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SIO209
Overview of Cloud Dynamics
Scripps Institution of Oceanography
University of California
Dr. Piotr J. Flatau
[email protected]
Based on notes by W. R. Cotton
Chapter 1
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Cloud dynamics - definition
Cloud Dynamics is the study of the evolution of clouds including their
formation and dissipation mechanisms
cloud air motions
forces creating those motions.
Cloud dynamics also includes the interaction of cloud air motions with
precipitation processes
solar and terrestrial radiation
smaller and larger scales of atmospheric motion.
Generally, cloud dynamics involve a macroscopic view of clouds in which cloud particles
are described from an ensemble perspective rather than a detailed examination of
individual cloud particle physics.
The detailed examination of individual cloud particle physics is referred to as cloud
microphysics.
Cloud physics - physics related to clouds
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Forms and importance
Depending on the larger scale environment, clouds take on a variety of forms
layer-type clouds such as boundary layer stratocumulus and middle tropospheric stratus
to deep convective clouds and thunderstorms.
Clouds may have a major impact on the
general circulation of the atmosphere
the earth's radiation and hydrological budget
and the chemistry of the atmosphere and precipitation.
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Role of Convective Clouds
Convective clouds:
Vertically transport heat, moisture, gases, aerosols, and momentum from the earth's
surface to the low, middle, and upper troposphere and even the lower stratosphere.
Convective clouds also transport particles and gases, such as air pollutants, into the
upper troposphere and lower stratosphere where they may reside for long periods of
time and undergo photochemical transformations.
Convective clouds can also function as 'wet' chemical reactors transforming particles
and gases into acid precipitation.
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Layered clouds
Layer clouds
vertically mix constituents through shallow layers
transport air in slow slantwise ascent over large horizontal distances.
large horizontal extent
stratus and cirrus clouds absorb and reflect solar radiation
absorb longwave or terrestrial radiation emitted by the earth's surface
emajor impact on the global heat budget.
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Clouds – Cumulus clouds
Cumulus clouds
primarily buoyancy-driven clouds
the air parcels rise due to their buoyancy expand as pressure decreases
and cool adiabatically at a constant rate of 10°C/km.
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Cloud convection
As a parcel ascends and cools adiabatically
relative humidity of the parcel increases
at approximately 100% relative humidity hygroscopic aerosol particles (i.e. salt particles)
take on water vapor to form cloud droplets.
air parcel becomes saturated at the Lifting Condensation Level (LCL).condensation of
vapor onto cloud drops releases latent heat of condensation and the heat is diffused to
the surrounding air
parcel cools at a lesser rate (approximately 6°C/km in the lower troposphere in middle
latitude summertime) - the wet adiabatic lapse rate.
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Cloud convection
As shown in Figure 1.2, an air parcel rising through the LCL will become warmer than it
would, had it cooled dry adiabatically. In fact if the parcel can ascend to the level of free
convection (LFC) it will become warmer than its surroundings and rise as a buoyant
convective cloud. The environmental lapse rate shown in Figure 1.2 is said to be
conditionally unstable since the instability depends upon there being sufficient moisture
in the ascending parcel to reach saturation.
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Convection in real clouds
cloudy air parcels can mix with surrounding cloud-free air parcels
evaporative cooling - reducing the temperature of the resultant mixture. One of the
entrainment processes impact cloud buoyancy and on the growth of precipitation
particles
3D cloud models vs. parcel models
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Diagrams – skew T
shallow, small diameter cumulus clouds - tradewind cumulus and fair weather cumulus.
form from buoyant thermals (i.e., blobs of warm air) that develop in the atmospheric
boundary layer (ABL).
sounding is unstable to dry air motions near the earth's surface
nearly neutral up to a height Z the ABL top
this stable layer of air is called a capping inversion.
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Clouds – liquid water content
thermals form in the ABL
small and only weakly buoyant
larger and more buoyant.
more buoyant thermals may ascend to the LCL where they become saturated, thus
forming a cloud
lose their buoyancy slightly above the LCL - slowly evaporate (“forced cumuli”)
as shown in Figure 1.3.
level of free convection - latent heat of condensation is liberated to allow the cloud
to ascend to greater heights in the atmosphere “active cumuli”
environmental stability
mixing (environmental stability and vertical shear of the horizontal wind)
capping inversion, the cloud quickly loses its buoyancy and becomes a
nonbuoyant “passive”
How Much Water mass is in a
Cloud?
