This document discusses condensation and the various cloud and fog formations that result from condensation in the atmosphere. It begins by defining condensation as the process where a gas transforms into a liquid due to changes in pressure and temperature. It then discusses the key factors needed for condensation to occur, including cooling air to below its dew point and the presence of condensation nuclei. The document goes on to describe different types of clouds and fogs that form via condensation, including stratus, cumulus, and nimbostratus clouds, and radiation, advection, upslope and freezing fogs. Key characteristics and formation mechanisms are provided for each cloud and fog type.

1. Geronimo R. Rosario

2.  Condensation is the process of a substance in a gaseous
state transforming into a liquid state. This change is caused
by a change in pressure and temperature of the substance.
Condensation can form
dew, fog, or clouds and
they all need saturated air
to develop.
Condensation is the
direct cause of precipitation.
It is the reverse of
evaporation.
Water vapor is changed
from the vapor state and
becomes droplets of water.

3.  The necessary condition:
cooling of air to below its dew point until it is saturated
[individual / combined changes in air volume, pressure,
temperature / R.H.]
 The sufficient condition:
presence of condensation nuclei
[hygroscopic particles – wettable substances]

4.  The necessary condition:
cooling of air to below its dew point until it is saturated
- radiation cooling
- advective cooling
- orographic and frontal uplifting & cooling
- convective or adiabatic cooling

5.  The sufficient condition:
presence of condensation nuclei
- Condensation does not take place easily in clear or
pure air which can be cooled below its dew point
without condensation occurring.
hygroscopic particles – wettable substances
They attract water-vapour molecules when the
moisture content is near saturation point.
e.g. dust, sea salt from evaporated spray,
sulphur acid from combustion, volcanism

6.  Hygroscopic-
water - seeking
nuclei . Ex.
Ocean salt, dust
and smoke
 Hydrophobic-
water-repelling
such as oils,
gasoline, and
paraffin waxes


7.  Cloud condensation
nuclei or CCNs (also
known as cloud seeds) are
small particles typically 0.2
µm, or 1/100th the size of
a cloud droplet on which
water vapour condenses.
 Water requires a non-
gaseous surface to make
the transition from a
vapour to a liquid; this
process is
called condensation.

8.  Aitken nuclei- radius less than 0.2 m
 Large nuclei- Particles ranging in size from 0.2 to
1 μm
 Giant nuclei,- are much larger and have radii
exceeding 1 μm.
◦ The condensation nuclei most favorable for producing
clouds (called cloud condensation nuclei) have radii of
0.1 μm or more.
◦ Usually, between 100 and 1000 nuclei of this size exist in
a cubic centimeter of air.
◦ Condensation nuclei are extremely light (many have a
mass less than one-trillionth of a gram), so they can
remain suspended in the air for many days.

10.  1. Dew
 2. Fog
 3. Cloud

11.  Dew- is the water droplets formed by
condensation of water vapor on a relatively cold
surface of an object.
 It forms when the temperature of an object drops
below the dew point temperature.
 Dew point temperature- the temperature to
which moist air is cooled at constant pressure and
at constant water vapor to reach saturation with
respect to water. It is not directly measured, rather
it is obtained from measurements of the dry-bulb
temperature and the wet-bulb depression

12.  Frost: the ice crystals formed by deposition of
water vapor on a relatively cold surface of an
object.
 It forms when the temperature of an object drops
below the frost point temperature.
 Frost point temperature: the temperature to
which moist air is cooled at constant pressure and
at constant water vapor to reach saturation with
respect to ice.
 It differs from the dew point temperature as the air
temperature is at or below 0oC .

