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Transcript
ENERGY, HEAT AND TEMPERATURE 5/24/2017 (c) Vicki Drake, SMC 1 ENERGY The ability or capacity to perform work on some form of matter Matter is any substance that takes up space and has mass Earth’s atmosphere is considered ‘matter’ – all the gas molecules and particulates Energy may be considered as either Kinetic or Potential Source of Energy for Earth: Sun Lecture will describe how the Sun’s energy works on Earth’s atmosphere 5/24/2017 (c) Vicki Drake, SMC 2 Potential Energy Stored Energy: Value of potential energy (PE) determined by work capability Total amount of stored energy due to position Potential energy examples: A battery Water behind a dam Any object lifted against pull of gravity 5/24/2017 (c) Vicki Drake, SMC 3 Kinetic Energy Energy in motion Value of Kinetic Energy (KE) is determined by the speed and mass of object Ek = ½ mv2 where Ek is kinetic energy, m is the mass of the object and v2 is the square of the velocity of the mass Examples of atmospheric KE Heat energy Solar energy Light energy Electrical energy 5/24/2017 (c) Vicki Drake, SMC 4 Internal Energy Internal Energy is the stored PE and KE of atoms and molecules in any kind of matter or substance In theory: PE = KE The energy associated with random, disordered motion of molecules 5/24/2017 (c) Vicki Drake, SMC 5 1st Law of Thermodynamics (Newton) Conservation of Energy: Energy cannot be created or destroyed. It can only change form (i.e., converted to another type of energy). Energy is a constant in the universe Conversion of Energy examples: Heater/Furnace: Chemical → Heat Automobile Engine: Chemical → Mechanical Nuclear: Heat → Kinetic → Optical Battery: Chemical Sound or Mechanical or Optical or… 5/24/2017 (c) Vicki Drake, SMC 6 Temperature: Measuring Energy Temperature is a measurement of the average kinetic energy of atoms/molecules in a substance Temperature is measured using a Thermometer A thermometer measures the temperature of a system in a quantitative way. ‘Mercury-in-glass’ type has a bulb filled with mercury that expands into a capillary when warmed. Rate of expansion calibrated on glass scale 5/24/2017 (c) Vicki Drake, SMC 7 Thermometer Scales: Interpreting Energy Fahrenheit: developed by Gabriel Fahrenheit in the 1700s. Boiling point of water: 2120 Freezing point of water: 320 Celsius: developed by Carolus Linnaeus using ‘centrigrade’ measure Boiling point of water: 1000 Freezing point of water: 00 Kelvin: An absolute temperature scale, based on Absolute Zero, developed by William Thompson and Lord Kelvin Boiling point of water: 373K Freezing point of water:273K Absolute Zero: 0 degrees K -2730C or -4590F 5/24/2017 (c) Vicki Drake, SMC 8 What is Heat Energy? Heat represents energy in the process of being transferred from one object to another because of a temperature difference. Heat energy transfers are ‘one-way’ in natural environment Heat energy transfer is from warmer objects to colder objects 5/24/2017 (c) Vicki Drake, SMC 9 What is Heat Capacity? The ratio of the amount of heat energy absorbed by a substance Heat capacity is measured by a temperature increase in the receiving object that corresponds to the amount of heat energy applied to that object Rapid temperature increase means the substance has a low heat capacity Slow temperature increase means the substance has a high heat capacity 5/24/2017 (c) Vicki Drake, SMC 10 What is Specific Heat Capacity? The amount of heat required to raise the temperature of 1 gram (1 g) of any substance by 1 degree Celsius All objects have their own specific heat capacity – the rate at which they will absorb heat energy and register a temperature increase The specific heat capacity of water is the baseline against which all other substances are measured Water has a baseline specific heat capacity of 1.0, while soil has a specific heat capacity of 0.2 (as measured against water). Water can absorb 5 times more heat energy than ‘soil’ before a temperature increase is registered. Water has a high specific heat capacity Water heats slowly and releases heat slowly Soil has a low specific heat capacity Soil absorbs heat energy quickly and releases heat energy quickly 5/24/2017 (c) Vicki Drake, SMC 11 Latent Heat – “Hidden Heat” Latent heat is energy absorbed and/or released by a substance during a ‘change of phase’ or ‘change of state of being’. Latent heat is measured according to water’s response to absorbing or releasing energy. Water is the only substance that