Types of Clouds and Their Role in the Atmosphere

Clouds
Awan dan Sistem Bumi
Clouds Type 1
Clouds Type 2

Awan dan Sistem Bumi
Roni Marudut Situmorang
(@ronimarudut)

Awan
Kumpulan butiran-butiran kecil air
atau kristal-kristal es yang
melayang di udara

Identifikasi Awan
Awan tinggi
* biasanya terbentuk diatas ketinggian
6000m
* terbentuk hampir seluruhnya dari kristal
es
* agak tipis dan putih; menjelang matahari
terbit/terbenam berwarna merah, orange
dan kuning

Awan tinggi
Cirrus
seperti belaian tipis rambut/bulu
melintas dari barat ke timur
mencirikan cuaca yang baik dan nyaman
Cirrocumulus
seperti gumpalan kecil kapas, putih-bundar, individu atau
dalam barisan
menutupi hanya sebagian kecil dari langit
bintik-bintik yang memantulkan warna merah dan kuning
menjadikan awan ini paling indah
Cirrostratus
tipis seperti lembaran-lembaran menutupi seluruh langit
matahari dan bulan dibalik awan ini masih terlihat
kalau awan ini tebal, langit seperti putih berkilauan
terbentuk sebelum badai sehingga dapat digunakan
meramal hujan dalam 12 – 24 jam

Awan menengah
* Berada pada ketinggian 2000 – 7000 m
* Terdiri dari butiran-butiran air bila suhu
cukup rendah terdapat juga kristal es
Awan rendah
* Berada pada ketinggian < 2000 m
* Hampir seluruhnya terdiri dari butiran air

Awan Menengah
 Alto cumulus
seperti gumpalan kapas lebih besar dari cirrocumulus, abu-abu,
bergulung dalam gelombang yang sejajar
kalau muncul pada pagi hari musim panas mengisyaratkan hujan
menjelang sore hari
 Altostratus
berwarna abu-abu atau biru abu-abu
menutup langit sampai beratus-ratus kilometer
pada bagian awan yang tipis, matahari/bulan masih terlihat
lebih tebal dari cirrostratus sehingga pada permukaan tanah
tidak menimbulkan bayangan
mengisyaratkan hujan yang terus menerus, relatif lama

Awan rendah
 Nimbostratus
berwarna abu-abu gelap
matahari dan bulan dibalik awan ini tidak terlihat
karena rendah sering tersapu angin membentuk sebaran-
sebaran awan stratus fructus
Mengisyaratkan hujan yang terus menerus dengan intensitas
rendah
 Stratocumulus
awan bergumpal yang rendah, berwarna cerah sampai abu-abu
gelap
muncul dalam kelompok dengan langit biru diantaranya
sering muncul menjelang matahari terbenam
jarang terjadi hujan dari awan ini
 Stratus
awan keabu-abuan yang seragam menutup seluruh langit
menyerupai kabut tetapi tidak menyentuh tanah
biasanya tidak terjadi hujan atau kadang-kadang hanya rintik-
rintik

Awan yang tumbuh vertikal
Cumulus :
seperti kapas, garis luar yang jelas, dasar rata
1000 m diatas tanah, lebar sekitar 1 km
puncak awan berbentuk menara
terpisah-pisah dengan langit biru diantaranya
puncak seperti kubah/menara
menjelang sore menjadi jauh lebih besar, tumbuh vertikal, mirip
kembang kol menjadi cumulus congetus
menyebabkan hujan yang menyebar
Cumulus Cumulus
congetus
Cumulonimbus

Jika cumulus congetus terus bertumbuh vertikal akan terbentuk
cumulonimbus
 Cumulonimbus
awan badai dengan dasar gelap ketinggian dasar 300 m
puncaknya > 12.000 m

ENVI 1400 : Meteorology and Forecasting 12
Cloud Classification
Four latin terms form the basis for the naming of
clouds:
– Cirrus : fibrous or hair-like
– Cumulus : a heap or pile
– Stratus : a horizontal sheet or layer
– Nimbus : rain-bearing
The prefix Alto is used to indicate medium altitude
clouds.
Terms, and basic classifications first proposed by Luke Howard in 1803.
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/cldtyp/home.rxml - good online guide

High Level:
– Cloud base above 6000m
– Are all forms of cirrus (ice clouds)
Medium Level:
– Cloud base
2000-6000m
Low level:
– Cloud base below 2000m (within boundary
layer)

High-Level Clouds
Cirrus (Ci): White, delicate, fibrous
in appearance. Forms in patches or
narrow bands. May for comma-
shaped streaks or “mare’s tails”
(cirrus uncinus)
Cirrus clouds are formed entirely
of ice crystals. These grow and
evaporate slowly, leading to soft
edges to clouds.

