The Project Components

Compilation of regional cirrus physical and microphysical properties
The First ISCCP Regional Experiment (FIRE), the European Cloud and Radiation Experiment (EUCREX), the Central Equatorial Pacific Experiment (CEPEX) and the SUbsonic aircraft Contrail and Cloud Effects Special Study (SUCCESS) provide measurements of ice particle size distribution, shape information and cloud geometries which will be analysed from a global perspective.
Angular behaviour and polarisation of observed and modelled cirrus using POLDER
The imaging radiometer-polarimeter POLDER (Polarisation of Earth's Reflectances) onboard the Japanese satellite ADEOS measures multi-angular polarised reflectances of the solar radiation in up to 14 viewing angles in eight narrow spectral bands. These are very sensitive to the shape of scatterers, and therefore POLDER is well adapted to determine the dominating shape of ice crystals in cirrus clouds, in addition to the cirrus cloud optical thickness and height.
Angular and spectral behaviour of observed and modelled cirrus using ATSR-2
ATSR-2 onboard the European satellite ERS-2 measures narrow-band radiances over a spectral range covering infrared to visible wavelengths at two viewing geometries. This instrument has the best spatial resolution (1 to 3 km), and allows an independent retrieval of cirrus microphysical properties (shape and size) and physical properties (cloud height, optical depth and ice water path).
Long-term retrieval of cirrus effective mean ice crystal sizes from TOVS
The relatively high spectral resolution of the TIROS-N Operational Vertical Sounder (TOVS) system onboard the NOAA polar orbiters makes these instruments especially reliable for the retrieval of cirrus properties. The NOAA/NASA Pathfinder TOVS Path-B data set provides eight years of atmospheric temperature and water vapour profiles as well as cloud and surface properties. In addition to cloud height and emissivity we will retrieve mean effective ice crystal sizes for cirrus clouds by taking advantage of the dependence of spectral cirrus emissivity differences on this parameter.
Sensitivity analysis of computed fluxes to changes in cirrus microphysics
Although ice crystals have complicated non-spherical shapes, in most GCM's their radiative properties are still calculated using an assumption of sphericity. Nevertheless, using more realistic shapes and sizes in a GCM can result in large changes in the radiative fluxes which drive the atmospheric circulation. For reliable predications of climate change and natural hazards it is essential to assume the correct size and shapes of ice crystals and to compute their radiative properties accurately. To improve the calculation of cirrus radiative properties in CGM's, we will compare different models for simulating solar and thermal fluxes and investigate their sensitivity to the microphysical properties of the crystals.
Effect of parametrisations on radiative fluxes using co-locates TOVS-ScaRaB observations
The radiation effect due to changes of microphysical properties within cirrus clouds can be very important. Therefore the correlations between cirrus micro- and macrophysical properties can be tested by integrating them together with TOVS-retrieved cirrus macrophysical properties into advanced radiative tranfer computations (which take into account the non-sphericity of the ice crystals) and by comparing the computed radiative fluxes to the cirrus associated radiative fluxes provided by the Scanner for Radiation Budget (ScaRaB) instrument onboard the Russian Meteor-3/7 satellite. For this quantitative analysis we will develop angular direction models (ADMs), taking care of the anisotropy of the underlying scene, using a combination of neural network techniques and Monte Carlo simulations.

Last modified: Tue Mar 20 15:57:43 MET 2001