HR: 16:00h
AN: GC34A-02    [Abstracts]
TI: Proxy Measures of 4-Year Differences in Cloud Radiative Forcing Using MISR Data from the Terra Satellite
AU: * Davies, R
EM: Roger.Davies@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Moroney, C M
EM: Catherine.M.Moroney@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AB: The MISR instrument on the Terra satellite has functioned almost flawlessly since its launch in December 1999. While many of its products relating to cloud properties and top-of-atmosphere radiative fluxes are still being refined, consistently (re)processed products based on data measured in 2000 and 2004 can now be compared to examine potential trends in spectral albedo and cloud-top heights. These measures can even be interpreted as proxies of trends in cloud radiative forcing. Here we present the 4-year differences obtained so far on a seasonal, regional, and global basis. Of particular initial interest is an assessment of MISR's sensitivity to trend detection, given its careful approach to radiometric calibration, relevant to albedo trends, and to its use of purely geometric (stereo) techniques to detect trends in cloud-top heights. Preliminary analysis indicates a sampling sensitivity of approximately ñ0.002 and ñ25 m in the global, monthly, 4-year difference of spectral albedo and cloud-top height, respectively. By minimizing the uncertainties due to sampling sensitivity, it is then possible to examine trends due to other factors, including residual calibration uncertainty, as well as apparent secular, periodic and episodic changes in the climate system. While MISR makes no direct measurements of the longwave effect of clouds, changes in their height may be used as a proxy for this, noting that a height change of +200 m is roughly equivalent to an albedo reduction of 0.01 in terms of its global mean significance. Thus, comparison on this basis also provides indicators of trends in net cloud radiative forcing. So far, we note that many of the 4-year anomalies in albedo and height appear to have compensating effects, whereby higher clouds are associated with larger albedos.
DE: 1640 Remote sensing
DE: 1694 Instruments and techniques
DE: 3360 Remote sensing
SC: Global Climate Change [GC]
MN: 2005 Joint Assembly