13.  Frozen dew - The transformation of liquid dew
into tiny beads of ice when the air temperature
drops below freezing.
 Frost forms is the same way as dew except it
occurs when the dewpoint is below freezing.
True frost forms when the temperature is
below freezing. The moisture goes straight from a
gas to a solid.
 If the moisture goes from a gas to a liquid and
then to a solid then the result will be frozen dew

14.  1. Hoar frost
 2. Advection frost
 3. Window frost
 4. White frost
 5. Rime
 6. Black frost

15.  Hoar frost (also hoarfrost, radiation frost,
or pruina) refers to white ice crystals deposited on
the ground or loosely attached to exposed objects,
such as wires or leaves.
They form on cold, clear nights
when conditions are such that
heat radiates out to the open air
faster than it can be replaced
from nearby sources, such as
wind or warm objects.
Deposition of water vapor from
air of low humidity.

16.  Advection frost (also called wind frost) refers to
tiny ice spikes that form when very cold wind is
blowing over tree branches, poles, and other
surfaces.
 It looks like rimming on the edges of flowers and
leaves and usually forms against the direction of
the wind. It can occur at any hour, day or night.
 From cold wind over cold surfaces

17.  Window frost (also called fern frost or ice
flowers) forms when a glass pane is exposed to
very cold air on the outside and warmer,
moderately moist air on the inside.
 If the pane is not a good insulator (for example, if
it is a single pane window), water vapour
condenses on the glass forming frost patterns.

18.  White frost is a solid deposition of ice that forms
directly from water vapor contained in air.
 White frost forms when there is a relative
humidity above 90% and a temperature below −8 °C
and it grows against the wind direction, since air
arriving from windward has a higher humidity than
leeward air, but the wind must not be strong or it
damages the delicate icy structures as they begin to
form.
 White frost resembles a heavy coating of hoar frost
with big, interlocking crystals, usually needle-shaped.

19.  Black frost (or "killing frost") is not strictly
speaking frost at all, because it is the condition
seen in crops when the humidity is too low for frost
to form, but the temperature falls so low that plant
tissues freeze and die, becoming blackened,
hence the term "black frost".
 Black frost often is called "killing frost" because
white frost tends to be less cold, partly because
the latent heat of freezing of the water reduces the
temperature drop.
 Without visible ice at low temperatures

20.  Rime is a type of ice deposition that occurs
quickly, often under heavily humid and windy
conditions.
 Technically speaking, it is not a type of frost, since
usually supercooled water drops are involved, in
contrast to the formation of hoar frost, in which
water vapour desublimates slowly and directly.

21.  Rime is a rough white ice deposit which forms on
vertical surfaces exposed to the wind. It is formed
by supercooled water droplets of fog freezing on
contact with a surface it drifts past.
 Glaze can only form when supercooled rain or
drizzle comes into contact with the ground, or non-
supercooled liquid may produce glaze if the
ground is well below 0 °C. Glaze is a clear ice
deposit that can be mistaken for a wet surface and
can be highly dangerous.

22.  defined when visibility < 1 km
 Condensation on less active
nuclei
 Fogs form when air saturates (its
relative humidity reaches around
100 percent), and the water
vapor within the air mass
condenses on small particles in
the air to form liquid cloud
droplets.
is a visible mass consisting of cloud water droplets or ice
crystals suspended in the air at or near the Earth's
surface.

23.  Mist is defined as 'when there is such obscurity
and the associated visibility is equal to or exceeds
1000 m'.
 Mist and fog are often used interchangeably - and
they are closely related - but there is a key
difference which depends on how far you can see
through them.
 The defining difference between mist and fog is
visibility; if it is less than 1,000 metres we call it
'fog' and if visibility is greater than 1,000 metres
we call it 'mist'.

24.  Haze is also another term
associated with fog but
technically are different from
each other.
 Haze is traditionally an
atmospheric phenomenon
where dust, smoke and other
dry particles obscure the clarity
of the sky.
 Dry haze is when there are
dust or salt particles in the air
that hinder visibility.
Wet haze occurs when water
vapor condenses on the
particles, which happens at a
relative humidity of around
75%.

