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Lunar libration a complication

Lunar libration a complication. Extinction demonstrates precision. The lunar phase function. Measured albedos. Hourly variation. Roughly 1/3 coverage, independent of lunar phase. Hourly variation. Seasonal variations. Observations. Simulation. Spectroscopy an intriguing possibility.

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Lunar libration a complication

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  1. Lunar libration a complication

  2. Extinction demonstrates precision

  3. The lunar phase function

  4. Measured albedos

  5. Hourly variation Roughly 1/3 coverage, independent of lunar phase

  6. Hourly variation

  7. Seasonal variations Observations Simulation

  8. Spectroscopy an intriguing possibility • Hi-res spectroscopy has revealed much about other planets • Few, if any, whole earth visible spectra • LEO satellite spectrometers available • Earthshine spectrum • Earthshine passes 3 times through the atmosphere, moonlight once • Line depths, shapes, and ratios might provide global information on molecular amounts, temperatures, and profiles

  9. F. Very, 1914

  10. Palomar 60” echellespectrometer MS ES Sky ES-Sky/MS Solar hydrogen Atmospheric oxygen

  11. Some words on programmatics • Present team • SEK, Phil Goode (NJIT/BBSO) • Two postdocs (PRC, Russia) • One tech, one grad student (US) • Funding at $100k/yr (DOE, NASA) • Two additional stations planned for continuous coverage • Crimea, Hunan

  12. Three-pronged attack on the problem • Computational modeling • Conservation of mass, momentum, energy • Grid in longitude, latitude, altitude • Process studies • Seb-grid scale parameterizations • Coupling of the various componets • Monitoring (what is the climate doing?)

  13. Observations are essential to understanding global change • Monitoring and process studies are complementary, but equally important • The monitoring requirements are stringent • Regional or global converate to average spatial variability • Long time series to average temporal variability, identify modes, and detect gradual changes • High precision to detect small shifts • But the Earth is big, the modern record is short, and precision is difficult from any platform

  14. The Moon offers a “new” method for monitoring the Earth • Earthshine visible on the lunar disk can reflect the changing climate • Intensity, Color, Spectrum • Outline • Albedo and climate • Earthshin • Photometry • Historical measurements (1927-1934; 1940-1960) • The present program (Caltech, NJIT)

  15. The albedo sets the input to the climate heat engine • Shortware input (visible, 0.5 mm, 6000 K) • Longwave output (IR, 15 mm, 255 K) • Global and seasonal average is A ~ 0.30

  16. The earth’s albedo is highly variable • Local albedo depends upon: • Surface type • Solar zenith angle (time of day) • Meteorology (clouds) • The global albedo varies with the seasons • North/South land symmetry • Snow/ice cover

  17. The climate is very sensitive to A • Te=255K is the temperature at 6 km • Atmosphere transparent to 15 mm radiation • Not the surface temperature (287 K) • Linearization of the power balance gives dT/DA~-1.5K/0.01 • Similar to that observed in models • Real data are sparse and ambiguous • Greenhouse effect on A uncertain • Doubling CO2 will likely increase T by 1.5-4.5K • Clouds increase (type changes) but snow/ice decrease

  18. Satellites are the standard way to measure the albedo • Low-earth orbit (few 100 km) • Observe one spot (10 km) at at time; average over pixels • Incomplete space/time converate • Expensive • Tough to calibrate at a fraction of a percent • Subject to failures (none now working) • Complex scene models required to analyze data • Precision of about 0.7%

  19. Earthshine is reflected from the earth to illuminate the moon • Ghostly glow of the dark part of the lunar disk • E/S ~Albedo X geometry X moon properties • Intensity varies during the month • Largest when phase ~pi (full earth, crescent moon) • Smallest when phase ~0 (full moon, crescent earth) • Measure by A. Danjon (1927-34) and J. Dubois (1940-1960)

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