Response of Moist Convection to the Spectral Feature of the Surface Flux Field at Model Resolution across the Gray Zone

2022 ◽  
Author(s):  
J.‐H. Ryu ◽  
S.‐L. Kang
Keyword(s):  
Spectral Feature ◽  
Surface Flux ◽  
Moist Convection ◽  
Gray Zone ◽  
Model Resolution

scholarly journals Spatial and temporal variability of clouds and precipitation over Germany: multiscale simulations across the "gray zone"

2015 ◽  
Vol 15 (21) ◽  
pp. 12361-12384 ◽  
Author(s):  
C. Barthlott ◽  
C. Hoose
Keyword(s):  
Cloud Formation ◽  
Small Scale ◽  
Spatial And Temporal Variability ◽  
Gray Zone ◽  
Model Resolution ◽  
Eddy Simulation ◽  
Cosmo Model ◽  
Weather Events ◽  
Temporal And Spatial Variability ◽  
Convergence Zones

Abstract. This paper assesses the resolution dependance of clouds and precipitation over Germany by numerical simulations with the COnsortium for Small-scale MOdeling (COSMO) model. Six intensive observation periods of the HOPE (HD(CP)2 Observational Prototype Experiment) measurement campaign conducted in spring 2013 and 1 summer day of the same year are simulated. By means of a series of grid-refinement resolution tests (horizontal grid spacing 2.8, 1 km, 500, and 250 m), the applicability of the COSMO model to represent real weather events in the gray zone, i.e., the scale ranging between the mesoscale limit (no turbulence resolved) and the large-eddy simulation limit (energy-containing turbulence resolved), is tested. To the authors' knowledge, this paper presents the first non-idealized COSMO simulations in the peer-reviewed literature at the 250–500 m scale. It is found that the kinetic energy spectra derived from model output show the expected −5/3 slope, as well as a dependency on model resolution, and that the effective resolution lies between 6 and 7 times the nominal resolution. Although the representation of a number of processes is enhanced with resolution (e.g., boundary-layer thermals, low-level convergence zones, gravity waves), their influence on the temporal evolution of precipitation is rather weak. However, rain intensities vary with resolution, leading to differences in the total rain amount of up to +48 %. Furthermore, the location of rain is similar for the springtime cases with moderate and strong synoptic forcing, whereas significant differences are obtained for the summertime case with air mass convection. Domain-averaged liquid water paths and cloud condensate profiles are used to analyze the temporal and spatial variability of the simulated clouds. Finally, probability density functions of convection-related parameters are analyzed to investigate their dependance on model resolution and their impact on cloud formation and subsequent precipitation.

A Lagrangian Perspective on Parameterizing Deep Convection

2019 ◽  
Vol 147 (11) ◽  
pp. 4127-4149 ◽  
Author(s):  
Ron McTaggart-Cowan ◽  
Paul A. Vaillancourt ◽  
Ayrton Zadra ◽  
Leo Separovic ◽  
Shawn Corvec ◽  
...  
Keyword(s):  
Numerical Models ◽  
Spatial Scales ◽  
Deep Convection ◽  
Convective Precipitation ◽  
Moist Convection ◽  
Gray Zone ◽  
Convective Initiation ◽  
Intermittent Behavior ◽  
Cloud Properties ◽  
Deep Moist Convection

Abstract The parameterization of deep moist convection as a subgrid-scale process in numerical models of the atmosphere is required at resolutions that extend well into the convective “gray zone,” the range of grid spacings over which such convection is partially resolved. However, as model resolution approaches the gray zone, the assumptions upon which most existing convective parameterizations are based begin to break down. We focus here on one aspect of this problem that emerges as the temporal and spatial scales of the model become similar to those of deep convection itself. The common practice of static tendency application over a prescribed adjustment period leads to logical inconsistencies at resolutions approaching the gray zone, while more frequent refreshment of the convective calculations can lead to undesirable intermittent behavior. A proposed parcel-based treatment of convective initiation introduces memory into the system in a manner that is consistent with the underlying physical principles of convective triggering, thus reducing the prevalence of unrealistic gradients in convective activity in an operational model running with a 10 km grid spacing. The subsequent introduction of a framework that considers convective clouds as persistent objects, each possessing unique attributes that describe physically relevant cloud properties, appears to improve convective precipitation patterns by depicting realistic cloud memory, movement, and decay. Combined, this Lagrangian view of convection addresses one aspect of the convective gray zone problem and lays a foundation for more realistic treatments of the convective life cycle in parameterization schemes.

scholarly journals How robust and (un)certain are regional climate models over the Himalayas?

2014 ◽  
Vol 8 (6) ◽  
pp. 6251-6270 ◽  
Author(s):  
A. P. Dimri
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Regional Climate ◽  
Regional Climate Models ◽  
Surface Flux ◽  
Western Himalayas ◽  
Subgrid Scale ◽  
Model Resolution ◽  
Physical Processes ◽  
Event Scale

Abstract. Regional Climate Model(s) (RCMs) are sensitive towards presentation of regional climate of Indian winter monsoon (IWM) over the western Himalayas (WH). They illustrate robust nature in representing regional climate at mountain scale and even at event scale. While downscaling outputs, from these models, at basin level for hydrological and glaciological studies, it is found that RCMs fail to provide realistic figures. And hence, in the present paper, using the Siachen glacier basin as a reference, debate and deliberation on RCMs' uncertainly and high order of deviation from real observations is presented. Results from RCMs thus need "further tuning" if they are used for hydrological and glacier studies. Reasons for such uncertainties could be due to the improper representation of topography, missing subgrid scale processes, surface flux characteristics, various physical processes etc. at such finer model resolution and scale. At present, this paper only deliberates and brings out issues pertaining to such complexities to provide an insight for future course of studies, if understood correctly.

scholarly journals Impacts of Updraft Size and Dimensionality on the Perturbation Pressure and Vertical Velocity in Cumulus Convection. Part II: Comparison of Theoretical and Numerical Solutions and Fully Dynamical Simulations

2016 ◽  
Vol 73 (4) ◽  
pp. 1455-1480 ◽  
Author(s):  
Hugh Morrison
Keyword(s):  
Vertical Velocity ◽  
Numerical Solutions ◽  
Pressure Effects ◽  
Cumulus Convection ◽  
Moist Convection ◽  
Gray Zone ◽  
Thermal Buoyancy ◽  
Wide Range ◽  
Perturbation Pressure ◽  
2D And 3D

Abstract This paper compares simple theoretical expressions relating vertical velocity, perturbation pressure, updraft size, and dimensionality for cumulus convection, derived in Part I, with numerical solutions of the anelastic buoyant perturbation pressure Poisson equation and vertical velocity w. A range of thermal buoyancy profiles representing shallow to deep moist convection are tested for both two-dimensional (2D) and three-dimensional (3D) updrafts. The theoretical expressions give similar results for w and perturbation pressure difference from updraft top to base Δp compared to the numerical solutions over a wide range of updraft radius R. The theoretical expressions are also consistent with 2D and 3D fully dynamical updraft simulations initiated by warm bubbles of varying width. Implications for nonhydrostatic modeling in the “gray zone,” with a horizontal grid spacing Δx of O(1–10) km where convection is generally underresolved, are discussed. The theoretical and numerical solutions give a scaling of updraft velocity with R (~Δx) consistent with fully dynamical 2D and 3D simulations in the gray zone, with a rapid decrease of maximum w at relatively small R and a slower decrease at large R. These results suggest that an incorrect representation of perturbation pressure may be an important contributor to biases in convective strength at these resolutions. The theoretical solutions also provide a concise physical interpretation of the “virtual mass” coefficient in convection parameterizations and can be easily incorporated into these schemes to provide a consistent scaling of perturbation pressure effects with R, updraft height, and the buoyancy profile.

A Large-Eddy Simulation Study of Moist Convection Initiation over Heterogeneous Surface Fluxes

2011 ◽  
Vol 139 (9) ◽  
pp. 2901-2917 ◽  
Author(s):  
Song-Lak Kang ◽  
George H. Bryan
Keyword(s):  
Surface Flux ◽  
Surface Fluxes ◽  
Heterogeneous Surface ◽  
Cloud Base ◽  
Convergence Zone ◽  
Phase Lag ◽  
Moist Convection ◽  
Surface Moisture ◽  
Large Eddy ◽  
Convection Initiation

