The behavior of isolated thunderstorm cells has been thoroughly explored through numerical simulation, including the relationship between cell intensity and longevity and the local buoyancy and shear. Observations have shown that cell propagation and intensity may be further modulated by interaction with nearby cells. The interaction may be fostered by differing propagation characteristics as a result of mesoscale boundaries, cell age, splitting, and/or rotational properties. Interaction can be destructive (e.g. one storm interrupting the inflow to another) or constructive (e.g. one cell intercepting the gust front of another).

We are simulating idealized cell interaction with the WRF model. The environment was taken from soundings extracted near the location of cell formation in a prior MM5 simulation (Jewett et al. 2000) of the 19 April 1996 Illinois tornado outbreak. Part of the motivation of this work was the observation (Lee et al., 2000) that cell merging preceded many of the tornado events on this day, as well as earlier studies (e.g. Wolf and Szoke 1996) finding cell intensification after the apparent juxtaposition of a leading cell's rear-flank downdraft with a trailing storm's forward-flank downdraft.

A pilot study carried out in cooperation with data mining scientists at NCSA consisted of 95 simulations in which initial warm thermal placement and properties were varied. For a given value of peak surface rotation, the duration over which substantial rotation was maintained near the ground varied significantly, such that strong rotation and long-lived rotation need not coincide. On 19 April 1996, most tornadoes (some of low-F3 intensity) were short-lived. Further analysis is underway and additional, systematic simulations are being carried out to relate cell intensity, age, and relative position to their rotational characteristics. Results will be presented at the Conference.

REFERENCES

Jewett, B. F., B. D. Lee and R. B. Wilhelmson, 2000: Initation and evolution of severe convection in the 19 April 1996 Illinois Tornado Outbreak. Preprints, 20th Conf. on Severe Local Storms, Orlando, 74-77.

Lee, B. D., B. F. Jewett and R. B. Wilhelmson, 2000: Supercell differentiation and organization for the 19 Apri l1996 Illinois Tornado Outbreak. Preprints, 20th Conf. on Severe Local Storms, Orlando, 222-225.

Wolf, R., and E. Szoke, 1996: A multiscale analysis of the 21 July 1993 Northeast Colorado Tornadoes. Preprints, 18th Conf. on Severe Local Storms, Amer. Meteor. Soc., San Francisco, 403-407.