Numerical simulation of tornadogenesis in a high-precipitation supercell. Part I : Storm evolution and transition into a bow echo

A nested grid primitive equation model (RAMS version 3b) was used to simulate a high-precipitation (HP) supercell, which produced two weak tornadoes. Six telescoping nested grids allowed atmospheric flows ranging from the synoptic scale down to the tornadic scale to be represented in the simulation. All convection in the simulation was initiated with resolved vertical motion and subsequent condensation‐latent heating from the model microphysics; no warm bubbles or cumulus parameterizations were used. Part I of this study focuses on the simulated storm evolution and its transition into a bow echo. The simulation initially produced a classic supercell that developed at the intersection between a stationary front and an outflow boundary. As the simulation progressed, additional storms developed and interacted with the main storm to produce a single supercell. This storm had many characteristics of an HP supercell and eventually evolved into a bow echo with a rotating comma-head structure. An analysis of the storm’s transition into a bow echo revealed that the interaction between convective cells triggered a series of events that played a crucial role in the transition. The simulated storm structure and evolution differed significantly from that of classic supercells produced by idealized simulations. Several vertical vorticity and condensate maxima along the flanking line moved northward and merged into the mesocyclone at the northern end of the convective line during the bow echo transition. Vorticity budget calculations in the mesocyclone showed that vorticity advection from the flanking line into the mesocyclone was the largest positive vorticity tendency term just prior to and during the early phase of the transition in both the low- and midlevel mesocyclone, and remained a significant positive tendency in the midlevel mesocyclone throughout the bow echo transition. This indicates that the flanking line was a source of vertical vorticity for the mesocyclone, and may explain how the mesocyclone was maintained in the HP supercell even though it was completely embedded in heavy precipitation. The simulated supercell also produced two weak tornadoes. The evolution of the simulated tornadoes and an analysis of the tornadogenesis process will be presented in Part II.

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

[2]  A. Arakawa,et al.  A Potential Enstrophy and Energy Conserving Scheme for the Shallow Water Equations , 1981 .

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

[4]  W. Cotton,et al.  Interactions between Upper and Lower Tropospheric Gravity Waves on Squall Line Structure and Maintenance , 1990 .

[5]  C. J. Tremback,et al.  A surface temperature and moisture parameterization for use in mesoscale numerical models , 1985 .

[6]  W. Skamarock,et al.  Three-Dimensional Evolution of Simulated Long-Lived Squall Lines , 1994 .

[7]  Jerome M. Schmidt.  Numerical and Observational Investigations of Long-Lived Mcs-Induced Severe Surface Wind Events: the Derecho , 1991 .

[8]  K. Browning.  THE ORGANIZATION OF SEVERE LOCAL STORMS , 1968 .

[9]  R. Pielke,et al.  Thermally Forced Gravity Waves in an Atmosphere at Rest , 1991 .

[10]  Robert B. Wilhelmson,et al.  Observed and numerically simulated structure of a mature supercell thunderstorm , 1981 .

[11]  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 .

[12]  Interactions between a Developing Mesoscale Convective System and Its Environment. Part II: Numerical Simulation , 2000 .

[13]  Brian E. Mapes,et al.  Gregarious Tropical Convection , 1993 .

[14]  S. Barnes,et al.  Mesoscale objective map analysis using weighted time-series observations , 1973 .

[15]  Robert B. Wilhelmson,et al.  A Numerical Study of Storm Splitting that Leads to Long-Lived Storms , 1978 .

[16]  William R. Cotton,et al.  Multiscale Evolution of a Derecho-Producing Mesoscale Convective System , 1998 .

[17]  Joseph B. Klemp,et al.  A Study of the Tornadic Region within a Supercell Thunderstorm , 1983 .

[18]  Caskey,et al.  GENERAL CIRCULATION EXPERIMENTS WITH THE PRIMITIVE EQUATIONS I . THE BASIC EXPERIMENT , 1962 .

[19]  D. Stensrud,et al.  Mesoscale Convective Systems in Weakly Forced Large-Scale Environments. Part III: Numerical Simulations and Implications for Operational Forecasting , 1994 .

[20]  Robert A. Houze,et al.  Radar Characteristics of Tropical Convection Observed During GATE: Mean Properties and Trends Over the Summer Season , 1977 .

[21]  M. Weisman.  The Role of Convectively Generated Rear-Inflow Jets in the Evolution of Long-Lived Mesoconvective Systems , 1992 .

[22]  R. Pielke,et al.  A comprehensive meteorological modeling system—RAMS , 1992 .

[23]  Richard Rotunno,et al.  On the Linear Theory of the Land and Sea Breeze , 1983 .

[24]  D. Stensrud,et al.  Mesoscale Convective Systems in Weakly Forced Large-Scale Environments. Part II: Generation of a Mesoscale Initial Condition , 1994 .

[25]  C. Doswell,et al.  The Operational Meteorology of Convective Weather. Volume 1. Operational Mesoanalysis. , 1982 .

[26]  S. L. Barnes.  Oklahoma Thunderstorms on 29–30 April 1970. Part II: Radar-Observed Merger of Twin Hook Echoes , 1978 .

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

[28]  Margaret A. LeMone,et al.  Momentum Transport by a Line of Cumulonimbus , 1983 .

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

[30]  R. Carbone,et al.  The Evolution and Structure of a “Bow–Echo-Microburst” Event. Part II: The Bow Echo , 1992 .

[31]  G. E. Hill.  Factors Controlling the Size and Spacing of Cumulus Clouds as Revealed by Numerical Experiments , 1974 .

