Microphysical and optical properties of cirrus and contrails: cloud field study on 13 October 1989

During the intensive International Cirrus Experiment (ICE) conducted over North Sea during the Fall of 1989, natural cirrus and contrail-induced cirrus have been analysed from in situ and remote sensing measurements (lidar and infrared radiometer). These two clouds primarily formed in a same range of altitude (8200 m/-37 C). Analysis of the measurements depicts distinctive microphysical and optical properties in the two kinds of cirrus. Natural cirrus exhibits sheared fallstreaks of ice crystals up to 750 #mu#m size near the base level. From the top to the base of this cloud the mean values of ice water content and particle concentration increase from 15 to 50 mg/m"3 and from 26 to 60 l"-"1 respectively. The corresponding visible optical depth is around 2.0. Greatest particle concentration and smallest ice crystals are measured at all levels in contrails leading to an optical depth of 0.8 in the denser cloud despite an ice water content which never exceeds 18 mg/m"3. These results are consistent with remote measurements from which the backscattering to extinction ratio k is deduced. The largest values of k (0.047 sr"-"1) are found in a young-life contrail and can be theoretically explained by a spherical shape of small ice crystals. Non-spherical ice particles with larger mean diameter are found in natural cirrus and lead to lower values of k (around 0.02 sr"-"1). (orig.)38 refs.SIGLEAvailable from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman