Understanding Solar Radiation and Thermal Nomenclature for Earth Science Applications

1. Monday, Oct. 2: Clear-sky radiation; solar attenuation, Thermal nomenclature

2. Sun Earth Y-axis: Spectral radiance, aka monochromatic intensity units: watts/(m^2*ster*wavelength) Blackbody curves provide the envelope to Sun, earth emission

4. Sun Earth visible

5. Depth of penetraion into earth’s atmosphere of solar UV 1 Angstrom= 10-10 m. Photoionization @ wavelengths < 0.1 micron (1000 angstroms) Photodissociation @ wavelengths < 0.24 microns: O2 -> 2O Ozone dissociation @wavelengths < 0.31 micron Visible spectrum 0.39 to 0.76 micron

7. Thermal Radiation: • scattering negligible • absorption,emission is what matters • Math gets complicated: thousands of absorption lines, each • varying individually with pressure, temperature Natural Doppler broadening: Half-width goes as T1/2 Lorentz (Pressure) broadening: Half-width goes as P/T(0.5-1.0) natural absorption < 20 km, pressure broadening > 50 km Doppler broadening (Freq shift)/half-width

8. Continuing efforts to improve database on line absorption strengths and Halfwidths: H20 continuum, Microwave lines, are examples 16 micron 7 micron

9. Thermal Radiation transmits through an atmospheric layer According to: +J ds emission • I = intensity • = air density r = absorbing gas amount k =mass extinction coeff. rk = volume extinction coeff. Path length ds Inverse length unit Extinction=scattering+absorption ~ 0

10. Langley plot T = e-sec  Ln (Iinf/I) =sec Beer’s Law used to assess solar constant in pre-satellite days, now used to calibrate instrumentation & determine aerosol&cloud optical depth from ground

11. Transmission through a layer, ignoring scattering and emission: dI = -I kabs sec dz After integration: T = e-sec  Beer’s Law or Lambert’s Law T = transmissivity;  = optical depth, or thickness Consequence: most radiation is absorbed/emitted at an optical depth of 1.

12. brightening Limb Effects darkening affects ALL terrestrial remote sensing

13. Limb Sounding as a Remote Sensing Technique: • first get the temperature from Planck function radiance • then use radiance in an absorbing/emitting wavelength • to get atmospheric concentration at that height HIRDLS

14. To calculate the broadband infrared emission, One simplification is to group lines together, Use spectral-band-average values for absorption - “band” models. A more elegant solution is to group lines by their absorption lines strengths, and integrate over that. Only works in infrared

15. Full radiative transfer equation for infrared/microwave (I.e. ignores scattering): attenuation emission Plane-parallel approximation: the earth is flat. -> the temperature, atmospheric density is a function of height (or pressure) alone. Curvature of earth ignored, atmosphere assumed to be horizontally homogeneous. Flux density with “flux transmissivity”

16. Radiative heating rate profiles: -or- Cooling to space approximation: Ignore all intervening layers Manabe & Strickler, 1965 Rodgers & Walshaw, 1966, QJRMS

17. Remote temperature sensing • CO2 particularly suited (well-mixed & emissive) (what part of the Earth is this from ?)

18. Weighting function

19. If scattering is also included: • 3 radiatively-important • scatterer parameters: • optical depth (how much stuff • Is there ?) • single-scattering albedo ksca/(kscat + kabs) (how much got • Scattered rather than absorbed ?) • asymmetry parameter g, or phase function P(cos : • (describe how it scatters)

20. Wednesday: • results from top of atmosphere radiation • Balance • questions up to 4.40 • some other aerosol, greenhouse gas, • results

21. Whether/how solar radiation scatters when it impacts gases,aerosols,clouds,the ocean surface depends on 1. ratio of scatterer size to wavelength: Size parameter x = 2*pi*scatterer radius/wavelength Sunlight on a flat ocean Sunlight on raindrops X large X small Scattering neglected IR scattering off of air, aerosol Microwave scattering off of clouds Microwave (cm)