scholarly journals Evaluation of the Bulk Mass Flux Formulation Using Large-Eddy Simulations

2020 ◽  
Vol 77 (6) ◽  
pp. 2115-2137
Author(s):  
Jian-Feng Gu ◽  
Robert Stephen Plant ◽  
Christopher E. Holloway ◽  
Todd R. Jones ◽  
Alison Stirling ◽  
...  
Keyword(s):  
Vertical Distribution ◽  
Mass Flux ◽  
Deep Convection ◽  
Eddy Simulation ◽  
Vertical Fluxes ◽  
Bulk Mass ◽  
Flux Approximation ◽  
Large Eddy ◽  
Moisture Fluxes ◽  
Heat And Moisture

Abstract In this study, bulk mass flux formulations for turbulent fluxes are evaluated for shallow and deep convection using large-eddy simulation data. The bulk mass flux approximation neglects two sources of variability: the interobject variability due to differences between the average properties of different cloud objects, and the intraobject variability due to perturbations within each cloud object. Using a simple cloud–environment decomposition, the interobject and intraobject contributions to the heat flux are comparable in magnitude with that from the bulk mass flux approximation, but do not share a similar vertical distribution, and so cannot be parameterized with a rescaling method. A downgradient assumption is also not appropriate to parameterize the neglected flux contributions because a nonnegligible part is associated with nonlocal buoyant structures. A spectral analysis further suggests the presence of fine structures within the clouds. These points motivate investigations in which the vertical transports are decomposed based on the distribution of vertical velocity. As a result, a “core-cloak” conceptual model is proposed to improve the representation of total vertical fluxes, composed of a strong and a weak draft for both the updrafts and downdrafts. It is shown that the core-cloak representation can well capture the magnitude and vertical distribution of heat and moisture fluxes for both shallow and deep convection.

scholarly journals On the Equivalence of Two Schemes for Convective Momentum Transport

2012 ◽  
Vol 69 (12) ◽  
pp. 3491-3500 ◽  
Author(s):  
David M. Romps
Keyword(s):  
Large Eddy Simulation ◽  
Pressure Gradient ◽  
Mass Flux ◽  
Deep Convection ◽  
Momentum Transport ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Convective Momentum Transport

Abstract The Gregory–Kershaw–Inness (GKI) parameterization of convective momentum transport, which has a tunable parameter C, is shown to be identical to a parameterization with no pressure gradient force and a mass flux smaller by a factor of 1 − C. Using cloud-resolving simulations, the transilient matrix for momentum is diagnosed for deep convection in radiative–convective equilibrium. Using this transilient matrix, it is shown that the GKI scheme underestimates the compensating subsidence of momentum by a factor of 1 − C, as predicted. This result is confirmed using a large-eddy simulation.

A Simple Model of Convective Drafts Accounting for the Perturbation Pressure Term

2019 ◽  
Vol 76 (10) ◽  
pp. 3129-3149 ◽  
Author(s):  
Julien Leger ◽  
Jean-Philippe Lafore ◽  
Jean-Marcel Piriou ◽  
Jean-François Guérémy
Keyword(s):  
Shape Factor ◽  
Deep Convection ◽  
Vertical Wind Shear ◽  
Total Cell ◽  
Convection Scheme ◽  
Eddy Simulation ◽  
Downward Pressure ◽  
Pressure Term ◽  
Large Eddy ◽  
Perturbation Pressure

Abstract A simple anelastic two-column model of convective updraft accounting explicitly for the perturbation pressure term is developed. There is no vertical wind shear in the environment, and two geometries (slab or axial) are possible. A shape factor is introduced to account for transport by a nonuniform horizontal profile of the vertical velocity in the updraft and its environment. The perturbation buoyancy profile being prescribed, three parameters must be prescribed: depth and aspect ratio of the updraft and the total cell size. The model is tested for idealized buoyancy profiles and evaluated against a large-eddy simulation of daytime development of deep convection. The model behavior agrees with our understanding of the perturbation pressure within clouds. The simulated updraft quickly responds to the buoyancy field (~5 min), shorter than the convection time scale, so that a steady model could be developed. Below the updraft core, a downward pressure gradient is simulated allowing the updraft to overcome a barrier of convective inhibition. This model is designed to be implemented in a convection scheme to replace classical drag formulations of the updraft model.

scholarly journals ANÁLISE DA PROPAGAÇÃO E MANUTENÇÃO DOS VÓRTICES GERADOS POR UM MICROBURST ESTÁTICO E ISOLADO

2016 ◽  
Vol 38 ◽  
pp. 41
Author(s):  
Giuliano Demarco ◽  
Vagner Anabor ◽  
Umberto Rizza ◽  
Franciano Scremin Puhales ◽  
Luís Gustavo Nogueira Martins ◽  
...  
Keyword(s):  
Quantitative Analysis ◽  
Large Eddy Simulation ◽  
Vortex Ring ◽  
Deep Convection ◽  
Extreme Weather Events ◽  
Dynamical Process ◽  
Eddy Simulation ◽  
Wind Gusts ◽  
Weather Events ◽  
Large Eddy

