The Use of Vertical Wind Shear versus Helicity in Interpreting Supercell Dynamics

A series of idealized simulations of supercell storms are presented for environments representing straight through circular hodographs to clarify the character of the storm dynamics over the large spectrum of hodograph shapes commonly observed. The primary emphasis is on comparing and contrasting recent theories of supercell dynamics, based on updraft‐shear interactions, storm-relative environmental helicity (SREH), and Beltrami-flow solutions, to help clarify the degree to which each theory can represent the essential storm dynamics. One of the particular questions being addressed is whether storm dynamics are significantly different for straight versus curved hodographs, which has become a point of some controversy over recent years. In agreement with previous studies, the authors find that the physical processes that promote storm maintenance, rotation, and propagation are similar for all hodograph shapes employed, and are due primarily to nonlinear interactions between the updraft and the ambient shear, associated with the localized development of rotation on the storm’s flank. Significant correlations between the updraft and vertical vorticity are also observed across the shear spectrum, and, in agreement with predictions of linear theories associated with SREH, this correlation increases for increasing hodograph curvature. However, storm steadiness and propagation must already be known or inferred for such concepts to be applied, thus limiting the applicability of this theory as a true predictor of storm properties. Tests of the applicability of Beltrami solutions also confirm reasonable agreement for purely circular hodographs, for which the analytical solutions are specifically designed. However, analysis of the model results indicates that the terms ignored for such solutions, representing the nonlinear effects associated with storm rotation, are more significant than those retained over most of the hodograph spectrum, which severely limits the general applicability of such analyses.

[1]  Kelvin K. Droegemeier,et al.  The Influence of Helicity on Numerically Simulated Convective Storms , 1993 .

[2]  H. Bluestein,et al.  Some Observations of a Splitting Severe Thunderstorm , 1979 .

[3]  Joseph B. Klemp,et al.  The Influence of the Shear-Induced Pressure Gradient on Thunderstorm Motion , 1982 .

[4]  Joseph B. Klemp,et al.  The Dependence of Numerically Simulated Convective Storms on Vertical Wind Shear and Buoyancy , 1982 .

[5]  G. Brier,et al.  Some applications of statistics to meteorology , 1958 .

[6]  Douglas K. Lilly,et al.  The Structure, Energetics and Propagation of Rotating Convective Storms. Part II: Helicity and Storm Stabilization , 1986 .

[7]  Robert Davies-Jones,et al.  Streamwise Vorticity: The Origin of Updraft Rotation in Supercell Storms , 1984 .

[8]  M. Weisman,et al.  Simulations of shallow supercell storms in landfalling hurricane environments , 1996 .

[9]  Charles A. Doswell,et al.  On the Environments of Tornadic and Nontornadic Mesocyclones , 1994 .

[10]  D. Lilly.  The Structure, Energetics and Propagation of Rotating Convective Storms. Part I: Energy Exchange with the Mean Flow , 1986 .

[11]  Robert A. Maddox,et al.  An Evaluation of Tornado Proximity Wind and Stability Data , 1976 .

[12]  Robert B. Wilhelmson,et al.  Simulations of Right- and Left-Moving Storms Produced Through Storm Splitting , 1978 .

[13]  N. Phillips,et al.  Scale Analysis of Deep and Shallow Convection in the Atmosphere , 1962 .

[14]  D. Lilly,et al.  The linear stability and structure of convection in a circular mean shear , 1996 .

[15]  J. Klemp,et al.  The Simulation of Three-Dimensional Convective Storm Dynamics , 1978 .

[16]  Joseph B. Klemp,et al.  DYNAMICS OF TORNADIC THUNDERSTORMS , 1987 .

[17]  K. Browning.  Airflow and Precipitation Trajectories Within Severe Local Storms Which Travel to the Right of the Winds , 1964 .

[18]  C. Doswell,et al.  Severe Thunderstorm Evolution and Mesocyclone Structure as Related to Tornadogenesis , 1979 .

[19]  R. Rotunno.  On the evolution of thunderstorm rotation , 1981 .

[20]  D. Durran,et al.  An Upper Boundary Condition Permitting Internal Gravity Wave Radiation in Numerical Mesoscale Models , 1983 .

[21]  Joseph B. Klemp,et al.  The structure and classification of numerically simulated convective storms in directionally varying wind shears , 1984 .

[22]  Robert E. Schlesinger,et al.  A Three-Dimensional Numerical Model of an Isolated Thunderstorm. Part II: Dynamics of Updraft Splitting and Mesovortex Couplet Evolution , 1980 .

[23]  D. Raymond.  A Model for Predicting the Movement of Continuously Propagating Convective Storms , 1975 .

[24]  The Dynamical Structure and Evolution of Thunderstorms and Squall Lines , 1979 .

[25]  H. Brooks,et al.  Hodograph Curvature and Updraft Intensity in Numerically Modeled Supercells , 1993 .

[26]  C. W. Newton,et al.  DYNAMICAL INTERACTIONS BETWEEN LARGE CONVECTIVE CLOUDS AND ENVIRONMENT WITH VERTICAL SHEAR , 1959 .

[27]  Joseph B. Klemp,et al.  On the Rotation and Propagation of Simulated Supercell Thunderstorms , 1985 .

[28]  Brynn W. Kerr,et al.  Storm-Relative Winds and Helicity in the Tornadic Thunderstorm Environment , 1996 .

[29]  Stanley L. Barnes,et al.  Some Aspects of a Severe, Right-Moving Thunderstorm Deduced from Mesonetwork Rawinsonde Observations. , 1970 .