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Lecture 5

EESA01- UTSC Lecture 5 Earth’s Energy, Water and Hydrology

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Department
Environmental Science
Course
EESA01H3
Professor
Carl Mitchell
Semester
Fall

Description
Environment lecture 5 Assignments due 15 days after tutorial, due in dropboxes Midterm covers all up to 6 lecture Water- relates to second assignment Energy flux  The rate (amount per time) of energy (joules) received at a surface= power in J/s aka a Watt (W)  Energy we get is emitted at us as a wave, that wavelength is inversely proportional to the temp of the surface of what is emitting the radiation  How much energy is coming in? Relates to how you feel, eg hot or cold  Power per surface area is an Energy Flux and is measured in W/m^2 o If take watt, and see how much there is over a meter squared = energy flux o We talk about how much energy we get from sun in W/m^2  Physical equation- Stefan boltzmann law o Stefan Boltzmann law- The rate of energy emitted by a substance o o Temp to the power of 4 in kelvin. eg temp of earth into kelvin to the power of 4 o Sigma is the constant. 5678 easy to remember, will be given o Epsilon- a characteristic called emissivity, the efficiency at which a given surface can emit energy. Eg fuel efficiency. 97% fuel efficient, 3% is lost o Only thing that has an emissivity of 1.0 is the sun, a black body emitter, emit at 100% efficiency, everything else has emissivity between 0 and 9.999  Eg find the variables and ask about the energy flux Solar constant  Solar constant- the rate at which insolation (incoming solar radiation) is received at the outer atm of Earth  Energy flux is important because we want to know how much energy is going in and coming out  Solar constant 1367 watts per meter squared  Energy hitting earth averages at 342 W/m^2  Energy hitting the earth is way less, because it is geometric problem o When sun radiation is hitting the earth, it’s not hitting the whole sphere, just a circle o 4πr^2 vs πr^2 o 1367/4=342 o Latitude controls Fig 14.4  Not to say 342 watts everywhere on average, lots of other major controls on how much solar radiation hits the surface of the earth  Latitude- how direct the hit is o Thickness of the atmosphere of which the radiation has to move through o Eg equator, direct hit, going through least amount of atm possible and concentrating more sunlight on one spot o Higher latitudes- same amount of radiation spread out big area therefore it’s cooler as you go away from equator o Also If wrapped atm of equal width around the earth ,at the higher latitudes the atm start to bend towards the poles, and so same thickness but some rays are hitting the earth at an angle eg 60 degree angle, so more atmosphere the sunlight has to go through eg greenhouse gases and clouds. More chances if it being absorbed and reflected  At equator- sunlight directly hitting directly- air obsorbs less energy ue to shorter path through atm o More sunlight per unit of surface area  Near poles- low angle of incoming sunlight- air absorbs more energy due to longer path through atm o Less sunlight per unit of surface area Earth’s energy balance Fg 15.1  Incoming solar radiation 342, as get close to surface of earth, have greenhouse gases o Most abundant greenhouse gas is water, eg as clouds o Relative constant amount of water whereas the other gases like co2 is increasing o Solar radiation comes in, a lot gets absorbed by atm, a lot is reflected and 50% is actually absorbed into surface o If have incoming shortwave radiation, and is reflected away, that reflected radiation remains as same wavelength, shortwave o If it is absorbed by the surface of the earth and remitted it is remitted according to wien’s displacement law, as to the temp of the earth not the sun. So when absorbed and re-emitted the earth is much cooler, so less energy flux, so it is much longer wavelength. That’s why most radiation outgoing from earth is long wave  Some energy going through transpiration, and thermals (temp related things)  A lot gets emitted back as long wave and a lot of greenhouse gases absorb it and atm is cool and re-emits to space and back down towards earth as longwave since it is cold. A lot of back and forth of longwave radiation between earth and atm o Called the greenhouse effect- greenhouses have glass, lets radiation goes in and much less to leave. Hot because radiation stays in, longwave increase. Earth works the same thing, atm works as the glass. If no greenhouse gases earth would always be very very cold. o Greenhouse effect and global warming are related o Global warming is the acceleration of greenhouse effect because of increasing greenhouse gases in the atm o Keeping more energy near surface of earth so gets warmer, losing energy= get colder o Greenhouse gas concentration is increasing, so accumulating energy and getting warmer Albedo  Earth reflects about 30% of the insolation it receives and another 20% is absorbed in the atm  50% gets through  Reflectivity= albedo  Albedo is a number between 0 and 1, represented by alpha o Related to subastances surface properties o o Lighter colour- higher albedo, doesn’t absorb much energy (0.8-0.95) o Asphalt- lower albedo- absorb a lot of energy (0.05-0.1) o 50% of avail energy that gets by drives important processes eg photosynthesis and climate (evaporation, winds)  Eg. Surface with/out snow. o Surface without snow or ice absorbs more heat o Surface with snow and ice reflects more heat o Because water is an unstable surface, it’s albedo is not constant  Snow albedo= 0.85-95. High  Water from .1 t to .7. eg wind, wavy, curls, hits water at many angles low albedo. Clear flat water, with sun going straight down high albedo What takes more energy?  