Parameterization of Cloud Microphysics Based on the Prediction of Bulk Ice Particle Properties. Part II: Case Study Comparisons with Observations and Other Schemes

Abstract

A new microphysics scheme has been developed based on the prediction of bulk particle properties for a single ice-phase category, in contrast to the traditional approach of separating ice into various predefined species (e.g., cloud ice, snow, and graupel). In this paper, the new predicted particle properties (P3) scheme, described in Part I of this series, is tested in three-dimensional simulations using the Weather Research and Forecasting (WRF) Model for two contrasting well-observed cases: a midlatitude squall line and winter orographic precipitation. Results are also compared with simulations using other schemes in WRF. Simulations with P3 can produce a wide variety of particle characteristics despite having only one free ice-phase category. For the squall line, it produces dense, fast-falling, hail-like ice near convective updraft cores and lower-density, slower-falling ice elsewhere. Sensitivity tests show that this is critical for simulating high precipitation rates observed along the leading edge of the storm. In contrast, schemes that represent rimed ice as graupel, with lower fall speeds than hail, produce lower peak precipitation rates and wider, less distinct, and less realistic regions of high convective reflectivity. For the orographic precipitation case, P3 produces areas of relatively fast-falling ice with characteristics of rimed snow and low- to medium-density graupel on the windward slope. This leads to less precipitation on leeward slopes and more on windward slopes compared to the other schemes that produce large amounts of snow relative to graupel (with generally the opposite for schemes with significant graupel relative to snow). Overall, the new scheme produces reasonable results for a reduced computational cost.

McSnow: A Monte‐Carlo Particle Model for Riming and Aggregation of Ice Particles in a Multidimensional Microphysical Phase Space

“…Hence, various attempts have been made to introduce additional prognostic variables like a bulk rimed mass or particle volume to overcome these issues (Connolly et al, ; Mansell et al, ; Milbrandt & Morrison, ; Morrison & Grabowski, ; Stoelinga et al, ). The most advanced bulk approach in this regard is the predicted particle properties (P3) scheme (Milbrandt & Morrison, 2016; Morrison & Milbrandt, ; Morrison et al, ). Besides mass and number, this scheme predicts the rime mass and the rime volume.…”

Uncertainty from the choice of microphysics scheme in convection-permitting models significantly exceeds aerosol effects

“…Such limitations have led to the development in more recent years of new representations of ice microphysics in bulk schemes, such as approaches which separately prognose ice mass mixing ratios grown by riming and vapour deposition (Morrison and Grabowski, 2008), approaches where particle habit evolution is predicted by prognosing the mixing ratios of ice crystal axes (Harrington et al, 2013) and approaches where ice-phase particles are represented by several physical properties that evolve freely in time and space (Morrison and Milbrandt, 2015). Although these developments are relatively new, they have already been shown to improve simulations of observed squall lines and orographic precipitation when compared to traditional two-moment bulk schemes (Morrison et al, 2015a).…”

Thermodynamic Constraints on the Morphology of Simulated Midlatitude Squall Lines

“…2a and 2b, respectively; see also thick solid FIG. This sounding is similar to those used in several numerical studies of idealized SLs (e.g., Rotunno et al 1988;Weisman et al 1988;Weisman 1992Weisman , 1993Bryan et al 2003;Weisman and Rotunno 2004;Bryan 2005;Bryan et al 2006;Morrison et al 2009;Seigel et al 2013). Schematic representation of the type of soundings under consideration as displayed on a skew T-lnp chart.…”

“…The conserved thermodynamic variable in SAM is the liquid/ice water static , and the convective inhibition (CIN) are in units of J kg 21 , ICAPE is in J m 22 3 10 26 , and PW is in kg m 22 . A version of the doublemoment microphysics parameterization of Morrison et al (2005) was employed for cloud (water and ice) and precipitating (rain, snow, and graupel) phenomena. The definition of DCAPE is as in Gilmore and Wicker (1998) energy; consequently, moist static energy in temperature units h is used instead of equivalent potential temperature.…”