1. Tornadogenesis: Our Current Understanding and Unanswered Questions for VORTEX2 The Second Verification of the Origins of Rotation in Tornadoes Experiment Photo by Herb Stein Yvette Richardson Penn State University AMS Meeting Kansas City, MO 12 February 2009

6. Objectives Basic Structure of a Supercell reflectivity after Lemon and Doswell (1979) Eric Nguyen

8. What we knew before VORTEX1 The importance of a downdraft pre-existing vertical vorticity at the surface initially negligible vertical vorticity at the surface zeroth order assumption: no baroclinity or viscous effects; vortex lines are material lines

9. Roberto Giudici

10. Courtesy of Dave Blanchard NSSL archive photo Courtesy of Dave Blanchard

11. Horizontal vorticity also can be generated baroclinically by buoyancy gradients associated with a storm’s cool outflow, and the tilting of this vorticity can be important in the development of low-level rotation in supercells. What we knew before VORTEX1 Importance of storm-generated horizontal vorticity  shaded and contoured Vertical cross-section across gust front

17. What are the biggest unanswered questions in the study of tornadogenesis? nontornadic nontornadic tornadic nontornadic Why do storms with seemingly similar structure differ in their tornado production?

18. What are the biggest unanswered questions in the study of tornadogenesis? Wakimoto et al. (2004) tornadic tornadic nontornadic Why are the most intense mesocyclones not necessarily the ones most likely to be associated with tornadogenesis?

19. A C Wakimoto and Fujita (1981) DOW1 image from 2 June 1995 Tornadoes and low-level mesocyclones are virtually always found to have anticyclonic vorticity on the opposite side of the hook echo/RFD—such vorticity couplets suggest that the tilting of vorticity by a downdraft is important.

20. purely barotropic process purely baroclinic process negative buoyancy no baroclinic vorticity generation; vortex lines are frozen in the fluid; vortex lines passing through low-level vorticity maximum form U’s (not observed). observed case: vortex lines passing through low-level vorticity maximum form arches Straka, J. M., E. N. Rasmussen, R. P. Davies-Jones, and P. M. Markowski, 2007: An observational and idealized numerical examination of low-level counter-rotating vortices toward the rear flank of supercells. E. J. Severe Storms Met. , 2 (8), 1-22. Markowski, P. M., J. M. Straka, E. N. Rasmussen, R. P. Davies-Jones, Y. Richardson, and J. Trapp, 2008: Vortex lines within low-level mesocyclones obtained from pseudo-dual-Doppler radar observations. Mon. Wea. Rev. , 136 , in press.

21. The fact that baroclinic vorticity generation seems to be important does not necessarily imply that TG becomes increasingly likely as the baroclinity (and cold pool strength) increase!

22. What are the biggest unanswered questions in the study of tornadogenesis? What role, if any, do secondary gust fronts play? Marquis et al. 2008 Wurman et al. 2007 RFD

25. 1 May 2008 Storm-environment interactions (on days when storm motion or road network is not conducive to tornadogenesis mission) 2 June 1995 cloud shadow

30. In situ measurements Tornado in-situ probes Stick Net Mobile Mesonets Rawinsondes Disdrometers

33. Nested deployment strategy

34. If possible, take advantage of fixed observing systems in OK

35. Situational Awareness Display Will include mobile mesonet data, radar data, roads, and terrain Available over the mobile digital network

38. http://www.vortex2.org