A Five-Year Radar-Based Climatology of Tropopause Folds and Deep Convection over Wales, United Kingdom

AbstractA five-year (2006–10) radar-based climatology of tropopause folds and convective storms was constructed for Wales, United Kingdom, to determine how deep, moist convection is modulated by tropopause folds. Based on the continuous, high-resolution data from a very high frequency (VHF) wind-profiling radar located at Capel Dewi, Wales, 183 tropopause folds were identified. Tropopause folds were most frequent in January with a secondary maximum in July. Based on data from the U.K. weather radar network, a climatology of 685 convective storms was developed. The occurrence of convective storms was relatively high year-round except for an abrupt minimum in February–April. Multicellular lines (43.5%) were the most common morphology with a maximum in October, followed by isolated cells (33.1%) with a maximum in May–September, and nonlinear clusters (23.4%) with a maximum in November–January. Convective storms were associated with 104 (56.8%) of the tropopause folds identified in this study, with the association strongest in December. Of the 55 tropopause folds observed on the eastern side of an upper-level trough, 37 (67.3%) were associated with convective storms, most commonly in the form of multicellular lines. Of the 128 tropopause folds observed on the western side of an upper-level trough, 42 (32.8%) were associated with convective storms, most commonly isolated cells. These results suggest that more organized storms tend to form in environments favorable for synoptic-scale ascent.

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Numerical Simulations of Interactions between Gravity Waves and Deep Moist Convection

Journal of the Atmospheric Sciences ◽

10.1175/jas3418.1 ◽

2005 ◽

Vol 62 (5) ◽

pp. 1480-1496 ◽

Cited By ~ 2

Author(s):

Zachary A. Eitzen ◽

David A. Randall

Keyword(s):

Gravity Waves ◽

Deep Convection ◽

Velocity Versus ◽

Moist Convection ◽

Vertical Grid ◽

Wave Energy Flux ◽

Deep Moist Convection ◽

Vertically Propagating ◽

The Tropics ◽

The Waves

Abstract This study uses a numerical model to simulate deep convection both in the Tropics over the ocean and the midlatitudes over land. The vertical grid that was used extends into the stratosphere, allowing for the simultaneous examination of the convection and the vertically propagating gravity waves that it generates. A large number of trajectories are used to evaluate the behavior of tracers in the troposphere, and it is found that the tracers can be segregated into different types based upon their position in a diagram of normalized vertical velocity versus displacement. Conditional sampling is also used to identify updrafts in the troposphere and calculate their contribution to the kinetic energy budget of the troposphere. In addition, Fourier analysis is used to characterize the waves in the stratosphere; it was found that the waves simulated in this study have similarities to those observed and simulated by other researchers. Finally, this study examines the wave energy flux as a means to provide a link between the tropospheric behavior of the convection and the strength of the waves in the stratosphere.

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Evaluating the conservation of energy variables in simulations of deep moist convection

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0351.1 ◽

2021 ◽

Author(s):

John M. Peters ◽

Daniel R. Chavas

Keyword(s):

Heat Capacity ◽

Numerical Models ◽

Deep Convection ◽

Squall Line ◽

Moist Convection ◽

Conservation Of Energy ◽

Deep Moist Convection ◽

Static Energy ◽

Hydrostatic Balance ◽

Latent Heats

AbstractIt is often assumed in parcel theory calculations, numerical models, and cumulus parameterizations that moist static energy (MSE) is adiabatically conserved. However, the adiabatic conservation of MSE is only approximate because of the assumption of hydrostatic balance. Two alternative variables are evaluated here: MSE −IB and MSE +KE, wherein IB is the path integral of buoyancy (B) and KE is kinetic energy. Both of these variables relax the hydrostatic assumption and are more precisely conserved than MSE. This article quantifies the errors that result from assuming that the aforementioned variables are conserved in large eddy simulations (LES) of both disorganized and organized deep convection. Results show that both MSE −IB and MSE +KE better predict quantities along trajectories than MSE alone. MSE −IB is better conserved in isolated deep convection, whereas MSE −IB and MSE +KE perform comparably in squall line simulations. These results are explained by differences between the pressure perturbation behavior of squall lines and isolated convection. Errors in updraft B diagnoses are universally minimized when MSE−IB is assumed to be adiabatically conserved, but only when moisture dependencies of heat capacity and temperature dependency of latent heating are accounted for. When less accurate latent heat and heat capacity formulae were used, MSE−IB yielded poorer B predictions than MSE due to compensating errors. Our results suggest that various applications would benefit from using either MSE −IB or MSE +KE instead of MSE with properly formulated heat capacities and latent heats.