exists in all three ‘states of being’ at the same time at earth’s ambient temperature and air pressure. Solid (ice Liquid (water) Gas (water vapor) 5/24/2017 (c) Vicki Drake, SMC 12 Latent Heat and Change of Phase: Absorption and Release of Energy 5/24/2017 (c) Vicki Drake, SMC 13 Latent Heat – “Hidden Heat” ’ When change of phase is from a solid to a liquid and then to a gas, heat energy is absorbed. This heat is ‘latent’ heat and cannot easily be measured as the ice melts into liquid water and then evaporates into water vapor. When the change of phase is from a gas to a liquid to a solid, heat energy is released into the surrounding atmosphere. This heat is also ‘latent’ heat, but the resulting increase in temperature of the surroundings can be measured as the water vapors condenses into droplets and then into ice crystals. 5/24/2017 (c) Vicki Drake, SMC 14 Change of Phase: Water Evaporation – heat energy absorbed by a substance changing water from a liquid to a gas (vapor) phase Evaporation is a ‘cooling’ process for a surface as heat energy is absorbed by water droplets, converting to a vapor, from surrounding atmosphere – “Latent Heat” (not easily measured) Condensation – heat energy released by a water changing from a gas to a liquid phase Condensation is a ‘heating’ process for a surface as heat energy is released by water vapor, converting to liquid droplets, into surrounding atmosphere – “Latent Heat” (easily measured as “Sensible Heat”) 5/24/2017 (c) Vicki Drake, SMC 15 Latent Heat’s Role in Energy Latent heat is an important source of energy in atmosphere Heated water vapor molecules released during evaporation are swept to higher latitudes and altitudes Condensation of vapor to liquid releases heat energy to upper atmosphere Main energy source for: Thunderstorms Hurricanes Other mid-latitude cyclonic storms 5/24/2017 (c) Vicki Drake, SMC 16 Heat Transportation Mechanisms in the Atmosphere Three processes work together to transport heat energy throughout the atmosphere and around the globe. Conduction Convection Radiation 5/24/2017 (c) Vicki Drake, SMC 17 Conduction Molecule-to-molecule transfer of heat energy Heat flows from warm to cold The greater the temperature difference, the more rapid the heat exchange Effective only in lower atmosphere where molecules are ‘compressed’ at the surface 5/24/2017 (c) Vicki Drake, SMC 18 Convection Transfer of heat by currents in a fluid (liquid or gas) Uneven heating of Earth’s surface sets up conditions of warm air rising and cooler air sinking: Thermals Important part of heat transfer by expansion, rising, cooling and sinking of air within the lower atmosphere 5/24/2017 (c) Vicki Drake, SMC 19 Radiation Radiant energy traveling in waves that release energy when they are absorbed by an object Waves have both magnetic and electric properties: ElectroMagnetic Spectrum Energy travels at the speed of light (C): EM Spectrum – total amount of solar energy from Sun 300,000 km/sec 186,000 miles/sec 5/24/2017 (c) Vicki Drake, SMC 20 Characteristics of Radiant Waves Crests and troughs Wavelength (λ) – Distance from one crest to another Measured in units of meters, centimeters, micrometers (10-6) and nanometers (10-9) Higher energy waves have short wavelengths (higher frequency) 5/24/2017 (c) Vicki Drake, SMC 21 Radiation – Temperature Connection All objects in universe (above Absolute Zero of -273K) emit radiation The higher the temperature of the object, the greater the amount of radiation emitted Stephen-Boltzmann’s law: E~σT4 E = Maximum rate of radiation emitted per square meter of an object σ = a constant (5.67 x 10-8 W/m2K4) T = Temperature of the object (in Kelvin) 5/24/2017 (c) Vicki Drake, SMC 22 Radiation: Solar Energy vs Earth Energy Solar energy = 6000 K (10,5000F) Earth energy = 288 K (590F, 150C) λmax for the Sun: ~0.5 μm (micrometer) the wavelength for “Blue” in the Visible Light portion of EM λ max for the Earth: 10 μm (micrometer) the wavelength for Far Infrared (heat energy) in the EM Spectrum 5/24/2017 (c) Vicki Drake, SMC 23 Earth Energy Balance 5/24/2017 (c) Vicki Drake, SMC 24 Daily Temperature Variations Daily Temperature Lag Continual warming of air at Earth’s surface after Sun as reached solar peak at Noon Graph depicts the time of maximum insolation at local noon, while the maximum air temperatures occur past local noon 5/24/2017 (c) Vicki Drake, SMC 25 Daytime Heating Air closest to surface heats through conduction and convection processes Conduction is not effective – strong