A developing supercell thunderstorm in Texas

Weather ◽  
2020 ◽  
Vol 75 (5) ◽  
Keyword(s):  
Supercell Thunderstorm

scholarly journals Comparison between Dual-Doppler and EnKF Storm-Scale Wind Analyses: Observing System Simulation Experiments with a Supercell Thunderstorm

2012 ◽  
Vol 140 (12) ◽  
pp. 3972-3991 ◽  
Author(s):  
Corey K. Potvin ◽  
Louis J. Wicker
Keyword(s):  
System Simulation ◽  
Radar Data ◽  
Model Errors ◽  
Radar Observations ◽  
Low Level ◽  
Flow Evolution ◽  
Supercell Thunderstorm ◽  
Wind Retrievals ◽  
Observing System Simulation Experiment ◽  
Microphysical Parameterization

Abstract Kinematical analyses of mobile radar observations are critical to advancing the understanding of supercell thunderstorms. Maximizing the accuracy of these and subsequent dynamical analyses, and appropriately characterizing the uncertainty in ensuing conclusions about storm structure and processes, requires thorough knowledge of the typical errors obtained using different retrieval techniques. This study adopts an observing system simulation experiment (OSSE) framework to explore the errors obtained from ensemble Kalman filter (EnKF) assimilation versus dual-Doppler analysis (DDA) of storm-scale mobile radar data. The radar characteristics and EnKF model errors are varied to explore a range of plausible scenarios. When dual-radar data are assimilated, the EnKF produces substantially better wind retrievals at higher altitudes, where DDAs are more sensitive to unaccounted flow evolution, and in data-sparse regions such as the storm inflow sector. Near the ground, however, the EnKF analyses are comparable to the DDAs when the radar cross-beam angles (CBAs) are poor, and slightly worse than the DDAs when the CBAs are optimal. In the single-radar case, the wind analyses benefit substantially from using finer grid spacing than in the dual-radar case for the objective analysis of radar observations. The analyses generally degrade when only single-radar data are assimilated, particularly when microphysical parameterization or low-level environmental wind errors are introduced. In some instances, this leads to large errors in low-level vorticity stretching and Lagrangian circulation calculations. Nevertheless, the results show that while multiradar observations of supercells are always preferable, judicious use of single-radar EnKF assimilation can yield useful analyses.

Comparison of Two-Moment Bulk Microphysics Schemes in Idealized Supercell Thunderstorm Simulations

2011 ◽  
Vol 139 (4) ◽  
pp. 1103-1130 ◽  
Author(s):  
Hugh Morrison ◽  
Jason Milbrandt
Keyword(s):  
Three Dimensional ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Cold Pool ◽  
Fall Velocity ◽  
Surface Precipitation ◽  
Single Category ◽  
Supercell Thunderstorm ◽  
Drop Size Distributions ◽  
Reduced Surface

Idealized three-dimensional supercell simulations were performed using the two-moment bulk microphysics schemes of Morrison and Milbrandt–Yau in the Weather Research and Forecasting (WRF) model. Despite general similarities in these schemes, the simulations were found to produce distinct differences in storm structure, precipitation, and cold pool strength. In particular, the Morrison scheme produced much higher surface precipitation rates and a stronger cold pool, especially in the early stages of storm development. A series of sensitivity experiments was conducted to identify the primary differences between the two schemes that resulted in the large discrepancies in the simulations. Different approaches in treating graupel and hail were found to be responsible for many of the key differences between the baseline simulations. The inclusion of hail in the baseline simulation using the Milbrant–Yau scheme with two rimed-ice categories (graupel and hail) had little impact, and therefore resulted in a much different storm than the baseline run with the single-category (hail) Morrison scheme. With graupel as the choice of the single rimed-ice category, the simulated storms had considerably more frozen condensate in the anvil region, a weaker cold pool, and reduced surface precipitation compared to the runs with only hail, whose higher terminal fall velocity inhibited lofting. The cold pool strength was also found to be sensitive to the parameterization of raindrop breakup, particularly for the Morrison scheme, because of the effects on the drop size distributions and the corresponding evaporative cooling rates. The use of a more aggressive implicit treatment of drop breakup in the baseline Morrison scheme, by limiting the mean–mass raindrop diameter to a maximum of 0.9 mm, opposed the tendency of this scheme to otherwise produce large mean drop sizes and a weaker cold pool compared to the hail-only run using the Milbrandt–Yau scheme.

