ABSTRACT
More accurate methods to measure the ice water content of cirrus
clouds are needed. We propose to attempt this difficult measurement
using the University of Wisconsin High Spectral Resolution Lidar
(HSRL) and radar observations. The HSRL provides calibrated
measurements of the scattering cross section. Because cirrus particles
are large compared to the 532 nm wavelength transmitted by the lidar,
the scattering cross section is just 2 times the total area of
particles per unit volume. Because ice crystals are non-spherical and
often oriented by the aerodynamic forces it is important to note that
this is the particle area projected on a plane perpendicular to the
lidar beam. We are currently working to measure the effective radius
of the ice particles (again projected on a plane perpendicular to the
lidar beam) by observing multiple scattering in the lidar beam. Theory
shows that the multiple scattering is robustly related to the angular
width of the diffraction peak in the scattering phase function and
this width is a directly related to particle area. Together these
measurements provide the cross sectional area per particle and the
total number of particles. The fall velocity of ice crystals is dependent
on the horizontal projection of the particle area and on the particle mass.
Thus, Doppler fall velocities measured by radar coupled with
HSRL measurements offer the potential to determine ice water mass. This
poster describes progress on this recently initiated project.
UW Lidar // April 5, 2001 // root@lidar.ssec.wisc.edu