1. Thunderstorm Structure and Evolution Eric A. Pani The University of Louisiana at Monroe

2. 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

3. Visual appearance of cell Source: http://www.photolib.noaa.gov/historic/nws/wea00079.htm Cell 1Cell 2

4. Radar appearance of cell Source: http://www.met.tamu.edu/ADRAD/tutor/RHI.gif) Cell 1 Cell 2 Cell 3 Cell 4 Cell 5

5. 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

6. 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 w max ~ 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

7. Towering Cumulus Stage (Source: http://www.photolib.noaa.gov/historic/nws/wea00088.htm)

8. 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)

9. Mature Stage

10. Dissipating Stage (~10 minutes) Downdraft formation signals death of storm in non-severe cases Spreading downdraft below storm cuts off supply of high θ e 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)

11. Dissipating Stage (Source: http://www.worldsurface.com/browse/entry.asp?entryid=5448)

12. 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

13. 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

14. 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

15. 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

16. Propagation of Multicell Storms Cell motion Storm motion