scholarly journals What is the Intrinsic Predictability of Tornadic Supercell Thunderstorms?

2020 ◽  
Vol 148 (8) ◽  
pp. 3157-3180 ◽  
Author(s):  
Paul M. Markowski
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Initial Conditions ◽  
Convective Available Potential Energy ◽  
Formation Time ◽  
Time Duration ◽  
Near Surface ◽  
Layer Structures ◽  
Supercell Storms ◽  
Lifting Condensation Level

Abstract A 25-member ensemble of relatively high-resolution (75-m horizontal grid spacing) numerical simulations of tornadic supercell storms is used to obtain insight on their intrinsic predictability. The storm environments contain large and directionally varying wind shear, particularly in the boundary layer, large convective available potential energy, and a low lifting condensation level. Thus, the environments are extremely favorable for tornadic supercells. Small random temperature perturbations present in the initial conditions trigger turbulence within the boundary layers. The turbulent boundary layers are given 12 h to evolve to a quasi–steady state before storms are initiated via the introduction of a warm bubble. The spatially averaged environments are identical within the ensemble; only the random number seed and/or warm bubble location is varied. All of the simulated storms are long-lived supercells with intense updrafts and strong mesocyclones extending to the lowest model level. Even the storms with the weakest near-surface rotation probably can be regarded as weakly tornadic. However, despite the statistically identical environments, there is considerable divergence in the finescale details of the simulated storms. The intensities of the tornado-like vortices that develop in the simulations range from EF0 to EF3, with large differences in formation time and duration also being exhibited. The simulation differences only can be explained by differences in how the initial warm bubbles and/or storms interact with turbulent boundary layer structures. The results suggest very limited intrinsic predictability with respect to predicting the formation time, duration, and intensity of tornadoes.

scholarly journals 100 Years of Progress in Boundary Layer Meteorology

2019 ◽  
Vol 59 ◽  
pp. 9.1-9.85 ◽  
Author(s):  
Margaret A. LeMone ◽  
Wayne M. Angevine ◽  
Christopher S. Bretherton ◽  
Fei Chen ◽  
Jimy Dudhia ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Numerical Models ◽  
Cloud Microphysics ◽  
Lessons Learned ◽  
The Arctic ◽  
Surface Model ◽  
Near Surface ◽  
Boundary Layer Meteorology ◽  
Weather And Climate

AbstractOver the last 100 years, boundary layer meteorology grew from the subject of mostly near-surface observations to a field encompassing diverse atmospheric boundary layers (ABLs) around the world. From the start, researchers drew from an ever-expanding set of disciplines—thermodynamics, soil and plant studies, fluid dynamics and turbulence, cloud microphysics, and aerosol studies. Research expanded upward to include the entire ABL in response to the need to know how particles and trace gases dispersed, and later how to represent the ABL in numerical models of weather and climate (starting in the 1970s–80s); taking advantage of the opportunities afforded by the development of large-eddy simulations (1970s), direct numerical simulations (1990s), and a host of instruments to sample the boundary layer in situ and remotely from the surface, the air, and space. Near-surface flux-profile relationships were developed rapidly between the 1940s and 1970s, when rapid progress shifted to the fair-weather convective boundary layer (CBL), though tropical CBL studies date back to the 1940s. In the 1980s, ABL research began to include the interaction of the ABL with the surface and clouds, the first ABL parameterization schemes emerged; and land surface and ocean surface model development blossomed. Research in subsequent decades has focused on more complex ABLs, often identified by shortcomings or uncertainties in weather and climate models, including the stable boundary layer, the Arctic boundary layer, cloudy boundary layers, and ABLs over heterogeneous surfaces (including cities). The paper closes with a brief summary, some lessons learned, and a look to the future.

