Hugh Morrison & Jason A. Milbrandt JAS (2015), p287-311 Parameterization of Cloud Microphysics Based on the Prediction of Bulk Ice Particle Properties. Part I: Scheme Description and Idealized Tests Hugh Morrison & Jason A. Milbrandt JAS (2015), p287-311

Introduction Liquid water: Cloud (< 50-100 μm) growing mainly by vapor diffusion. Rain growing primarily by collision-coalescence Ice particles have a wide range of densities and complex shapes A large sensitivity with ice is partitioned into categories, and changes in thresholds or rates for conversion between ice species in simulations.

overview Predicted Particle Properties (P3) scheme To track particle evolution mechanisms of ice growth [vapor deposition, aggregation and riming (dry and wet growth)] Prognostic variables (dynamical tendencies from advection and subgrid-scale mixing and microphysical tendency) & predicted quantities (derived directly from the prognostic variables) total ice mass (qi), ice number (Ni) ice mass from rime growth (qrim), bulk rime volume (Brim)

(From Ahrens，p.132) 水氣結冰在物体上，成為霜。 (From Ahrens，p.191) 過冷水滴碰上任何0oC以下固體，會快速在固體上結成霜狀冰，此過程稱為淞化(rime)。冰晶在下降過程中，因下降速度大於小水滴，沿途可以併吞過冷水滴而迅速成長。在劇烈對流中，可以形成冰雹 (From Ahrens，p.200) (From Ahrens，p.201)

ice mass from rime growth (qrim), bulk rime volume (Brim) Fr: mass fraction mva: the crystal mass grown by vapor diffusion and aggregation mr: the total particle mass of a partially rimed crystal Dth: critical sizes separating small spherical ice from dense nonspherical (or unrimed) ice Dgr: dense nonspherical ice from graupel Dcr: graupel from partially rimed crystals

RS: rimed snow GS: graupel-like snow LG: lump graupel Dm dominated by small spherical ice

Idealized 2D squall-line simulations WRF3.4.1 Δx = 1 km (500 km), with 80 vertical levels (20 km) Baseline results Ice is initiated after approximately 10 min Significant horizontal asymmetry develops over time in response to the environmental shear After 4 h the storm reaches a mature phase (leading edge of convection and trailing stratiform precipitation)

Vertical cross sections for BASE at 2 h

Vertical cross sections for BASE at 6 h mva mr Front to rear at midlevels (4-8 km) general decrease in D, F, ρand V

Idealized 2D squall-line simulations Sensitivity test qi (color) averaged from 3.5 to 4.5 h θ’ (counter) at 4.5 h

Discussion and conclusions I Uncertain: aggregation and riming efficiencies parameters associated with melting and vapor diffusion  require close coordination with additional OBS studies This does not preclude more than one free ice-phase category in the same grid box and time. One of the main limitations of the current P3 scheme: its inability to represent different ice types in the same location and time for a given particle size

Discussion and conclusions II Idealized 2D squall-line sensitivity tests showed the impacts of Fr and ρr on the mass of ice condensate aloft and the surface precipitation rate. Fr > 0.7 in locations without liquid water in the convective region Fr ~ 0.05-0.3 for locations in the stratiform region from liquid water The addition of prognostic variables (qrim, Brim) is needed. @ 6h