This study uses large-eddy simulations to investigate processes of moist convection initiation (CI) over heterogeneous surface fluxes. Surface energy balance is imposed via a 180° phase lag of the surface moisture flux (relative to the sensible heat flux), such that the relatively warm surface is relatively dry (and the relatively cool surface is relatively wet). As shown in previous simulations, a mesoscale circulation forms in the presence of surface-flux heterogeneity, which coexists with turbulent fluctuations. The mesoscale convergence zone of this circulation develops over the relatively warm surface, and this is where clouds first form. Convection initiation occurs sooner as the amplitude of the heterogeneity increases, and as the surface moisture increases (i.e., Bowen ratio decreases). Shallow clouds initiate when boundary layer heights (zi) become greater than the lifting condensation level (LCL). Deep precipitating clouds initiate when the LCL and level of free convection (LFC) are roughly the same when averaged over the relatively warm surface, which is equivalent to the mean convective inhibition (CIN) becoming nearly zero. From the perspective of the entire (mesoscale) domain, cases with strongly heterogeneous surfaces have a wider distribution of both zi and LCL. Thus, a comparison of zi with LCL over a mesoscale area (i.e., within one mesoscale model grid box) may lead to misleading conclusions about CI and cloud-base height. It is also shown that as the amplitude of the surface-flux heterogeneity increases the mesoscale convergence zone becomes narrower and stronger. Furthermore, CI occurs earlier over relatively wet surfaces partly because turbulent eddies are more vigorous owing to slightly greater buoyancy.

Numerical Simulations of Orographic Convection across Multiple Gray Zones

2020 ◽  
Vol 77 (10) ◽  
pp. 3301-3320
Author(s):  
Daniel J. Kirshbaum
Keyword(s):  
Deep Convection ◽  
Cloud Layer ◽  
Inertial Subrange ◽  
Moist Convection ◽  
Gray Zone ◽  
Robust Solution ◽  
Turbulent Transition ◽  
Orographic Convection ◽  
Orographic Cloud ◽  
Convection Initiation

AbstractIdealized simulations are used to determine the sensitivity of moist orographic convection to horizontal grid spacing Δh. In simulated mechanically (MECH) and thermally (THERM) forced convection over an isolated ridge, Δh is varied systematically over both the deep-convection (Δh ~ 10–1 km) and turbulence (Δh ~ 1 km–100 m) gray zones. To aid physical interpretation, a new parcel-based bulk entrainment/detrainment diagnosis for horizontally heterogeneous flows is developed. Within the deep-convection gray zone, the Δh sensitivity is dominated by differences in parameterized versus explicit convection; the former initiates convection too far upstream of the ridge (MECH) and too early in the diurnal heating cycle (THERM). These errors stem in part from a large underprediction of parameterized entrainment and detrainment. Within the turbulence gray zone, sensitivities to Δh arise from the representation of both subcloud- and cloud-layer turbulence. As Δh is decreased, MECH exhibits stronger cloud-layer entrainment to enhance the convective mass flux Mco, while THERM exhibits stronger detrainment to suppress Mco and delay convection initiation. The latter is reinforced by increased subcloud turbulence at smaller Δh, which leads to drying and diffusion of the central updraft responsible for initiating moist convection. Numerical convergence to a robust solution occurs only in THERM, which develops a fully turbulent flow with a resolved inertial subrange (for Δh ≤ 250 m). In MECH, by contrast, turbulent transition occurs within the orographic cloud, the details of which depend on both physical location and Δh.

Unusual Microstructure in Shock-Compacted Graphite

1970 ◽  
Vol 28 ◽  
pp. 474-475
Author(s):  
Lucien F. Trueb
Keyword(s):  
Mechanical Characteristic ◽  
Compression Wave ◽  
Gray Zone ◽  
Flyer Plate ◽  
Compacted Graphite ◽  
The Impact

Crushed and statically compressed Madagascar graphite that was explosively shocked at 425 kb by means of a planar flyer-plate is characterized by a black zone extending for 2 to 3 nun below the impact plane of the driver. Beyond this point, the material assumes the normal gray color of graphite. The thickness of the black zone is identical with the distance taken by the relaxation wave to overtake the compression wave.The main mechanical characteristic of the black material is its great hardness; steel scalpels and razor blades are readily blunted during attempts to cut it. An average microhardness value of 95-3 DPHN was obtained with a 10 kg load. This figure is a minimum because the indentations were usually cracked; 14.8 DPHN was measured in the gray zone.

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