I. Physical Principles: The foundation & the tools Newton's laws: forces, pressure, motion Energy: Temperature, radiant energy II. Atmospheric & Ocean Physics: First element of climate and environmental science Atmospheric structure (T, P in "4-D") Winds, Weather, General Circulation, Climate III. Atmospheric & Ocean Biogeochemistry: Second element of climate and environmental science Atmospheric and ocean composition, past and present Human impact, global change IV. Intersection: what we know, would like to know, will never know, and what can we contribute to the debate. L-2 L-3 Solid bodies emit thermal radiation at rates that depend on temperature. Hot bodies (sun) emit more radiation at shorter wavelengths than cold bodies (earth). Emission rate=!T4 Road map to EPS 5 Lectures 3 and 4: Atmosphere Heat, Energy, Radiation Black Bodies, Planck Function, Stefan Boltzmann Law Planets radiate on average at the Effective Temperature, to maintain energy balance with sun and space, Absorption of ir in the atmosphere traps energy, radiating back to the surface and causing it to warm up. Teff = [Fs(1 - A)/(4!)]! = 252.6 K Tg = [n + 1]1/4Teff. Effective T, greenhouse effect Feedback! Atmospheric Radiation: The Earth receives energy from the sun (on average 344 W/m2) and emits the same amount to space The energy balance of planet earth The temperature of the earth’s surface has been remarkably constant over geologic time. Even the dramatic cooling during the ice age represented a change of only 3° C in the global average surface temperature, occurring over thousands of years. Seasonal changes in temperature, although large in a particular place, correspond to very tiny changes in global mean temperature. How is this remarkably steady condition maintained? To maintain the long-term stability of earth’s temperature, the planet must radiate to space a flux of energy sufficient to just balance the input from the sun, i.e. the earth is, to good approximation, in radiative energy balance.1. Atoms form chemical bonds by rearranging electrons in the outer (valence) shell to localize the electrons between the nuclei. 2. Light may be regarded as both a propagating electric field in the shape of a sine wave and as particles called photons. The relationship between the speed of light (c), its wavelength ("), and its frequency (#), is c = "#. 3. Every photon has a specific energy proportional to its frequency, or inversely proportional to its wavelength, E = hc/" = h#. 4.! Most atmospheric gases can neither emit nor absorb light at the long wavelengths (infrared) emitted by cold objects, such as the Earth. Those relatively rare atmospheric molecules that can absorb infrared radiation have asymmetric distribution of charge (e.g. a dipole, like the water molecule) that causes the molecules to experience a force due to the oscillating electric field of the light. 5.! Matter can emit light only at wavelengths that it can absorb. 6. Matter emits radiation depending on its temperature. The total flux of radiation emitted is given by the Stefan-Boltzmann equation, Flux (W m-2) = !T4, where ! is the Stefan-Boltzmann constant, 5.67x10-8 W m-2 K-4. The flux as a function of wavelength is given by the Planck function, FLUX (") = [2$ hc2 / "5 ]/[exp( hc/(" kT) ) – 1 ], (W m-2 m-1). A brief introduction to light and matter 6 Protons, neutrons, electrons, and electrostatic forces. •!Atoms are the fundamental chemical building blocks of matter, the smallest unit that retains chemical identity. An atom is made up of protons (positive charge), neutrons (zero charge), and electrons (negative charge). The protons and neutrons are packed together in the nucleus and the electrons forming a cloud of negative charge around the nucleus. •!The size of an atom (diameter of the electron cloud) is ~10-10 m, but the nucleus is smaller by factor 100. The atomic unit of length is the Ångström, 1 Å % 10-10 m, named to honor Anders Ångström (1814-1874), Swedish physicist who improved the precision in measuring the wavelength of spectral lines. •!Electrostatic forces are responsible for holding atoms together or forcing them apart. When electric charges, q1 and q2 are distance r apart, the electrostatic force between them is F = q1q2/r2, and the energy of interaction is E = q1q2/r (the energy it takes to bring them to distance r from infinity). If the charges are of like sign (both + or both -), the force is repulsive, the energy is positive, and the charges will tend to fly apart. Charges with opposite signs are attracted and the electrostatic force pulls the charges together. q is the charge, it comes in multiples of the electron charge. + - + - E electric field torque on the dipole (molecule) "electroscope" apparatus for determining the charge on an electron F = q1q2 / r2Density of electron charge (net negative charge, shown in red and green) relative to the positions of the nuclei and inner-shell electrons (net positive charge, dark blue) in the molecule Si3. The maxima of electron density between the nuclei provide clouds of negative charge that attract the positively-charge nuclei and hold the molecule together. (Figure by Dr. Masao Arai, National Institute for Research in Inorganic Materials, Japan.) Electrostatic forces hold the atoms in a molecule together (or can push them apart…). Molecules that have opposite electric charges at either end (“dipole moment”) can absorb or emit electromagnetic radiation (light) in ways that affect the heat balance of the earth. The major molecules of air (O2, N2) do not have dipole moments, and they cannot emit or absorb light in this way. To understand why dipole moments are important in absorption and emission of light, we need to study the properties of light. Light and radiant heat (infrared radiation) propagate through space as waves, called electromagnetic waves because there are an electric field and a magnetic field associated with each wave (the magnetic field is not important for our purposes). The O atom in water partially pulls the electrons away from the H atoms, giving its side of the molecule a small negative charge (-2&) and the H side a small positive charge (+& on each H-atom). If we could take a snapshot of a light wave as it traveled for 1 s, it would be 3'108 m long, and would look like the sine wave shown in the figure. The distance between two successive crests on the wave is called the wavelength