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Cu
Cumulus clouds transport heat, moisture, momentum, and passive materials (i.e. gases,
particulates, pollutants) from the ABL into the lower troposphere.
Aalter the thermodynamic stability in the cloud layer by heating the lower parts of the
layer by condensational latent heat release and cooling the upper part of the cloud layer
by evaporation of droplets and by longwave radiation cooling
From a cloud microphysics point of view two time scales are important: (1) the
Lagrangian time scale (Tp) or time it takes a parcel of air to enter the base of a cloud
and exit the top and (2) the total lifetime of the cloud (TL).
Ordinary cumuli have typical depths of the order of 1500 m and characteristic updraft
speeds of 3 m/s, therefore
Tp = 1500/3= 500s ~ 10 minutes
This represents the time available for initiation of precipitation formation. Once initiated,
precipitation can continue over the remaining lifetime of the cloud. Typical ordinary
cumulus cloud lifetimes are on the order of 10-30 min.
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Cu climate role
Cu in tropical tradewind regions; effect the earth radiation budget
low clouds, tops are only slightly cooler than the earth's surface
they radiate much of the infrared radiation emitted from the earth's surface
liquid water content in cumulus clouds is relatively large, they reflect much of the sun's
radiation that is incident at their tops
ordinary cumulus clouds contribute to a net cooling of the atmosphere.
The amount of net cooling, however, is proportional to the cloud coverage; their impact
on global cooling is thus less than that of stratocumulus clouds.
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Towering cumulus clouds
cumulus congestus clouds
resemble Cu
more condensed liquid water, have greater updraft and downdraft speeds, and live
longer
1) a more unstable subcloud and cloud layer
2) the absence of a pronounced capping inversion
3) the presence of some form of sub-cloud horizontal convergence.
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Towering cumulus clouds
examples of atmospheric circulations
that produce subcloud convergence.
Because the atmosphere behaves
almost as an incompressible fluid,
horizontal convergence near the
ground causes upward motion which
can trigger larger-scale clouds and
supply the clouds with energy in the
form of heat and moisture
a Cold Front
Figure 1.4: Examples of atmospheric circulations that produce sub-cloud moisture
convergence, (a) Sea breeze convergence in coastal areas, (b) Rising motions over
a heated hill, (c) Forced ascent over a mountain, which can be enhanced by
organized slope flow due to heating of the higher terrain, (d) Convergence along
cold frontal boundaries associated with extra-tropical cyclonic storms or cold pools
associated with thunderstorms or mesoscale convective systems.
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Towering cumulus clouds
lifetime of towering cumulus clouds is 20 min to 45 min
typical parcel lifetimes 5000m updrafts on the order of 10m/s = 500sec
more condensed liquid water: greater potential of producing precipitation particles
non-freezing clouds
raindrops collision and subsequent coalescence between larger and smaller drops.
faster falling raindrops unleash the upper part of the cloud from its burden of condensed
water giving it extra buoyancy
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Towering cumulus clouds
settling drops into the lower part of the cloud accumulate condensed water there and
causes greater loading of the updraft, sometimes weakening it to form a downdraft.
rain falls into the subcloud layer: droplets begin to evaporate: cooling the air enhancing
the strength of the downdraft.
as the downdraft slows down near the ground, the cool diverging air can lift the low-level
moist air to resupply the cloud updraft with moisture thus sustaining the cloud.
If vertical shear of the horizontal wind is present, precipitation can fall away from the
updraft air, thus a diverging downdraft can form without destroying or weakening the
updraft
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Towering cumulus clouds
Towering cloud have tops colder than 0°C
freezing of supercooled raindrops, activation of ice nuclei, and vapor deposition growth
of ice crystals is possible
latent heat of freezing and sublimation released during ice particle growth contributes to
cloud buoyancy.
this boost in buoyancy leads to explosive growth of towering cumuli with some towers
penetrating into the lower stratosphere.
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Cu congestus - climate
sweep larger quantities of pollutants
vertically transport more heat, moisture and momentum into the middle and upper
troposphere than do ordinary cumuli
latent heat released from an ensemble of towering cumulus clouds in a region can
contribute to large scale tropospheric circulations, especially in equatorial regions
towering cumulus clouds precipitate, they contribute albeit weakly to the global
hydrological budget
their contribution to the earth's radiation budget is relatively small partly due to the
smaller area coverage of towering cumuli than ordinary cumuli, and to the fact that they
penetrate into the middle troposphere, where the cooling effects of reflecting shortwave
radiation is nearly balanced by warming due to absorption and emission of longwave
radiation.
