Transcript Physics of Water in the Climate System

Physics of Water in the
Climate System
Jessie Cherry
International Arctic Research Center &
Arctic Region Supercomputing Center, UAF
Outline
• Physical Properties of Freshwater
and Saline Water (quiz)
• The Water Cycle and Water in the
Climate System
• Water and Climate Research in
Practice (personal experience)
• Lab introduction
Part I: Physical and Chemical
Properties of Freshwater and
Saline Water
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Cohesion and Adhesion
Solvent
Heat Capacity & Heat of Vaporization
Miscibility and Condensation
Density and Salinity
Thermal Stratification
Quiz (think about these questions)
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What are some of the physical and chemical properties of water?
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Water is more than just plain old water -- it actually has some very unusual properties.
True False
(1) Water contracts (gets smaller) when it freezes.
True False
(2) Water has a high surface tension.
True False
(3) Condensation is water coming out of the air.
True False
(4) More things can be dissolved in sulfuric acid than in water.
True False
(5) Rainwater is the purest form of water.
True False
(6) It takes more energy to heat water at room temperature to 212 F than
it does to change 212 F water to steam.
True False
(7) If you evaporate an 8-inch glass full of water from the Great Salt Lake
(with a salinity of about 20% by weight), you will end up with about 1 inch of salt.
True False
(8) Sea water is slightly more basic (the pH value is higher) than most
natural fresh water.
True False
(9) Raindrops are tear-shaped.
True False
(10) Water boils quicker at Denver, Co. than at the beach.
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Water molecule
Cohesion and Adhesion
Surface tension
http://en.wikipedia.org/wiki/Surface_tension
Diagram shows, in crossection, a needle floating on the surface of
water. Its weight, f_w, depresses the surface, and is balanced by
the surface tension forces on either side, f_s, which are each
parallel to the water's surface at the points where it contacts the
needle. Notice that the horizontal components of the two f_s
arrows point in opposite directions, so they cancel each other, but
the vertical components point in the same direction and therefore
add up.
Capillary Action
Capillary action
refers to the
process of
water moving
up a narrow
tube against
the force of
gravity.
Solvent
Water is the universal solvent
H2O <--> H+ OHNaCl <--> Na+ Cl-
Molecular differences
between phases
Specific heat capacity &
vaporization
• Second highest of any known chemical
compound (after ammonia)
• High heat of vaporization (45 kJ/mol)
• Both caused by extensive hydrogen
bonding
• Helps moderate Earth’s climate
Acidity of water
• Theoretical value of pH is 7 at 298 K
(neutral)
• In practice, pure water is hard to make
• Air exposure dissolves CO2, forming a
dilute solution of carbonic acid (also
NOx and SOx make acid rain)
Freezing point & density
• Solid is much less dense than liquid
• Maximum density of fresh water at 4 deg C
• Many implications for life, such as in ponds
Water density calculator
http://www.csgnetwork.com/h2odenscalc.html
Triple Point
Miscibility and condensation
Saturation vapor pressure es
The saturation vapor pressure is the static
pressure of a vapor when the vapor phase of
some material is in equilibrium with the liquid
phase of that same material. The saturation
vapor pressure of any material is solely
dependent on the temperature of that
material. As temperature rises the saturation
vapor pressure rises nonlinearly.
Temp vs. es
Saturation vapor pressure and
Dew point
An example is water vapor when air is saturated with
water vapor. It is the vapor pressure usually found
over a flat surface of liquid water, and is a dynamic
equilibrium where the rate of condensation of water
equals the rate of evaporation of water. In general,
the higher the temperature, the higher the vapor
pressure. When air is at the saturation vapor
pressure, it is said to be at the dew point. Thus, at
saturation vapor pressure, air has a relative humidity
of 100% and condensation occurs with any increase
of water vapor content or a reduction in temperature.
