Modeling of Cloud Microphysics: Can We Do Better?

Abstract

Representation of cloud microphysics is a key aspect of simulating clouds. From the early days of cloud modeling, numerical models have relied on an Eulerian approach for all cloud and thermodynamic and microphysics variables. Over time the sophistication of microphysics schemes has steadily increased, from simple representations of bulk masses of cloud and rain in each grid cell, to including different ice particle types and bulk hydrometeor concentrations, to complex schemes referred to as bin or spectral schemes that explicitly evolve the hydrometeor size distributions within each model grid cell. As computational resources grow, there is a clear trend toward wider use of bin schemes, including their use as benchmarks to develop and test simplified bulk schemes. We argue that continuing on this path brings fundamental challenges difficult to overcome. The Lagrangian particle-based probabilistic approach is a practical alternative in which the myriad of cloud and precipitation particles present in a natural cloud is represented by a judiciously selected ensemble of point particles called superdroplets or superparticles. The advantages of the Lagrangian particle-based approach when compared to the Eulerian bin methodology are explained, and the prospects of applying the method to more comprehensive cloud simulations—for instance, targeting deep convection or frontal cloud systems—are discussed.

Combining In Situ and Satellite Observations to Understand the Vertical Structure of Tropical Anvil Cloud Microphysical Properties During the TC4 Experiment

“…In spite of increasing attention, representation of cloud properties and microphysical processes in numerical models is nevertheless ambiguous (Boucher et al, 2013; Grabowski et al, 2019; Jiang et al, 2012; Randall et al, 2007; Su et al, 2013). Cloud vertical structures at regional scale are critical in predicting future climate in climate models (Cesana & Chepfer, 2012).…”

“…The vertically inhomogeneous structures of clouds are important considerations for theoretical cloud modeling, satellite remote sensing, and in situ observations (e.g., Feofilov et al, 2015; Grabowski et al, 2019; Hashino et al, 2013; Korolev et al, 2017; Reinhart et al, 2014; Seo & Biggerstaff, 2006). Often, the inhomogeneous structures of clouds are quantitatively represented by the vertical variability of microphysical properties for different hydrometeor species in the atmosphere, which often vary over certain range and covary with each other.…”

Comparison of a Spectral Microphysics and a Two-Moment Cloud Scheme: Numerical Simulations of the Cloud-Topped Marine Boundary Layer

“…In the literature, a large number of spectral and bulk microphysics cloud schemes of different complexity exists ranging from simple one-or two-moment schemes with the cloud-water mixing ratio, or both the cloud-water mixing ratio and the total droplet number concentration, as prognostic variables (e.g., Kessler 1969;Sundqvist et al 1989;Khairoutdinov and Kogan 2000;Milbrandt and Yau 2005;Morrison et al 2005;Morrison and Gettelman 2008;Lim and Hong 2010), to spectral approaches where cloud and raindrops are represented by particle size distributions (e.g., Clark 1973;Kogan 1991;Lynn et al 2005;Khain et al 2009Khain et al , 2015. Grabowski et al (2019) present a comprehensive overview of progress in the field of cloud microphysical parametrizations made during the last decades. Several studies exist dealing with a comparison of spectral versus bulk microphysics cloud schemes (e.g., Khain et al 2009;Fan et al 2012;Lee and Baik 2018).…”

Multi-layer Cloud Conditions in Trade Wind Shallow Cumulus – Confronting Models with Airborne Observations

“…However, there are several other factors to be considered (Lamer et al, 2018). On the one hand, particle size distributions (PSDs) in models are typically represented by bulk 35and spectral microphysical schemes, or Lagrangian superparticles (e.g., Grabowski et al, 2019). Bulk microphysics schemes predict changes in condensate using one to three moments.…”

“…and spectral microphysical schemes, or Lagrangian superparticles (e.g., Grabowski et al, 2019). Bulk microphysics schemes predict changes in condensate using one to three moments.…”