Evolution of zero-pressure-gradient boundary layers from different tripping conditions

2015 ◽  
Vol 783 ◽  
pp. 379-411 ◽  
Author(s):  
I. Marusic ◽  
K. A. Chauhan ◽  
V. Kulandaivelu ◽  
N. Hutchins
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Initial Conditions ◽  
Reynolds Numbers ◽  
Streamwise Velocity ◽  
Mean Flow ◽  
Flow Parameters ◽  
The Mean ◽  
Inflow Conditions

In this paper we study the spatial evolution of zero-pressure-gradient (ZPG) turbulent boundary layers from their origin to a canonical high-Reynolds-number state. A prime motivation is to better understand under what conditions reliable scaling behaviour comparisons can be made between different experimental studies at matched local Reynolds numbers. This is achieved here through detailed streamwise velocity measurements using hot wires in the large University of Melbourne wind tunnel. By keeping the unit Reynolds number constant, the flow conditioning, contraction and trip can be considered unaltered for a given boundary layer’s development and hence its evolution can be studied in isolation from the influence of inflow conditions by moving to different streamwise locations. Careful attention was given to the experimental design in order to make comparisons between flows with three different trips while keeping all other parameters nominally constant, including keeping the measurement sensor size nominally fixed in viscous wall units. The three trips consist of a standard trip and two deliberately ‘over-tripped’ cases, where the initial boundary layers are over-stimulated with additional large-scale energy. Comparisons of the mean flow, normal Reynolds stress, spectra and higher-order turbulence statistics reveal that the effects of the trip are seen to be significant, with the remnants of the ‘over-tripped’ conditions persisting at least until streamwise stations corresponding to $Re_{x}=1.7\times 10^{7}$ and $x=O(2000)$ trip heights are reached (which is specific to the trips used here), at which position the non-canonical boundary layers exhibit a weak memory of their initial conditions at the largest scales $O(10{\it\delta})$, where ${\it\delta}$ is the boundary layer thickness. At closer streamwise stations, no one-to-one correspondence is observed between the local Reynolds numbers ($Re_{{\it\tau}}$, $Re_{{\it\theta}}$ or $Re_{x}$ etc.), and these differences are likely to be the cause of disparities between previous studies where a given Reynolds number is matched but without account of the trip conditions and the actual evolution of the boundary layer. In previous literature such variations have commonly been referred to as low-Reynolds-number effects, while here we show that it is more likely that these differences are due to an evolution effect resulting from the initial conditions set up by the trip and/or the initial inflow conditions. Generally, the mean velocity profiles were found to approach a constant wake parameter ${\it\Pi}$ as the three boundary layers developed along the test section, and agreement of the mean flow parameters was found to coincide with the location where other statistics also converged, including higher-order moments up to tenth order. This result therefore implies that it may be sufficient to document the mean flow parameters alone in order to ascertain whether the ZPG flow, as described by the streamwise velocity statistics, has reached a canonical state, and a computational approach is outlined to do this. The computational scheme is shown to agree well with available experimental data.

scholarly journals The equilibria of vesicles adhered to substrates by short-ranged potentials

2013 ◽  
Vol 469 (2153) ◽  
pp. 20120729 ◽  
Author(s):  
Maurice J. Blount ◽  
Michael J. Miksis ◽  
Stephen H. Davis
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Layer Structure ◽  
Two Dimensional ◽  
Adhesive Interaction ◽  
Contact Potential ◽  
Layer Structures ◽  
Bending Stresses ◽  
Dimensional Boundary ◽  
Horizontal Substrate

In equilibrium, a vesicle that is adhered to a horizontal substrate by a long-range attractive, short-range repulsive force traps a thin layer of fluid beneath it. In the asymptotic limit that this layer is very thin, there are quasi-two-dimensional boundary-layer structures near the edges of the vesicle, where the membrane's shape is governed by a balance between bending and adhesive stresses. These boundary layers are analysed to obtain corrections to simpler models that instead represent the adhesive interaction by a contact potential, thereby resolving apparent discontinuities that arise when such models are used. Composite expansions of the shapes of two-dimensional vesicles are derived. When, in addition, the adhesive interaction is very strong, there is a nested boundary-layer structure for which the adhesive boundary layers match towards sharp corners where bending stresses remain important but adhesive stresses are negligible. Outside these corners, bending stresses are negligible and the vesicle's shape is given approximately by the arc of a circle. Simple composite expansions of the vesicle's shape are derived that account for the shape of the membrane inside these corners.