Bad Meteorology
• The reason clouds form when air cools
is that cold air cannot hold as much
water vapor as warm air. WRONG!
Quiz: answers
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What are some of the physical and chemical properties of water?
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(1) Like most liquids, water contracts (gets smaller) when it freezes.
-False
Actually, water expands (gets less dense) when it freezes, which is
unusual for liquids. Think of ice -- it is one of the few items that floats as a solid. If it didn't,
then lakes would freeze from the bottom up (that would mean we'd have to wear wet suits
when ice skating!), and some lakes way up north would be permanent blocks of ice.
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(2) Water has a high surface tension.
-True
Water has the highest surface tension among common liquids (mercury
is higher). Surface tension is the ability of a substance to stick to itself (cohere). That is why
water forms drops, and also why when you look at a glass of water, the water "rises" where
it touches the glass (the "meniscus"). Plants are happy that water has a high surface tension
because they use capillary action to draw water from the ground up through their roots and
stems.
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(3) Condensation is water coming out of the air.
-True
This is actually true -- water that forms on the outside of a cold glass or
on the inside of a window in winter is liquid water condensing from water vapor in the air. Air
contains water vapor (humidity). In cold air, water vapor condenses faster than it
evaporates. So, when the warm air touches the outside of your cold glass, the air next to the
glass gets chilled, and some of the water in that air turns from water vapor to tiny liquid
water droplets.
Clouds in the sky and the "cloud" you see when you exhale on a cold day are condensed
water-vapor particles.
(It is a myth that clouds form because cold air cannot hold as much water vapor as warm
air!)
(4) More things can be dissolved in sulfuric acid than in water.
-False
Not true. Sulfuric acid might be able to dissolve a car, but water isn't
known as the "Universal Solvent" for nothing! It can dissolve more substances than any
other liquid. This is lucky for us... what if all the sugar in your soft drink ended up as a pile at
the bottom of the glass? The water you see in rivers, lakes, and the ocean may look clear,
but it actually contains many dissolved elements and minerals, and because these elements
are dissolved, they can easily move with water over the surface of the earth.
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(5) Rainwater is the purest form of water.
-False
Actually, distilled water is "purer." Rainwater contains small amounts of
dissolved minerals that have been blown into the air by winds. Rainwater contains tiny
particles of dust and dissolved gasses, such as carbon dioxide and sulfur dioxide (yep, acid
rain). That doesn't mean rainwater isn't very clean -- normally only about 1/100,000th of the
weight of rain comes from these substances.
In a way, the distillation process is responsible for rainwater. Distilled water comes from
water vapor condensing in a closed container (such as a glass jar). Rain is produced by
water vapor evaporating from the earth and condensing in the sky. Both the closed jar and
the earth (via its atmosphere) are "closed systems," where water is neither added or lost.
(6) It takes more energy to heat cold water to 212o F than it does to change 212o F water to
steam.
-False
First, water at boiling temperature (212o F at sea level) is not really the
same as boiling water. When water first reaches boiling it has not begun to turn to steam
yet. More energy is needed to begin turning the boiling liquid water into gaseous water
vapor. The bonds holding water molecules as a liquid are not easily broken. If I remember
correctly, it takes about seven times as much energy to turn boiling water into steam as it
does to heat water at room temperature to the boiling point.
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(7) If you filled a glass full of water from the Great Salt Lake, when it
evaporated there would be 1 inch of salt left.
-True
They don't call it the Great SALT Lake for nothing.
Water in the Great Salt Lake varies in salinity both by location and in
time. In this example, we are assuming about a 20-percent salt
concentration. In other words, about one-fifth of the weight of the water
comes from salt. And how much saltier is Great Salt Lake water than
seawater? Quite a bit. Seawater has a salt concentration of about 3 1/2
percent.
(8) Sea water is slightly more basic (the pH value is higher) than most
natural fresh water.
