Simultaneous evaluation of ice cloud microphysics and nonsphericity of the cloud optical properties using hydrometeor video sonde and radiometer sonde in situ observations

This study utilizes hydrometeor sonde and radiometer sonde in situ observations to simultaneously evaluate ice cloud microphysics and radiative fluxes. In addition, the impact of nonsphericity and heterogeneous ice nucleation schemes on radiative fluxes are examined using a double-moment bulk cloud microphysics scheme on a midlatitude frontal system. The distribution of simulated outgoing longwave radiation (OLR) is systematically reduced by assuming the presence of columnar ice crystals instead of planar ice crystals because of the difference in the effective radii (the projected area) between the two shapes. However, the choice of the heterogeneous ice nucleation schemes drastically changes the distribution of OLR by modifying the number concentration of the cloud ice (Ni) (more than tenfold). The observed shortwave fluxes are useful for evaluating the simulated number concentration of cloud ice when nonspherical single scattering properties are used instead of spherical single scattering properties. The dependence of the asymmetry factor on the effective radius is the key to quantitatively estimating the ice cloud radiative forcing and determining the aerosol indirect effect on ice clouds. Based on the comparison of shortwave fluxes, the cloud microphysics scheme was found to underestimate the Ni near the cloud base (a robust bias). A possible method of modifying the bias is discussed.