scholarly journals The Impact of Spatial Variations of Low-Level Stability on the Life Cycle of a Simulated Supercell Storm

2010 ◽  
Vol 138 (5) ◽  
pp. 1738-1766 ◽  
Author(s):  
Conrad L. Ziegler ◽  
Edward R. Mansell ◽  
Jerry M. Straka ◽  
Donald R. MacGorman ◽  
Donald W. Burgess
Keyword(s):  
Boundary Layer ◽  
Life Cycle ◽  
Cold Pool ◽  
Ambient Flow ◽  
Low Level ◽  
Inversion Region ◽  
Supercell Storm ◽  
Outflow Boundary ◽  
The Right ◽  
The Impact

Abstract This study reports on the dynamical evolution of simulated, long-lived right-moving supercell storms in a high-CAPE, strongly sheared mesoscale environment, which initiate in a weakly capped region and subsequently move into a cold boundary layer (BL) and inversion region before dissipating. The storm simulations realistically approximate the main morphological features and evolution of the 22 May 1981 Binger, Oklahoma, supercell storm by employing time-varying inflow lateral boundary conditions for the storm-relative moving grid, which in turn are prescribed from a parent, fixed steady-state mesoscale analysis to approximate the observed inversion region to the east of the dryline on that day. A series of full life cycle storm simulations have been performed in which the magnitude of boundary layer coldness and the convective inhibition are varied to examine the ability of the storm to regenerate and sustain its main updraft as it moves into environments with increasing convective stability. The analysis of the simulations employs an empirical expression for the theoretical speed of the right-forward-flank outflow boundary relative to the ambient, low-level storm inflow that is consistent with simulated cold-pool boundary movement. The theoretical outflow boundary speed in the direction opposite to the ambient flow increases with an increasing cold-pool temperature deficit relative to the ambient BL temperature, and it decreases as ambient wind speed increases. The right-moving, classic (CL) phase of the simulated supercells is supported by increasing precipitation content and a stronger cold pool, which increases the right-moving cold-pool boundary speed against the constant ambient BL winds. The subsequent decrease of the ambient BL temperature with eastward storm movement decreases the cold-pool temperature deficit and reduces the outflow boundary speed against the ambient winds, progressing through a state of stagnation to an ultimate retrogression of the outflow boundary in the direction of the ambient flow. Onset of a transient, left-moving low-precipitation (LP) phase is initiated as the storm redevelops on the retrograding outflow boundary. The left-moving LP storm induces compensating downward motions in the inversion layer that desiccates the inflow, elevates the cloudy updraft parcel level of free convection (LFC), and leads to the final storm decay. The results demonstrate that inversion-region simulations support isolated, long-lived supercells. Both the degree of stratification and the coldness of the ambient BL regulate the cold-pool intensity and the strength and capacity of the outflow boundary to lift BL air through the LFC and thus regenerate convection, resulting in variation of supercell duration in the inversion region of approximately 1–2 h. In contrast, horizontally homogeneous conditions lacking an inversion region result in the development of secondary convection from the initial isolated supercell, followed by rapid upscale growth after 3 h to form a long-lived mesoscale convective system.

scholarly journals Understanding the Impact of Radar and In Situ Observations on the Prediction of a Nocturnal Convection Initiation Event on 25 June 2013 Using an Ensemble-Based Multiscale Data Assimilation System

2018 ◽  
Vol 146 (6) ◽  
pp. 1837-1859 ◽  
Author(s):  
Samuel K. Degelia ◽  
Xuguang Wang ◽  
David J. Stensrud ◽  
Aaron Johnson
Keyword(s):  
Data Assimilation ◽  
Great Plains ◽  
Cold Pool ◽  
Radar Observations ◽  
Low Level ◽  
In Situ Observations ◽  
Outflow Boundary ◽  
Convection Initiation ◽  
The Impact

