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We present 870 $\mu$m ALMA polarization observation toward the ClassI\hspace{-.1em}I protoplanetary disk around AS 209, which has concentric,multiple gaps and rings. We successfully detect the polarized emission and findthat the polarization orientations and fractions have distinct characteristicsbetween the inner and outer regions. In the inner region, the polarizationorientations are parallel to the minor axis of the disk, which is consistentwith the self-scattering model. The mean polarization fraction in the region is$\sim$0.2\%, which is lower than the expected value when the grains have themaximum polarization efficiency, which corresponds to $\lambda$/2$\pi$ $\sim$140 $\mu$m in grain radius. In the outer region, we detect $\sim$1.0\%polarization and find that the polarization orientations are almost in theazimuthal directions. Moreover, the polarization orientations have systematicangular deviations from the azimuthal directions with $\Delta$$\theta$ $\sim$4\fdg5 $\pm$ 1\fdg6. The pattern is consistent with a model that radiallydrifting dust grains are aligned by the gas flow against the dust grains. Weconsider possible scenarios of the grain dynamics at the AS 209 ring which canreproduce the polarization pattern. However, the directions of the observedangular deviations are opposite to what is predicted under the fact that thedisk rotates clockwise. This poses a question in our understandings of thealignment processes and/or grain dynamics in protoplanetary disks.

An Observational Study for Grain Dynamics in the AS 209 Disk with Submillimeter Polarization