Answer: Changing water at 100 Celsius into water vapour at 100 Celsius o Energy to make the phase change is higher than raising the temp by a lot in the same phase  This is because of Latent energy What happens to the energy- 3 main uses  3 main uses of the 50% of insolation that is absorbed by Earth  Heating the ground- ground heat flux, low amount of energy  Providing warmth- Sensible heat flux, energy that makes you feel warm, can measure and feel by thermometer, can sense it  Changing phases of water- Latent heat flux- it is hidden, can’t measure it using a thermometer. Latent energy  What does it do?- it mostly breaks or forms h bonds in different phases of water o Recall h20 is not linear, net positive charge on H. bent molecule. o net negative charge at one end, net + charge on other end. Because bent, it is polar, 2 poles. When put multiple molecules in with each other + attracted to net -, + repel +, the attraction, not a fully covalent bond, it is a hydrogen bond. No full on exchange of atomic properties.  So if have ice, low energy, cold, those molecules are not moving around. In ice, polar mol are in a stable structure  Melt ice, by increasing temp, but if don’t break the h bonds, it won’t become anymore fluid. Things are liquid because the structure breaks down  Water molecules some are h bonded  When almost all of h bonds are broken. High energy bouncing everywhere, is water vapour  Need to put in latent energy to break the h bonds  From water to ice, latent energy has to come out so the h bonds can form  Amount of energy required to break or form the bonds is very large  Eg 1 kg of water and raise temp by 1 degree c. it will take 4.19 kJ of energy or 1000 calories  Latent heat of fusion: To take kilo of ice to water at 0 degrees, just changing the phase, breaking the h bonds takes 334kJ per kg.  Latent heat of vaporization: If took kg of water and change to water vapour at same temp, would take 2260 kj/kg- about as much as to change by 500 degrees in temperature.  Radiation comes in, reflected, accumulates in surface earth so what does the radiation do?- get emitted as long wave or used to change the phase of water and or change the temp of the surface (sensible heat) Partitioning  Energy used to change phase of water is huge on water because we have a lot of water  Latent vs sensible. o Sweat- body is trying to cool you down by evaporating, it takes up energy that is coming from you and energy from environment that would be making you warmer. o If there is a surface with water to evaporate, the energy from surface will be used to evaporate that water  No sweat, energy will be expressed as sensible heat  If start to sweat, then all the energy gained and continuing to come in will be used to evaporate the sweat.  Desert/ Oasis example o Somewhere on earth where there is not a lot of water eg desert, the net r is total amount of energy going into system. o Because there is no water in the desert, no water, latent energy is almost 0. A lot of radiation is in sensible heat and little bit is ground heat.  All lines would equal the yellow line, net R o But when you have water, the oasis. Then the vast majority of energy is going into evaporating the water in the oasis. The largest heat flux would be the latent. And low amounts of sensible and ground.  Energy Isn’t changing the temp, it is changing the phase Hydrology  The portioning of energy, specifically towards latent energy, is fundamental to global hydrology (movement of water)  Hydrology- science of water, its global circulation, distribution, and properties, specifically water at, near or below earth`s suface o Circulations- how it move around o Distribution- where is it, how much o Properties- what is it, how is energy being used to do different things  Hydrologic cycle- simplified model of how water, ice and water vapour flows, from place to place o including between surface of atmosphere eg evaporation, evapotranspiration- very important flux  Most important fluxes of water is evaporation and precipitation- vast majority of how water gets in and out of something Key processes in the hydrologic cycle  Precipitation- the condensation of water vapour in the atm resulting in its return to Earth`s surface o water needs to condense, form droplets and hit the earth again  Evapotranspiration- the release of water into the atm through a combo of phase change from open surfaces and release of water vapour by plants  Infiltration- penetration of water through the soil surface o key process but not key input in water balances. Whatever Hits surface and gets sucked into the subsurface. Any lower is percolation  Runoff- flow of water across or under earth’s surface under force of gravity. o gather water to rivers and drain the runoff.  Ground water flow-the movement of
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