Thunderstorm Structure and Evolution Eric A. Pani The University of Louisiana at Monroe.
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Transcript of Thunderstorm Structure and Evolution Eric A. Pani The University of Louisiana at Monroe.
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Thunderstorm Structure and Evolution
Eric A. Pani
The University of Louisiana at Monroe
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Background
Thunderstorm Project (1949) Building block: Cell Cell identified by
visual observation of cumuliform turrets during early stages of development before precip formed
radar observations once precip formed Thunderstorms consist of more than one cell Each cell has distinct life cycle
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Visual appearance of cell
Source: http://www.photolib.noaa.gov/historic/nws/wea00079.htm
Cell 1 Cell 2
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Radar appearance of cell
Source: http://www.met.tamu.edu/ADRAD/tutor/RHI.gif)
Cell 1
Cell 2
Cell 3Cell 4
Cell 5
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Life Cycle of Thunderstorm
Three stages (Towering) Cumulus Mature Dissipating
Entire life cycle ~ 30-60 minutes but thunderstorms composed of many cells so storm life is longer
Form where convergence exists and air conditionally unstable
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Towering Cumulus Stage (~15 minutes) Updraft strong enough so
identifiable from ordinary convection Dominated by updrafts but may
have downdrafts at cloud edge Air converges into cell from miles
around, perhaps not uniformly wmax ~ 10 ms-1 @ ~ 5 km with
convergence ~ 2 x 10-3 s-1 (10-6 s-1 synoptic scale)
May have adiabatic ascent in updraft core
Precip begins in latter part of this stage with first radar echo detected around melting level
Source: http://cjonline.com/images/050799/form1.jpg
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Towering Cumulus Stage
(Source: http://www.photolib.noaa.gov/historic/nws/wea00088.htm)
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Mature Stage (~10 minutes)
Often defined when precip reaches ground; presence of updraft/downdraft couplet may be better
Downdraft results from precip drag initially, then evaporative cooling
Downdraft air from middle troposphere
-1°C buoyancy over 5 km produces downdraft of 15-20 ms-1
Gust front produced when downdraft reaches ground
Downdraft dissipates cloud by evaporating droplets (d~20 μm)
(Source: http://cjonline.com/images/050699/form2.jpg)
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Mature Stage
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Dissipating Stage (~10 minutes) Downdraft formation signals
death of storm in non-severe cases
Spreading downdraft below storm cuts off supply of high θe air
Precip aloft no longer supported by updraft, descends, and scavenges cloud drops
Dissipates lower portion of cloud
Source: http://cjonline.com/images/050699/form3.jpg)
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Dissipating Stage
(Source: http://www.worldsurface.com/browse/entry.asp?entryid=5448)
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Classes of thunderstorms
Single cell Non-severe: air mass thunderstorm Severe: supercell
Multicell (all non-severe, all severe, or mixture) Individual: thunderstorm Cluster: MCC, tropical cloud cluster Line: squall line
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Single Cell Thunderstorms
(Source: http://www.photolib.noaa.gov/historic/nws/wea00087.htm)
(Source: http://www.inclouds.com/display.php?picID=WxClds06b_06)
Air Mass Thunderstorm Supercell Thunderstorm
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Multicell Thunderstorms
(Source: http://operations.ocs.ou.edu/~nebain/chase7/imagery.htm)
(Source: http://orbit-net.nesdis.noaa.gov/arad/fpdt/pix/WDXSE19a.gif)
Thunderstorm
Squall Line
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Multicell Thunderstorms
(Source: http://wind.mit.edu/~emanuel/geosys/fig6.8f.gif)
(Source: http://www.ncdc.noaa.gov/img/satellite/satelliteseye/tornadoes/galva94/galvair1.gif)
Mesoscale Convective Complex
Tropical Cloud Cluster
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Propagation of Multicell Storms
Cell motion
Storm motion