PHYC40050-L02-Energy

PHYC40050-L02-Energy - Climate, Climate Change Nuclear...

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Unformatted text preview: Climate, Climate Change Nuclear Power and the Alternatives Climate, Climate Change Nuclear Power and the Alternatives PHYC 40050 Peter Lynch Meteorology & Climate Centre School of Mathematical Sciences University College Dublin PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics TRANSFER OF ENERGY CONDUCTION CONDUCTION Lecture 2 The Energy Cycle of the Atmosphere • Transfer of energy through matter Transfer • Air is a poor conductor • Only important at the Earth's surface CONVECTION CONVECTION • Transfer of energy by movement of mass • Can only take place in fluids - e.g. Air • Energy transported upward by convective flow • Convection on a global scale creates worldwide atmospheric circulation ADVECTION ADVECTION RADIATION RADIATION PHYC 40050 Environmental Physics • Horizontal movement of air PHYC 40050 Environmental Physics Convection Advection PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics 1 LATENT HEAT Latent heat is the heat absorbed or released Latent by unit mass of water when it changes phase. Phase Changes Latent heat of melting / fusion Latent Latent of vaporization / condensation Latent Latent heat of sublimation / deposition Latent All conversions are relevant in atmospheric physics PHYC 40050 Environmental Physics Fig. 2-5, p. 33 PHYC 40050 Environmental Physics The EM Spectrum PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Planck’s Law for blackbody radiation: u( λ) = 8πhc 1 λ5 e hc / λkT − 1 (J/m3 /m) Wien’s Displacement Law: The hotter the object, the higher the curve: Stefan-Boltzmann Law λm = 2.9 × 10−3 m K -1 (m) T Stefan-Boltzmann Law: R = σT 4 (W/m2 ) PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics 2 Solar Radiation and Terrestrial Radiation The hotter the object, the shorter the wavelength: Wien’s displacement law Huge difference in the temperature of the Earth and of the Sun. Spectra are effectively disjoint. We speak of short wave radiation (solar) and long wave radiation (terrestrial). PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Energy Transfer in the Atmosphere PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics The Solar Constant The average amount of solar energy The reaching the outer limits of the atmosphere. This “constant” actually varies slightly. This Changes by about 0.1% over the Changes eleven year solar cycle. Mean value: 1368 W/m². Mean W/m² PHYC 40050 Environmental Physics Zenith Angle PHYC 40050 Environmental Physics 3 PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics THE EARTH’S ORIENTATION Earth's axis is not perpendicular to the Earth's plane of its orbit around the sun. It is tilted 23.5º from the perpendicular: It 23.5º Inclination of the axis. Without this inclination we would have no Without seasons. This changes the solar zenith angle of the This sun, and the area covered by a beam of sunlight. PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics THE EARTH’S ORIENTATION Area covered by beam of sunlight is Area proportional to 1/cos of the solar zenith angle In Belfield, solar zenith angle of the sun is In Belfield, 75º in December and 30º degrees in June. 75º 30º Ratio of 1/cos of the angles is about 3.3. Ratio Three times as much energy falls on unit Three area at the ground in Summer as in Winter. Energy Fluxes 4 x 342 = 1368 PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics 4 INCOMING SOLAR RADIATION 25% penetrates directly to earth's surface. 26% scattered by atmosphere but then reaches the surface. Total of 51% reaches surface. 31% reflected back to space by clouds, atmospheric scattering, and reflective surfaces, e.g. snow and ice. 19% absorbed by clouds and atmosphere PHYC 40050 Environmental Physics Energy and Matter Emission Emission Absorption Absorption Reflection Reflection Scattering Scattering PHYC 40050 Environmental Physics ABSORPTION • Gases are excellent absorbers. When radiation is absorbed, When energy is converted into internal molecular motion – temperature rises. Significant absorbers are: Significant Oxygen and ozone Water vapour Carbon dioxide PHYC 40050 Environmental Physics REFLECTION - ALBEDO The fraction of energy that is reflected by a The surface is called its albedo. albedo. Albedo of the earth as a whole is ~30%. Albedo Albedo of fresh snow is 80-85%. Albedo 80Thick cloud - 70 to 80%. Thick Water - depends on elevation of the Sun, Water from 50 to 80% near horizon, 3-5% at 90º. 390º. Soil - 10% Soil PHYC 40050 Environmental Physics SCATTERING Produces diffuse light. Produces Shorter wavelengths (blue and violet) are Shorter scattered more effectively than longer wavelengths (red and orange). Sky appears blue when viewed at noon. Sky At sunset, scattering depletes amount of blue At light - sky appears reddish. Scattering more efficient as particle gets larger Scattering - aerosols or dust. PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics 5 LATITUDINAL HEAT BALANCE The global amount of incoming solar radiation is The nearly