scholarly journals Convective Organization in Evolving Large-Scale Forcing Represented by a Highly Truncated Numerical Archetype

2018 ◽  
Vol 75 (8) ◽  
pp. 2827-2847 ◽  
Author(s):  
Jun-Ichi Yano ◽  
Mitchell W. Moncrieff
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Momentum Transport ◽  
Phase Iii ◽  
Cold Pools ◽  
Time Period ◽  
Toga Coare ◽  
Data Source ◽  
Convective Momentum Transport ◽  
Convection Parameterization

Abstract Considered as a prognostic generalization of mass-flux-based convection parameterization, the highly truncated nonhydrostatic anelastic model with segmentally constant approximation (NAM–SCA) is tested with time-evolving large-scale forcing. The 20-day GATE Phase III period is taken as a major data source. The main advantage of the NAM–SCA parameterization is consistency with subgrid-scale dynamics as represented by the nonhydrostatic anelastic formulation. The approach explicitly generates important dynamical structures of convection (e.g., mesoscale circulations, cold pools) spontaneously without further tuning or treatment as additional subcomponents. As with other convection parameterizations, the numerical simulation of the precipitation rate, the apparent heat source, and the apparent moisture sink is straightforward and reasonably insensitive to the numerical procedures. However, convective momentum transport by organized convection turns out to be difficult even with NAM–SCA, especially for the inherently three-dimensional shear-parallel systems. Modifications of NAM–SCA regarding the large-scale forcing formulation improves the mesoscale momentum transport. Simulation of the full 120-day TOGA COARE period demonstrates the performance of NAM–SCA in different meteorological conditions and its capacity to operate over a longer time period.

scholarly journals Cloud-Resolving Model Simulations of KWAJEX: Model Sensitivities and Comparisons with Satellite and Radar Observations

2007 ◽  
Vol 64 (5) ◽  
pp. 1488-1508 ◽  
Author(s):  
Peter N. Blossey ◽  
Christopher S. Bretherton ◽  
Jasmine Cetrone ◽  
Marat Kharoutdinov
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Longwave Radiation ◽  
Radiative Fluxes ◽  
Model Simulations ◽  
Time Period ◽  
Ground Validation ◽  
Cloud Resolving Model ◽  
Sensitivity Studies ◽  
Upper Level

Abstract Three-dimensional cloud-resolving model simulations of a mesoscale region around Kwajalein Island during the Kwajalein Experiment (KWAJEX) are performed. Using observed winds along with surface and large-scale thermodynamic forcings, the model tracks the observed mean thermodynamic soundings without thermodynamic nudging during 52-day simulations spanning the whole experiment time period, 24 July–14 September 1999. Detailed comparisons of the results with cloud and precipitation observations, including radar reflectivities from the Kwajalein ground validation radar and International Satellite Cloud Climatology Project (ISCCP) cloud amounts and radiative fluxes, reveal the biases and sensitivities of the model’s simulated clouds. The amount and optical depth of high cloud are underpredicted by the model during less rainy periods, leading to excessive outgoing longwave radiation (OLR) and insufficient albedo. The simulated radar reflectivities tend to be excessive, especially in the upper troposphere, suggesting that simulated high clouds are precipitating large hydrometeors too efficiently. Occasionally, large-scale advective forcing errors also seem to contribute to upper-level cloud and relative humidity biases. An extensive suite of sensitivity studies to different microphysical and radiative parameterizations is performed, with surprisingly little impact on the results in most cases.

Simulation, Modeling, and Dynamically Based Parameterization of Organized Tropical Convection for Global Climate Models

2017 ◽  
Vol 74 (5) ◽  
pp. 1363-1380 ◽  
Author(s):  
Mitchell W. Moncrieff ◽  
Changhai Liu ◽  
Peter Bogenschutz
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Global Climate ◽  
Tropical Convection ◽  
Global Climate Models ◽  
Momentum Transport ◽  
Vertical Shear ◽  
Convergence Zone ◽  
Convective Momentum Transport ◽  
Organized Convection