Supercell thunderstorm charge structure variability and influences on spatial lightning flash relationships with the updraft

2021 ◽  
Author(s):  
Christopher J. Schultz ◽  
Daniel J. Cecil
Keyword(s):  
Negative Charge ◽  
Spatial Scales ◽  
Subsequent Development ◽  
Lightning Flash ◽  
Charge Structure ◽  
Kinematic Characteristics ◽  
Tennessee Valley ◽  
Initial Charge ◽  
Supercell Thunderstorm ◽  
Cloud Ice

Abstract Relationships between lightning flashes and thunderstorm kinematics and microphysics are important for applications such as nowcasting of convective intensity. These relationships are influenced by cloud electrification structures and have been shown to vary in anomalously electrified thunderstorms. This study addresses transitional relationships between active charge structure and lightning flash location in the context of kinematic and microphysical updraft characteristics during the development of an anomalously electrified supercell thunderstorm in the Tennessee Valley on 10 April 2009. The initial charge structure within the updraft was characterized as an anomalous dipole in which positive charge was inferred in regions of precipitation ice (i.e., graupel and hail) and negative charge was inferred in regions of cloud ice (i.e., aggregates and ice crystals). During subsequent development of the anomalous charge structure, additional minor charge layers as well as evidence of increasing horizontal complexity were observed. Microphysical and kinematic characteristics of the charge structure also evolved to include increasing observations of negative charge in precipitation ice regions, indicating the emergence of more prominent normal charging alongside dominant anomalous charging. Simultaneously, lightning flash initiation locations were also increasingly observed in regions of faster updrafts and stronger horizontal gradients in updraft speed. It is suggested that continuous variability in charging behavior over meso-gamma spatial scales influenced the evolution of lightning flash locations with respect to the updraft structure. Further work is necessary to determine how this variability may impact lightning flash relation-ships, including lightning flash rate, with bulk microphysical and kinematic characteristics and related applications.

scholarly journals “Near Ground” Vertical Vorticity in Supercell Thunderstorm Models

2017 ◽  
Vol 74 (6) ◽  
pp. 1757-1766 ◽  
Author(s):  
Richard Rotunno ◽  
Paul M. Markowski ◽  
George H. Bryan
Keyword(s):  
Numerical Models ◽  
Vertical Axis ◽  
Lower Surface ◽  
Lagrangian Analysis ◽  
Near Surface ◽  
Vertical Vorticity ◽  
Final Approach ◽  
History Of ◽  
Vorticity Dynamics ◽  
Supercell Thunderstorm

Abstract Numerical models of supercell thunderstorms produce near-ground rotation about a vertical axis (i.e., vertical vorticity) after the development of rain-cooled outflows and downdrafts. The physical processes involved in the production of near-ground vertical vorticity in simulated supercells have been a subject of discussion in the literature for over 30 years. One cause for this lengthy discussion is the difficulty in applying the principles of inviscid vorticity dynamics in a continuous fluid to the viscous evolution of discrete Eulerian simulations. The present paper reports on a Lagrangian analysis of near-ground vorticity from an idealized-supercell simulation with enhanced vertical resolution near the lower surface. The parcel that enters the low-level maximum of vertical vorticity has a history of descent during which its horizontal vorticity is considerably enhanced. In its final approach to this region, the parcel’s enhanced horizontal vorticity is tilted to produce vertical vorticity, which is then amplified through vertical stretching as the parcel rises. A simplified theoretical model is developed that exhibits these same features. The principal conclusion is that vertical vorticity at the parcel’s nadir (its lowest point), although helpful, does not need to be positive for rapid near-surface amplification of vertical vorticity.