The Southern Brazilian region is specially affected by extreme weather events, very often intense wind gusts coming from deep convection may develop itself as a microburst producing winds higher than 100 km/h. In order to understand the physical and dynamical process evolved in this phenomena, a static and isolated microburst is produced through a Large Eddy Simulation. A quantitative analysis of propagation an maintenance of the microburst vortex ring is performed in order to understand its evolution.

scholarly journals On the Parameterization of Convective Downdrafts for Marine Stratocumulus Clouds

2020 ◽  
Vol 148 (5) ◽  
pp. 1931-1950 ◽  
Author(s):  
Elynn Wu ◽  
Handa Yang ◽  
Jan Kleissl ◽  
Kay Suselj ◽  
Marcin J. Kurowski ◽  
...  
Keyword(s):  
Mass Flux ◽  
Turbulent Transport ◽  
Eddy Diffusivity ◽  
Moisture Profile ◽  
Marine Stratocumulus ◽  
Eddy Simulation ◽  
Single Column ◽  
Stratocumulus Clouds ◽  
Heat And Moisture Transport ◽  
Heat And Moisture

Abstract The role of nonlocal transport on the development and maintenance of marine stratocumulus (Sc) clouds in coarse-resolution models is investigated, with a special emphasis on the downdraft contribution. A new parameterization of cloud-top-triggered downdrafts is proposed and validated against large-eddy simulation (LES) for two Sc cases. The applied nonlocal mass-flux scheme is part of the stochastic multiplume eddy-diffusivity/mass-flux (EDMF) framework decomposing the turbulent transport into local and nonlocal contributions. The complementary local turbulent transport is represented with the Mellor–Yamada–Nakanishi–Niino (MYNN) scheme. This EDMF version has been implemented in the Weather Research and Forecasting (WRF) single-column model (SCM) and tested for three model versions: without mass flux, with updrafts only, and with both updrafts and downdrafts. In the LES, the downdraft and updraft contributions to the total heat and moisture transport are comparable and significant. The WRF SCM results show a good agreement between the parameterized downdraft turbulent transport and LES. While including updrafts greatly improves the modeling of Sc clouds over the simulation without mass flux, the addition of downdrafts is less significant, although it helps improve the moisture profile in the planetary boundary layer.

scholarly journals A Mixed Scheme for Subgrid-Scale Fluxes in Cloud-Resolving Models

2010 ◽  
Vol 67 (11) ◽  
pp. 3692-3705 ◽  
Author(s):  
C.-H. Moeng ◽  
P. P. Sullivan ◽  
M. F. Khairoutdinov ◽  
D. A. Randall
Keyword(s):  
Deep Convection ◽  
A Priori ◽  
Subgrid Scale ◽  
Eddy Simulation ◽  
Mixed Scheme ◽  
Lower Cloud ◽  
Large Eddy ◽  
Momentum Fluxes ◽  
Tropical Deep Convection ◽  
Relationship Of

Abstract A large-domain large-eddy simulation of a tropical deep convection system is used as a benchmark to derive and test a mixed subgrid-scale (SGS) scheme for scalar and momentum fluxes in cloud-resolving models (CRMs). The benchmark simulation resolves a broad range of scales ranging from mesoscale organizations, through gravity waves and individual clouds, down to energy-containing turbulent eddies. A spectral analysis shows that the vertical-velocity kinetic energy peaks at scales from hundreds of meters in the lower cloud layer to several kilometers higher up; these scales are typical grid sizes of today’s CRMs. The analysis also shows that a significant portion of the scalar and momentum fluxes in the benchmark simulation are carried by motions smaller than several kilometers (i.e., smaller than a typical grid resolution of CRMs). The broad range of scales of the benchmark simulation is split into two components: filter scale (mimicking CRM resolvable scale) and subfilter scale (mimicking CRM SGS), using filter widths characteristic of a typical CRM grid spacing. The local relationship of the subfilter-scale fluxes to the filter-scale variables is examined. This leads to a mixed SGS scheme to represent the SGS fluxes of scalars and momentum in CRMs. A priori tests show that the mixed SGS scheme yields spatial distributions of subfilter-scale fluxes that correlate much better with those retrieved from the benchmark when compared with an eddy viscosity/diffusivity scheme that is commonly used in today’s CRMs.

scholarly journals The Atmospheric Overturning Induced by Hector the Convector

2017 ◽  
Vol 74 (10) ◽  
pp. 3271-3284 ◽  
Author(s):  
Thibaut Dauhut ◽  
Jean-Pierre Chaboureau ◽  
Patrick Mascart ◽  
Olivier Pauluis
Keyword(s):  
Gravity Waves ◽  
Lower Stratosphere ◽  
Deep Convection ◽  
Lower Troposphere ◽  
Convective System ◽  
Entrainment Rate ◽  
Northern Australia ◽  
Upper Troposphere ◽  
Eddy Simulation ◽  
Large Eddy