The initiation of new convection at night in the Great Plains contributes to a nocturnal maximum in precipitation and produces localized heavy rainfall and severe weather hazards in the region. Although previous work has evaluated numerical model forecasts and data assimilation (DA) impacts for convection initiation (CI), most previous studies focused only on convection that initiates during the afternoon and not explicitly on nocturnal thunderstorms. In this study, we investigate the impact of assimilating in situ and radar observations for a nocturnal CI event on 25 June 2013 using an ensemble-based DA and forecast system. Results in this study show that a successful CI forecast resulted only when assimilating conventional in situ observations on the inner, convection-allowing domain. Assimilating in situ observations strengthened preexisting convection in southwestern Kansas by enhancing buoyancy and locally strengthening low-level convergence. The enhanced convection produced a cold pool that, together with increased convergence along the northwestern low-level jet (LLJ) terminus near the region of CI, was an important mechanism for lifting parcels to their level of free convection. Gravity waves were also produced atop the cold pool that provided further elevated ascent. Assimilating radar observations further improved the forecast by suppressing spurious convection and reducing the number of ensemble members that produced CI along a spurious outflow boundary. The fact that the successful CI forecasts resulted only when the in situ observations were assimilated suggests that accurately capturing the preconvective environment and specific mesoscale features is especially important for nocturnal CI forecasts.

Impacts of Assimilating Measurements of Different State Variables with a Simulated Supercell Storm and Three-Dimensional Variational Method

2013 ◽  
Vol 141 (8) ◽  
pp. 2759-2777 ◽  
Author(s):  
Guoqing Ge ◽  
Jidong Gao ◽  
Ming Xue
Keyword(s):  
Potential Temperature ◽  
Three Dimensional ◽  
Horizontal Wind ◽  
Cold Pool ◽  
State Variables ◽  
Wind Fields ◽  
Simulation Experiments ◽  
Supercell Storm ◽  
The Impact ◽  
Analysis Quality

Abstract This paper investigates the impacts of assimilating measurements of different state variables, which can be potentially available from various observational platforms, on the cycled analysis and short-range forecast of supercell thunderstorms by performing a set of observing system simulation experiments (OSSEs) using a storm-scale three-dimensional variational data assimilation (3DVAR) method. The control experiments assimilate measurements every 5 min for 90 min. It is found that the assimilation of horizontal wind can reconstruct the storm structure rather accurately. The assimilation of vertical velocity , potential temperature , or water vapor can partially rebuild the thermodynamic and precipitation fields but poorly retrieves the wind fields. The assimilation of rainwater mixing ratio can build up the precipitation fields together with a reasonable cold pool but is unable to properly recover the wind fields. Overall, data have the greatest impact, while have the second largest impact. The impact of is the smallest. The impact of assimilation frequency is examined by comparing results using 1-, 5-, or 10-min assimilation intervals. When is assimilated every 5 or 10 min, the analysis quality can be further improved by the incorporation of additional types of observations. When are assimilated every minute, the benefit from additional types of observations is negligible, except for . It is also found that for , , and measurements, more frequent assimilation leads to more accurate analyses. For and , a 1-min assimilation interval does not produce a better analysis than a 5-min interval.

How does vertical wind shear influence entrainment in squall lines?

2021 ◽  
Author(s):  
Jake P. Mulholland ◽  
John M. Peters ◽  
Hugh Morrison
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Leading Edge ◽  
Vertical Wind ◽  
Squall Line ◽  
Cold Pool ◽  
Low Level ◽  
Boundary Shear ◽  
Squall Lines ◽  
Outflow Boundary

AbstractThe influence of vertical wind shear on updraft entrainment in squall lines is not well understood. To address this knowledge gap, a suite of high-resolution idealized numerical model simulations of squall lines were run in various vertical wind shear (hereafter “shear”) environments to study the effects of shear on entrainment in deep convective updrafts. Low-level horizontal mass flux into the leading edge of the cold pool was strongest in the simulations with the strongest low-level shear. These simulations consequently displayed wider updrafts, less entrainment-driven dilution, and larger buoyancy than the simulations with comparatively weak low-level shear. An analysis of vertical accelerations along trajectories that passed through updrafts showed larger net accelerations from buoyancy in the simulations with stronger low-level shear, which demonstrates how less entrainment-driven dilution equated to stronger updrafts. The effects of upper-level shear on entrainment and updraft vertical velocities were generally less pronounced than the effects of low-level shear. We argue that in addition to the outflow boundary-shear interactions and their effect on updraft tilt established by previous authors, decreased entrainment-driven dilution is yet another beneficial effect of strong low-level shear on squall line updraft intensity.