scholarly journals Impact of Environmental Heterogeneity on the Dynamics of a Dissipating Supercell Thunderstorm

2015 ◽  
Vol 143 (10) ◽  
pp. 4244-4277 ◽  
Author(s):  
Casey E. Davenport ◽  
Matthew D. Parker
Keyword(s):  
Environmental Heterogeneity ◽  
Wind Profile ◽  
Environmental Temperature ◽  
Dominant Role ◽  
Source Region ◽  
Vertical Acceleration ◽  
Supercell Thunderstorm ◽  
The Mean ◽  
Wind Profiles ◽  
Morphology Changes

Abstract On 9 June 2009, the Second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) sampled a supercell as it traversed through an increasingly stable environment with decreasing bulk shear and storm-relative helicity. To investigate the impacts of the observed environmental heterogeneity on storm morphology, a series of idealized simulations were conducted. Utilizing the base-state substitution modeling technique, the separate effects of the changing wind profile and the increasingly stable boundary layer were evaluated. The varying base-state environment in each experiment elevated the mean source region of updraft parcels. These elevated parcels were drier (with less instability), and more negatively impacted by entrainment. Thus, as the updraft ingested a larger fraction of elevated parcels, its buoyancy was depleted, leading to demise. Unsurprisingly, the increasingly stable low-level environment played a dominant role in this process; however, wind profile modifications also elevated the mean source region of updraft parcels, which independently impacted storm strength and morphology. Changes to the storm’s internal dynamical processes were assessed using the diagnostic pressure equation. The evolution in total vertical acceleration was primarily related to changes in accelerations that were connected to updraft rotation, as well as shifts in buoyancy. The dynamical accelerations weakened and became maximized at a different altitude, resulting in an increasingly elevated updraft parcel source region. Overall, this study finds that a shifting updraft parcel source region can significantly impact storm maintenance; importantly, such a shift can result from changes in environmental temperature, moisture, or wind profiles.

Effective Storm-Relative Helicity and Bulk Shear in Supercell Thunderstorm Environments

2007 ◽  
Vol 22 (1) ◽  
pp. 102-115 ◽  
Author(s):  
Richard L. Thompson ◽  
Corey M. Mead ◽  
Roger Edwards
Keyword(s):  
Lower Bounds ◽  
Broad Spectrum ◽  
Model Analysis ◽  
Vertical Shear ◽  
Upper And Lower Bounds ◽  
Wide Range ◽  
Equilibrium Level ◽  
Supercell Thunderstorm ◽  
Convective Inhibition ◽  
Minimum Constraints

Abstract A sample of 1185 Rapid Update Cycle (RUC) model analysis (0 h) proximity soundings, within 40 km and 30 min of radar-identified discrete storms, was categorized by several storm types: significantly tornadic supercells (F2 or greater damage), weakly tornadic supercells (F0–F1 damage), nontornadic supercells, elevated right-moving supercells, storms with marginal supercell characteristics, and nonsupercells. These proximity soundings served as the basis for calculations of storm-relative helicity and bulk shear intended to apply across a broad spectrum of thunderstorm types. An effective storm inflow layer was defined in terms of minimum constraints on lifted parcel CAPE and convective inhibition (CIN). Sixteen CAPE and CIN constraint combinations were examined, and the smallest CAPE (25 and 100 J kg−1) and largest CIN (−250 J kg−1) constraints provided the greatest probability of detecting an effective inflow layer within an 835-supercell subset of the proximity soundings. Effective storm-relative helicity (ESRH) calculations were based on the upper and lower bounds of the effective inflow layer. By confining the SRH calculation to the effective inflow layer, ESRH values can be compared consistently across a wide range of storm environments, including storms rooted above the ground. Similarly, the effective bulk shear (EBS) was defined in terms of the vertical shear through a percentage of the “storm depth,” as defined by the vertical distance from the effective inflow base to the equilibrium level associated with the most unstable parcel (maximum θe value) in the lowest 300 hPa. ESRH and EBS discriminate strongly between various storm types, and between supercells and nonsupercells, respectively.

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