Abstract A new approach for treating organized convection in global climate models (GCMs) referred to as multiscale coherent structure parameterization (MCSP) introduces physical and dynamical effects of organized convection that are missing from contemporary parameterizations. The effects of vertical shear are approximated by a nonlinear slantwise overturning model based on Lagrangian conservation principles. Simulation of the April 2009 Madden–Julian oscillation event during the Year of Tropical Convection (YOTC) over the Indian Ocean using the Weather Research and Forecasting (WRF) Model at 1.3-km grid spacing identifies self-similar properties for squall lines, MCSs, and superclusters embedded in equatorial waves. The slantwise overturning model approximates this observed self-similarity. The large-scale effects of MCSP are examined in two categories of GCM. First, large-scale convective systems simulated in an aquaplanet model are approximated by slantwise overturning with attention to convective momentum transport. Second, MCSP is utilized in the Community Atmosphere Model, version 5.5 (CAM5.5), as tendency equations for second-baroclinic heating and convective momentum transport. The difference between MCSP and CAM5.5 is a direct measure of the global effects of organized convection. Consistent with TRMM measurements, the MCSP generates large-scale precipitation patterns in the tropical warm pool and the adjoining locale; improves precipitation in the intertropical convergence zone (ITCZ), South Pacific convergence zone (SPCZ), and Maritime Continent regions; and affects tropical wave modes. In conclusion, the treatment of organized convection by MCSP is salient for the next generation of GCMs.

scholarly journals Exploring the Role of Eddy Momentum Fluxes in Determining the Characteristics of the Equinoctial Hadley Circulation: Fixed-SST Simulations

2016 ◽  
Vol 73 (6) ◽  
pp. 2427-2444 ◽  
Author(s):  
Martin S. Singh ◽  
Zhiming Kuang
Keyword(s):  
Large Scale ◽  
Hadley Circulation ◽  
Momentum Transport ◽  
Secondary Importance ◽  
Wide Domain ◽  
Domain Configuration ◽  
Momentum Fluxes ◽  
Convective Momentum Transport ◽  
Mean Circulation

Abstract The influence of eddy momentum fluxes on the equinoctial Hadley circulation is explored using idealized simulations on an equatorial beta plane in which the sea surface temperature (SST) distribution is fixed. By comparing simulations run in a wide-domain configuration, in which large-scale eddies are present, to simulations in which the model domain is too narrow to permit baroclinic instability, the role of large-scale eddies in determining the characteristics of the Hadley circulation is elucidated. The simulations also include an explicit representation of deep convection, allowing for an evaluation of the influence of convective momentum transport on the zonal-mean circulation. The simulated eddy momentum fluxes are much weaker in the narrow-domain configuration than in the wide-domain case, and convective momentum transport is found to be of secondary importance. As a result, many characteristics of the narrow-domain Hadley circulation are well described by axisymmetric theory and differ from those of the wide-domain case. Nevertheless, the strength of the Hadley circulation is similar irrespective of the domain width. The sensitivity of this result to the strength of the eddy forcing is investigated using narrow-domain simulations forced by artificial sinks of zonal momentum. As the magnitude of the momentum sink increases, the Hadley circulation strengthens, but the increase is relatively modest except at very strong forcing magnitudes. The results suggest that the fixed-SST boundary condition places a strong thermodynamic constraint on the Hadley circulation strength and that one should consider the energy budget as well as the angular momentum budget in order to fully understand the influence of large-scale eddies on the zonal-mean circulation in the tropics.

scholarly journals The Sensitivity of Momentum Transport and Severe Surface Winds to Environmental Moisture in Idealized Simulations of a Mesoscale Convective System

2011 ◽  
Vol 139 (5) ◽  
pp. 1352-1369 ◽  
Author(s):  
Kelly M. Mahoney ◽  
Gary M. Lackmann
Keyword(s):  
Three Dimensional ◽  
Grid Cell ◽  
Mesoscale Convective System ◽  
Momentum Transport ◽  
Convective System ◽  
Surface Winds ◽  
Convective Systems ◽  
Stratiform Region ◽  
Mesoscale Convective ◽  
Convective Momentum Transport

Analysis of a pair of three-dimensional simulations of mesoscale convective systems (MCSs) reveals a significant sensitivity of convective momentum transport (CMT), MCS motion, and the generation of severe surface winds to ambient moisture. The Weather Research and Forecasting model is used to simulate an idealized MCS, which is compared with an MCS in a drier midlevel environment. The MCS in the drier environment is smaller, moves slightly faster, and exhibits increased descent and more strongly focused areas of enhanced CMT near the surface in the trailing stratiform region relative to that in the control simulation. A marked increase in the occurrence of severe surface winds is observed between the dry midlevel simulation and the control. It is shown that the enhanced downward motion associated with decreased midlevel relative humidity affects CMT fields and contributes to an increase in the number of grid-cell occurrences of severe surface winds. The role of a descending rear-inflow jet in producing strong surface winds at locations trailing the gust front is also analyzed, and is found to be associated with low-level CMT maxima, particularly in the drier midlevel simulation.