scholarly journals Diurnal Preconditioning of Subtropical Coastal Convective Storm Environments

2017 ◽  
Vol 145 (9) ◽  
pp. 3839-3859 ◽  
Author(s):  
Joshua S. Soderholm ◽  
Hamish A. McGowan ◽  
Harald Richter ◽  
Kevin Walsh ◽  
Tony Wedd ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Doppler Radar ◽  
Deep Convection ◽  
Sea Breeze ◽  
Return Flow ◽  
Convective Storm ◽  
Convective Boundary ◽  
Near Surface ◽  
Mesoscale Convective ◽  
Supercell Storms

Boundary layer evolution in response to diurnal forcing is manifested at the mesobeta and smaller scales of the atmosphere. Because this variability resides on subsynoptic scales, the potential influence upon convective storm environments is often not captured in coarse observational and modeling datasets, particularly for complex physical settings such as coastal regions. A detailed observational analysis of diurnally forced preconditioning for convective storm environments of South East Queensland, Australia (SEQ), during the Coastal Convective Interactions Experiment (2013–15) is presented. The observations used include surface-based measurements, aerological soundings, and dual-polarization Doppler radar. The sea-breeze circulation was found to be the dominant influence; however, profile modification by the coastward advection of the continental boundary layer was found to be an essential mechanism for favorable preconditioning of deep convection. This includes 1) enhanced moisture in the city of Brisbane, potentiality due to an urban heat island–enhanced land–sea thermal contrast, 2) significant afternoon warming and moistening above the sea breeze resulting from the advection of the inland convective boundary layer coastward under prevailing westerly flow coupled with the sea-breeze return flow, and 3) substantial variations in near-surface moisture likely associated with topography and land use. For the 27 November 2014 Brisbane hailstorm, which caused damages exceeding $1.5 billion Australian dollars (AUD), the three introduced diurnal preconditioning processes are shown to favor a mesoscale convective environment supportive of large hailstone growth. The hybrid high-precipitation supercell storm mode noted for this event and previous similar events in SEQ is hypothesized to be more sensitive to variations in near-surface and boundary layer instability in contrast to contemporary supercell storms.

Response of Simulated Squall Lines to Low-Level Cooling

2008 ◽  
Vol 65 (4) ◽  
pp. 1323-1341 ◽  
Author(s):  
Matthew D. Parker
Keyword(s):  
Boundary Layer ◽  
Initial Conditions ◽  
Cold Pool ◽  
Jet Streams ◽  
Near Surface ◽  
Low Level ◽  
Convective Systems ◽  
Central United States ◽  
Low Level Jet ◽  
Nocturnal Inversion

Abstract Organized convection has long been recognized to have a nocturnal maximum over the central United States. The present study uses idealized numerical simulations to investigate the mechanisms for the maintenance, propagation, and evolution of nocturnal-like convective systems. As a litmus test for the basic governing dynamics, the experiments use horizontally homogeneous initial conditions (i.e., they include neither fronts nor low-level jet streams). The simulated storms are allowed to mature as surface-based convective systems before the boundary layer is cooled. In this case it is then surprisingly difficult to cut the mature convective systems off from their source of near-surface inflow parcels. Even when 10 K of the low-level cooling has been applied, the preexisting system cold pool is sufficient to lift boundary layer parcels to their levels of free convection. The present results suggest that many of the nocturnal convective systems that were previously thought to be elevated may actually be surface based. With additional cooling, the simulated systems do, indeed, become elevated. First, the CAPE of the near-surface air goes to zero: second, as the cold pool’s temperature deficit vanishes, the lifting mechanism evolves toward a bore atop the nocturnal inversion. Provided that air above the inversion has CAPE, the system then survives and begins to move at the characteristic speed of the bore. Interestingly, as the preconvective environment is cooled and approaches the temperature of the convective outflow, but before the system becomes elevated, yet another distinct behavior emerges. The comparatively weaker cold pool entails slower system motion but also more intense lifting, apparently because it is more nearly balanced by the lower-tropospheric shear. This could explain the frequent observation of intensifying convective systems in the evening hours without the need for a nocturnal low-level jet. The governing dynamics of the simulated systems, as well as the behavior of low-level tracers and parcel trajectories, are addressed for a variety of environments and degrees of stabilization.

