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Robert Cahalan Head, Climate & Radiation Branch (Code 613.2) robert.f.cahalan@nasa.gov (301) 614-5390 Curriculum Vitae |
Education
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Research Interests
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Professional Activities and Experience
- Bob Cahalan is Project Scientist for the SOlar Radiation and Climate Experiment, or SORCE, which is part of the Earth Observing System (EOS). SORCE was built at University of Colorado's Laboratory for Atmospheric and Space Physics (LaSP), and launched in January 2003, at Kennedy Space Center on an Orbital Sciences Pegasus. To understand the scientific context of SORCE see SORCE Introduction, and to learn the specifics about SORCE, download one of these NASA publications:
- Brochure (1.4 Mb)
- Fact Sheet (164 Kb)
- Writer's Guide (504 Kb)
Background
Dr. Robert Cahalan is Head of the Climate and Radiation Branch at NASA/Goddard, which he joined in 1979, coming from NCAR in Boulder CO. He is also Visiting Senior Research Scientist at UMCP/ESSIC, Adjunct Professor of Physics at UMBC, Lead Scientist for THOR lidar, Acting Vice President of the International Radiation Commission, NASA Project Scientist for the EOS SORCE mission that launched in January 2003, Project Scientist of the International Intercomparison of 3D Radiation Codes (I3RC), and NASA representative to the U.S. Climate Change Science Program (CCSP), where he has chaired the Observations Working Group. He is a member of the DoE ARM Science Team, and the NASA EOS-Landsat Science Team. Dr. Cahalan has been a graduate advisor at universities in the USA, Canada, and the Netherlands, and Visiting Scientist at NCAR, Aspen Center for Physics, Institute of Theoretical Physics in Warsaw, and ECMWF in Reading, England. Dr. Cahalan's research focuses on climate and cloud structure, developing retrieval techniques that extend the "independent pixel approximation" (IPA) by use of 3D transfer methods, and parameterizations such as the "effective thickness approximation" (ETA) that relate cloud optical properties to cloud structure. With colleagues at GSFC and LANL Dr Cahalan led development of a new measurement approach "Thickness from Offbeam Returns", realized in Goddard's innovative THOR lidar system that combines a multiple field-of-view wide-angle receiver with 3D retrieval methods to determine the thickness of optically thick cloud layers. THOR is now being adapted to measure thickness of snow and sea ice layers. Dr. Cahalan directs the Intercomparison of 3D Radiative Codes (I3RC) that has developed a set of benchmarks used to certify 3D radiative transfer codes, and is now coordinating a community 3D coding effort.
Dr. Cahalan has also studied predictability and chaos in simple climate models, beginning with a paper on fluctuation-dissipation in stochastic energy balance models, followed by one on the diffusive "cloud dot" model,
and a paper with G. North on a stochastically forced "doubly decoupled" diffusive energy balance model. In 1990 he published a paper with his son Gabriel on "Chaotic rhythms of a dripping faucet" which uses a simple quadratic Henon model to predict chaotic intervals between successive drips of a leaky faucet for a certain range of mean drip rates, and shows successive attractor bifurcations as drip rates increase, as well as intermittency and apparent intransitivity at certain fixed drip rates. Dr. Cahalan enjoys using the "climate" of a leaky faucet to motivate discussions of the richer complexity of the climate of Earth.
Latest Publications
Miyahara, H., G. Wen, R. F. Cahalan, and A. Ohmura, 2008: Deriving Historical Total Solar Irradiance from Lunar Borehole Temperatures. Geophys. Res. Lett., 35, L02716, doi 10.1029/2007GL032171. [Abstract] [Full Text (PDF)]
Marshak, A., G. Wen, J. Coakley, L. Remer, N. G. Loeb, and R. F. Cahalan, 2008: A simple model for the cloud adjacency effect and the apparent bluing of aerosols near clouds. J. Geophys. Res., 113, D14S17, doi:10.1029/2007JD009196. [Abstract] [Full Text (PDF)]
Sud, Y. C., G. K. Walker, Y. P. Zhou, G. A. Schmidt, W. K.-M. Lau, and R. F. Cahalan, 2008: Effects of doubled CO2 on tropical Sea-Surface Temperatures (SSTs) for onset of deep convection and maximum SST – GCM simulations based inferences. Geophy. Res. Lett. 35, L12707, doi:10.1029/2008GL033872Click. [Abstract] [Full Text (PDF)]
Wen, G., A. Marshak, and R. F. Cahalan, 2008: Role of Molecular Rayleigh Scattering in the Enhancement of Clear Sky Radiance in the Vicinity of Cumulus Clouds. J. Geophys. Res (Yoram J. Kaufman Special issue). (Submitted) [Abstract] [Full Text (PDF)]
Oreopoulos, L., S. Platnick, G. Hong, P. Yang, and R. F. Cahalan, 2008: The shortwave radiative forcing bias of liquid and ice clouds from MODIS observations. J. Climate. (Submitted) [Abstract] [Full Text (PDF)]
Oreopoulos, L., R. Cahalan, and S. Platnick, 2007: The plane-parallel albedo bias of liquid clouds from MODIS observations. J. Climate, 20, 5114-5125. [Abstract] [Full Text (PDF)]
Wen, G., A. Marshak, R. F. Cahalan, L. A. Remer, and R. G. Kleidman, 2007: 3D aerosol-cloud radiative interaction observed in collocated MODIS and ASTER images of cumulus cloud fields. J. Geophys. Res., 112, D13204, doi 10.1029/2006JD008267. [Abstract] [Full Text (PDF)]
Varnai, T., and R. F. Cahalan, 2007: Potential for airborne offbeam lidar measurements of snow and sea ice thickness. J. Geophys. Res., 112, C12S90, doi:10.1029/2007JC004091. [Abstract] [Full Text (PDF)]
Wen, G., A. Marshak, and R. F. Cahalan, 2006: Impact of 3D Clouds on Clear Sky Reflectance and Aerosol Retrieval in a Biomass Burning Region of Brazil. IEEE Geo. Rem. Sens. Lett., 3, 169-172. [Abstract] [Full Text (PDF)]
Marshak, A., S. Platnick, T. Varnai, G. Wen, and R. F. Cahalan, 2006: Impact of 3D radiative effects on satellite retrievals of cloud droplet sizes. J. Geophys. Res., 111, DO9207, doi:10.1029/2005JD006686. [Abstract] [Full Text (PDF)]
Latest Images of the Week
TIM Instrument on SORCE Observes Total Solar Irradiance (TSI) During Mercury Transit (Dec 24, 2006)
Response of Lunar Climate to Historical Variation of Total Solar Irradiance (Oct 1, 2006)
The Sun's Variations as seen by SORCE’s Spectral Irradiance Monitor (SIM) (Oct 30, 2005)
Does Titan Have an Ocean? (Jan 23, 2005)
Cheyenne Meets Catarina: First South Atlantic Hurricane Ever Recorded (Oct 31, 2004)
Venus Transit Reduces Solar Energy Input to Earth (Jun 6, 2004)
THOR lidar system: Halo method determines cloud layer thicknesses using multiple fields-of-view. (Feb 15, 2004)
Pancake Sea Ice (Jan 18, 2004)