25. • Type of CN affects fog
• Over the ocean
– Fewer, larger drops
• Over urban areas
– More, smaller drops
– Lower visibility
– London Fog
• Chemical reactions can
cause fog to become acidic
• If temperatures drop below
freezing, freezing fog
may result

26.  by cooling the air
(air is cooled below
its saturation point
(dew point)
 by evaporation
and mixing - water
vapor is added to the
air by evaporation,
and the moist air
mixes with relatively
dry air.

27.  Radiation fog
 Advection fog
 Upslope fog
 Evaporation or
steam fog
 Precipitation or
frontal fog

28.  Results from radiation cooling of the ground and
the surrounding air.
 It occurs at night
 It requires clear skies and fairly high relative
humidity.
 Under these circumstances, the ground and the
air just above it will cool rapidly.
 Because the relative humidity is so high, just a
small amount of cooling will lower the temperature
to the dew point.

29. • Form upward from the
ground
– Deepest around sunrise
– May intensify after
sunrise (dew
evaporation)
• “Burns Off” with more
insolation
– Dissipates from bottom up
– Dissipates easily around
edges (thin, mixing

30. • type of fog where warm,
moist air moves over
cooler land and/or water,
cooling the air moving over
it to its dew point
• Breeze required
• May combine with radiation
fog
• radiational fog tends to
form in calm conditions
over inland areas,
advection fog tends to
form in breezier conditions
along coastlines

32.  A type of fog where it forms when
winds blow air up a slope (called
orographic lift), adiabatically
cooling it as it rises, and causing
the moisture in it to condense.
 Air expands adiabatically (cooling
or warming that results when air
expands or contracts, but not
because heat was added or
removed.)
 This is the only type of fog that
forms adiabatically.
 If the dew point is reached, an
extensive layer of fog may form.

34.  forms over bodies of water
overlain by much colder air.
The most common form,
which occurs when colder air
overlies
 Warmer water, is often called
steam fog since the
condensing water vapor looks
like steam rising from the
water
 This commonly occurs over
lakes in autumn, particularly
in the early morning hours,
when cold air moves over
water that is still warm from
summer

35.  Lake-effect snow is produced during cooler atmospheric conditions
when a cold air mass moves across long expanses of warmer lake
water, warming the lower layer of air which picks up water vapor from
the lake, rises up through the colder air above, freezes and is deposited
on the leeward (downwind) shores.

36.  forms as precipitation falls into drier air below the
cloud, the liquid droplets evaporate into water
vapor.
 As the rain falls through the layer of cold air, some
of the water from the rain drops evaporates
 If enough water vapor is added to the air it can
become saturated, resulting in condensation into
very tiny water droplets (fog)
 This most commonly is associated with warm
fronts in winter when warm air rises over cold air
which is why this type of fog is sometimes called
frontal fog

38.  Ground fog is fog that
obscures less than 60% of
the sky and does not extend
to the base of any overhead
clouds. However, the term is
sometimes used to refer to
radiation fog.
 Valley fog forms in mountain
valleys, often during winter. It
is the result of a temperature
inversion caused by heavier
cold air settling into a valley,
with warmer air passing over
the mountains above.

39.  Freezing fog occurs when
liquid fog droplets freeze to
surfaces, forming white soft or
hard rime. This is very common
on mountain tops which are
exposed to low clouds. It is
equivalent to freezing rain, and
essentially the same as the ice
that forms inside a freezer
which is not of the "frostless" or
"frost-free" type.
 Ice fog is any kind of fog where
the droplets have frozen into
extremely tiny crystals or ice in
midair. Generally this requires
temperatures at or below
−35 °C (−30 °F), making it
common only in and near the
Arctic and Antarctic regions.

40.  As air moves onshore, it crosses the coastline at nearly a right angle. This causes
the air to flow together or converge in the vicinity of the headlands. This area of weak
convergence causes the surface air to rise and cool just a little. If the rising air is
close to being saturated, it will cool to its dew point, and fog will form. Meanwhile,
near the beach area, the surface air spreads apart or diverges as it crosses the
coastline. This area of weak divergence creates sinking and slightly warmer air.
Because the sinking of air increases the separation between air temperature and
dew point, fog is less likely to form in this region..

