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Spanning the Gap from Bulk to Bin: A Novel Spectral Microphysics Method

De Jong, Emily K. and Bischoff, Tobias and Nadim, Ali and Schneider, Tapio (2022) Spanning the Gap from Bulk to Bin: A Novel Spectral Microphysics Method. . (Unpublished)

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Microphysics methods for climate models typically track one, two, or three moments of a droplet size distribution for various categories of liquid, ice, and aerosol. Such methods rely on conversion parameters between these categories, which introduces uncertainty into predictions. While higher-resolution options such as bin and Lagrangian schemes exist, they require too many degrees of freedom for climate modeling applications and introduce numerical challenges. Here we introduce a flexible spectral microphysics method based on collocation of basis functions. This method generalizes to a linear bulk scheme at low resolution and a smoothed bin scheme at high resolution. Tested in an idealized box setting, the method improves spectral accuracy for droplet collision-coalescence and improves precipitation predictions relative to bulk methods; furthermore, it generalizes well to multimodal distributions with less complexity than a bin method. The potential to extend this collocation representation to multiple hydrometeor classes suggests a path forward to unify liquid, ice, and aerosol microphysics in a single, flexible, computational framework for climate modeling.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper package ItemCloudy.jl package ItemLagrangian microphysics package PySDM
De Jong, Emily K.0000-0002-5310-4554
Bischoff, Tobias0000-0003-3930-2762
Nadim, Ali0000-0002-4294-3344
Schneider, Tapio0000-0001-5687-2287
Additional Information:License: Attribution-NonCommercial 4.0 International. We thank Anna Jaruga, Melanie Bieli, Clare Singer, Zach Lebo, and John Seinfeld for feedback, insights, and discussion. Additional thanks go to Jakob Shpund for providing access to the Bott flux method bin implementation. E. de Jong was supported by a Department of Energy Computational Sciences Graduate Fellowship. This research was additionally supported by Eric and Wendy Schmidt (by recommendation of Schmidt Futures) and the Heising-Simons Foundation. The implementation of basis function collocation and examples used in this work can be found in the package RBFCloud.jl at The 3-moment bulk scheme uses the package Cloudy.jl, available at, and the Lagrangian microphysics package PySDM is available at
Funding AgencyGrant Number
Department of Energy (DOE)UNSPECIFIED
Schmidt Futures ProgramUNSPECIFIED
Heising-Simons FoundationUNSPECIFIED
Record Number:CaltechAUTHORS:20220520-649616000
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:114831
Deposited By: George Porter
Deposited On:20 May 2022 20:57
Last Modified:20 May 2022 20:57

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