Lecture 01- Maggg

8/21/2019 Lecture 01- Maggg

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Introduction

This presentation gives you a general and

basic overview of the weather and climate

system in terms of the processes and forcing

mechanisms that takes place in each

component and interactions among them that

determine the observed climate in time and

space; so as to provide an insight into thephysical principles involved in the climate

system.

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weather and climate system

Weatheris the mix of events that happen each

day in our atmosphere including temperature,

rainfall and humidity. Weather is not the same

everywhere. Perhaps it is hot, dry and sunnytoday where you live, but in other parts of the

world it is cloudy, raining or even snowing.

Everyday, weather events are recorded and

predicted by meteorologists worldwide.

http://www.eo.ucar.edu/basics/

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Note thinness of atmosphere in light blue

Earth diameter = 13,000 km

Atmosphere: 99% below 50 km, 50% below 5.5 km 3


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Systems theory!A system is a assemblage of interrelated parts that work together by way of

some driving process

Processes generally have a structure that is defined by its parts andprocesses. These can be represented by mathematical equations and thus

can be modelled.

Examples:

Planetary system - is a planet in space that orbits a star and that maintainssome level of dynamics between its lithosphere, atmosphere and

hydrosphere. Some planetary systems, like the Earth, can also have a

biosphere. Earth is a closed system. [Is this strictly true?]

Ecosystem - is a system that models relationships and interactions between

the various biotic and abiotic components making up a community ororganisms and their surrounding physical environment.

An abiotic environmental system - the movement of air by wind, the

weathering of rock into soil and the formation of precipitation. These

processes derive their energy directly or indirectly from the Sun's radiation

that is received at the Earth's surface.


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Simple box model system approach with values orattributes in boxes and processes linking the boxes.

[ Limitations of direct observations. Can make predictions of

the future.]


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The climate system

Is an interactive system consisting of five

major components: the atmosphere, the

hydrosphere, the cryosphere, the land surface

and the biosphere, forced or influenced by

various external forcing mechanisms, the most

important of which is the Sun. Also the direct

effect of human activities on the climatesystem is considered an external forcing.

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Role of each component of the

climate system

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1. Atmosphere

Composition and structure

the most unstable and rapidly changing part of the

system composed of mechanical mixture of different

gases, solid particles, and liquid droplets suspendedabove the surface of the earth.

Gravity binds the atmospheric mass in a shallow depth

above the surface of the earth such that its density,

and therefore the atmospheric pressure decreaseswith height almost a similar way. Other forces are

pressure gradient, friction and Coriolis force.

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Note thinness of atmosphere in light blue

Earth diameter = 13,000 km

Atmosphere: 99% below 50 km, 50% below 5.5 km 9


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1. Atmosphere..


The Earths dry atmosphere is composed mainly ofnitrogen (N2, 78.1% volume mixing ratio), oxygen

(O2, 20.9% volume mixing ratio, and argon (Ar,0.93% volume mixing ratio).

These gases have only limited interaction with theincoming solar radiation and they do not interact

with the infrared radiation emitted by the Earth.They do not interact with the infrared radiationemitted by the Earth.

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1. Atmosphere


However, there are a number of trace gases, such

as carbon dioxide (CO2), methane (CH4), nitrous

oxide (N2O) and ozone (O3), which do absorb andemit infrared radiation. These so called

greenhouse gases, with a total volume mixing

ratio in dry air of less than 0.1% by volume, play

an essential role in the Earths energy budget.

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1. Atmosphere


The atmosphere also contains water vapor (H2O),

which is a natural greenhouse gas. Its volume mixing

ratio is highly variable, but it is typically in the order of1%.

Because these greenhouse gases absorb the infrared

radiation emitted by the Earth and emit infrared

radiation up- and downward, they tend to raise thetemperature near the Earths surface. Water vapor,

CO2 and O3 also absorb solar short-wave radiation.

