Tornadoes and Tornadoes and Tornadic StormsTornadic Storms

Robert Davies-Jones, R. Jeffrey Robert Davies-Jones, R. Jeffrey Trapp, and Howard B. Trapp, and Howard B.

BluesteinBluestein

Presentation by Christopher Presentation by Christopher MedjberMedjber

Severe Convective Storms,Severe Convective Storms, Meteorological Monographs, Meteorological Monographs, 28, no. 50, American Meteorological Society, pg. 167-28, no. 50, American Meteorological Society, pg. 167-

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IntroductionIntroduction DefinitionsDefinitions Climatological distribution Climatological distribution of Tornadoesof Tornadoes

Midlevel and Near-Midlevel and Near-Ground Ground MesocyclogenesisMesocyclogenesis

Mesocyclone observationsMesocyclone observations

DefinitionsDefinitions SupercellSupercell

Long-lived (> 1 hr)Long-lived (> 1 hr) Has a single, quasi-steady Has a single, quasi-steady rotating updraft (mesocyclone)rotating updraft (mesocyclone) Has a high degree of spatial Has a high degree of spatial correlation between its correlation between its mesocyclone and updraftmesocyclone and updraft

Supercell Supercell CharacterizationCharacterization

Low precipitation (LP) supercellLow precipitation (LP) supercell Moderate precipitation Moderate precipitation

(“Classic”) supercell(“Classic”) supercell High precipitation (HP) High precipitation (HP)

supercellsupercell

DefinitionsDefinitions TornadoTornado

A violently rotating, narrow A violently rotating, narrow column of aircolumn of air Average diameter of ~100 mAverage diameter of ~100 m Extends to the ground from the Extends to the ground from the interior of a cumulonimbus or interior of a cumulonimbus or cumulus congestuscumulus congestus Appears as a condensation Appears as a condensation funnel pendant from cloud base funnel pendant from cloud base and/or as a swirling cloud of dust and/or as a swirling cloud of dust and debris rising from the groundand debris rising from the ground

TornadoesTornadoes

Type I and Type I and Type IIType II

Type I TornadoesType I Tornadoes Forms within a mesocyclone, Forms within a mesocyclone, with the parent storm being with the parent storm being either an isolated supercell, a either an isolated supercell, a supercell in a line of supercell in a line of thunderstorms, a miniature thunderstorms, a miniature supercell containing a small supercell containing a small mesocyclone, or a miniature mesocyclone, or a miniature supercell within the rainbands supercell within the rainbands of landfalling tropical cyclonesof landfalling tropical cyclones

Type II TornadoesType II Tornadoes Is not associated with a Is not associated with a mesocirculation (i.e. mesocirculation (i.e. mesocyclone)mesocyclone) Generally form from small Generally form from small and weak vortices along a and weak vortices along a stationary or slowly moving stationary or slowly moving windshiftwindshift

Climatological Climatological Distribution of Distribution of

TornadoesTornadoes Tornadoes occur worldwide!Tornadoes occur worldwide! Tornadoes are most prevalent in Tornadoes are most prevalent in

the “Great Plains” of the United the “Great Plains” of the United States and in north-east India-States and in north-east India-BangladeshBangladesh

““Tornado Ally” (area extending Tornado Ally” (area extending from north Texas northward to from north Texas northward to western Iowawestern Iowa

Climatological Climatological Distribution of Distribution of

TornadoesTornadoes Over past 50 years, annual Over past 50 years, annual

tornado reports have increased tornado reports have increased from 200 to 1200from 200 to 1200

Likely due to population density, Likely due to population density, improved reporting procedures, improved reporting procedures, etc.etc.

Not due to global climate change!Not due to global climate change!

Tornado DeathsTornado Deaths Death tolls have decreasedDeath tolls have decreased Mean tornado-warning Mean tornado-warning lead time of 13 minuteslead time of 13 minutes Improvements in public Improvements in public awareness, education, awareness, education, forecasting, issuances of forecasting, issuances of watches and warnings, and watches and warnings, and the operational use of WSR-the operational use of WSR-88D radar88D radar

Midlevel and Near-Midlevel and Near-ground ground

MesocyclogenesisMesocyclogenesis At midlevels, mesocyclone At midlevels, mesocyclone

develops from the tilting of develops from the tilting of horizontal vorticity associated with horizontal vorticity associated with the vertical shear of the windsthe vertical shear of the winds

Near the ground, mesocyclone Near the ground, mesocyclone develops form due to tilting of develops form due to tilting of horizontal vorticity from low-level horizontal vorticity from low-level density gradientsdensity gradients

Mesocyclone Mesocyclone ObservationsObservations

Time-lapse photographyTime-lapse photography Doppler RadarDoppler Radar

- Use of inbound and - Use of inbound and outbound outbound

Doppler velocitiesDoppler velocities Only about 50% of Only about 50% of objectively defined objectively defined mesocyclones produce mesocyclones produce tornadoestornadoes

The EndThe EndYou Should Clap NowYou Should Clap Now