-True
Neutral water (such as distilled water) has a pH of 7,
which is in the middle of being acidic and alkaline. Seawater happens
to be slightly alkaline (basic), with a pH of about 8. Most natural water
has a pH of between 6-8, although acid rain can have a pH as low as 4.
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(9) Raindrops are tear-shaped.
-False
When you think of a drop of falling water you probably think it looks like
. When a drop of water comes out of a faucet, yes, it does have a tear shape. That is
because the back end of the water drop sticks to the water still in the faucet until it can't hold
on any more. But, using high-speed cameras, scientists have found that falling raindrops
look more like a small hamburger bun! Gravity and surface tension come into play here. As
rain falls, the air below the drop pushes up from the bottom, causing the drop to flatten out
somewhat. The strong surface tension of water holds the drop together, resulting in a bun
shape (minus the sesame seeds).
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(10) Water boils quicker at Denver, Co. than at the beach.
-True
The boiling point of water gets lower as you go up in altitude. At beach
level, water boils at 212o Fahrenheit. But at 5,000 feet, about where Denver is located,
water boils at 202.9o F, and up at 10,000 feet it boils at 193.7o F. This is because as the
altitude gets higher, the air pressure (the weight of all that air above you) becomes less.
Since there is less pressure pushing on a pot of water at a higher altitude, it is easier for the
water molecules to break their bonds and attraction to each other and, thus, it boils more
easily.
Quiz available: :
http://ga.water.usgs.gov/edu/sc3.html
Other resources:
http://en.wikipedia.org/wiki/Water
http://www.physicalgeography.net/fundamentals/8a.html
http://fermi.jhuapl.edu/people/babin/vapor/index.html
http://www.uni.edu/~iowawet/H2OProperties.html
http://www.planetguide.net/book/chapter_2/water_cycle.html
Part II: The Water Cycle and Water in
the Climate System
• Where did water come from and why do
we still have it?
• Global stocks and fluxes
• Applying what we know about the
properties of water
• Water and climate change
Origin of water
• The most commonly held theory is that carbonaceous
chondrites arriving on earth at the end of the
consolidation brought water with them.
• Others think that water was brought by comets
striking the earth after the consolidation. Comets are
Kuiper belt or Oort cloud objects normally less than
20km in diameter, formed of ice (~80%) and rock.
• Still others tend to the out-gassing theory; that after
the creation of the earth water was present in
gaseous form in the various envelopes (layers?)
surrounding the earth.
Keeping water here
Five main factors, listed below in descending
order of importance, are though to have led
to the conservation of water in its three
states on the earth:
1. The breakdown of radioactive elements in
the earth's mantle (since consolidation) has
contributed to a significant increase in
terrestrial temperature. This phenomenon
led to the degassing of certain elements
contained in the earth into the atmosphere.
Keeping water here
2. Earth is positioned perfectly in the solar
system, neither too far nor too close to the sun.
Its temperature, albeit slightly too low, allows
water to exist in forms other than ice in the
warmer parts. The greenhouse effect, due to the
carbon dioxide in the atmosphere, leads to ideal
conditions for water to exist in its liquid state in
abundance on the surface.
Keeping water here
3. The earth, as is the case with all massive
bodies, has a gravitational well. Gravity acts
in relation the mass of the two objects, and in
the inverse of the distance squared between
them. Due to the relatively great mass of the
earth, it will tend to prevent molecules of gas
escaping from the atmosphere into space.
Keeping water here
4. The existence of a satellite orbiting around the earth,
the moon, has led to a stabilization of the earth's
rotational axis. As a result the earth's climatic
conditions (dependent on the rotational axis) have
also remained relatively stable over time. This
stabilizing characteristic has meant that liquid water
has remained on earth's surface in great quantity.
The appearance of life 3.5 billion years ago led to to
the oceans absorbing large amounts of carbon
dioxide, in the order of several hundred of millions of
tons per year. This in turn led to a reduction in the
greenhouse effect, and earth's temperature reduced
to the current average of about 15°C.