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Energy (heat) trapped at surface

(atmosphere, ocean surface and land)


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Without atmosphere?

-18oC global average, large diurnal swings

Similar to the Moons Climate

With atmosphere

15oC global average, moderate diurnal swings


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1. Atmosphere


The atmospheric distribution of ozone and its role inthe Earths energy budget is unique. Ozone in thelower part of the atmosphere, the troposphere andlower stratosphere, acts as a greenhouse gas.

Higher up in the stratosphere there is a natural layerof high ozone concentration, which absorbs solarultra-violet radiation. In this way this so-called ozone

layer plays an essential role in the stratospheresradiative balance, at the same time filtering out thispotentially damaging form of radiation.

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Beside these gases, the atmosphere also contains solidand liquid particles (aerosols) and clouds, whichinteract with the incoming and outgoing radiation in acomplex and spatially very variable manner.

The most variable component of the atmosphere iswater in its various phases such as vapour, clouddroplets, and ice crystals. Water vapour is the strongestgreenhouse gas.

For these reasons and because the transition between

the various phases absorb and release much energy,water vapour is central to the climate and its variabilityand change.

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1. Atmosphere

The role of Atmosphere in influencing the

climate system (physical processes)

Rapid movement of water - Clouds, Rain &

Snow (Fresh Water) formation

Erosion by Water and Wind

Protection (of life and surface)

Conducts Sound

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1. Atmosphere

Other physical mechanism

Radiative processes: Solar and terrestrial energytransfer, absorption and reflection process are

critical to the earths energy balance Chemical composition: affects absorption or

transmission of solar radiation (aerosols, watervapor, carbon dioxide, ozone); also act as a

condensation nuclei, enhancing clouds to formand precipitation to fall(aerosols, dust or sulfateparticles).

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1. Atmosphere

Chemical processes: determine the atmospheric

composition, provide a link to human society, key

factor in climate. For example global warming

Dynamic processes: The global circulation play akey role in determining distribution of

radioactively and chemically active species, cloud

formation, and exchange of heat and moisture

between the atmosphere and the oceans. Cloudsare a critical ingredient of climate .Approximately

a half of the earth is covered by cloud at any time.

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2. Hydrosphere

The hydrosphere is the component of the

climate system comprising all liquid surface

and subterranean water, both fresh water,

including rivers, lakes and aquifers, and salinewater of the oceans and seas. Fresh water

runoff from the land returning to the oceans

in rivers influences the oceans compositionand circulation.

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2. Hydrosphere

The oceans cover approximately 70% of the

Earths surface. They store and transport a

large amount of energy and dissolve and store

great quantities of carbon dioxide. Theircirculation, driven by the wind (wind stress)

and by density contrasts caused by salinity

and thermal gradients (the so-calledthermohaline circulation), is much slower than

the atmospheric circulation.

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2. Hydrosphere.

Density of the ocean, a function of temperature andsalinity, is much larger than of the atmosphere, and isnearly uniform with depth, whereas the density ofatmosphere decreases with height.

Oceans are the earths principal time varying reservoirs

of moisture and thermal energy because of its largeheat capacity. 90% of solar radiation reaching the

ocean surface is absorbed, 50% in the upper 5 m andthe rest penetrates to deeper levels.

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3. Cryosphere

They vary seasonally and inter-annually, causing

large annual variations in continental heating and

upper ocean mixing and also in energy exchange

between the surface and the atmosphere. The large continental ice sheets do not change

rapidly enough to cause regional and annual

climatic anomalies, but play a major role inclimatic changes during hundreds to thousands of

years.

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3. Cryosphere

The cryosphere, including the ice sheets of Greenland and

Antarctica, continental glaciers and snow fields, sea ice and

permafrost, derives its importance to the climate system from

its high reflectivity (albedo) for solar radiation, its low

thermal conductivity,its large thermal inertia and, especially,its critical role in driving deep ocean water circulation.

Because the ice sheets store a large amount of water,variations in their volume are a potential source of sea level

variations.

