Heat Energy Solar and gravitational energy are the fundamental sources of energy for the Earth's climate system. Air-sea exchanges of heat (& freshwater) change density and drive circulation. - heat source into the ocean is solar radiation - heat lost from the ocean by: - latent heat (evaporation) - conduction (sensible) - longwave radiation - reflected solar - ocean circulation moves (transports) heat Geography “Physical Geography of the World’s Oceans”

heat into top of atmosphere = 100% Earth’s heating: incoming shortwave solar radiation

heat out of top of atmosphere = 100% Earth’s cooling: reflected solar radiation, longwave, latent, and sensible heat

atmosphere’s heat budget by % heat into atmosphere = 60%; 37% from land & ocean

atmosphere’s heat budget by % heat into atmosphere = 60%; 37% from land & ocean heat out of atmosphere = 60%

Earth’s heat budget (W m -2 ) Qsw = Qlw + Qlat + Qsens 168 W m -2 = 66 W m W m W m -2 in balance; no net heating or cooling

Earth’s heat budget (W m -2 ) Longwave radiation: Earth’s surface  atmosphere = 350 W m -2 Atmosphere  Earth’s surface = 324 W m W m -2 heats atmosphere

ocean’s heat budget

ocean’s heat budget by % Qsw = Qlw + Qlat + Qsens 100% = 41% + 53% + 6% on average no net heating or cooling

electromagnetic spectrum units 1 nm = m EMR exhibits wave- like and particle-like properties. Indivisible particles of light are defined as photons.

blackbody radiation – blackbody is a perfect emitter and absorber of radiation (i.e. appears black). Blackbodies emit at all λ’s. However, λ of maximum emission is inversely proportional to temperature. higher T lower λ peak Wien’s law: λ max ~ 1 / T Stefan-Boltzmann formula: total energy emitted ~ T K Earth

atmosphere is largely transparent in visible atmosphere absorbs in IR vis  IR 

- the atmosphere absorbs little (~5%) radiation in visible wavelengths -water vapor, CO2, methane, ozone, CFC’s, (and other greenhouse gases) absorb some of the infrared radiation emitted by the earth -with no greenhouse effect, Earth’s surface would average a frigid -18°C (0°F) -water vapor, clouds, and CO2 (in that order) produce the most greenhouse warming, raising Earth’s mean surface temperature to 15°C (59°F)

changes in overhead position of sun cause variations in Earth’s solar heating

changing solar incidence angle sun overhead at Tropic of Capricorn on summer solstice in southern hemisphere 24-hour sunlight south of Antarctic circle

changing solar incidence angle sun overhead at Tropic of Cancer on summer solstice in northern hemisphere 24-hour sunlight north of Arctic circle

changing solar incidence angle solar radiation spread over larger area at high latitude

changing solar incidence angle more reflection at high latitudes longer path through atmosphere at high latitudes Earth’s radius = 6371 km atmosphere’s thickness ~100 km so figure not to scale

solar radiation at Earth’s surface (W m -2 )

solar radiation directly heats water beneath the sea surface UV IR ~50% of solar energy attenuated in top 1 m

Most solar energy quickly “attenuated” by seawater and converted to heat. Some wavelengths can penetrate to depths of 100m

seawater and things in it alter the spectral shape of the solar field (“bio-optics”) seawater and things in it have fairly unique light absorbing and scattering properties solar radiation can be back-scattered to space

SeaWiFS ocean color data El Nino: low chlorophyll La Nina: high chlorophyll

heat loss terms - latent heat flux (Q lat ) energy required to change state (evaporate) of water most important in tropics & midlatitudes - longwave radiation (Q lw ) net thermal IR emission from ocean - sensible heat flux (Q sen ) transfer from high to low temp. to equalize difference typically small

latent heat evaporation process needs energy to overcome molecular forces of attraction between water particles; this input of heat energy causes a drop in ocean temperature

2. / latent heat Figure 7-11 in text; another error 3. / 0. Energy to heat 1 gm ice by 1 °C = 2.05 J/g

latent heat loss

longwave heat loss

sensible heat loss

net ocean heat gain or loss (“net surface heat flux”)

net ocean heat gain or loss (“net surface heat flux”)

poleward heat transport via ocean & atmosphere heat gain & loss vs. latitude temperature of oceans ~ constant distribution of heat changes

Global Heat Budget

surface warming decreases density (thus stratifies) surface cooling increases density (thus destratifies)

Readings (Earth’s heat budget): Text Chapter 7 (pgs 126 – 134) Reader pgs. 189 – 198 Readings (Ocean and Atmosphere): Text Chapter 8 (pgs 138 – 147) Reader pgs. 51 – 61 HW #2 assigned; Due Friday 31 Oct 2008 Midterm on Wednesday 5 Nov 2008