The Impact of Mixed-Phase Microphysical Processes on the Turbulence in Low-level Clouds in the Arctic

2021 ◽  
Author(s):  
Jan Chylik ◽  
Roel Neggers
Keyword(s):  
Boundary Layer ◽  
Climate Models ◽  
Weather Forecast ◽  
Mixed Phase ◽  
The Arctic ◽  
Contributing Factors ◽  
Microphysics Scheme ◽  
Low Level ◽  
Microphysical Processes ◽  
The Impact

<p>The proper representation of Arctic mixed-phased clouds remains a challenge in both weather forecast and climate models. Amongst the contributing factors is the complexity of turbulent properties of clouds. While the effect of evaporating hydrometeors on turbulent properties of the boundary layer has been identified in other latitudes, the extent of similar studies in the Arctic has been so far limited.</p><p>Our study focus on the impact of heat release from mixed-phase microphysical processes on the turbulent properties of the convective low-level clouds in the Arctic. We  employ high-resolution simulations, properly constrained by relevant measurements.<br>Semi-idealised model cases are based on convective clouds observed during the recent campaign in the Arctic: ACLOUD, which took place May--June 2017 over Fram Strait. The simulations are performed in Dutch Atmospheric Large Eddy Simulation (DALES) with double-moment mixed-phase microphysics scheme of Seifert & Beheng.</p><p>The results indicate an enhancement of boundary layer turbulence is some convective regimes.<br>Furthermore, results are sensitive to aerosols concentrations. Additional implications for the role of mixed-phase clouds in the Arctic Amplification will be discussed.</p>

scholarly journals Generalization and application of the flux-conservative thermodynamic equations in the AROME model of the ALADIN system

2016 ◽  
Author(s):  
D. Degrauwe ◽  
Y. Seity ◽  
F. Bouyssel ◽  
P. Termonia
Keyword(s):  
Life Cycle ◽  
Energy Budget ◽  
Moisture Transport ◽  
Climate Model ◽  
Heavy Precipitation ◽  
Cold Pool ◽  
Nwp Model ◽  
The Impact ◽  
Thermodynamic Equations ◽  
Physical Parameterizations

Abstract. General yet compact equations are presented to express the thermodynamic impact of physical parameterizations in a NWP or climate model. By expressing the equations in a flux-conservative formulation, the conservation of mass and energy is a built-in feature of the system. Moreover, the centralization of all thermodynamic calculations guarantees a consistent thermodynamical treatment of the different processes. The generality of this physics-dynamics interface is illustrated by applying it in the AROME NWP model. The physics-dynamics interface of this model currently makes some approximations, which typically consist of neglecting some terms in the total energy budget, such as the transport of heat by falling precipitation, or the effect of diffusive moisture transport. Although these terms are usually quite small, omitting them from the energy budget breaks the constraint of energy conservation. The presented set of equations allows to get rid of these approximations, in order to arrive at a consistent and energy-conservative model. A verification in an operational setting shows that the impact on monthly-averaged, domain-wide meteorological scores is quite neutral. However, under specific circumstances, the supposedly small terms may turn out not to be entirely negligible. A detailed study of a case with heavy precipitation shows that the heat transport by precipitation contributes to the formation of a region of relatively cold air near the surface, the so-called cold pool. Given the importance of this cold pool mechanism in the life-cycle of convective events, it is advisable not to neglect phenomena that may enhance it.

scholarly journals Near-Surface Thermodynamic Sensitivities in Simulated Extreme-Rain-Producing Mesoscale Convective Systems

2017 ◽  
Vol 145 (6) ◽  
pp. 2177-2200 ◽  
Author(s):  
Russ S. Schumacher ◽  
John M. Peters
Keyword(s):  
Water Vapor ◽  
Initial Conditions ◽  
Weather Prediction ◽  
Mesoscale Convective Systems ◽  
Cold Pool ◽  
Near Surface ◽  
Low Level ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Outflow Boundary

Abstract This study investigates the influences of low-level atmospheric water vapor on the precipitation produced by simulated warm-season midlatitude mesoscale convective systems (MCSs). In a series of semi-idealized numerical model experiments using initial conditions gleaned from composite environments from observed cases, small increases in moisture were applied to the model initial conditions over a layer either 600 m or 1 km deep. The precipitation produced by the MCS increased with larger moisture perturbations as expected, but the rainfall changes were disproportionate to the magnitude of the moisture perturbations. The experiment with the largest perturbation had a water vapor mixing ratio increase of approximately 2 g kg−1 over the lowest 1 km, corresponding to a 3.4% increase in vertically integrated water vapor, and the area-integrated MCS precipitation in this experiment increased by nearly 60% over the control. The locations of the heaviest rainfall also changed in response to differences in the strength and depth of the convectively generated cold pool. The MCSs in environments with larger initial moisture perturbations developed stronger cold pools, and the convection remained close to the outflow boundary, whereas the convective line was displaced farther behind the outflow boundary in the control and the simulations with smaller moisture perturbations. The high sensitivity of both the amount and location of MCS rainfall to small changes in low-level moisture demonstrates how small moisture errors in numerical weather prediction models may lead to large errors in their forecasts of MCS placement and behavior.