Abstract The overturning of Hector the Convector, a tropical multicellular convective system of northern Australia that regularly overshoots into the stratosphere, is synthesized at the scale of a large-eddy simulation. The isentropic analysis offers the advantage of filtering out the reversible motions due to gravity waves and taking into account the turbulent fluxes that contribute to the vertical transport. Two key circulations are characterized: the troposphere deep overturning and the mass exchange due to the overshoots into the stratosphere. The transition from deep to very deep convection is associated with a change in the diabatic tendency inside the tallest updrafts: the latent heat release due to the formation of a large amount of icy hydrometeors exceeds the loss of energy due to mixing with the drier, colder air of the environment. In agreement with a previous study of Hector examining the properties of its two tallest updrafts, the entrainment rate exhibits a minimum during the very deep convection phase as low as 0.04 km−1. The overturning intensity corroborates the Eulerian computation of the vertical mass flux in the midtroposphere and in the lower stratosphere. It however gives a lower estimate of the flux in the upper troposphere, filtering out the reversible motions, and a larger estimate in the lower troposphere and at the tropopause, where slow vertical motions contribute significantly to the transport.

scholarly journals A Closure for Updraft–Downdraft Representation of Subgrid-Scale Fluxes in Cloud-Resolving Models

2014 ◽  
Vol 142 (2) ◽  
pp. 703-715 ◽  
Author(s):  
Chin-Hoh Moeng
Keyword(s):  
Deep Convection ◽  
Eddy Diffusivity ◽  
Subgrid Scale ◽  
Model Framework ◽  
Horizontal Gradients ◽  
Eddy Simulation ◽  
Viscosity Models ◽  
Closure Scheme ◽  
Large Eddy ◽  
Convection Layer

Abstract A closure relationship between subgrid-scale (SGS) updraft–downdraft differences and resolvable-scale (RS) variables is proposed and tested for cloud-resolving models (CRMs), based on a data analysis of a large-eddy simulation (LES) of deep convection. The LES flow field is partitioned into CRM-RS and CRM-SGS using a cutoff scale that corresponds to a typical CRM grid resolution. This study first demonstrates the capability of an updraft–downdraft model framework in representing the SGS fluxes of heat, moisture, and momentum over the entire deep convection layer. It then formulates a closure scheme to relate SGS updraft–downdraft differences to horizontal gradients of RS variables. The closure is based on the idea that largest SGS and smallest RS motions are spectrally linked and hence their horizontal fluctuations must be strongly communicated. This relation leads to an SGS scheme that expresses vertical SGS fluxes in terms of horizontal gradients of RS variables, which differs from conventional downgradient eddy diffusivity models. The new scheme is shown to better represent the forward and backscatter energy transfer between CRM-RS and CRM-SGS components than conventional eddy-viscosity models.

Convective Bursts, Downdraft Cooling, and Boundary Layer Recovery in a Sheared Tropical Storm

2013 ◽  
Vol 141 (3) ◽  
pp. 1048-1060 ◽  
Author(s):  
John Molinari ◽  
Jaclyn Frank ◽  
David Vollaro
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Potential Temperature ◽  
Tangential Velocity ◽  
Vertical Wind Shear ◽  
Surface Heat ◽  
Tropical Storm ◽  
Convective Bursts ◽  
Moisture Fluxes ◽  
Heat And Moisture

Abstract Tropical Storm Edouard (2002) experienced episodic outbreaks of convection downshear within the storm core in the presence of 11–15 m s−1 of ambient vertical wind shear. These outbreaks lasted 2–6 h and were followed by long periods with no deep convection. Flights from U.S. Air Force reconnaissance aircraft within the boundary layer were used to investigate the cause of one such oscillation. Low equivalent potential temperature θe air filled the boundary layer as convection ceased, creating a 4–6-K deficit in θe within the convective region. Soundings within 110 km of the center were supportive of convective downdrafts, with midlevel relative humidity below 15% and large downdraft CAPE. Deep convection ceased within 75 km of the center for more than 8 h. Tangential velocity reached hurricane force locally during the convective outbreak, then became nearly symmetric after convection stopped, arguably as a result of axisymmetrization, and the storm weakened. Nevertheless, the corresponding lack of convective downdrafts during this period allowed surface heat and moisture fluxes to produce substantial increases in boundary layer entropy. A new burst of convection followed. Consistent with recent papers it is argued that tropical cyclone intensification and decay can be understood as a competition between surface heat and moisture fluxes (“fuel”) and low-entropy downdrafts into the boundary layer (“antifuel”).

Sign in / Sign up

Export Citation Format

Share Document