[32]  Robert G. Fovell,et al.  Effect of vertical wind shear on numerically simulated multicell storm structure , 1989 .

[33]  J. Simpson,et al.  Seeding Cumulus in Florida: New 1970 Results , 1971, Science.

[34]  S. Nelson,et al.  The Hybrid Multicellular–Supercellular Storm—an Efficient Hail Producer. Part I: An Archetypal Example , 1987 .

[35]  Joseph B. Klemp,et al.  Structure and Evolution of Numerically Simulated Squall Lines , 1988 .

[36]  Robert H. Johns,et al.  Derechos: Widespread Convectively Induced Windstorms , 1987 .

[37]  Louis J. Wicker,et al.  Simulation and Analysis of Tornado Development and Decay within a Three-Dimensional Supercell Thunderstorm , 1995 .

[38]  Jesslyn F. Brown,et al.  Development of a land-cover characteristics database for the conterminous U.S. , 1991 .

[39]  L. Lemon.  The Flanking Line, a Severe Thunderstorm Intensification Source , 1976 .

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

[41]  Charles A. Doswell,et al.  The Tornado : its structure, dynamics, prediction, and hazards , 1993 .

[42]  G. Foote,et al.  Case Study of a Hailstorm in Colorado. Part III: Airflow From Triple-Doppler Measurements. , 1983 .

[43]  Yuh-Lang Lin,et al.  The Structure and Evolution of a Numerically Simulated High-Precipitation Supercell Thunderstorm , 1998 .

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

[45]  S. Barnes,et al.  A Technique for Maximizing Details in Numerical Weather Map Analysis , 1964 .

[46]  H. Brooks,et al.  Numerical simulation of a low-precipitation supercell thunderstorm , 1992 .

[47]  Howard B. Bluestein,et al.  A Synoptic and Photographic Climatology of Low-Precipitation Severe Thunderstorms in the Southern Plains , 1983 .

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

[49]  William R. Cotton,et al.  A Numerical Investigation of Several Factors Contributing to the Observed Variable Intensity of Deep Convection over South Florida , 1980 .

[50]  D. Dowell,et al.  Observations of Low-Level Baroclinity Generated by Anvil Shadows , 1998 .

[51]  Peter L. Wolf.  WSR-88D Radar Depiction of Supercell–Bow Echo Interaction: Unexpected Evolution of a Large, Tornadic, “Comma-Shaped” Supercell over Eastern Oklahoma , 1998 .

[52]  Mitchell W. Moncrieff,et al.  A Numerical Investigation of the Organization and Interaction of the Convective and Stratiform Regions of Tropical Squall Lines , 1988 .

[53]  Joanne Simpson,et al.  Cloud interactions and merging - Numerical simulations , 1984 .

[54]  H. Davies,et al.  A lateral boundary formulation for multi-level prediction models. [numerical weather forecasting , 1976 .

[55]  S. Nelson,et al.  The Hybrid Multicellular–Supercellular Storm—an Efficient Hail Producer. Part II. General Characteristics and Implications for Hail Growth , 1987 .

[56]  Alan R. Moller,et al.  The Operational Recognition of Supercell Thunderstorm Environments and Storm Structures , 1994 .

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

[58]  J. Klemp,et al.  A Three-Dimensional Numerical Simulation of Splitting Severe Storms on 3 April 1964 , 1981 .

[59]  P. Wetzel,et al.  Evapotranspiration from Nonuniform Surfaces: A First Approach for Short-Term Numerical Weather Prediction , 1988 .

[60]  R. Rotunno,et al.  A Theory for Strong, Long-Lived Squall Lines , 1988 .

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

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

[63]  M. Weisman.  The Genesis of Severe, Long-Lived Bow Echoes , 1993 .

[64]  D. Lilly,et al.  On the numerical simulation of buoyant convection , 1962 .

[65]  P. Ray,et al.  An Investigation of the Transition from Multicell to Supercell Storms , 1986 .

[66]  Roger A. Pielke,et al.  A parameterization of heterogeneous land surfaces for atmospheric numerical models and its impact on regional meteorology , 1989 .

[67]  William R. Cotton,et al.  An Intense, Quasi-Steady Thunderstorm over Mountainous Terrain. Part IV: Three-Dimensional Numerical Simulation. , 1986 .

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

[69]  M. Miller,et al.  Numerical simulations showing the role of the downdraught in cumulonimbus motion and splitting , 1978 .

[70]  Edward J. Zipser,et al.  Momentum Flux by Lines of Cumulonimbus over the Tropical Oceans , 1984 .

[71]  W. Cotton,et al.  New RAMS cloud microphysics parameterization part I: the single-moment scheme , 1995 .

[72]  OFTHERMOFORMINGM. K. Warby,et al.  Numerical simulation , 1990 .

[73]  N. Westcott.  A Historical Perspective on Cloud Mergers , 1984 .

[74]  T. Clark,et al.  Severe Downslope Windstorm Calculations in Two and Three Spatial Dimensions Using Anelastic Interactive Grid Nesting: A Possible Mechanism for Gustiness , 1984 .

[75]  J. Barnes.  Linear Baroclinic Instability in the Martian Atmosphere , 1984 .

[76]  J. Smagorinsky,et al.  GENERAL CIRCULATION EXPERIMENTS WITH THE PRIMITIVE EQUATIONS , 1963 .

[77]  Numerical simulation of intense multi-scale vortices generated by supercell thunderstorms , 1998 .

[78]  D. Durran,et al.  The Influence of Convectively Generated Thermal Forcing on the Mesoscale Circulation around Squall Lines , 1996 .