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4. The land surface

Approximately 30% of the earth surface is land, thelower boundary of the atmosphere.

It include slowly changing extent, position, andorographic features of the continent; and morevarying characteristics of lakes, rivers, soilmoisture and vegetation.

Land surface also has a wide range of heterogeneityin distribution of soil properties as well asvegetation cover.

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4. The land surfaces

Due to its relative low heat capacity, local

thermal conditions are much more responsive

to net radiation from the atmosphere than are

oceans. For example, when wet, it canexchange water with the atmosphere more

rapidly than the oceans because of greater

surface roughness, but when dry, it providesno water at all the atmosphere.

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The land surfaces

Land surface albedo (fraction of reflected solarradiation) varies with type of surface cover. Vegetationand soils have large spectral variations of albedo, fromgenerally low values at the visible wavelengths to much

higher values in the near infra-red. The land and its biomes are variable parts of the

climate on all time scales. Inclusion of the biophysics ofthe energy and material exchange between the

atmosphere and the land biosphere is important tosimulation of the effects of deforestation.

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4. The land surfaces

Role of land surfaces

Land is crucial for human requirements, but it is

less important than oceans because it provides

less thermal energy storage and negligiblehorizontal transport.

Land surface is more variable and changeable than

the oceans for many of the coupling processes

namely; exchange of moisture, momentum and

heat with the atmosphere.

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5. The biosphere

Vegetation and soils at the land surface

control how energy received from the Sun is

returned to the atmosphere. Some is returned

as long-wave (infrared) radiation, heating theatmosphere as the land surface warms.

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5. The biosphere

The influence of climate on the biosphere is

preserved as fossils, tree rings, pollen and

other records, so that much of what is known

of past climates comes from such bioticindicators.

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5. The biosphere

Role of biosphere

The marine and terrestrial biospheres have a majorimpact on the atmospheres composition. The biotainfluence the uptake and release of greenhouse gases.

Through the photosynthetic process, both marine andterrestrial plants (especially forests) store significantamounts of carbon from carbon dioxide. Thus, thebiosphere plays a central role in the carbon cycle, as

well as in the budgets of many other gases, such asmethane and nitrous oxide. Find out seasonalvariations of CO2 gas in the atmosphere.

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Summary of the interactions between

the components

Atmosphere and ocean interactions: These are two fluid components of the climate

system. Each contained organized circulation, chaoticmotions and random turbulence.

They react to perturbations on every different timescales due to differences in their densities and heatcapacities.

Interactions between, and within them occur on manyscales and tend to be concentrated close to their

boundary as well as internally where gradients of thephysical properties such as temperature, and densityare large.

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Summary of interactions

Atmosphere and ocean interactions: If temperature of the lower atmosphere over the

oceans departs from the surface temperature of theoceans, vigorous exchange of heat and moisture

between the two fluids occur and temperature of theatmosphere adjusts to that of the oceans; i.e. theatmosphere is influenced by the ocean throughchanges in sea surface (SST).

The ocean are the earths principal time varying

reservoirs of the thermal energy and moisture. Theatmosphere is much smaller reservoir because of thedifferences in density between the troposphericatmosphere and sea water.

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Surface ocean currents

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The flow pattern of the major subsurface ocean currents is illustrated in

the figure shown below. Near surface warm currents are drawn in red,

blue color is the deep cold currents. Note how this system is continuously

moving water from the surface to deep within the oceans and back to the

top ocean.

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Land and Ocean interactions

Significant amount of thermal energy are not stored inthe land because its conductivity is much smaller thanthe effective turbulent conductivity of the oceansarising from the mixing and convection. Therefore, only

shallow layers of land are important in storing heatwhile the oceans extends to an average depth of about3,8000m.

Due to differential heating between land and oceans

because of the differences in heat capacities, see-breeze like circulation develop such as the seasonalmonsoons.

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Lecture 01- Maggg