A PDF-Based Parameterization of Subgrid-Scale Hydrometeor Transport in Deep Convection

Wong, May; Ovchinnikov, Mikhail

doi:10.1175/jas-d-16-0146.1

Cited by 2 publications

(2 citation statements)

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“…Model simulations of midlatitude continental and tropical oceanic convection analyzed in this paper are taken from Wong and Ovchinnikov (). A cloud‐resolving model called System for Atmospheric Modeling, or SAM (version 6.10.6, Khairoutdinov & Randall, ), is used to simulate two Intensive Observation Periods conducted by the U.S. Department of Energy Atmospheric Radiation Measurement Climate Research Facility over Southern Great Plains (SGP) in north central Oklahoma in June of 1997 (Xu et al, ) and near Darwin, Australia, in January of 2006 (the Tropical Warm Pool International Cloud Experiment, or TWP‐ICE; May et al, ).…”

Section: Approachmentioning

confidence: 99%

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Dependence of Vertical Alignment of Cloud and Precipitation Properties on Their Effective Fall Speeds

et al. 2019

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The vertical structure of clouds unresolved in large‐scale weather prediction and climate models is controlled by an overlap assumption. When a binary representation (cloud or no cloud) of subgrid horizontal variability is replaced by a probability density function (PDF) treatment of cloud‐related variables, a cloud occurrence overlap needs to be replaced by a PDF overlap. The PDF overlap can be quantified by a correlation length scale, z0, indicating how rapidly rank correlation of distributions at two levels diminishes with increasing level separation. In this study, we show that z0 varies widely for different properties (e.g., number and mass mixing ratios) and different hydrometeor types (cloud liquid and ice, rain, snow, and graupel) and that corresponding fall speed, Vf, is the primary factor controlling the degree of their vertical alignment, with vertical shear of the horizontal wind playing a smaller role. Linear and power law parametric relationships between z0 and Vf are derived using cloud‐resolving simulations of convection under midlatitude continental and tropical oceanic conditions, as well as observations from vertically pointing dual‐frequency radar profilers near Darwin, Australia. The functional form of z0‐Vf relationship is further examined using simple conceptual models that link variability in horizontal and vertical directions and provide insights into the role of Vf and wind shear. Being based on a physical property (i.e., fall speed) of hydrometeors rather than artificially defined and model‐specific hydrometeor types, the proposed parameterization of vertical PDF overlap can be applied to a wide range of microphysics treatments in regional and global models.

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Section: Approachmentioning

confidence: 99%

“…The slightly shortened time step for SGP reflects stricter computational stability requirements for modeling more intense vertical motions in continental compared to the maritime convection. Further datails on the model setup can be found in Wong et al () and Wong and Ovchinnikov ().…”

Section: Approachmentioning

confidence: 99%

Dependence of Vertical Alignment of Cloud and Precipitation Properties on Their Effective Fall Speeds

et al. 2019

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Parameterization of Vertical Profiles of Governing Microphysical Parameters of Shallow Cumulus Cloud Ensembles Using LES with Bin Microphysics

Khain

Heiblum

Blahak

et al. 2019

Journal of the Atmospheric Sciences

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Shallow convection is a subgrid process in cloud-resolving models for which their grid box is larger than the size of small cumulus clouds (Cu). At the same time such Cu substantially affect radiation properties and thermodynamic parameters of the low atmosphere. The main microphysical parameters used for calculation of radiative properties of Cu in cloud-resolving models are liquid water content (LWC), effective droplet radius, and cloud fraction (CF). In this study, these parameters of fields of small, warm Cu are calculated using large-eddy simulations (LESs) performed using the System for Atmospheric Modeling (SAM) with spectral bin microphysics. Despite the complexity of microphysical processes, several fundamental properties of Cu were found. First, despite the high variability of LWC and droplet concentration within clouds and between different clouds, the volume mean and effective radii per specific level vary only slightly. Second, the values of effective radius are close to those forming during adiabatic ascent of air parcels from cloud base. These findings allow for characterization of a cloud field by specific vertical profiles of effective radius and of mean liquid water content, which can be calculated using the theoretical profile of adiabatic liquid water content and the droplet concentration at cloud base. Using the results of these LESs, a simple parameterization of cloud-field-averaged vertical profiles of effective radius and of liquid water content is proposed for different aerosol and thermodynamic conditions. These profiles can be used for calculation of radiation properties of Cu fields in large-scale models. The role of adiabatic processes in the formation of microstructure of Cu is discussed.

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A PDF-Based Parameterization of Subgrid-Scale Hydrometeor Transport in Deep Convection

Cited by 2 publications

References 40 publications

Dependence of Vertical Alignment of Cloud and Precipitation Properties on Their Effective Fall Speeds

Dependence of Vertical Alignment of Cloud and Precipitation Properties on Their Effective Fall Speeds

Parameterization of Vertical Profiles of Governing Microphysical Parameters of Shallow Cumulus Cloud Ensembles Using LES with Bin Microphysics

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