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We study the $3~\mu$m scattering feature of water ice detected in the outerdisk of HD 142527 by performing radiative transfer simulations. We show that anice mass abundance at the outer disk surface of HD 142527 is much lower thanestimated in a previous study. It is even lower than inferred from far-infraredice observations, implying ice disruption at the disk surface. Next, wedemonstrate that a polarization fraction of disk-scattered light varies acrossthe ice-band wavelengths depending on ice grain properties; hence, polarimetricspectra would be another tool for characterizing water-ice properties. Finally,we argue that the observed reddish disk-scattered light is due to grains with afew microns in size. To explain the presence of such grains at the disksurface, we need a mechanism that can efficiently oppose dust settling. If weassume turbulent mixing, our estimate requires $\alpha\gtrsim2\times10^{-3}$,where $\alpha$ is a non-dimensional parameter describing the vertical diffusioncoefficient of grains. Future observations probing gas kinematics would behelpful to elucidate vertical grain dynamics in the outer disk of HD 142527.

The water-ice feature in near-infrared disk-scattered light around HD 142527: Micron-sized icy grains lifted up to the disk surface?