A Simple Dynamical Model with Features of Convective Momentum Transport

2009 ◽  
Vol 66 (2) ◽  
pp. 373-392 ◽  
Author(s):  
Andrew J. Majda ◽  
Samuel N. Stechmann
Keyword(s):  
Dynamic Model ◽  
Large Scale ◽  
Intraseasonal Oscillation ◽  
Momentum Transport ◽  
Linear Stability Theory ◽  
Westerly Wind ◽  
Mean Flow ◽  
Flow Interactions ◽  
The Mean ◽  
Convective Momentum Transport

Abstract Convective momentum transport (CMT) plays a central role in interactions across multiple space and time scales. However, because of the multiscale nature of CMT, quantifying and parameterizing its effects is often a challenge. Here a simple dynamic model with features of CMT is systematically derived and studied. The model includes interactions between a large-scale zonal mean flow and convectively coupled gravity waves, and convection is parameterized using a multicloud model. The moist convective wave–mean flow interactions shown here have several interesting features that distinguish them from other classical wave–mean flow settings. First an intraseasonal oscillation of the mean flow and convectively coupled waves (CCWs) is described. The mean flow oscillates due to both upscale and downscale CMT, and the CCWs weaken, change their propagation direction, and strengthen as the mean flow oscillates. The basic mechanisms of this oscillation are corroborated by linear stability theory with different mean flow background states. Another case is set up to imitate the westerly wind burst phase of the Madden–Julian oscillation (MJO) in the simplified dynamic model. In this case, CMT first accelerates the zonal jet with the strongest westerly wind aloft, and then there is deceleration of the winds due to CMT; this occurs on an intraseasonal time scale and is in qualitative agreement with actual observations of the MJO. Also, in this case, a multiscale envelope of convection propagates westward with smaller-scale convection propagating eastward within the envelope. The simplified dynamic model is able to produce this variety of behavior even though it has only a single horizontal direction and no Coriolis effect.

Convective Momentum Transport by Rainbands within a Madden–Julian Oscillation in a Global Nonhydrostatic Model with Explicit Deep Convective Processes. Part I: Methodology and General Results

2012 ◽  
Vol 69 (4) ◽  
pp. 1317-1338 ◽  
Author(s):  
Tomoki Miyakawa ◽  
Yukari N. Takayabu ◽  
Tomoe Nasuno ◽  
Hiroaki Miura ◽  
Masaki Satoh ◽  
...  
Keyword(s):  
Large Scale ◽  
Layer Structure ◽  
Propagation Speed ◽  
Momentum Transport ◽  
Madden Julian Oscillation ◽  
Convective Envelope ◽  
Upper Troposphere ◽  
Nonhydrostatic Model ◽  
The Mean ◽  
Convective Momentum Transport

Abstract The convective momentum transport (CMT) properties of 13 215 rainbands within a Madden–Julian oscillation (MJO) event simulated by a global nonhydrostatic model are examined. CMT vectors, which represent horizontal accelerations to the mean winds due to momentum flux convergences of deviation winds, are derived for each rainband. The CMT vectors are composited according to their locations relative to the MJO center. While a similar number of rainbands are detected in the eastern and western halves of the MJO convective envelope, CMT vectors with large zonal components are most plentiful between 0° and 20° to the west of the MJO center. The zonal components of the CMT vectors exhibit a coherent directionality and have a well-organized three-layer structure: positive near the surface, negative in the low to midtroposphere, and positive in the upper troposphere. In the low to midtroposphere, where the longitudinal difference in the mean zonal wind across the MJO is 10 m s−1 on average, the net acceleration due to CMT contributes about −16 m s−1. Possible roles of the CMT are proposed. First, the CMT delays the eastward progress of the low- to midtroposphere westerly wind, hence delaying the eastward migration of the convectively favorable region and reducing the propagation speed of the entire MJO. Second, the CMT tilts the MJO flow structure westward with height. Furthermore, the CMT counteracts the momentum transport due to large-scale flows that result from the tilted structure.

