Influence of low-level blocking and turbulence on the microphysics of a mixed-phase cloud in an inner-Alpine valley

Abstract. Previous studies that investigated orographic precipitation have primarily focused on isolated mountain barriers. Here we investigate the influence of low-level blocking and shear-induced turbulence cloud microphysics formation in a complex inner-Alpine valley. The analysis focuses mid-level post-frontal environment feeder induced by an in-valley circulation. Observations were obtained from extensive set instruments including ground-based remote sensing instrumentation, situ instrumentation tethered-balloon system measurements. During this event, boundary layer was characterized blocked flow enhanced region strong vertical wind shear at between valley stronger cross-barrier aloft. Cloud radar observations indicated changes microphysical properties within turbulent linear depolarization ratio (i.e., change particle shape or density) increased reflectivity ice growth). Based habits observed surface, suggest riming, aggregation needle growth occurred layer. Collisions fragile crystals (e.g., dendrites, needles) Hallett–Mossop process might contributed to secondary production. Additionally, presence above small-scale topographic feature, which dissipated when turned unblocked state. Our indicate (due downstream barrier) created circulation, led production local updrafts cloud. Although did not enhance particular case (since majority sublimated falling through subsaturated above), propose effects such as can induce clouds valleys leeward slope foothills upstream main barrier, where they act seeder–feeder mechanism.