41.  Fog dissipates usually in an
hour through solar heating
 It takes several hours in the
valley and coastal regions
particularly during cold
season.
 Fog clears at outer edges
first.
 Dissipation maybe affected
by wind, fog thickness,
overlying cloud layers and
underlying surfaces ( snow
cover, cool lakes or ocean
and soil condition)

44.  A cloud is a visible
aggregate of tiny
water droplets and/or
ice crystals
suspended in the
atmosphere and can
exist in a variety of
shapes and sizes.


45.  In 1802 an Englishman by the name of Luke Howard
invented the cloud naming system that is still in use
today. Howard used Latin names to describe clouds.
• part of a cloud's name describes height
• part tell us something about the cloud’s shape
 The prefixes denoting heights are:
cirro, high clouds above 20,000 feet;
alto are mid level clouds between 6,000 – 20,000 ft
There is no prefix for low level clouds.
 The names denoting shapes are:
cirrus mean curly or fibrous
stratus means layered
cumulus means lumpy or piled.
Nimbo or nimbus is added to indicate that a cloud
can produce precipitation.

46. • Properties:
– Variety of sizes
– Contain water drops
and/or ice crystals
– Various heights
– Stratospheric clouds
rare, but important for
creation of the ozone
hole

51.  Clouds that grow high up into the atmosphere
rather than spreading across the sky.
 They span all levels of the troposphere and can
even rise up into the stratosphere.
 Clouds with vertical growth develop by warm air
rising from the surface
 Types of CVD
 Cumulus
 Cumulonimbus

53.  Cumulus humilis
◦ Develop primarily from
convection
◦ Associated with fair
weather
◦ Usually evaporate shortly
after formation and are
vertically limited
 Cumulus fractus
◦ Ragged-edge cumulus
clouds that are smaller
than cumulus humilis and
scattered across the sky.
◦ strong tattered edges;
◦ rapidly changing contours.

54.  Cumulus congestus
◦ More organized
development as cloud
towers appear
◦ Each tower is indicative of
uplift cells
◦ Cells are short lived but are
constantly replaced
◦ Each tower progresses
higher
◦ Large height extension; like
cauliflower-looking forms.
 Cumulus mediocris
◦ Moderate development in
height.
◦ Not so wide, not so tall

55.  Cumulus virga
◦ look like a rod or stripe
◦ responsible for cloud
seeding.
◦ This is because it carries
the small particles to
different cloud formation.
 Cumulus praecipitatio
◦ look like puffy cotton balls in
the sky
◦ With precipitation
◦ common in most parts of
the world although they are
more frequently visible in
tropical climates where
there is a higher level of
humidity in the area

56.  Cumulus velum
◦ With a veil (from ice) on the
upper part of the subsequent
swelling - sometimes broken
◦ sail-shaped clouds and they
appear as a thin sheet of
cloud
◦ argely formed during fair
weath
 Cumulus pileus
◦ with flat cap or hood (ice
crystals).
◦ buffer between cumulus or
cumulonimbus formations

57.  Cumulus arcus
◦ horizontally formed cloud
and it is a low level cloud
which usually produces a
drizzle or rain.
◦ Shield cloud and looks like a
wall cloud
 Cumulus tuba
◦ white clouds seen on sunny
days and usually against the
blue sky. This heap of cloud
has a flat basis that is seen
in the middle and its vertical
development produces a
tower-like or even a
cauliflower's shape.
◦ with funnel cloud or tornado

58.  Cumulus pannus
◦ shreds or patches of clouds
which are large, cottony or
even puffy in nature
◦ These clouds can be seen
around the globe except in
Antarctica since it is very
cold there
 Cumulus radiatus
◦ also known as cloud streets
because they appear to form
as parallel lines that run
across the sky
◦ Less common