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Size-Resolved Evaluation of Simulated Deep Tropical Convection

Monthly Weather Review ◽

10.1175/mwr-d-17-0378.1 ◽

2018 ◽

Vol 146 (7) ◽

pp. 2161-2182 ◽

Cited By ~ 13

Author(s):

Fabian Senf ◽

Daniel Klocke ◽

Matthias Brueck

Keyword(s):

Deep Convection ◽

Winter Season ◽

Power Laws ◽

Moist Convection ◽

Modeling Framework ◽

Western Atlantic ◽

Spatial Coupling ◽

Wide Range ◽

Realistic Representation ◽

Deep Moist Convection

Abstract Deep moist convection is an inherently multiscale phenomenon with organization processes coupling convective elements to larger-scale structures. A realistic representation of the tropical dynamics demands a simulation framework that is capable of representing physical processes across a wide range of scales. Therefore, storm-resolving numerical simulations at 2.4 km have been performed covering the tropical Atlantic and neighboring parts for 2 months. The simulated cloud fields are combined with infrared geostationary satellite observations, and their realism is assessed with the help of object-based evaluation methods. It is shown that the simulations are able to develop a well-defined intertropical convergence zone. However, marine convective activity measured by the cold cloud coverage is considerably underestimated, especially for the winter season and the western Atlantic. The spatial coupling across the resolved scales leads to simulated cloud number size distributions that follow power laws similar to the observations, with slopes steeper in winter than summer and slopes steeper over ocean than over land. The simulated slopes are, however, too steep, indicating too many small and too few large tropical cloud cells. It is also discussed that the number of larger cells is less influenced by multiday variability of environmental conditions. Despite the identified deficits, the analyzed simulations highlight the great potential of this modeling framework for process-based studies of tropical deep convection.

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A Lagrangian Perspective on Parameterizing Deep Convection

Monthly Weather Review ◽

10.1175/mwr-d-19-0164.1 ◽

2019 ◽

Vol 147 (11) ◽

pp. 4127-4149 ◽

Cited By ~ 2

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.

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Rapid Filamentation Zones in Intense Tropical Cyclones

Journal of the Atmospheric Sciences ◽

10.1175/jas3595.1 ◽

2006 ◽

Vol 63 (1) ◽

pp. 325-340 ◽

Cited By ~ 104

Author(s):

Christopher M. Rozoff ◽

Wayne H. Schubert ◽

Brian D. McNoldy ◽

James P. Kossin

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

Coherent Structures ◽

Deep Convection ◽

Relative Vorticity ◽

Moist Convection ◽

Vortex Interaction ◽

Tangential Wind ◽

Stratiform Precipitation ◽

Deep Moist Convection

Abstract Intense tropical cyclones often possess relatively little convection around their cores. In radar composites, this surrounding region is usually echo-free or contains light stratiform precipitation. While subsidence is typically quite pronounced in this region, it is not the only mechanism suppressing convection. Another possible mechanism leading to weak-echo moats is presented in this paper. The basic idea is that the strain-dominated flow surrounding an intense vortex core creates an unfavorable environment for sustained deep, moist convection. Strain-dominated regions of a tropical cyclone can be distinguished from rotation-dominated regions by the sign of S21 + S22 − ζ2, where S1 = ux − υy and S2 = υx + uy are the rates of strain and ζ = υx − uy is the relative vorticity. Within the radius of maximum tangential wind, the flow tends to be rotation-dominated (ζ2 > S21 + S22), so that coherent structures, such as mesovortices, can survive for long periods of time. Outside the radius of maximum tangential wind, the flow tends to be strain-dominated (S21 + S22 > ζ2), resulting in filaments of anomalous vorticity. In the regions of strain-dominated flow the filamentation time is defined as τfil = 2(S21 + S22 − ζ2)−1/2. In a tropical cyclone, an approximately 30-km-wide annular region can exist just outside the radius of maximum tangential wind, where τfil is less than 30 min and even as small as 5 min. This region is defined as the rapid filamentation zone. Since the time scale for deep moist convective overturning is approximately 30 min, deep convection can be significantly distorted and even suppressed in the rapid filamentation zone. A nondivergent barotropic model illustrates the effects of rapid filamentation zones in category 1–5 hurricanes and demonstrates the evolution of such zones during binary vortex interaction and mesovortex formation from a thin annular ring of enhanced vorticity.