Evaluation of the Surface Wind Field over Land in WRF Simulations of Hurricane Wilma (2005). Part II: Surface Winds, Inflow Angles, and Boundary Layer Profiles

2021 ◽  
Author(s):  
David S. Nolan ◽  
Brian D. McNoldy ◽  
Jimmy Yunge ◽  
Forrest J. Masters ◽  
Ian M. Giammanco
Keyword(s):  
Boundary Layer ◽  
Wind Field ◽  
Initial Conditions ◽  
Surface Wind ◽  
Storm Track ◽  
South Florida ◽  
Modeling Framework ◽  
Near Surface ◽  
Hurricane Wilma ◽  
Wind Events

AbstractThis is the second of a two-part study that explores the capabilities of a mesoscale atmospheric model to reproduce the near-surface wind fields in hurricanes over land. The Weather Research and Forecasting Model (WRF) is used with two planetary boundary layer parameterizations: the Yonsei University (YSU) and the Mellor-Yamada-Janjić (MYJ) schemes. The first part presented the modeling framework and initial conditions used to produce simulations of Hurricane Wilma (2005) that closely reproduced the track, intensity, and size of its wind field as it passed over South Florida. This part explores how well these simulations can reproduce the winds at fixed points over land by making comparisons to observations from airports and research weather stations. The results show that peak wind speeds are remarkably well reproduced at several locations. Wind directions are evaluated in terms of the inflow angle relative to the storm center, and the simulated inflow angles are generally smaller than observed. Localized peak wind events are associated with vertical vorticity maxima in the boundary layer with horizontal scales of 5-10 km. The boundary layer winds are compared to wind profiles obtained by velocity-azimuth display (VAD) analyses from National Weather Service Doppler radars at Miami and Key West; results from these comparisons are mixed. Nonetheless the comparisons to surface observations suggest that when short-term hurricane forecasts can sufficiently predict storm track, intensity, and size, they will also be able to provide useful information on extreme winds at locations of interest.

Observations Pertaining to Precipitation within the Northeast Pacific Stratocumulus-to-Cumulus Transition

2019 ◽  
Vol 148 (3) ◽  
pp. 1251-1273
Author(s):  
Mampi Sarkar ◽  
Paquita Zuidema ◽  
Bruce Albrecht ◽  
Virendra Ghate ◽  
Jorgen Jensen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Initial Conditions ◽  
Mixed Boundary ◽  
Cloud Droplet ◽  
Mie Scattering ◽  
Cumulus Clouds ◽  
Different Depths ◽  
High Precipitation

Abstract Three genuine stratocumulus-to-cumulus transitions sampled during the Cloud System Evolution over the Trades (CSET) campaign are documented. The focus is on Lagrangian evolution of in situ precipitation, thought to exceed radar/lidar retrieved values because of Mie scattering. Two of the three initial stratocumulus cases are pristine [cloud droplet number concentrations (Nd) of ~22 cm−3] but occupied boundary layers of different depths, while the third is polluted (Nd ~ 225 cm−3). Hourly satellite-derived cloud fraction along Lagrangian trajectories indicate that more quickly deepening boundary layers tend to transition faster, into more intense but more occasional precipitation. These transitions begin either in the morning or late afternoon, suggesting that preceding night processes can precondition or delay the inevitable transition. The precipitation shifts toward larger drop sizes throughout the transition as the boundary layers deepen, with aerosol concentrations only diminishing in two of the three cases. Ultraclean (Nd < 1 cm−3) cumulus clouds evolved from pristine stratocumulus cloud with unusually high precipitation rates occupying a shallow, well-mixed boundary layer. Results from a simple one-dimensional evaporation model and from radar/lidar retrievals suggest subcloud evaporation likely increases throughout the transition. This, coupled with larger drop sizes capable of lowering the latent cooling profile, facilitates the transition to more surface-driven convection. The coassociation between boundary layer depth and precipitation does not provide definitive conclusions on the isolated effect of precipitation on the pace of the transition. Differences between the initial conditions of the three examples provide opportunities for further modeling studies.