59.  Cumulus mamma
 Common white and puffy,
these clouds look like
cotton balls or bubbles that
are hanging downwards
from the sky.
 The cumulus mamma
clouds tend to have a flat
base and appear lumpy.
They do not necessarily
form in a large formation
and it is quite common to
see small, free flying
formations of the cumulus
mamma cloud

61. Cumulonimbus mamma Cumulonimbus incus
Cumulonimbus pannus Cumulonimbus calvus

62. Cumulonimbus arcus Cumulonimbus capillatus
Cumulonimbus pileus Cumulonimbus praecipitatio

63. Cumulonimbus tuba Cumulonimbus velum
Cumulonimbus virga

64.  Low clouds, with their bases lying below 2000 m
(6500 ft), are almost always composed of water
droplets; however, in cold weather, they may
contain ice particles and snow.
 Types
◦ Stratus
◦ Stratocumulus
◦ Nimbostratus

66.  Stratus fractus
 appear during a cloudy day
having a dark gray to almost
white color as they are made up
of water droplets and generally
formed in precipitation.
 look like ragged sheets which
became separated from a large
stratus clouds because of the
wind.
 Stratus nebulosus
 uniformly layered, foggish-
looking and monotonous.
 most common forms of stratus
clouds

67.  Stratus opacus
 look like any other stratus
clouds that are flat and have
no features at all
 usually comes in different
forms and sizes sometimes
resembling different animals
or creatures.
 they almost entirely cover the
sky and blocks out the sun in
the area.
 Stratus praecipitatio
 normally relatively featureless
and will partially or fully cover
the sky.
 Initially they may be light grey
but progressively they will
darken as they absorb more
moisture
 Rain cloud

68.  Stratus translucidus
 characterized by its veil-
like features and are thinly
spread out in the sky such
that the moon or the sun is
still recognizable.
 Stratus undulatus
 typically seen as slabs of
cloud that can actually
cover the whole sky; the
only distinguishing feature
can be the waves as the
base of the clouds are
ruffled by the wind.

70.  Stratocumulus lenticularis
 Stratocumulus cumulogenitus
 Stratocumulus radiatus
 Stratocumulus castellanus
 Stratocumulus translucidus
 Stratocumulus undulatus
 Stratocumulus lacunosus
 Stratocumulus stratiformis
 Stratocumulus duplicatus
 Stratocumulus praecipitatio
 Stratocumulus perlucidus
 Stratocumulus virga
 Stratocumulus mamma
 Stratocumulus opacus

71. Stratocumulus castellanus Stratocumulus cumulogenitus
Stratocumulus lacunosusStratocumulus duplicatos

72. Stratocumulus lenticularis Stratocumulus mamma
Stratocumulus mamma Stratocumulus opacus

73. Stratocumulus perlucidus Stratocumulus praecipitatio
Stratocumulus radiatus Stratocumulus stratiformis

74. Stratocumulus translucidus Stratocumulus undulatus
Stratocumulus virga

76.  Nimbostratus pannus
 look like tubes
 essentially flat featureless and
essentially boring.
 cover the sky with a grey and
depressing clouds which
signifies that something is
developing and the weather may
be changing for the better
 Nimbostratus praecipitatio
 generally bring heavier
precipitation
 They are not accompanied by
thunder or lightning
 Will generally last longer and are
constant

77.  Nimbostratus virga
 have shoots of rain
falling like triangular
wedges that are wider
at the top, near the
base of the cloud that
reach a point
somewhere above the
ground without
touching it.
 Rain bearing cloud

78. oBases between 2000 and 6000 m (6-19,000 ft)
oLargely composed of liquid drops
oCarry the “alto” prefix
oAltostratus is typically thick enough to almost
fully obscure the sun or moon and blanket the
sky from horizon to horizon
oAltocumulus, typically typified by a banded
arrangement of billowy clouds

80.  Altocumulus castellanus
 Altocumulus undulatus
 Altocumulus mamma
 Altocumulus stratiformis
 Altocumulus virga
 Altocumulus lacunosus
 Altocumulus perlucidus
 Altocumulus radiatus
 Altocumulus lenticularis
 Altocumulus duplicatus
 Altocumulus undulatus
 Altocumulus floccus
 Altocumulus opacus
 Altocumulus translucidus

