In situ observation of cirrus scattering phase functions with 22 degrees and 46 degrees halos: Cloud field study on 19 February 1998

Observations of halos and related phenomena due to ice crystals are commonl y reported from ground observations and presented in the literature. Nevert heless, ice crystal characteristics have only been poorly documented from i n situ measurements performed in halo-producing cirrus with simultaneous ob servations of optical phenomena. Using the Polar Nephelometer, a new instru ment for in situ measuring of the scattering phase function of cloud drople ts and ice particles, 22 degrees and 46 degrees halo features have been evi denced during a cirrus uncinus cloud case study between -30 degreesC and -3 8 degreesC. Simultaneous microphysical measurements were made with a 2D-C p robe manufactured by Particle Measuring Systems Inc. (PMS). The results sho w that ice crystal properties derived from 2D-C measurements do not present substantial differences when comparing cirrus cloud samples with and witho ut halos. Consequently, the cloud scattering properties appear to be domina ted by small ice particles (smaller than about 100 mum), which are poorly d ocumented with conventional PMS probes. The halo occurrences are observed i n only a few cloud portions (2%), which are characterized by small horizont al scales (100-400 m). Furthermore, the observed 22 degrees and 46 degrees peak features are smoothed out with regard to modeling results relative to geometric pristine-crystal shape. These differences are discussed by using the new Inhomogeneous Hexagonal Monocrystal theoretical model of light scat tering.