Biosphere/Atmosphere InteractionsBiology 164/264

2007

Joe Berry joeberry@globalecology.stanford.eduChris Field cfield@globalecology.stanford.eduAdam Wolf adamwolf@stanford.edu

Basic questions to be addressed by this course:

• What are the major fluxes of energy and matter between the atmosphere and land ecosystems?

• What determines the temperature of leaves, plants, soils, and ecosystems?

• What controls rates of plant photosynthesis and transpiration?

• How do atmospheric processes interact with ecosystem processes to control CO2 and water exchanges?

• How do characteristics of the land surface influence the motions of the atmosphere?

• How do characteristics of the land surface influence climate?• How do greenhouse gases exchanged by ecosystems

influence climate?• How can we measure and model the exchanges of matter

and energy from the leaf to the global scale?

Mechanics• 2 lectures per week – TTh 11-11:50

– Bio T 185• 1 lab per week – Tuesday 2-5

– Carnegie Global Ecology (260 Panama Street)• 1 optional Matlab/problem session – Thursday 4-6

– Carnegie Global Ecology (260 Panama Street)

• Grading: – Bio 164:

• Weekly problem/program 60%• Final project data analysis 20%• Class participation 10%• Labs (weekly data sets) 10%

– Bio 264: • Weekly problem/program 40%• Final integrated program 20%• Final project data analysis 20%• Class participation 10%• Labs (weekly data sets) 10%

– Problem/programs in Matlab– No midterm, no final, no papers

Labs

• January 16– Principles of environmental sensors & data loggers– Radiation sensors

• January 23– Environmental sensors – wind, humidity, soil moisture, water potential

• January 30– Environmental sensors – CO2, water vapor

• February 6– Leaf gas exchange

• February 13– Leaves – fluorescence, spectral reflectance, isotope exchange

• February 20– Canopy gas exchange – eddy flux hardware

• February 27– Canopy gas exchange – environmental conditions at an eddy flux installation

• March 6– Canopy gas exchange – vegetation status and fluxes at an eddy flux installation

• March 13– Canopy gas exchange – setting up an eddy flux system

• For each lab, each pair will be responsible for collecting, analyzing, and turning in a data set collected from at least one sensor or system

Texts

• Campbell, G. S. and J. M. Norman. 1998. An Introduction to Environmental Biophysics. Springer, New York. 286 pp. (core)

• Hartmann, D. L. 1994. Global Physical Climatology. Academic Press, San Diego. 411 pp. (optional)

• Stull, R. B. 2000. Meteorology for Scientists and Engineers. Brooks Cole, Pacific Grove. 503 pp. (optional)

• Bonan, G. B. 2002. Ecological climatology: Concepts and applications. Cambridge University Press, New York. 678 pp. (optional)

What sets the temperature of

objects and ecosystems?

Heat-trapping or greenhouse gases trap thermal radiation on its way to space.

Energy in = Energy out + storage

What controls the temperature of the planet?

What controls rates of photosynthesis?

Pho

tosy

nthe

tic c

apac

ity

Leaf nitrogen

Evergreen sclerophylls

Deciduous trees

Annual weeds

How do plants cope with extreme environments?

What controls the carbon balance of ecosystems?

What controls the movements of the atmosphere?

How do ecosystems influence climate?

Radiation

• All objects at temperatures above absolute zero emit radiation.

• Photons carry a unique amount of energy that depends on wavelength

• E = hc/• Where h is Planck’s constant (6.63*10-34 Js), c is

the speed of light (3*1010m s-1), and is wavelength (m).

Thermal Radiation

• Stephan-Boltzmann Law•• = 5.67 * 10-8 W m-2 K-4

• Earth approximates a black body at 288 K -- Emits 390 W m-2

• Black body = emissivity () = 1• Note: the emissivity of plants is close to 1, but

other objects can have very different values

B =T4

Absorptance and Emissivity

• Absorbed radition is proportional to absorptance

• Emitted radiation in proportional to emissivity = absorptance

Blackbody radiation

• Amount increases with T4

• Wavelength of maximum proportional to 1/T

Wien Law

•

• objects at 300k maximum emission at about 10 micrometers

m = 2897T

Solar energy

• Solar output 3.84*1034 W• extra-atmosphere – the sun is close to a 5760 K black body• radiant emittance = 6.244*107 W m-2

• most of the solar energy is in the range of 0.3 – 2.5 micrometers• about 50% is visible (0.4 – 0.7) and about 50% is infrared (>

0.7)•

The solar (not so) constant• Integrating this emittance over the size of the sun and the

distance to the earth leads to a radiation at the outside of the atmosphere of 1360 W m-2

• Integrating over the spherical surface leads to an average radiation of about 342 W m-2

The solar spectrum

Atmospheric transmission

• Absorption– Average absorption by the atmosphere 62 W m-2

• Scattering– Raleigh (small particle) – shortest wavelengths scattered preferentially

out of the solar beam– Mie (large particle) – little wavelength dependence– Average reflected solar radiation by the atmosphere 77 W m-2

• Effects of clouds• Scattering and reflectance• The greenhouse effect

– Increased absorptance of thermal radiation means increased radiation directed back to the surface

– Increased absorptance in the atm effectively increases the height at which the atmosphere is radiating back to space

Atmospheric absorption

The cosine law

SN = Sicos

Spatial distribution of solar energy