Fig. 2: Importance of turbulence-ice microphysics interactions.
From: Dissecting cirrus clouds: navigating effects of turbulence on homogeneous ice formation
Turbulent Damköhler number, Da, and transition length scale, L*, for homogeneous freezing vs dissipation rate of turbulence kinetic energy, ε, estimated for conditions in the upper troposphere (220 K, 230 hPa) and evaluated for a mean updraught speed of 0.1 m/s. The grey shading marks the range of ε-values frequently observed in the upper troposphere, and the orange shading indicates the range of homogeneous freezing layer depths. Da is evaluated at an average depth of 15 m. L* is defined as the length scale at which Da = 1. The dashed curve shows L* neglecting ice crystal sedimentation. Da-values are similar for conditions in the TTL (190 K, 100 hPa), but sedimentation effects are small, so that L* approximately follows the dashed curve.