equal to the outgoing terrestrial radiation. However is not true at any given latitude. However In general there is a surplus of energy at the equator In - i.e. More radiation comes in than goes out. There is also a deficit of energy at the poles. There poles. Why then do the poles not get colder and the Why equator hotter? Because heat is transported from the equator to the Because poles by ocean currents and by the atmosphere. PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Fig. 2-20, p. 50 Temperature Variations Diurnal Temperature Cycle PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Air Temperature Data Daily mean temperature is determined by two Daily methods, (a) average of 24 hourly measurements (a) (b) the average of the maximum and minimum (b) temperatures for the day. Controls on Temperature Latitude Latitude Surface type Surface Elevation and aspect Elevation Differential heating of land and water. Differential Ocean currents. Ocean Cloud cover and albedo Cloud Daily temperature range is the difference Daily between the max and min temperatures. Monthly mean temperature is obtained from Monthly the average of the daily mean for the month Annual mean temperature is the average of Annual the monthly means Annual temperature range is the difference Annual between the coldest monthly mean and the warmest monthly mean PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics 6 Latitudinal Effect Incoming Solar Energy (TOA) PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Surface Characteristics Effect of Altitude PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Effect of Aspect Effect of Aspect PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics 7 Differential Heating of Land and Water As water is heated, convection distributes the heat As through a large mass. In contrast, heat does not penetrate deeply into In soil or rock - heat can only be transferred by conduction. conduction. Net result: a relatively thick layer of water is Net heated to moderate temperatures, while only a thin layer of land is heated to much higher temperatures. Land versus Water versus Specific heat is almost three times greater Specific for water than for land PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Effect of Ocean Currents Effect of clouds on the daytime energy budget at the surface PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Effect of Cloud Cover Energy in and out PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics 8 DAILY TEMPERATURE CYCLE Before sunrise, the temperature is controlled by Before net long-wave radiation from the surface ---longthe ground cools. As sun comes up, solar radiation is absorbed As and the temperature of the ground increases. In general the incoming solar energy is more In than the net outgoing thermal energy, so the grounds heats up. Ground continues to heat up until the amount of Ground incoming solar energy equals the amount of outgoing thermal energy. This occurs typically at about three in the This afternoon. PHYC 40050 Environmental Physics CONTROLS OF TEMPERATURE RANGE Latitude - determines the intensity of the sun, and Latitude the length of the day. Surface type - land and water contrast, bare soil Surface versus vegetation. Elevation and aspect . Elevation Relationship to large bodies of water. Relationship water. Ocean currents. Ocean currents. Cloud cover - reduces the diurnal temperature Cloud range. PHYC 40050 Environmental Physics Interannual Temperature Variations Average or normal temperatures Average Long-term Temperature Variations Long- Anomalies Anomalies Volcanoes Volcanoes El Niño / La Niña El Niñ Niñ PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Volcanoes PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics 9 Picture from Space Shuttle 3 weeks after the eruption of Mt. Pinatubo Temperature in Spokane and Boise after the eruption of Mount St. Helens PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Lapse Rates and Stability Lapse rate is the rate at which the real Lapse atmosphere falls off with altitude – the environmental lapse rate An average value is 6.5 ºC per kilometer An This should be compared with the This adiabatic lapse rate of 10 ºC. If the environmental lapse rate is less If than 10 ºC, then the atmosphere is absolutely stable If greater than 10 ºC, it is absolutely If unstable PHYC 40050 Environmental Physics (A) Mid-afternoon Diurnal Temperature Variation (B) Evening and Nocturnal Temperature inversion (C) Sunrise (D) Mid-morning PHYC 40050 Environmental Physics TEMPERATURE INVERSIONS When the temperature profile increases When with altitude, this is known as a temperature inversion. inversion. Two main types – subsidence inversion Two and radiation inversion (nocturnal inversion). Very important during pollution events – Very trap pollutants close to the surface. PHYC 40050 Environmental Physics Temperature Inversions PHYC 40050 Environmental Physics 10 Effect of a temperature inversion End of Lecture 2 PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics 11 ...
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