Cirrostratus (Cs): Thin,
transparent sheet or veil; sun
clearly visible & casting shadows
at surface. A halo may be seen
around the sun (or moon).
Sheets of cirrostratus may cover
entire sky, and be up to several
1000m deep.

Cirrocumulus (Cc): Thin white patch or
sheet of cloud; appears dappled or rippled.
Dappling results from convective overturning
within the cloud, ripples from gravity waves.
Aircraft contrails: condensation
from aircraft exhaust. May
dissipate quickly, or be very long-
lived depending on conditions.

Medium-Level Clouds
Altostratus (As): A greyish
sheet of cloud, may be fibrous
or uniform in appearance.
Thin enough in parts to make
out the sun, but no halo.

Altocumulus (Ac): white or grey
patches arranged in sheets. Shape
and texture are variable.
There are several distinct sub-classes
of altocumulus

Altocumulus lenticularis (Ac len):
white or grey lenticular (lens
shaped) clouds formed by the lifting
of air over a topographic barrier.

Altocumulus castellanus
(Ac cas): white or grey, broken
cumulus-like clouds; upper part
appearing castle-like.
Sometimes arranged in lines.

Altocumulus undulatus (Ac und):
white or grey patches or sheets of
cloud with an undulating or rippled
appearance.

Low-Level Clouds
Cumulus (Cu): Brilliant white to grey,
dense detached clouds. Forms clumped
or heaped (cauliflower-like) shapes,
usually with sharp outlines and flat base.
Field of Cu often have bases all at same
(lifting condensation) level.

Cumulus humilis (Cu hum):
small cumulus, of limited vertical
extent, may have a flattened
appearance. Also called fair-
weather cumulus

Cumulus mediocris : cumulus,
of moderate vertical extent.

Cumulus congestus:
crowded (congested) field of
cumulus or greater vertical
extent. May produce rain.

Pileus : cap clouds that form above large cumulus as the upward
motion of the convective cloud distorts the layer of air above (pileus is
latin for skull-cap)

Cumulonimbus (Cb) : huge towering cloud, dark base and white sides. Associated with heavy rain, thunderstorms, and
hail. Frequently has an anvil shaped top.

mammatus : smooth, rounded shapes sometimes formed on the
underside of cumulonimbus; they result from downdrafts within the
cloud.

Stratocumulus (Sc) : white or grey sheet of
cloud, usually formed in mounds or rolls.

Stratocumulus with virga – hair-like strands of falling rain,
which evaporate below cloud before reaching the surface.

Stratus (St) : grey featureless layer of cloud with a uniform
base. Often associated with drizzle or snow.

Nimbostratus (Ns) : Dark grey,
featureless, thick layer of cloud.
Associated with prolonged
precipitation. Commonly forms
in frontal systems

Precipitation
• Cloud droplets require a condensation nuclei on which
to form; growth then occurs by deposition of water
molecules from vapour.
– Growth is limited by local supersaturation of the vapour
– Growth rate decreases as droplet size increases
• Cloud droplets are typically 10 to 30 µm in diameter.
Growth/evaporation can occur within a few 10s of
seconds.
• Rain drops are typically 0.5 to 5 mm in diameter, growth
from the vapour would take several hours – longer than
the lifetime of typical convective clouds.

• In order to grow into rain drops, cloud droplets must
grow by coalescence
– Larger droplets fall faster than small ones, and can collide with
them
– The process by which a sufficient number of large enough
droplets is generated remains a topic of active research
• Ice crystals provide a more efficient process
– Saturation vapour pressure over ice is less than that over water
⇒ ice crystals grow at expense of water droplets
– If ice crystal touches a droplet, the droplet freezes
– Once large enough, ice crystals – or clumps of crystals – fall
past droplets and collect them. Rapid growth of soft hail pellet
(graupel) by riming.
– Graupel falls from cloud, melting before reaching the surface as
rain

Cloud Radiative Effects
• Clouds play an important controlling role in the
global radiation budget.
– Reflection of incoming solar (short-wave) radiation
– Absorption of both solar and thermal infra red (long-
wave) radiation (incoming & outgoing)
– Emission of infra red radiation (up and down)
• The altitude, type, and thickness of cloud, along
with that of clouds above & below determines
whether the local net effect is to warm or cool
the air & surface below.