Keeping water here
5. The outer core, believed to be liquid following seismic
studies, is at a temperature of 5000°C, causing the
ionization of elements in the core. As the earth
rotates on its axis the core too rotates, leading to a
dynamo effect and a huge magnetic field. One effect
of this magnetic field is that it deflects the solar wind
from the earth, and therefore prevents certain
molecules (for example water vapor) from being
vaporized from the atmosphere into space.
Additionally the magnetic field opposes the escape of
molecules by acting on the ionized molecules that
form the upper atmosphere.
Global Stocks and Fluxes
USGS Water Cycle
Distribution of Earth’s Water
Usable by humans
Reservoirs and Fluxes
Residence Time: definition
• It is the average time a substance spends within a
specified region of space, such as a reservoir.
• It is also a measure of the average age of the water
in that reservoir, though some water will spend much
less time than average, and some much more.
• Assuming size of reservoir stays the same, residence
times are estimated by dividing the volume of the
reservoir by the rate by which water either enters or
exits the reservoir.
• An alternative method to estimate residence times,
gaining in popularity particularly for dating
groundwater, is the use of isotopic techniques.
Residence Time of Water Molecules
in the Hydrologic Cycle
Average reservoir residence times
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Oceans 3,200 years
Glaciers 20 to 100 years
Seasonal snow cover 2 to 6 months
Soil moisture
1 to 2 months
Groundwater: shallow 100 to 200 years
Groundwater: deep
10,000 years
Lakes
50 to 100 years
Rivers
2 to 6 months
Atmosphere
9 days
Residence Time challenges:
• Measuring reservoirs
• Measuring fluxes
• Reservoirs are rarely constant
Applying what we know about
the properties of water to the
Earth System
Specific heat capacity and heat of
vaporization
Speaking of Fluxes…
A short review of global
ocean-atmosphere circulation
Zonally averaged radiative
balance on Earth
Add Rotation
• Coriolis effect is reason for the direction of the
atmosphere’s prevailing winds
• K-12 explanations at
http://trampleasure.net/science/coriolis/
http://en.wikipedia.org/wiki/Coriolis_effect
Hadley Circulation I
Hadley Circulation II
Comparative Latent Heat
• latent heat of condensation or
vaporization = 2.5 x 106 J kg-1
• latent heat of fusion or melting = 3.34 x
105 J kg-1
• latent heat of deposition or sublimation
= 2.83 x 106 J kg-1
Average Sensible Heat Flux
http://earth.usc.edu/~geol150/weather/images/shtfl_web.gif
Water in the atmosphere
Global Water Vapor from
Satellite
http://weather.msfc.nasa.gov/GOES/globalwv.
html
As water vapor is transported, so is latent
heat. This represents a redistribution of
energy.
Average Latent Heat Flux
http://earth.usc.edu/~geol150/weather/images/lhtfl_web.gif
Annual Mean Precipitation (Kg/m2/day)
Annual Mean Evap Rate (Kg/m2/day)
Climate zones and water
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1. The equatorial region (ITCZ): Rising branch of Hadley cell;
upward motion, adiabatic cooling, saturation, high clouds, convection,
heavy rain. Evaporation is less high than in the subtropics because the
relative humidity in the air is high.
2. Subtropics: Sinking branch of Hadley cell; downward motion,
adiabatic warming, relative humidity of the air is low, cloud formation
suppressed, strong ocean evaporation because air near surface is fairly
dry; land areas at these latitudes are location of many of world's
deserts.
3. Midlatitudes: Moderately rainy because of synoptic storms
especially along storm tracks; western parts of continents drier in
summer because of oceanic high pressure that brings cool dry air down
from north.
4. Polar regions: Sinking air suppresses precipitation; thus the polar
regions are deserts (snow-covered only because the small
accumulation of snow every year doesn't melt/sublime very much, not
because it snows a lot there).