temperature differences found just above surface Convection of warm rising air (Thermals) redistribute air vertically Sun is most intense at local Solar Noon (“local meridian”) Post-meridian (p.m.): insolation (incoming shortwave solar radiation) continues to be greater than outgoing longwave heat energy from Earth Energy surplus develops for 2-4 hours after Solar Noon Lag time develops between solar maximum and maximum heating of Earth’s surface 5/24/2017 (c) Vicki Drake, SMC 26 Nighttime Cooling Lowered Sun angle, initially, spreads energy over wider area, reducing heat available to surface Earth’s surface and lower atmosphere lose more heat energy than gained Ground and air cooling via radiational cooling from Earth’s surface over night Night progresses – Earth’s surface and air layer closest to surface are cooler than upper level air Coldest time of 24-hour day? Just before sunrise! 5/24/2017 (c) Vicki Drake, SMC 27 Seasonal Lag time – Northern Hemisphere Over the year – the Earth’s temperature shows a temperature lag behind the Sun’s insolation 5/24/2017 (c) Vicki Drake, SMC 28 Temperature Data Diurnal Range of Temperature Difference between daily maximum and daily minimum temperatures Largest diurnal range: Dry, arid regions Low specific heat of soils Smallest diurnal range: Wet, humid regions High specific heat of water 5/24/2017 (c) Vicki Drake, SMC 29 What does diurnal range tell us? Regions that have a low diurnal range are usually located near a body of water Regions that have a high diurnal range are usually located away from water 5/24/2017 (c) Vicki Drake, SMC 30 Mean and Average Daily Temperature Average: Add all hourly values/24 Mean: Add Highest hourly value and Lowest hourly value/2 Collecting the average of mean daily temperatures for a particular location on a particular day for a 30-year period is the ‘normal’ or ‘average’ temperature for that place on that day 5/24/2017 (c) Vicki Drake, SMC 31 Average Monthly Temperature The average of the mean daily temperatures for a month Add all the mean daily temperatures, divide by the total number of days in the month (‘average’) Mean average monthly temperature: Add the highest mean daily temperature for the month to the lowest mean daily temperature for the month and divide by 2 5/24/2017 (c) Vicki Drake, SMC 32 Annual Range of Temperature The difference between the average temperature of the warmest month and coldest month Largest range – areas dominated by land “Continental” climates Smallest range – areas dominated by water “Maritime” climates 5/24/2017 (c) Vicki Drake, SMC 33 Mean Annual Temperatures The average temperature for any place for an entire year Add mean temperature for the warmest month to the mean temperature for the coldest month and divide by 2. Add all the average temperatures for each month (12 months) and divide by 12. 5/24/2017 (c) Vicki Drake, SMC 34 Controls on Temperature # 1 control: amount of incoming solar radiation (insolation) reaching the Earth Seasonal shift of insolation due to rotation, revolution and tilt of Earth’s axis Latitude: Temperatures near Equator are more consistent year-round Further away from Equator – more variability of temperatures and cooler overall 5/24/2017 (c) Vicki Drake, SMC 35 Latitude as a Temperature Control 5/24/2017 (c) Vicki Drake, SMC 36 Unequal Heating of Land and Water The difference in the specific heat of soils and water sets up conditions of differential heating and cooling of the land and water Specific heat of water is greater than the specific heat of ‘land’ ‘Land’ heats and cools at a faster rate than large bodies of water 5/24/2017 (c) Vicki Drake, SMC 37 Ocean Currents Ocean currents move cool polar waters to the tropics as well as moving warm tropical waters to the poles. Two types of ocean currents: Warm ocean currents Cool ocean currents 5/24/2017 (c) Vicki Drake, SMC 38 Elevation The lower atmosphere (troposphere) cools at a fairly consistent rate from lower to higher elevations Lapse rate: a change in temperature with a change in elevation Environmental lapse rate is the average cooling/heating rate for rising/sinking air ~60C/`1000 meters ~3.30F/1000 feet 5/24/2017 (c) Vicki Drake, SMC 39 Albedo of Earth’s surfaces Albedo is the amount of energy reflected back to space by different types of surfaces Ice/Snow have the highest albedo – the highest reflectance, low absorbance Vegetation has a low albedo – low relfectance, high absorbance Water has a low albedo, high absorbance 5/24/2017 (c) Vicki Drake, SMC 40