Vertical Transport
• Deep convective clouds play a major role
in mixing boundary layer air – along with
moisture, aerosol particles, and gases
(both natural and man-made pollutants) –
up into the free-troposphere.

Chemistry
• Clouds provide an environment within which
aqueous phase chemical reactions can take
place within the atmosphere
• Aerosol particles can be substantially modified
within clouds
– Aqueous phase reactions with gases dissolved in
droplets
– Coalescence of droplets brings multiple aerosol
particles together
• Chemically different aerosol may react
• On evaporation of droplet, a single aerosol particle is formed,
containing material from all contributing droplets

Cloud classification
• Originally by Luke Howard (1850’s)
• Currently used nomeclature based on Abercromy & Hildebrandsson (1887)
• Linnean system (genus, species)
• morphological only, not genealogical
Latin Root Translation Example
cumulus heap fair weather cumulus
stratus layer altostratus
cirrus curl of hair cirrus
nimbus rain cumulonimbus

Cloud subclassification
Further classification identifies clouds by height of cloud base.
3 levels
Examples:
the prefix "cirr-" (as in cirrus clouds) refers to high levels,
the prefix "alto-" (as in altostratus) refers to middle levels.

Relative heights vary zonally
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
16,000
18,000
20,000
metersagl
Tropics Midlatitudes Poles
H M L H M L H M L
tropopause

Cloud types and relative altitudes

High clouds
composed of ice
crystals
fibrous or filamentous
shape
ice crystal
concentration generally
very small

Cirrus uncinus (mares’ tails)
Height (km): 7-10 km+
Falling light snow [fallstreaks], not reaching the ground.
distorted by upper-tropospheric wind shear.

Cirrus uncinus
Cirrus floccus
Cirrus uncinus
Cirrus fibratus vertibratus
Cirrus

Cirrus
Cirrus spissatus
Cirrus spissatus with virga
Cirrus uncinus

Cirrostratus
continuous
sun shines thru, no precipitation
process: widespread ascent aloft,
or old thunderstorm anvil
halo

Cirrocumulus Cs broken into waves
sun shine thru, no precipitation
process: widespread ascent combined with
convective overturning in a thin layer.

Middle clouds
Altostratus clouds occur as uniformly gray
or white layers that totally or partially
cover the sky. They are usually so thick
that the sun is only dimly visible, as if
viewed through frosted glass.
* occur at altitudes where temperatures range between 0 and -25ºC (32 and -13ºF).
* composed of supercooled water droplets, or are in mixed-phase (supercooled
water droplets and ice crystals).

Altostratus
Height (km): base=2-6 km, can be thick, liquid or ice, no precipitation
reaching the ground. Process: widespread stable ascent, often preceding a
surface warm front.
Altostratus has a
uniform and diffuse
coverage

Iridescent Altostratus (difraction)

Altocumulus
base=2-6 km, usually thin, usually liquid, no precipitation.
Process: widespread ascent combined with convective overturning aloft
(left) or with wave activity (right)
clear regions  descending air
cloudy regions  ascending air

Altocumulus
Altocumulus castellanus
Altocumulus stratiformis
Sharp cloud boundaries
indicate the presence of
water droplets rather
than ice crystals.

Low-Level Clouds
* usually at temperatures above -5ºC (23ºF)
* composed mostly of water droplets.
geostationary
satellite
precipitation

Stratus
Base>0.1 km, top<3 km,
liquid (or ice), may have drizzle falling.
Process: stable ascent, mixing
Fog occurs when stratus meets the ground; when it lifts, it may
break up into stratocumulus.

Nimbostratus
steady light precipitation

Stratocumulus
Shallow, usually liquid, no precipitation
Process: forced or spontaneous overturning in a shallow layer

cumulus
Buoyantly rising air parcels (thermals) become saturated
Cu cloud base … LCL
Shallow or deep
LCL→
Cu humulis
Cu mediocris
Cumulonimbus

Fair-Weather Cumulus
Widely separated heap clouds of small
vertical development. With flat bottoms
and rounded tops, they resemble a flock
of sheep grazing in a pasture.