scholarly journals Seasonality and Regionality of the Madden–Julian Oscillation, Kelvin Wave, and Equatorial Rossby Wave

2007 ◽  
Vol 64 (12) ◽  
pp. 4400-4416 ◽  
Author(s):  
Hirohiko Masunaga
Keyword(s):  
Boundary Layer ◽  
Water Solution ◽  
Austral Summer ◽  
Longwave Radiation ◽  
Boreal Summer ◽  
Dynamical Structure ◽  
Madden Julian Oscillation ◽  
Kelvin Wave ◽  
Low Level ◽  
The Impact

Abstract The Madden–Julian oscillation (MJO), Kelvin wave, and equatorial Rossby (ER) wave—collectively called intraseasonal oscillations (ISOs)—are investigated using a 25-yr record of outgoing longwave radiation (OLR) measurements as well as the associated dynamical fields. The ISO modes are detected by applying bandpass filters to the OLR data in the frequency–wavenumber space. An automated wave-tracking algorithm is applied to each ISO mode so that convection centers accompanied with the ISOs are traced in space and time in an objective fashion. The identified paths of the individual ISO modes are first examined and found strongly modulated regionally and seasonally. The dynamical structure is composited with respect to the convection centers of each ISO mode. A baroclinic mode of the combined Rossby and Kelvin structure is prominent for the MJO, consistent with existing work. The Kelvin wave exhibits a low-level wind field resembling the shallow-water solution, while a slight lead of low-level convergence over convection suggests the impact of frictional boundary layer convergence on Kelvin wave dynamics. A lagged composite analysis reveals that the MJO is accompanied with a Kelvin wave approaching from the west preceding the MJO convective maximum in austral summer. MJO activity then peaks as the Kelvin and ER waves constructively interfere to enhance off-equatorial boundary layer convergence. The MJO leaves a Kelvin wave emanating to the east once the peak phase is passed. The approaching Kelvin wave prior to the development of MJO convection is absent in boreal summer and fall. The composite ER wave, loosely concentrated around the MJO, is nearly stationary throughout. A possible scenario to physically translate the observed result is also discussed.

scholarly journals The Impact of Low-Level Moisture Errors on Model Forecasts of an MCS Observed during PECAN

2017 ◽  
Vol 145 (9) ◽  
pp. 3599-3624 ◽  
Author(s):  
John M. Peters ◽  
Erik R. Nielsen ◽  
Matthew D. Parker ◽  
Stacey M. Hitchcock ◽  
Russ S. Schumacher
Keyword(s):  
Convective Available Potential Energy ◽  
Mesoscale Convective System ◽  
Squall Line ◽  
Convective System ◽  
Low Level ◽  
Eastern Flank ◽  
Western Flank ◽  
Mesoscale Convective ◽  
Outflow Boundary ◽  
The Impact

This article investigates errors in forecasts of the environment near an elevated mesoscale convective system (MCS) in Iowa on 24–25 June 2015 during the Plains Elevated Convection at Night (PECAN) field campaign. The eastern flank of this MCS produced an outflow boundary (OFB) and moved southeastward along this OFB as a squall line. The western flank of the MCS remained quasi stationary approximately 100 km north of the system’s OFB and produced localized flooding. A total of 16 radiosondes were launched near the MCS’s eastern flank and 4 were launched near the MCS’s western flank. Convective available potential energy (CAPE) increased and convective inhibition (CIN) decreased substantially in observations during the 4 h prior to the arrival of the squall line. In contrast, the model analyses and forecasts substantially underpredicted CAPE and overpredicted CIN owing to their underrepresentation of moisture. Numerical simulations that placed the MCS at varying distances too far to the northeast were analyzed. MCS displacement error was strongly correlated with models’ underrepresentation of low-level moisture and their associated overrepresentation of the vertical distance between a parcel’s initial height and its level of free convection ([Formula: see text], which is correlated with CIN). The overpredicted [Formula: see text] in models resulted in air parcels requiring unrealistically far northeastward travel in a region of gradual meso- α-scale lift before these parcels initiated convection. These results suggest that erroneous MCS predictions by NWP models may sometimes result from poorly analyzed low-level moisture fields.

