95-GHZ POLARIMETRIC RADAR MEASUREMENTS OF OROGRAPHIC CAP CLOUDS

The use of millimeter-wavelength radars for cloud microphysical resear ch was investigated in experiments at the Elk Mountain Observatory nea r Laramie, Wyoming, between April 1990 and March 1992. The 95-GHZ pola rimetric radar used in these experiments is a portable, high-power, du al-polarization radar capable of characterizing the complex scattering matrix in two pulses. The scatterer's polarimetric response is charac terized in terms of the Mueller matrix, a form that is seen to be conv enient for computing the response of a scatterer for any arbitrary com bination of transmit and receive antenna polarizations. This paper sum marizes the results of recent experiments carried out at the Elk Mount ain Observatory. Polarimetric data from orographic cap clouds are foun d to be sensitive to ice-particle orientation and composition. Compari son of radar-observed reflectivities with those computed from in situ images shows good agreement if the volume fraction of ice in ice-air m ixtures is taken into account.