May 26 - July 31
Tornadoes in the Southeast United States: Investigating the Relationship between Intensity, Damage, and Terrain
Melanie A. Zambron, David J. Bodine, and Anthony E. Reinhart
What is already known:
- Tornado research includes a variety of forecasting challenges, including estimating the real-time tornado intensity and identifying strong tornadoes with weak radar rotation signatures.
- Minimal previous research has been conducted on the interaction between complex terrain and tornadic circulations.
- Model simulations have shown that small changes in topography height impact the strength, structure, and path of a tornado.
- NEXRAD radar algorithms focusing on tornado detection (e.g., tornadic debris signature (TDS) and tornadic vortex signature (TVS)) provide additional warning decision support for NWS forecasters.
- Additional low level scans (SAILS) help mitigate temporal data gaps, but abrupt changes in terrain height and tornado intensity may still be missed.
What this study adds:
- Correlations among terrain, surface damage, and tornado intensity variables are explored for eight tornadoes from the southeast United States.
- This study discusses the relationship between range and beam height from NEXRAD radar systems and notes important differences in measuring tornado-level winds versus mesocyclone-level winds when compared to surface damage.
- Low-level rotational intensity and terrain show little correlation using NEXRAD velocity data, but observations in this study can be compared to future studies using more rapidly updating types of radar scans.
Abstract:
With minimal past research, the impacts of terrain on tornadic-scale circulations remain unclear. This study utilizes data from individual NEXRAD radars, Multi-Radar Multi-Sensor (MRMS) products, damage surveys, and geological surveys to investigate relationships among tornado intensity, surface damage, and terrain height. Eight tornadoes, combined into six cases, from 2-3 March 2020 and 12-13 April 2020 are examined. Correlations are calculated for each case between six variables: rotational intensity (ΔV), maximum EF-scale rating, maximum MRMS Rotation Track value, damage width, velocity couplet width, and terrain height. Data for each variable are recorded at the 0.5° elevation scan time steps from the NEXRAD radars. Four of the six cases utilized additional low-level scans (SAILS) on the 0.5° tilt, but time gaps between updates limit available velocity data. The importance in distinguishing between tornado-level and mesocyclone-level winds in radar velocities based on range and beam height is discussed. Strong correlation coefficients are evident in higher-rated tornadoes between intensity variables, such as maximum EF rating and ΔV. Calculations with terrain indicate some moderate correlation with intensity variables and all weak correlations with damage variables. The moderate terrain correlations consist of only cases in which the radar scanned mesocyclone-level winds, so tornado-level winds examined by radar show only weak correlations with terrain.