Physics of Water in the Climate System Jessie Cherry International Arctic Research Center & Arctic Region Supercomputing Center, UAF.

Physics of Water in the Climate System

Jessie CherryInternational 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

• Cohesion and Adhesion

• Solvent

• Heat Capacity & Heat of Vaporization

• Miscibility and Condensation

• Density and Salinity

• Thermal Stratification

Quiz (think about these questions)

• What are some of the physical and chemical properties of water?

• 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.

Water molecule

Cohesion and Adhesion

Surface tensionhttp://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+ OH-

NaCl <--> 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

• What are some of the physical and chemical properties of water?

• (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.

• (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.

• (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.

• (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.

• (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.

• (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).

• (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.

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.

Keeping water here

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• 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• 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

0 T 15 C 0 T 15 C4 C

Stratified Mixed

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)TurbidityDissolved oxygen Hardness Suspended sediment

Mathematical modeling

• 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/climate/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 = pv + cpT or pv = -cpT

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.