tornadoes

Q.14. What type of weather is associated with cumulonimbus clouds?

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?

Q.15. What weather condition follows cirrocumulus clouds?

Q.15. What weather condition follows cirrocumulus clouds?

A.15. PrecipitationA.15. Precipitation