Cumulus congestus
Larger and deeper → cauliflower appearances to
the tops. Base is flattish, representing the LCL.
Can produce showers.
Cloud top=5-7 km, above the
freezing level but usually still
liquid.

Cumulonimbus
Look at this animation

12 June 2004, Hastings NE. Photo by Doug Raflik

Cumulonimbus: the most active member of the cumulus family
Convective family over the South China Sea

Pop quizzes: cloud identification
A: cirrusA: cirrus
B: cirrostratusB: cirrostratus
C: cirrocumulusC: cirrocumulus
D: altostratusD: altostratus
E: altocumulusE: altocumulus
F: stratusF: stratus
G: stratocumulusG: stratocumulus
H: cumulus humilisH: cumulus humilis
I: cumulus congestusI: cumulus congestus
J: cumulonimbusJ: cumulonimbus
J: nimbostratusJ: nimbostratus

a mid-level
cloud in the
lee of
mountain
ranges
cirruscirrus
cirrostratuscirrostratus
cirrocumuluscirrocumulus
altostratusaltostratus
altocumulusaltocumulus
stratusstratus
stratocumulusstratocumulus
cumulus humiliscumulus humilis
cumulus congestuscumulus congestus
cumulonimbuscumulonimbus
nimbostratusnimbostratus

cirruscirrus
stratusstratus

Hint: it is overcast, but not raining
cirruscirrus
stratusstratus

Hint: this cloud layer is low
cirruscirrus
stratusstratus

Hint: this cloud layer is high
cirruscirrus
stratusstratus

this is a halo
cirruscirrus
stratusstratus

Hint:
it is raining
cirruscirrus
stratusstratus

A few other cloud visual clues
1. anvil development
process: buoyant ascent
lightning usual
(lightning is rare over the oceans)
much precip evaporates if LCL is high
view this animation

Cumulonimbus: Severe weather
lightning, thunder, heavy
rains, hail, strong winds,
and tornadoes …
Model simulations:
Typical thunderstorm
Severe thunderstorm

Cumulonimbus: Shelf clouds
We are just ahead of a severe thunderstorm. Dewpoints are in the mid-70s.
Winds gust to over 40 mph with the passage of this shelf cloud.
Evaporatively cooled air is pushed out of the precipitation area by the
downdraft, warm air slides up and over the gust front forming the concave-
shaped shelf cloud.

Cumulonimbus: Mammatus clouds
pockets of negatively-buoyant air, filled with snow
suspended from the anvil base

Mesoscale Convective Complexes
Radar animation

Orographic and wave clouds
Orographic clouds are produced by the flow of air interacting with
mountainous terrain. They often indicate areas of clear air turbulence.
mountain wave
lee wave

Lenticular clouds
Altocumulus lenticularis are the
"mountain-wave clouds." As
strong horizontal winds encounter
a mountain range, gravity waves
propagate upwards, and leeward.
Mountain waves
are stationary.

Ac lenticularis elsewhere
RH stratification may yield a ‘stack of pancakes’
Plymouth, NH, 3 Dec ‘96 Which one is liquid
which one ice ?

Mountain-wave turbulence
Föhn wall cloud, Rockies
turbulent rotor cloud in Owens Valley, CA, downwind of the Sierras.

Mountain-wave turbulence :
Banner clouds

Banner cloud or lenticular cloud ?
(same mountain)

Kelvin-Helmholtz waves and KH billows
KH waves form when strong wind shear overturns a stable layer (i.e., an
inversion).
They are usually invisible!
(CAT)

Breaking billows – an aviation hazard

← Kelvin-
Helmholtz
waves on
Jupiter.
Colors
indicate the
clouds'
altitudes:
blue is lowest
through red
as highest.

Cap clouds
Pileus, Latin for "skullcap,"
is a smooth cloud that forms
when a stable, humid layer aloft
forced to rise by a penetrating
Thunderstorm cell.
← cap cloud on a Cb
Pileus cloud
attached to
the top of a
cumuliform
cloud.

“Morning glory” roll clouds
These occur when a deep stable layer overruns a shallower stable layer.
Gravity waves ahead of the deep layer result in roll clouds, and may
cause severe turbulence.
λ ~1000 km

Air rises and condenses at the leading edge, and evaporates behind

These cigar-shaped clouds also occur in the US, mainly in spring

note the stably stratified layer below, and the more turbulent one above

Types of Clouds and Their Role in the Atmosphere

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