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Temperature Change 8/27/18 Heat (Q) Temperature Change • 1 calorie = 4.18 Joule ΔQ = m cwater ΔT • Heat : Total Kinetic Energy • Q in Joules • Temperature: Average Kinetic Energy • cwater = 4186 J/kg°C • m = mass. Per unit volume: m/vol = density of the • Heat that causes a change in water temperature: Sensible Heat • ΔQ = ρ cwater ΔT • vol Heat Capacity Latent Heat Substance Sp. Heat (cal per gm per °C) Water 1.000 •The heat absorbed or released in Ice .48 the change of phase of water. Wood .42 •Latent heat of fusion = 80cal/gm Brick .21 •Latent heat of evaporation= 540 Sand .20 cal/gm Air .17 •The 1 gm ice cube is 0°C. Copper .09 •What happens if it absorbs 5 cal of Gold .03 heat? Latent Heat Latent heat Latent Heat Latent Heat 1 8/27/18 Heat Fluxes Heat Fluxes Transfer of heat in/out of the ocean Transfer of heat in/out of the ocean surface • Flux = Quantity/(Area • Time) • Heat In - One Heat Flux • Heat Flux = Joule /(m2•s) – Shortwave Radiation or Insolation (Qs) • Heat Out - Three Heat Fluxes – Longwave or Back Radiation (Qb) • 1 Watt = 1 Joule/s These are the 2 heat fluxes involving • Heat Flux = W/m2 Radiation Heat Fluxes Heat In = Heat Out Transfer of heat in/out of the ocean is not true for the short-term surface • Shortwave Radiation or Insolation (Qs) • Longwave or Back Radiation (Qb) • Latent Heat Flux (Qe) • Sensible Heat Flux (Qh) Heat In = Heat Out Smaller Region of Ocean Advective Heat Flux • Sept: Measurements show Qs = Qb + • Qv Qe +Qh. What happens to the Bay’s temperature? • Qv is the only heat flux that • June: Measurements show Qs > Qb + does not transfer heat in and Qe +Qh. What happens to the Bay’s out of the ocean (through the temperature? surface) • June: Measurements show the Bay’s temperature was constant. How?? • Qv transfers heat in and out of a region 2 8/27/18 Heat Fluxes Qs - Qb - Qe - Qh 20 200 180 Bay +/- = 0 Unequal Surface Heating/Cooling Heating by Latitude Cooling Produces: Annual Average • Wind Driven Circulation (surface currents) – Pump heat poleward • Thermohaline Circulation (deep currents) – Pump cold water equatorward • Oceans circulate to redistribute heat, caused by the unequal heating/cooling at the surface. Stefan-Boltzmann Law Q (W/m2) = cT4(°K) C =5.67 x 10 -8 W/m2 °K4 EM Spectrum 3 8/27/18 Wien’s Law Energy Spectra 2897.8µm λ(µm) = T(! K) • What gives off longer wavelength energy, the Earth (10°C) or the Sun (6000°C)? Shortwave Budget Shortwave Radiation Albedo + + Transmissivity = 100% Albedo • Once the Sun’s radiation reaches Earth: • A certain % is reflected away • A certain % is absorbed in the atmosphere and is converted to heat Qs • The remainder is absorbed by the land/ ocean (Qs) Absorptivity Transmissivity Annual Global Average Annual Qs in W/m2 Radiative Budget 4 8/27/18 Latent Heat Latent Heat Flux (W/m2) • Qe = E • L • ρ – E - evaporation rate – L - latent heat of evaporation (540 cal/gm) – ρ - density • Qe = ce (qs - qa)W -3 – ce = 1.5 x 10 – qs = saturation vapor pressure (mb) – qa = actual vapor pressure (mb) – W = wind speed (m/s) Sat. Vapor Pressure Vapor Pressure When humidity = 90% is (qs - qa) a • Vapor Pressure - the air pressure produced by all large or small value? the water vapor in the air (a portion of the total air pressure). It is a measure of how much water is in . Saturation the air. Unit is millibar. • Saturation Vapor Pressure - the maximum amount (qs) of water vapor that can be in the air (i.e. when humidity is 100%). Its value depends on the air temperature Unsaturated • Actual Vapor Pressure - the actual amount of . water vapor in the air Qe and Temperature Qe = c(qs - qa)W • Late at night the temperature in Conway • When (q - q ) is small, air is close to s a suddenly plummets. What happens to the saturation, humidity is high, evaporation is latent heat flux? Why? small • T down, qs – qa down, humidity up, Qe down • When (qs - qa) is large, air is dry, humidity is low, easy to evaporate • The latent heat flux IS dependent on temperature, although temperature is not in the equation. • (qs - qa) is the opposite of humidity 5 8/27/18 Temp and Humidity (Global Annual Averages) For every 100 units of Energy that reach Earth: 22 units leave the oceans as Qe Latent Heat Flux Radiative Budget 22 Sensible Heat Flux Sensible Heat Flux (conduction/convection) • Qh = ch (Ts - Ta)W -3 – ch = 1.2 x 10 – Ts = sea temperature – Ta = air temperature – W = wind speed – When Ts > Ta, the sensible heat flux represents cooling • Bowen’s Ratio B = Qh/Qe 6 8/27/18 For every 100 units of Energy (Global Annual Averages) that reach Earth: For every 100 units of Energy that (Global Annual Averages) reach Earth: 7 units leave the oceans as Qh • 22 units leave the oceans as Qe Radiative Budget • 7 units leave the oceans as Qh (smallest of the 3 cooling terms) 22 7 • These fluxes do not transfer energy in/out of Earth system, but transfer energy from the oceans to the atmosphere. Radiative Budget Calculating Back Radiation (Qb) 2 4 • Radiation leaving ocean (W/m )= csb T(°K) • °K = °C + 273 • Need to know the % that returns to Earth (or escapes & becomes heat) to estimate Qb • Qb = Radiation leaving ocean - radiation returned to ocean Global Heat Budget Global Heat Budget • Animation • Heat In = Heat Out » Qs = Qe + Qb + Qh • On average: Qs= (44%)Qe + (42%)Qb + (14%)Qh • (W/m2) • Heat In = Heat Out Qs = Qe + Qb + Qh • On average: Qs= (44%)Qe + (42%)Qb + (14%)Qh • (W/m2) 7 .
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