scholarly journals The Characteristics of Numerically Simulated Supercell Storms Situated over Statically Stable Boundary Layers

2011 ◽  
Vol 139 (10) ◽  
pp. 3139-3162 ◽  
Author(s):  
Christopher J. Nowotarski ◽  
Paul M. Markowski ◽  
Yvette P. Richardson
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Stable Boundary Layer ◽  
Lapse Rate ◽  
Stable Layer ◽  
Near Surface ◽  
Stable Boundary Layers ◽  
Stable Boundary ◽  
Low Level ◽  
Supercell Thunderstorms

Abstract This paper uses idealized numerical simulations to investigate the dynamical influences of stable boundary layers on the morphology of supercell thunderstorms, especially the development of low-level rotation. Simulations are initialized in a horizontally homogeneous environment with a surface-based stable layer similar to that found within a nocturnal boundary layer or a mesoscale cold pool. The depth and lapse rate of the imposed stable boundary layer, which together control the convective inhibition (CIN), are varied in a suite of experiments. When compared with a control simulation having little surface-based CIN, each supercell simulated in an environment having a stable boundary layer develops weaker rotation, updrafts, and downdrafts at low levels; in general, low-level vertical vorticity and vertical velocity magnitude decrease as initial CIN increases (changes in CIN are due only to variations in the imposed stable boundary layer). Though the presence of a stable boundary layer decreases low-level updraft strength, all supercells except those initiated over the most stable boundary layers had at least some updraft parcels with near-surface origins. Furthermore, the existence of a stable boundary layer only prohibits downdraft parcels from reaching the lowest grid level in the most stable cases. Trajectory and circulation analyses indicate that weaker near-surface rotation in the stable-layer scenarios is a result of the decreased generation of circulation coupled with decreased convergence of the near-surface circulation by weaker low-level updrafts. These results may also suggest a reason why tornadogenesis is less likely to occur in so-called elevated supercell thunderstorms than in surface-based supercells.

scholarly journals Simple Solutions to Steady-State Cumulus Regimes in the Convective Boundary Layer

2013 ◽  
Vol 70 (11) ◽  
pp. 3656-3672 ◽  
Author(s):  
Jerôme Schalkwijk ◽  
Harmen J. J. Jonker ◽  
A. Pier Siebesma
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Mixed Layer ◽  
Large Scale ◽  
Initial Conditions ◽  
Cumulus Clouds ◽  
Modeling Framework ◽  
Convective Boundary ◽  
External Forcings ◽  
Lifting Condensation Level

Abstract A modeling framework is developed that extends the mixed-layer model to steady-state cumulus convection. The aim is to consider the simplest model that retains the essential behavior of cumulus-capped layers. The presented framework allows for the evaluation of stationary states dependent on external parameters. These states are completely independent of the initial conditions, and therefore represent an asymptote that might help deepen understanding of the dependence of the cloudy boundary layer on external forcings. Formulating separate equations for the lifting condensation level and the mixed-layer height, the dry and wet energetics can be distinguished. Regimes that can support steady-state cumulus clouds and regimes that cannot are identified by comparison of the dry and wet buoyancy effects. The dominant mechanisms that govern the creation and eventual depth of the cloud layer are identified. Model predictions are tested by comparison with a large number of independent large-eddy simulations for varying surface and large-scale conditions and are found to be in good agreement.

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