An analytical pattern-based method for estimation of a near-surface tornadic wind field

Abstract

Existing methods of in-situ measurement struggle to capture near-surface wind speeds during a tornado. The demand for accurate near-surface wind fields for the seemingly imminent tornado based design requires new methods of near-surface wind speed estimation, some of which use damage survey data. Information on tree-fall patterns included in damage survey data can and have been used as an indicator of the wind field. Thus, this paper develops an improved analytical method based on tree-fall patterns to estimate the near-surface wind field. This improved analytical model generates a translational steady-state tornado flow field under a superposition of a translational field and a rotational field. The rotational field can be generated by tornado vortex models, then the best-fit parameters for the selected vortex model to create a near-surface translational steady-state tornadic field. This wind field can be estimated on the basis of tornado-induced tree-fall patterns obtained by aerial photos. In this paper, an application is developed with the tree-fall survey data of the 2011 Joplin, MO tornado and used the Rankine vortex model.