Climate physics

The highlight of 2006 was the discovery of a significant decrease in global albedo from time series analysis of Multiangle Imaging Spectro-Radiometer (MISR) measurements. This appears to occur mainly during the northern latitude late Spring due to reduction in sea ice. At the same time, the apparently secular decrease in tropical high clouds, which had been noted from 2000 through 2005 appears to have reversed during 2006, possibly due the onset of the latest El Nino. Both of these interannual anomalies are significant factors affecting the rate of global warming, and whether or not they are sustained over the next few years will continue to be of great interest.

Height-resolved wind fields are not measured accurately over much of the globe due to sparse sampling by the radiosonde network. This puts a major crimp on operational weather prediction. A totally new technique for measuring these fields globally has been developed, using multi-angle measurements from a polar orbiter. Preliminary findings were published in previous years. This research reached maturity in 2006 with enhancements that significantly improved both the precision and quality control of the retrieved winds. Professor Roger Davies led this work in collaboration with a group at the Jet Propulsion Laboratory (JPL).

This research, involving a geometric stereo technique of operational pattern matching of cloud reflectivity to retrieve their (wind corrected) heights is now relatively mature and a paper describing comparison with other measures appeared in the International Journal of Remote Sensing. The cloud height work was led by R Davies, and the comparison effort was led by G. Seiz at ETH, Zurich.

One of the greatest challenges in the remote sensing of cloud properties is the treatment of complex geometry, and the need for a three-dimensional radiative transfer approach. Significant progress was made on this problem during 2006, firstly with a published study (in Remote Sensing of Environment) of the reconstruction of a deep convective cloud shape using multi-angle satellite measurements, and secondly with conference presentations of preliminary findings on the optical properties of this cloud by comparison against a three-dimensional radiative transfer model. Of particular interest is the new-found ability to handle cases of large optical depth that would otherwise be unattainable from space.

Research undertaken by a PhD student showed that the optical and microwave retrievals of cloud water for a variety of tropical clouds agree reasonably well when the clouds are small, but disagree substantially as the clouds become thicker, with neither technique appearing to make a useful measurement for the thickest cases.

In collaboration with the group led by N Loeb at NASA Langley, we published a paper in the Journal of Geophysical Research (JGR) on the fusion of measurements between the three instruments. While somewhat routine, this paper serves a useful check on the relative calibration stability of these instruments.

Again in collaboration with the group led by N Loeb at NASA Langley, we published a paper in GRL that shows excellent agreement between albedos estimated by MISR and CERES, made from the same satellite, but applying completely independent angular models.

For more information on any of the research areas above, please contact:

Professor Roger Davis
Phone: +64 9 373 7599 ext 88868
Email: r.davis@auckland.ac.nz

Or visit the profile of Professor Roger Davis.