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Cumulonimbus
convective clouds of significant vertical extent (often the entire depth of the troposphere)
precipitation processes play a major role in their lifecycle, organization, and energetics.
grow in an environment which is very unstable to wet convection
mechanism for producing low-level convergence often aids in producing them
fundamental unit of a cumulonimbus is called a cell which is defined by radar as a region
of concentrated precipitation and is also characterized by a region of coherent updraft
and downdraft.
cumulonimbus clouds are classified by the particular organization and lifecycle of their
cell(s).
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Cumulonimbus
convective clouds of significant vertical extent (often the entire depth of the troposphere)
precipitation processes play a major role in their lifecycle, organization, and energetics.
grow in an environment which is very unstable to wet convection
mechanism for producing low-level convergence often aids in producing them
fundamental unit of a cumulonimbus is called a cell which is defined by radar as a region
of concentrated precipitation and is also characterized by a region of coherent updraft
and downdraft.
cumulonimbus clouds are classified by the particular organization and lifecycle of their
cell(s).
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Cumulonimbus
The lifecycle of an ordinary thunderstorm
(a) The cumulus stage is characterized by one or
more towers fed by low-level convergence of
moist air. Air motions are primarily upward with
some lateral and cloud top entrainment depicted
(b) the mature stage is characterized by both
updrafts and downdrafts and rainfall.
Evaporative cooling at low-levels forms a cold
pool and gust front which advances, lifting
warm-moist, unstable air. An anvil at upper
levels begins to form
(c) The dissipating stage is characterized by
downdrafts and diminishing convective rainfall.
Stratiform rainfall from the anvil cloud is also
common. The gust front advances ahead of the
storm preventing air from being lifted at the gust
front into the convective storm.
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Cumulonimbus
cumulonimbus cloud - lifecycle 45 minutes to one hour
towering cumulus clouds
region of low-level convergence of warm, moist air
towering cumulus clouds merge to form a larger, precipitating cell
updrafts dominate the system during the growth stage and precipitation forms in the
upper levels of the towers
mature stage commences with rain settling in the sub-cloud layer
downdraft air spreads horizontally
at the interface between the cool, dense downdraft air and the warm, moist air, a gust
front forms.
the warm, moist air lifted by the gust front provides the fuel for maintaining the vigorous
updrafts
water loading and the entrainment of dry environmental air in the storm generate
downdrafts in the cloud interior, which rapidly transport precipitation particles to the subcloud air where they partially evaporate. The evaporatively chilled air strengthens the
low-level outflow and gust front.
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Cumulonimbus
warming occurs aloft by condensation and freezing in updrafts and cooling in downdrafts
at low-levels sustains the vigorous, convective cycle. The stronger the vertical shear of
the horizontal wind, the more likely the downdraft air will not weaken or destroy the
updrafts, and the efficiency of the machine increases. The intensity of precipitation from
the storm reaches a maximum during its mature stage.
Once the gust front advances too far ahead of the storm system, warm, moist air lifted at
the gust front does not enter the updraft of the storm. This marks the beginning of the
dissipation stage of the storm in which the updrafts weaken and the downdrafts
predominate. Rainfall intensity subsides, often turning into a period of light steady
rainfall.
10,000 m depth having updraft speeds on the order of 15 m/s, a Lagrangian Tp = 10,
000m/15ms^1 = 660sec
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Cumulonimbus
major contributors to rainfall in many regions, especially semi-arid regions
Latent heating associated with ensembles of ordinary cumulonimbi can play an
important role in driving planetary circulations in the tropics
cumulonimbi play an important role in vertically redistributing gases and particulates in
the atmosphere, spewing boundary layer material into the upper troposphere and lower
stratosphere and bringing higher-level atmospheric constituents down to the surface.
They also function as wet chemical reactors in which atmospheric gases and aerosol
become embedded in droplets and undergo chemical reactions.
lightning provides a major natural source for NOx's and ozone.
efficient scrubbers of the atmosphere in which the nucleation and scavenging of aerosol
particles by numerous small droplets, followed by the collection of those droplets by
raindrops focuses or concentrates the particulates onto a few big droplets. In this way,
cumulonimbi contribute substantially to acid precipitation
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Multicell thundestorms
composed of a number of cells, each undergoing a lifecycle of 45 to 60 minutes
may have lifetimes of several hours
favored in regions of strong conditional instability and moderate wind shear
produce hailstones sporadic episodes of tornadoes, flash floods
updrafts can be so strong that there isn't sufficient time to produce precipitation.
