The Initiation and Evolution of Multiple Modes of Convection within a Meso-Alpha-Scale Region

French, Adam J.; Parker, Matthew D.

doi:10.1175/2008waf2222136.1

Cited by 18 publications

(15 citation statements)

References 50 publications

(56 reference statements)

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“…The authors believe that quantities such as the strength of the capping inversion and the nature of the atmospheric moisture profiles do play a role in how storms evolve. For example, modeling work by French and Parker (2008) indicated that temperature perturbations within convective outflows were sensitive to changes in vertical moisture profiles. These perturbations, in addition to the amount of convective inhibition, can determine how effectively the outflows can generate new convection, which, in turn, would have an influence on future storm evolution.…”

Section: Summary and Discussionmentioning

confidence: 99%

Short-Term Convective Mode Evolution along Synoptic Boundaries

Dial¹,

Racy²,

Thompson³

2010

Weather and Forecasting

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This paper investigates the relationships between short-term convective mode evolution, the orientations of vertical shear and mean wind vectors with respect to the initiating synoptic boundary, the motion of the boundary, and the role of forcing for ascent. The dominant mode of storms (linear, mixed mode, and discrete) was noted 3 h after convective initiation along cold fronts, drylines, or prefrontal troughs. Various shear and mean wind vector orientations relative to the boundary were calculated near the time of initiation. Results indicate a statistical correlation between storm mode at 3 h, the normal components of cloud-layer and deeplayer shear vectors, the boundary-relative mean cloud-layer wind vector, and the type of initiating boundary. Thunderstorms, most of which were initially discrete, tended to evolve more quickly into lines or mixed modes when the normal components of the shear vectors and boundary-relative mean cloud-layer wind vectors were small. There was a tendency for storms to remain discrete for larger normal shear and mean wind components. Smaller normal components of mean cloud-layer wind were associated with a greater likelihood that storms would remain within the zone of linear forcing along the boundary for longer time periods, thereby increasing the potential for upscale linear growth. The residence time of storms along the boundary is also dependent on the speed of the boundary. It was found that the boundary-relative normal component of the mean cloud-layer wind better discriminates between mode types than does simply the ground-relative normal component. The influence of mesoscale forcing for ascent and type of boundary on mode evolution was also investigated. As expected, it was found that the magnitude and nature of the forcing play a role in how storms evolve. For instance, strong linear low-level convergence often contributes to rapid upscale linear growth, especially if the boundary motion relative to the mean cloud-layer wind prevents storms from moving away from the boundary shortly after initiation. In summary, results from this study indicate that, for storms initiated along a synoptic boundary, convective mode evolution is modulated primarily by the residence time of storms within the zone of linear forcing, the nature and magnitude of linear forcing, and secondarily by the normal component of the cloud-layer shear.

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Section: Summary and Discussionmentioning

confidence: 99%

Short-Term Convective Mode Evolution along Synoptic Boundaries

Dial¹,

Racy²,

Thompson³

2010

Weather and Forecasting

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show abstract

“…2) or similarly in the buoyancy-shear domain (see Stensrud et al 1997), however, these methods are not sufficient to unambiguously distinguish between modes. Similarly, French and Parker (2008) show that environmental variations in thermodynamic and wind shear profiles within a confined area were responsible for a multimode convective day in that region. Markowski et al (1998), for example, document that SREH is highly variable on small spatial and temporal scales.…”

Section: Importance Of Convective Morphologymentioning

confidence: 99%

The Influence of Upper-Tropospheric Potential Vorticity on Convective Morphology

Schumann

Roebber

2010

Monthly Weather Review

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Extensive research has illuminated the roles that buoyancy and vertical wind shear have in determining convective mode. The goal of this study is to examine synoptic forcing, as measured by the form of the waves on the dynamic tropopause and the strength of the resultant temperature advection, together with the environmental variables that are currently used to differentiate storm type. Logistic regression is used to make this discrimination and provides the preliminary results. First, multicellular lines and isolated rotating cells are associated with weaker synoptic forcing. Second, where an upper-level feature is present, multicellular convection (lines and clusters combined) is favored relative to isolated storms when there is stronger synoptic forcing, the shape of the upper-level potential vorticity (PV) feature is elongated, and there is a more southerly component in the deep-layer (0-6 km) mean wind. Third, when an upper-level feature is present and the convection is multicellular, clusters are favored relative to lines when the upper wave is not cut off (i.e., a wave structure promoting advection), provided that the deep-layer shear is not oriented at an optimal angle relative to a preexisting meridional boundary (as shown by prior research). Finally, if the convection is isolated, rotating storms may be favored for a broad area of PV advection, as measured by the relative equality of the zonal and meridional axes of the advection area, suggesting the importance of broader-scale destabilization. These findings are used to formulate testable hypotheses. Future model-based experiments using PV surgery or PV regression methods are proposed to clearly elucidate the dynamics behind these relationships.

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“…Generally speaking, significant tornadoes and large hail often occur with supercell thunderstorms (e.g., Doswell and Burgess 1993;Davies-Jones et al 2001) whereas widespread damaging straight-line winds are more frequently produced by linear modes, particularly bow echoes (e.g., Fujita 1978;Przybylinski 1995). This becomes complicated, however, in cases where multiple organizational modes are present within a localized area (e.g., French and Parker 2008), especially when these modes merge into a single system. This can help them anticipate which severe weather hazards may occur and how those hazards may change with time.…”

Section: Introductionmentioning

confidence: 99%

Observations of Mergers between Squall Lines and Isolated Supercell Thunderstorms

French

Parker

2012

Weather and Forecasting

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A set of 21 cases in which an isolated supercell merged with a squall line were identified and investigated using analyses from the Rapid Update Cycle (RUC) model, archived data from the Weather Surveillance Radar-1988 Doppler (WSR-88D) network, and severe storm reports. This analysis revealed two primary environments associated with these mergers: a weak synoptic forcing, weak to moderate shear environment (WF) and a strong synoptic forcing, strong shear environment (SF). These environments bear a strong resemblance to those identified for progressive (WF) and serial (SF) derechoes in past studies. Radar reflectivity data revealed a spectrum of storm evolution patterns that generally lead to the merged system organizing as a bow echo. At one extreme, observed exclusively in the WF environment, the entire squall line evolved into a large bow echo following the merger. At the other extreme, observed for several cases in the SF environment, a localized bowing segment developed embedded within the larger squall line. The remaining cases exhibited characteristics best described as a hybrid of these extremes. Storm rotation generally weakened and became concentrated in low levels following the merger, although the exact evolution differed between the two background environments. Finally, an analysis of storm reports revealed that hail reports were maximized premerger and severe wind reports postmerger in both environments, while the distribution of tornado reports varied. In the WF environment a larger fraction of tornado reports occurred postmerger, while tornado production was maximized premerger in the SF environment. This suggests an evolving severe weather threat during the course of the merger, the details of which depend on the background environment. * Current affiliation: South Dakota School of Mines and Technology, Rapid City, South Dakota.

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The Initiation and Evolution of Multiple Modes of Convection within a Meso-Alpha-Scale Region

Cited by 18 publications

References 50 publications

Short-Term Convective Mode Evolution along Synoptic Boundaries

Short-Term Convective Mode Evolution along Synoptic Boundaries

The Influence of Upper-Tropospheric Potential Vorticity on Convective Morphology

Observations of Mergers between Squall Lines and Isolated Supercell Thunderstorms

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