Earth’s water and energy
cycles are closely coupled!
Applying what we know about
the properties of water to the
Earth System
Buoyancy, density, and
dissolved salts
Observed Wind at the Surface
Ocean in Motion
Ocean Water: density
Water density calculator
http://www.csgnetwork.com/h2odenscalc.html
Normal temp-driven lake
overturning
Stratified
Mixed
4C
0
T
15 C
0
T
15 C
Thermalhaline circulation:
driven by density differences
Another effect of water’s high
heat capacity: sea breeze
Global Water Cycle and
Climate Change
• We already talked about how a warmer
atmosphere will cause more water to
evaporate, how does that effect climate?
• Water vapor is the most common GHG. Like
other GHGs, it absorbs IR radiation and
reradiates some of it back to the Earth.
• However, when the water vapor condenses to
form clouds, it may block some of the
incoming solar radiation (depends on cloud
type)
Intensification of the
water cycle?
• Climate change may lead to intensification
of the water cycle because more water is
circulating in the hydroclimate system
• Water cycle intensification for kids:
http://epa.gov/climatechange/kids/water_cycle_version2.html
Hadley Circulation II
Zonally averaged radiative
balance on Earth
Again, Earth’s energy and
water budgets are closely
connected!
Blank USGS Water Cycle
Part III: Water and Climate
Research in Practice
• Data from Observations
• Mathematical modeling
• Experimental
Surface Observations
Remote Sensing Observations
Common surface water &
oceanographic measurements
Temperature
pH
Specific conductance (salinity)
Turbidity
Dissolved oxygen
Hardness
Suspended sediment
Mathematical modeling
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Simple statistical models
Simple dynamical “box” models
General Circulation Models (climate)
Numerical Weather Prediction (NWS)
Sources of uncertainty in modeling
• Insufficient model
physics
• Missing model
physics
• Lack of high quality
observations for
validation
• Wide range of
potential human
behavior
Development of Climate Models
Some personal experiences
Now it’s your turn to practice
some water science!
Introduction to the lab
• Ocean Circulation Simulation
(http://eesc.columbia.edu/courses/ees/climate/labs/circ
/index.html)
• The purpose of this lab is for you to figure out
how to drive ocean circulation. You will also
determine how water masses are formed and
how currents develop. This will give you
insights into the nature of ocean circulation.
This lab exercise differs from typical labs
because you will decide which materials and
methods to use.
Lab Report
• http://eesc.columbia.edu/courses/ees/cli
mate/labs/lab_rpt.html
The End
Atmospheric Stability
Vertical moisture profile
Diabatic vs Adiabatic
• diabatic process: energy is added or
removed.
• adiabatic process: temperature
changes, but no heat is added or
removed. Adiabatic process are
common in the atmosphere.
First Law of Thermodynamics
when heat is added or removed from a gas there will
be some combination of an expansion of the gas and
an increase of temperature. An adiabatic process
represents a special case where no heat is added or
removed. Thus, the first law of thermodynamics
becomes:
0 = pv + cpT
or
pv = -cpT
Lapse Rates
• dry adiabatic lapse rate: rate at which a rising
parcel of unsaturated air cools
• saturated adiabatic lapse rate: rate at which a
rising parcel of saturated air cools. A
saturated parcel of air will cool less rapidly
than a rising unsaturated parcel of air.
• environmental lapse rate: rate at which the
ambient temperature decreases
Orographic precipitation
Bad Meteorology
• The reason clouds form when air cools is that cold air
cannot hold as much water vapor as warm air.
• Raindrops are shaped like teardrops.
• The greenhouse effect is caused when gases in the
atmosphere behave as a blanket and trap radiation
which is then reradiated to the earth.
• The water in a sink (or toilet) rotates one way as it
drains in the northern hemisphere and the other way
in the southern hemisphere. Called the Coriolis
Effect, it is caused by the rotation of the earth.