lunar libration a complication. extinction demonstrates precision
TRANSCRIPT
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
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
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?)
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
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)
The albedo sets the input to the climate heat engine
• Shortware input (visible, 0.5 m, 6000 K)
• Longwave output (IR, 15 m, 255 K)
• Global and seasonal average is A ~ 0.30
)1(4
4);1(
4
422
AC
TPP
TRPARCP
Eoutin
EoutEin
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
Clear Overcast
Land 0.16 0.50
Ocean 0.08 0.44
Desert 0.23
Snow 0.68
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
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%
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)