Observed by radar, these storms exhibit regions of very low radar reflectivity partially
surrounded by higher reflective cores (weak echo regions WERs)
produce more total lightning strikes and often with a higher frequency, thus being more
active producers of NOx's and ozone. Under weak wind conditions, multicell storms can
produce locally heavy convective rainfall. If such a persistent heavy raining storm is in a
polluted environment, such a storm can not only produce flash floods but also produce
“hotspots” of acidic precipitation.
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Supercell thundestorms
Supercell Storms
environmental conditional instability is large
vertical shear of the horizontal wind is also large
thunderstorms tend to organize into a single cell storm (two to six hours)
updraft in supercell storms is quite strong, often exceeding 40 m/s, and rotating.
the rotation of supercells can be discerned with the naked eye
persistent, weak echo region completely surrounded by heavy precipitation (bounded
weak echo region (BWER), or echo-free-vault) is a result of the very strong updrafts
which do not provide sufficient time for precipitation-sized particles to form and to the
centrifugal action of the rotating updraft which can thrust particles laterally from it.
produce large hailstones, sometimes in swaths as long as 300 km
spawning large, persistent tornadoes
Istrong updrafts (~ 40 m/s), a 12,000 m deep supercell has a Lagrangian time scale of
only Tp = 12, 000m/40m/s^1 = 300s,
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Supercell thundestorms
not responsible for producing heavy rainfall events since they move rapidly in the
environment characterized by strong vertical shear of the horizontal wind
they are not the major producers of acid precipitation events
do not produce as high a frequency of lightning flashes and associated chemical
changes as multicell thunderstorms
strong updrafts can inject large quantities of lower tropospheric pollutants into the upper
troposphere and lower stratosphere.
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MCS
Occasionally thunderstorms organize into systems on the scale of several hundred
kilometers and have durations of six to twelve hours or more. We call these systems
mesoscale convective systems (MCSs)
A characteristic of MCSs is that because they are so large and have long lifetimes, the
air flowing into and out of these thunderstorm systems is rather strongly effected by the
earth's rotation. As a result lower and middle tropospheric air flowing into MCSs normally
turns cyclonically (or counterclockwise in the northern hemisphere), while air flowing out
of MCSs in the upper troposphere turns anticyclonically (or clockwise in the northern
hemisphere).
In contrast, smaller rotating thunderstorms such as supercells acquire their rotation from
tilting of environmental vertical shear rather than the earth's rotation. The fact that MCSs
respond to the earth's rotation has a major impact on their organization, structure and
lifecycle.
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MCS
Systems that respond more strongly to the earth's rotation (i.e. last longer, have a larger
horizontal extent, and are at higher latitude) are more typified by slow slantwise ascent
(as contrasted with vertically erect convective updrafts and downdrafts) of moist, lowlevel air and slow slantwise descent of dry middle-level air. In addition to convective
showers, precipitation usually occurs as steady, stratiform rainfall.
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Squall Lines
Best known form of MCS organization is the squall line
occur at almost any latitude from the tropics to near the poles
a sharp roll-like line of clouds followed by a sudden wind squall or gust of 12 to 25 m/s.
Immediately behind the surface squall a heavy downpour starts, which may produce
as much as 30mm of rain in 30 minutes in the tropics.
Often the heavy downpour is followed by several hours of steady rainfall from the
stratiform-anvil cloud that trails the squall line.
Occasionally, squall lines exhibit both a trailing and a leading stratiform-anvil region. The
squall line is composed of two scales of motion:
(1) the cumulus scale, having a horizontal dimension on the order of 2 to 25 km and
(2) the mesoscale, characterized by air motions on a scale of 20 to 200 km.
The precipitation from squall lines reflects the presence of these two scales of motion,
as about 60% of the precipitation is in the form of intense showers and 40% is in the
form of steady, stratiform rainfall.
The largest and most violent squall lines are the pre-frontal lines that form in middle
latitudes. Typically they form along, or ahead of a cold front associated with a
vigorous, mid-latitude cyclonic storm.