81. Altocumulus castellanus Altocumulus duplicatus
Altocumulus floccus Altocumulus lacunosus

82. Altocumulus lenticularis Altocumulus mamma
Altocumulus opacus Altocumulus perlucidus

83. Altocumulus radiatus Altocumulus stratiformis
Altocumulus translucidus

84. Altocumulus virga Altocumulus undulatus

86. Altostratus duplicatus Altostratus mamma
Altostratus opacus Altostratus pannus

87. Altostratus praecipitatio Altostratus radiatus
Altostratus translucidus

88. Altostratus undulatus
Altostratus virga

89. ◦ Bases above 6000 m (19,000 ft)
◦ Composed of ice
◦ Cirrus is the most common
 Wispy appearance due to low water content and cold
temperatures
 Fall streaks may appear below as ice crystals descend
 Mares’ tails - horizontal swirls, occur in turbulent conditions
 Cirrostratus occurs when cirrus thickens and stretch across
the sky
 May form a halo about the sun or moon as entering light is
refracted 22o by cloud ice crystals
 Cirrocumulus occurs due to thickening causing a billowy
appearance which resembles fish scales - a mackerel sky

91. Cirrus castellanusCirrus aviaticus
Cirrus duplicatus Cirrus fibratus

92. Cirrus floccus Cirrus intortus
Cirrus radiatus Cirrus spissatus

93. Cirrus uncinus Cirrus undulatus
Cirrus vertebratus

95.  Cirrocumulus virga
 Cirrocumulus castellanus
 Cirrocumulus lacunosus
 Cirrocumulus floccus
 Cirrocumulus undulatus
 Cirrocumulus mamma
 Cirrocumulus lenticularis
 Cirrocumulus stratiformis

96. Cirrocumulus castellanus
Cirrocumulus lenticularisCirrocumulus lacunosus
Cirrocumulus floccus

97. Cirrocumulus mamma Cirrocumulus stratiformis
Cirrocumulus undulatus Cirrocumulus virga

99. Cirrostratus duplicatus Cirrostratus fibratus
Cirrostratus nebulosus Cirrostratus undulatus

101.  formed when water
vapor condenses and
freezes around small
particles (aerosols) that
exist in aircraft exhaust.
 Some of that water
vapor comes from the
air around the plane;
and, some is added by
the exhaust of the
aircraft.
 The exhaust of an
aircraft contains both
gas (vapor) and solid
particles.

102.  Lenticular clouds
 Form along the crest of
waves caused by air flowing
over mountains
 They are frequently lens
shaped which is why they are
called “lenticular” clouds
 They can form one above
another like a stack of
pancakes and, given their
unusual appearance, “UFO
sightings” are common when
these clouds are present

103.  The all-natural
light display,
meanwhile,
can be
attributed to a
scientific
phenomena
called cloud
iridescence.
 According to a
NASA news
thread called
“An Iridescent
Cloud Over
Colorado”, the
vivid clouds
appear when
tiny ice
crystals and
water droplets
linger around
multiple
clouds in the
sky.


104.  A localized lowering from the
rain-free base of a strong
thunderstorm.
 The lowering denotes a storm's
updraft where rapidly rising air
causes lower pressure just below
the main updraft, which
enhances condensation and
cloud formation just under the
primary cloud base.
 Wall clouds take on many shapes
and sizes.
 Some exhibit strong upward
motion and cyclonic rotation,
leading to tornado formation,
while others do not rotate and
essentially are harmless

105.  A low, horizontal,
sometimes wedge-
shaped cloud associated
with the thunderstorm
 Although often appearing
ominous, shelf clouds
normally do not produce
tornadoes

106.  created from instability
associated with air
flows having marked
vertical shear and
weak thermal
stratification.
 The common name for
this instability is
Kelvin-Helmholtz
instability.
 These instabilities are
often visualized as a
row of horizontal
eddies aligned within
this layer of vertical
shear.