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Parameterized Mesoscale Forcing Mechanisms for Initiating Numerically Simulated Isolated Multicellular Convection

Monthly Weather Review ◽

10.1175/2007mwr2133.1 ◽

2008 ◽

Vol 136 (7) ◽

pp. 2408-2421 ◽

Cited By ~ 22

Author(s):

Adrian M. Loftus ◽

Daniel B. Weber ◽

Charles A. Doswell

Keyword(s):

Cloud Model ◽

Deep Convection ◽

Initial Perturbation ◽

Three Dimensional ◽

Vertical Motion ◽

Heat Fluxes ◽

Convection Cell ◽

Moist Convection ◽

Near Surface ◽

Deep Moist Convection

Abstract Two methods designed to parameterize mesoscale ascent in a three-dimensional numerical cloud model via near-surface momentum and heat fluxes are presented and compared to the commonly used technique of an initial perturbation placed within the model initial condition. The flux techniques use a continuously reinforced thermal or convergent low-level wind field to produce upward vertical motion on the order of 10 cm s−1, by which deep, moist convection can be initiated. The sensitivity of the convective response to the type, strength, and size of the forcing is evaluated using numerical simulations of a conditionally unstable environment with weak unidirectional shear. Precipitation-free cloud processes are used to further simplify the model response to the forcing. The three methods tested produce an initial convective response, but only the momentum and heat flux methods are able to produce sustained deep convection that approximately resembles isolated multicellular convection. Cell regeneration periods, defined as the elapsed time between subsequent vertical velocity maxima passing through a constant level in the updraft region above the source, vary from 8 to 25 min, depending on the forcing type, magnitude, and geometry.

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Radiosonde observations of environments supporting deep moist convection initiation during RELAMPAGO-CACTI

Monthly Weather Review ◽

10.1175/mwr-d-20-0148.1 ◽

2020 ◽

Author(s):

T. Connor Nelson ◽

James Marquis ◽

Adam Varble ◽

Katja Friedrich

Keyword(s):

Complex Terrain ◽

Deep Convection ◽

Convective Available Potential Energy ◽

Environmental Parameters ◽

Convective Precipitation ◽

Moist Convection ◽

Spatiotemporal Resolution ◽

Close Proximity ◽

Deep Moist Convection ◽

Convection Initiation

AbstractThe Remote Sensing of Electrification, Lightning, and Mesoscale/Microscale Processes with Adaptive Ground Observations (RELAMPAGO) and Cloud, Aerosol, and Complex Terrain Interactions (CACTI) projects deployed a high-spatiotemporal-resolution radiosonde network to examine environments supporting deep convection in the complex terrain of central Argentina. This study aims to characterize atmospheric profiles most representative of the near-cloud environment (in time and space) to identify the mesoscale ingredients affecting storm initiation and growth. Spatiotemporal autocorrelation analysis of the soundings reveals that there is considerable environmental heterogeneity, with boundary layer thermodynamic and kinematic fields becoming statistically uncorrelated on scales of 1–2 hr and 30 km. Using this as guidance, we examine a variety of environmental parameters derived from soundings collected within close proximity (30 km and 30 min in space and time) of 44 events over 9 days where the atmosphere either: 1) supported the initiation of sustained precipitating convection, 2) yielded weak and short-lived precipitating convection, or 3) produced no precipitating convection in disagreement with numerical forecasts from convection-allowing models (i.e., Null events). There are large statistical differences between the Null event environments and those supporting any convective precipitation. Null event profiles contained larger convective available potential energy, but had low free tropospheric relative humidity, higher freezing levels, and evidence of limited horizontal convergence near the terrain at low levels that likely suppressed deep convective growth. We also present evidence from the radiosonde and satellite measurements that flow-terrain interactions may yield gravity wave activity that affects CI outcome.