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Cloud clusters
Many mesoscale convective systems do not exhibit a well-defined line organization of
the convective cells
convective cells are organized in a more or less random pattern
sometimes parallel to the upper level winds rather than perpendicular as in squall
lines, or with wind-parallel and -perpendicular bands coexisting.
cloud clusters in the tropics
mesoscale convective complexes (MCC's) in middle latitudes.
Cloud clusters range in size from slightly larger than a multicellular thunderstorm to large
aggregates of thunderstorms that may be nearly 1000 km in width. MCC's reside at
the larger end of the spectrum of cloud clusters and as such are more strongly
influenced by the earth's rotation. As a result MCC's tend to be longer lived and more
inertially stable than smaller scale mesoscale convective systems.
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Cloud clusters
Coud clusters and MCCs produce rainfall over a large areas exceeding 100,000 km2.
Like squall lines, most of the rainfall early in the MCC lifecycle is in convective
showers. As the systems mature, however, the rainfall transforms into primarily
stratiform, steady rain which can last for 6 to 12 hours.
If the systems move slowly, they can produce such a large volume of rainfall in a given
watershed that major, catastrophic floods occur.
Severe weather in the form of hail and tornadoes is often sporadic in MCC's, usually
occurring during the early, intense convective phase of the storm.
What is surprising is that as many as 25% of all MCC's produce severe, straight-line,
damaging winds in swaths 100 km or more in width and 500-1000 km in length. Such
severe straight-line wind events are called derechos.
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Cloud clusters - climate
giant vacuum cleaners sweeping often polluted boundary layer air into the middle and
upper troposphere and replacing it with clean middle tropospheric air.
MCC's have been found to remove boundary layer air over nearly one half a million
square kilometers
Scavenging by cloud particles and settle out in precipitation particles creating major acid
rain events. Other polllutants can be exported into the upper troposphere and lower
stratosphere.
Remove large quantities of water vapor from the lower troposphere and injecting it into
the middle and upper troposphere and lower stratosphere, and precipitating large
amounts to the surface. Latent heat deposited in the atmosphere is roughly
proportional to surface precipitation, these systems likewise play a major role in the
global energy budget, specially in the tropics where MCSs are frequent and cover a
large fraction of tropical latitudes.
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Marine stratocumulus
occupy large portions of the eastern Pacific and eastern Atlantic oceans and small
portions of the western Indian ocean.
cover 34% of the world's oceans at any given time; play an important role in the global
radiation budget.
well-mixed subcloud and cloud layer, capped by a strong temperature inversion and
drop in dew point temperature.
Large-scale sinking motion maintains the capping inversion which serves as a lid
preventing convective circulations in the stratocumulus cloud layer from penetrating
very far into the overlying stable airmass.
Typical lifetimes of stratus and stratocumulus clouds are long; being 6 to 12 h. The
parcel lifetimes for 1000 m deep clouds having vertical velocities 0.1 m/s. Lagrangian
timescale 10,000 sec.
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Marine stratocumulus
liquid water contents ranging from 0.05 to 0.25 g m^3 and long Lagrangian time-scales,
drizzle can form in the deepest, wettest stratus and stratocumulus clouds
The liquid water content, depth and strength of vertical motions vary considerably in
stratocumulus clouds.
Some stratocumulus clouds are driven primarily by the transport of heat and moisture
from the sea surface. Latent heat release during the condensation of vapor to form
cloud drops further invigorates the updrafts in the cloud layer, deepening the entire
layer beneath the capping inversion.
Radiative cooling near the top of the cloud layer is important to destabilization of the
cloud layer and to the intensity of convective overturning.
In other stratocumulus layers, heat and moisture fluxes from the ocean surface are
weak, and the intensity of convective overturning is regulated mainly by cloud top
radiative cooling and by evaporation of cloud drops near cloud top.
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Marine stratocumulus
Vertical shear of the horizontal wind also contributes to stratocumulus cloud formation
and to vertical mixing in stratocumulus clouds.
In some instances strong winds in the ABL can generate stratocumulus clouds even
where there is little or no temperature difference between the sea surface and
overlying air. It appears that vertical wind shear can also trigger sporadic episodes of
vertical mixing rather than continuous, homogeneous mixing.
Other factors affecting the intensity and bulk properties of stratocumulus are: the
strength of large-scale sinking motion, the occurrence of drizzle, and the presence of
middle and high clouds above the stratocumulus deck.
