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 104 - “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 + Qsens168 W m-2 = 66 W m-2 + 78 W m-2 + 24 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-2

26 W m-2 heats atmosphere

ocean’s heat budget

ocean’s heat budget by %

Qsw = Qlw + Qlat + Qsens100% = 41% + 53% + 6%

on average no net heating or cooling

electromagnetic spectrum

units 1 nm = 10-9 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: λmax ~ 1 / T

Stefan-Boltzmann formula: total energy emitted ~ T4

288 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 southof Antarctic circle

changing solar incidence angle

sun overhead at Tropic of Cancer on summer solstice in northern hemisphere

24-hour sunlight northof 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 kmatmosphere’s thickness ~100 kmso 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 (Qlat) energy required to change state (evaporate) of

watermost important in tropics & midlatitudes

- longwave radiation (Qlw)net thermal IR emission from ocean

- sensible heat flux (Qsen)transfer from high to low temp. to equalize

differencetypically 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