scholarly journals Recommendation and context: the missing links for increased life cycle impact in large industries

2019 ◽  
Vol 25 (2) ◽  
pp. 240-251 ◽  
Author(s):  
Emma Rex ◽  
Niklas Fernqvist ◽  
Sven-Olof Ryding
Keyword(s):  
Social Psychology ◽  
Life Cycle ◽  
Empirical Data ◽  
Information Barriers ◽  
Barriers And Enablers ◽  
Trade Offs ◽  
Large Production ◽  
The Right ◽  
The Impact

Abstract Purpose This study takes an open and explorative approach to investigating the impact, or lack of impact, of life cycle information on behaviours throughout large production companies. Based on cases where life cycle information has been provided, this paper analyses how life cycle information has been interpreted and acted upon—not only by the life cycle assessment (LCA) practitioner conducting the study but also by employees outside the environmental departments. Methods To understand the impact of life cycle information on everyday actions in organisations and how this impact can be enhanced, this study takes a grounded approach to following flows of life cycle information from the environmental department through other departments of an organisation. From the flows of information, the research team selected rich descriptions of empirical data that reflect action and inaction. Using interviews and documents, we collected barriers and enablers for acting on life cycle information. Barriers and enablers were interpreted and clustered into categories and arranged into concepts. Next, we reviewed the empirical data using theories from social psychology. Results and discussion The results show that it is difficult for life cycle information to result in subsequent action outside of environmental departments. The barriers to this action were partly due to the life cycle information per se such as gaps between what life cycle information is available and what life cycle information is needed. Barriers and enablers were also found in relation to the context in which life cycle information was applied and new behaviours were adopted, including timing and software structures, reward systems, trade-offs, and personal beliefs about the profession. The results suggest a new role of the life cycle proponent that includes providing the right life cycle information and understanding and influencing the expected agents’ situations. Conclusions Assisted by theories from social psychology, we found that behaviour can be changed if ‘recommendations’ and ‘contexts’ are considered when providing life cycle information. The paper suggests that the impact of life cycle information could increase if normative arguments about environmental visions, strategies, and overarching goals are aligned with enablers that focus on personal goals, such as meeting a deadline, reducing uncertainty, and reaching the threshold for a bonus.

scholarly journals The Structure, Evolution, and Dynamics of a Nocturnal Convective System Simulated Using the WRF-ARW Model

2017 ◽  
Vol 145 (8) ◽  
pp. 3179-3201 ◽  
Author(s):  
Benjamin T. Blake ◽  
David B. Parsons ◽  
Kevin R. Haghi ◽  
Stephen G. Castleberry
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Vertical Shear ◽  
Structure Evolution ◽  
Cold Pool ◽  
Density Current ◽  
Convective System ◽  
Low Level ◽  
Arw Model ◽  
Low Level Jet

Previous studies have documented a nocturnal maximum in thunderstorm frequency during the summer across the central United States. Forecast skill for these systems remains relatively low and the explanation for this nocturnal maximum is still an area of active debate. This study utilized the WRF-ARW Model to simulate a nocturnal mesoscale convective system that occurred over the southern Great Plains on 3–4 June 2013. A low-level jet transported a narrow corridor of air above the nocturnal boundary layer with convective instability that exceeded what was observed in the daytime boundary layer. The storm was elevated and associated with bores that assisted in the maintenance of the system. Three-dimensional variations in the system’s structure were found along the cold pool, which were examined using convective system dynamics and wave theory. Shallow lifting occurred on the southern flank of the storm. Conversely, the southeastern flank had deep lifting, with favorable integrated vertical shear over the layer of maximum CAPE. The bore assisted in transporting high-CAPE air toward its LFC, and the additional lifting by the density current allowed for deep convection to occur. The bore was not coupled to the convective system and it slowly pulled away, while the convection remained in phase with the density current. These results provide a possible explanation for how convection is maintained at night in the presence of a low-level jet and a stable boundary layer, and emphasize the importance of the three-dimensionality of these systems.

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