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Marine stratocumulus
stratocumulus clouds are low clouds and their tops are only slightly cooler than the
earth's surface.
They therefore radiate much of the infrared radiation emitted from the earth's surface.
Likewise since the liquid water content in stratocumulus clouds is relatively large, they
reflect much of the sun's radiation that is incident at their tops. As a consequence,
stratocumulus clouds contribute to a net cooling of the atmosphere.
Because stratocumulus clouds are nearly solid cloud decks, their contribution to a net
cooling is greater than that by shallow cumulus clouds.
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Marine stratocumulus
predictions with general circulation models of climatic changes due to greenhouse gases
must contain better algorithms for predicting stratocumulus cloud amounts and
optical depths.
general circulation models must predict the transition from solid stratocumulus decks to
broken cumulus layers. The reduced cloud coverage of a cumulus layer changes the
amount of net cooling produced by low-level clouds. Because the transition from
solid to broken cloud cover is a function of the fluxes of heat and moisture from the
sea surface as well as large scale sinking motions, which are in turn related to sea
surface temperatures and other factors, the general circulation model must also
predict sea surface temperatures accurately
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Middle and upper level clouds
vast sheets of middle and high-level clouds in the troposphere are ubiquitous, covering
between 30-40% of the earth at any one time
Global coverage of very thin cirrus clouds in the upper troposphere may be as high as
80%.
Unlike stratocumulus clouds, middle and high clouds may contribute to a net warming of
the troposphere.
Cirrus clouds, are relatively thin and as a result do not absorb or reflect much of the
sun's energy. On the other hand, they are excellent absorbers of longwave radiation
emitted by the earth's surface, thus inhibiting the escape of longwave radiation
energy to space. The reduced loss of longwave radiation to space contributes to a
net warming at the earth's surface much like so-called “greenhouse gases”.
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Middle and upper level clouds
cirrus clouds are radiatively thin, much of the upward infrared radiation is absorbed
uniformly through the cirrus layer contributing to a net warming of the cloud layer
middle tropospheric clouds, however, produce no net warming or cooling since the
opposing influence of reflection of solar radiation is balanced by absorption and
emission of longwave radiation at warmer temperatures.
Middle and high clouds can be produced by a variety of mechanisms.
Slow, slantwise ascent of moist air in extra-tropical cyclones can give rise to widespread
altostratus, altocumulus and cirrus clouds
deep convective clouds can inject large quantities of moisture and cloud debris into the
middle and upper troposphere. Organized convective systems such as tropical
cyclones and mesoscale convective systems are prolific producers of middle and
high clouds.
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Middle and upper level clouds
Owing to the small difference between ice saturation vapor pressures and environmental
vapor pressures at the cold temperatures in the upper troposphere, very small
additions of moisture or weak vertical motions and adiabatic cooling can create cirrus
clouds.
Thus jet contrails in regions of dense air traffic can release sufficient moisture in the
upper troposphere to create widespread thin cirrus cloud cover. If the contrails
become sufficiently widespread, they can alter the global radiation budget averaged
over the diurnal cycle, contributing, albeit slightly, to a “greenhouse-type” warming.
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Middle and upper level clouds
Many middle and high clouds are multilayered in structure.
The actual mechanisms responsible for multi-layering are still not well understood.
Likewise, some middle and high clouds exhibit a well-mixed thermodynamic structure
suggesting that radiative destabilization of the cloud layer may trigger convective
overturning.
Overall our knowledge of the dynamics of middle and high clouds remains rather
primitive. Only a few models have been developed for theoretically exploring their
structure. Because of their height above the ground, expensive high altitude aircraft
are required to sample them. Sensitive remote sensing devices such as lidars and
radars are now being developed and applied to the study of those clouds.
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Conclusions
Clouds and cloud systems described above are associated with larger scale weather
systems.
Middle and upper tropospheric layer clouds are associated with the gentle rising motions
in extra-tropical and tropical cyclones. Layer clouds also form as exhaust products of
deep convection embedded in tropical and extra-tropical cyclones.
the full spectrum of convective clouds we have discussed form in large scale cyclonic
storms. Squall lines, severe convective storms, ordinary thunderstorms, and towering
cumulus clouds form in the warm sector and along frontal bands of extratropical
cyclones.
The global climatology of cloud cover, precipitation, transports of pollutants and trace
gases, and latent heating is, therefore, strongly affected by the presence of large
mountain ranges, and the climatology of larger scale weather systems.