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Low-level Mesoscale and Cloud-scale Interactions Promoting Deep Convection Initiation

Monthly Weather Review ◽

10.1175/mwr-d-20-0391.1 ◽

2021 ◽

Author(s):

James N. Marquis ◽

Adam C. Varble ◽

Paul Robinson ◽

T. Connor. Nelson ◽

Katja Friedrich

Keyword(s):

Boundary Layer ◽

Deep Convection ◽

Convective Available Potential Energy ◽

Surface Wind ◽

Horizontal Wind ◽

Moist Convection ◽

Surface Precipitation ◽

Low Level ◽

Deep Moist Convection ◽

Convection Initiation

AbstractData from scanning radars, radiosondes, and vertical profilers deployed during three field campaigns are analyzed to study interactions between cloud-scale updrafts associated with initiating deep moist convection and the surrounding environment. Three cases are analyzed in which the radar networks permitted dual-Doppler wind retrievals in clear air preceding and during the onset of surface precipitation. These observations capture the evolution of: i) the mesoscale and boundary layer flow, and ii) low-level updrafts associated with deep moist convection initiation (CI) events yielding sustained or short-lived precipitating storms.The elimination of convective inhibition did not distinguish between sustained and unsustained CI events, though the vertical distribution of convective available potential energy may have played a role. The clearest signal differentiating the initiation of sustained versus unsustained precipitating deep convection was the depth of the low-level horizontal wind convergence associated with the mesoscale flow feature triggering CI, a sharp surface wind shift boundary or orographic upslope flow. The depth of the boundary layer relative to the height of the LFC failed to be a consistent indicator of CI potential. Widths of the earliest detectable low-level updrafts associated with sustained precipitating deep convection were ~3-5 km, larger than updrafts associated with surrounding boundary layer turbulence (~1-3-km wide). It is hypothesized that updrafts of this larger size are important for initiating cells to survive the destructive effects of buoyancy dilution via entrainment.

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Evaluation of scale-aware convection schemes at the kilometer-scale resolution

10.5194/egusphere-egu2020-5337 ◽

2020 ◽

Author(s):

Xu Zhang ◽

Jian-Wen Bao ◽

Baode Chen

Keyword(s):

Deep Convection ◽

Wrf Model ◽

Horizontal Resolution ◽

Theory And Practice ◽

Coarse Grained ◽

Great Effort ◽

Moist Convection ◽

Direct Evaluation ◽

Deep Moist Convection ◽

Convection Schemes

<p>Numerical weather predictions (NWP) models are increasingly run using kilometer-scale horizontal grid spacing at which convection is partially resolved and the use of a subgrid convection parameterization scheme is still required. Traditionally, subgrid deep convection has been represented by mass flux-based convection parameterizations based on the ensemble-mean closure concept. Recently, a great effort has been made to develop scale-aware subgrid convection schemes that can be used in kilometer-scale NWP models. However, direct evaluation of these schemes is rarely done using coarse-grained large-eddy simulation (LES).</p><p>In this study, an idealized LES of deep moist convection is performed to assess the performance of three widely-used scale-aware subgrid convection schemes in the Weather Research and Forecast (WRF) model that is run at 3-km horizontal resolution. It is found that the simulations using the three schemes not only differ from each other but also do not converge to the coarse-grained LES, indicating that further investigation is required as to what &#8220;scale-awareness&#8221; means in theory and practice.</p>

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Multi-Scale Transects of Three North American Drylines

Atmosphere ◽

10.3390/atmos11080854 ◽

2020 ◽

Vol 11 (8) ◽

pp. 854

Author(s):

Loren D. White ◽

Duanjun Lu

Keyword(s):

North American ◽

Mountainous Terrain ◽

Moist Convection ◽

Convective Storms ◽

Multi Scale ◽

West Texas ◽

Deep Moist Convection ◽

Using Data ◽

Over Time ◽

Observing Systems

North American drylines are distinct air mass boundaries that have often been examined for their relation to the initiation of severe convective storms. Three cases of drylines occurring in synoptically quiescent environments are analyzed using data obtained from a single mobile platform in concert with data from operational synoptic and mesoscale observing systems. Very distinct moisture contrasts were noted in a nocturnal April case in mountainous terrain in the Trans-Pecos region of West Texas. The other two cases revealed multi-step moisture transitions within synoptically diffuse moisture gradients. Their evolution over time suggests that such multi-step patterns may be associated with diurnal and geographic forcing transitions, as well as positioning of deep moist convection.

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