107.  pouch-like cloud
structures and a rare
example of clouds in
sinking air.
 Sometimes very
ominous in appearance,
mammatus clouds are
harmless and do not
mean that a tornado is
about to form; a
commonly held
misconception.
 mammatus are usually
seen after the worst of a
thunderstorm has
passed

108.  are found very high in the
Earth's atmosphere. They
are called Polar
Mesospheric Clouds when
they are viewed from
space, and are referred to
as noctilucent clouds
when viewed by observers
on Earth.
 Unlike lower clouds that are
associated with weather,
these clouds form at the
very edge of space in the
atmospheric layer called the
mesophere.
 scientists think these clouds
are made of frozen water or
ice crystals.

109.  Most clouds form as air parcels are lifted and cooled to
saturation
 The main mechanism for cooling air is to force it to rise. Air
expands as it rises, because the pressure decreases through
the atmosphere, and therefore cools. Eventually it may
become saturated and the water vapour then condenses into
water droplets to form cloud. If the temperature reaches
below about -20 deg C many of the water droplets will have
frozen so the cloud is mainly composed of ice crystals.
 Mechanisms that Lift Air
◦ Orographic Lift occurs as air is displaced over topographic
barriers such as mountains and hills
◦ On the windward side of the barrier, air is displaced toward
higher altitudes and undergoes adiabatic cooling, possibly
to saturation
◦ On the leeward side, descending air warms through
compression leading to a dry rainshadow

110. Orographic uplift (left) and
orographically induced clouds
(below)

111. ◦ When boundaries between
air of unlike temperatures
(fronts) migrate, warmer air
is pushed aloft
◦ This results in adiabatic
cooling and cloud formation
◦ Cold fronts occur when
warm air is displaced by
cooler air
◦ Warm fronts occur when
warm air rises over and
displaces coldA cold front (a) and
a warm front (b)

112.  Convergence
◦ Atmospheric mass is non-uniformly distributed over Earth
◦ Air advects from areas of more abundant mass to areas of
less mass
◦ Air moving into these low pressure regions converges
◦ Stimulates rising motions and adiabatic cooling
 Localized Convection
◦ Localized surface heating may lead to spatially limited free
convection
◦ Vertical motions are stimulated from the surface upward
resulting in towering clouds and a chance for intense
precipitation over small spatial scales

113.  water
 low T
 supersaturation
 Cloud Condensation Nuclei (CCN) or Ice Nuclei
(IN)

114.  Sky opacity- the amount of sky visible in relation
to the presence of cloud layers—is described on
the basis eighths or oktas.

115.  Why are clouds white?
Since light travels as waves of different lengths, each color has its very own unique wavelength.
Clouds are white because their water droplets or ice crystals are large enough to scatter the light
of the seven wavelengths (red, orange, yellow, green, blue, indigo, and violet), which combine to
produce white light.
Why do clouds turn gray?
Clouds are made up of tiny water droplets or ice crystals, usually a mixture of both. The water and
ice scatter all light, making clouds appear white. If the clouds get thick enough or high enough all
the light above does not make it through, hence the gray or dark look. Also, if there are lots of
other clouds around, their shadow can add to the gray or multicolored gray appearance.
Why do clouds float?
A cloud is made up of liquid water droplets. A cloud forms when air is heated by the sun. As it
rises, it slowly cools it reaches the saturation point and water condenses, forming a cloud. As long
as the cloud and the air that its made of is warmer than the outside air around it, it floats!
How do clouds move?
Clouds move with the wind. High cirrus clouds are pushed along by the jet stream, sometimes
traveling at more than 100 miles-per-hour. When clouds are part of a thunderstorm they usually
travel at 30 to 40 mph.
Why do clouds form at different heights in the atmosphere?
The characteristics of clouds are dictated by the elements available, including the amount of
water vapor, the temperatures at that height, the wind, and the interplay of other air masses.