scholarly journals Stochastic models for convective momentum transport

2008 ◽  
Vol 105 (46) ◽  
pp. 17614-17619 ◽  
Author(s):  
Andrew J. Majda ◽  
Samuel N. Stechmann
Keyword(s):  
Stochastic Model ◽  
Stochastic Models ◽  
Large Scale ◽  
Computer Models ◽  
Momentum Transport ◽  
Mean Flow ◽  
Stochastic Effects ◽  
Squall Lines ◽  
Convective Momentum Transport ◽  
Coupled Wave

The improved parameterization of unresolved features of tropical convection is a central challenge in current computer models for long-range ensemble forecasting of weather and short-term climate change. Observations, theory, and detailed smaller-scale numerical simulations suggest that convective momentum transport (CMT) from the unresolved scales to the resolved scales is one of the major deficiencies in contemporary computer models. Here, a combination of mathematical and physical reasoning is utilized to build simple stochastic models that capture the significant intermittent upscale transports of CMT on the large scales due to organized unresolved convection from squall lines. Properties of the stochastic model for CMT are developed below in a test column model environment for the large-scale variables. The effects of CMT from the stochastic model on a large-scale convectively coupled wave in an idealized setting are presented below as a nontrivial test problem. Here, the upscale transports from stochastic effects are significant and even generate a large-scale mean flow which can interact with the convectively coupled wave.

scholarly journals On the Definition of Precipitation Efficiency

2007 ◽  
Vol 64 (12) ◽  
pp. 4506-4513 ◽  
Author(s):  
Chung-Hsiung Sui ◽  
Xiaofan Li ◽  
Ming-Jen Yang
Keyword(s):  
Large Scale ◽  
Spatial Scales ◽  
Cloud Microphysics ◽  
Tropical Ocean ◽  
Precipitation Efficiency ◽  
Surface Rainfall ◽  
Time Period ◽  
Toga Coare ◽  
Highly Correlated ◽  
Definition Of

Abstract A modified definition of precipitation efficiency (PE) is proposed based on either cloud microphysics precipitation efficiency (CMPE) or water cycling processes including water vapor and hydrometeor species [large-scale precipitation efficiency (LSPE)]. These PEs are examined based on a two-dimensional cloud-resolving simulation. The model is integrated for 21 days with the imposed large-scale vertical velocity, zonal wind, and horizontal advections obtained from the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). It is found that the properly defined PEs include all moisture and hydrometeor sources associated with surface rainfall processes so that they range from 0% to 100%. Furthermore, the modified LSPE and CMPE are highly correlated. Their linear correlation coefficient and root-mean-squared difference are insensitive to the spatial scales of averaged data and are moderately sensitive to the time period of averaged data.

scholarly journals Convection Modeling of Pure-steam Atmospheres

2021 ◽  
Vol 923 (1) ◽  
pp. L15
Author(s):  
Xianyu Tan ◽  
Maxence Lefèvre ◽  
Raymond T. Pierrehumbert
Keyword(s):  
Gravity Waves ◽  
Large Scale ◽  
Three Dimensional ◽  
Basic Structure ◽  
Model Parameters ◽  
Moist Convection ◽  
Wide Range ◽  
Convective Parameterization Scheme ◽  
Pure Steam ◽  
Convection Parameterization

Abstract Condensable species are crucial to shaping planetary climate. A wide range of planetary climate systems involve understanding nondilute condensable substances and their influence on climate dynamics. There has been progress on large-scale dynamical effects and on 1D convection parameterization, but resolved 3D moist convection remains unexplored in nondilute conditions, though it can have a profound impact on temperature/humidity profiles and cloud structure. In this work, we tackle this problem for pure-steam atmospheres using three-dimensional, high-resolution numerical simulations of convection in postrunaway atmospheres. We show that the atmosphere is composed of two characteristic regions, an upper condensing region dominated by gravity waves and a lower noncondensing region characterized by convective overturning cells. Velocities in the condensing region are much smaller than those in the lower, noncondensing region, and the horizontal temperature variation is small. Condensation in the thermal photosphere is largely driven by radiative cooling and tends to be statistically homogeneous. Some condensation also happens deeper, near the boundary of the condensing region, due to triggering by gravity waves and convective penetrations and exhibits random patchiness. This qualitative structure is insensitive to varying model parameters, but quantitative details may differ. Our results confirm theoretical expectations that atmospheres close to the pure-steam limit do not have organized deep convective plumes in the condensing region. The generalized convective parameterization scheme discussed in Ding & Pierrehumbert is appropriate for handling the basic structure of atmospheres near the pure-steam limit but cannot capture gravity waves and their mixing which appear in 3D convection-resolving models.

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