1 / 26

Tornadogenesis in a Simulated Mesovortex : The Role of Surface Friction

Tornadogenesis in a Simulated Mesovortex : The Role of Surface Friction. Alex Schenkman Co-authors: Ming Xue and Alan Shapiro. Experiment Design. A 100-m simulation is nested within two larger, lower resolution grids.

joshwa
Download Presentation

Tornadogenesis in a Simulated Mesovortex : The Role of Surface Friction

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Tornadogenesis in a Simulated Mesovortex: The Role of Surface Friction Alex Schenkman Co-authors: Ming Xue and Alan Shapiro

  2. Experiment Design • A 100-m simulation is nested within two larger, lower resolution grids. • On the two outer grids, radar and conventional observations are assimilated via the Advanced Regional Prediction System (ARPS) 3DVAR and cloud analysis. • The outermost grid (2-km horiz. spacing) is used to forecast overall MCS and line-end vortex development. • A 400-m grid is nested within the 2-km grid and simulates mesovortices associated with the MCS. • The 100-m grid forecasts detailed evolution of a long-lived mesovortex and associated tornado-like vortex. • For more details on the experiment design see Schenkman et al. (2011a,b) and Schenkman et al. (JAS, in press).

  3. Vorticity decreases as parcel enters updraft Vorticity generated by friction Stretching in rotor

  4. Simulation without drag • Experiment is run without drag to further verify frictionally generated vorticity is cause of rotor. • Note: BCs and ICs still come from same 400-m simulation • Should have a limited impact as most of the frictionally-generated vorticity developed during the 100-m simulation.

  5. Conclusion Surface drag in the model is playing a key role in the generation of the rotor, associated low-level updraft, and thus tornadogenesis in this case. But how?

  6. Mountain rotor comparison • To determine the dynamics behind the rotor formation we examine rotors that form in the lee of mountains. • Doyle and Durran (2002) showed that rotors formed in the lee of mountains in simulations with surface drag turned on. Figure from Doyle and Durran (2007) • They attribute rotor formation to boundary layer separation that occurs when the flow encounters the adverse PGF associated with the first lee-wave.

  7. Mountain rotor comparison (cont’d) • To better compare our studies we note the following similarities: • In both studies there is a strong jet, beneath which there is a large horizontal vorticity maximum • An adverse PGF causes boundary layer separation in both studies. Lee-wave in Doyle and Durran. Gust front in our case. • Both studies are stably stratified.

  8. Conceptual Model

  9. Generality of Results?

  10. Figure adapted from Dowell and Bluestein (1997)

  11. Adapted from Frame and Markowski (2010)

More Related