The LaGrange Tornado during VORTEX2. Part I: Photogrammetric Analysis of the Tornado Combined with Single-Doppler Radar Data

Abstract

This study presents a single-Doppler radar analysis combined with cloud photography of the LaGrange, Wyoming, tornado on 5 June 2009 in an attempt to relate the radar-observed hook echo, weak-echo hole (WEH), and rotational couplet to the visual characteristics of the tornado. The tornado was rated EF2. The circulation at low levels went through two intensification periods based on azimuthal shear measurements. The first intensification was followed by the appearance of a brief funnel cloud. The second intensification was coincident with the appearance of a second funnel cloud that remained in contact with the ground until the tornado dissipated.A deep WEH rapidly formed within the hook echo after damaging wind was identified at the ground and before the appearance of a funnel cloud. The echo pattern through the hook echo on 5 June undergoes a dramatic evolution. Initially, the minimum radar reflectivities are near the surface (,15 dBZ) and the WEH does not suggest a tapered structure near the ground. Subsequently, higher reflectivities appear at low levels when the funnel cloud makes contact with the ground. During one analysis time, the increase of the echo within the WEH at low levels results in a couplet of high/low radar reflectivity in the vertical. This increase in echo at low levels is believed to be associated with lofted debris although none was visibly apparent until the last analysis time. The WEH was nominally wider than the visible funnel cloud. The dataset provides the first detailed analysis of the double-ring structure within a hook echo that has been reported in several studies. The inner high-reflectivity region is believed to be a result of lofted debris. At higher-elevation angles, a small secondary WEH formed within the first WEH when debris was lofted and centrifuged.A feature noted in past studies showing high-resolution vertical cross sections of single-Doppler velocity normal to the radar beam is an intense rotational couplet of negative and positive values in the lowest few hundred meters. This couplet was also evident in the analysis of the LaGrange tornado. The couplet was asymmetric with stronger negative velocities owing to the motion of the tornado toward the radar. The damaging wind observed by radar extended well beyond the condensation funnel in the lowest few hundred meters. However, another couplet indicating strong rotation was also noted aloft in a number of volume scans. The decrease in rotational velocities between the low-and upper-level couplets may be related to air being forced radially outward from the tornado center at a location above the intense inflow.

An Integrated Damage, Visual, and Radar Analysis of the 2013 Moore, Oklahoma, EF5 Tornado

“…The distance from the centerline to the EF0 isopleth is about 250 m. The photogrammetric funnel-size estimate is much smaller than the damage path width generally coinciding with the EF1 and EF2 isopleths. Previous research has revealed no consistent relationship between the condensation funnel size relative to the damage path width (e.g., Golden and Purcell 1978;Bluestein et al 1997;Wakimoto et al 2003). The tornadic wind field based on tree fall and debris is highly convergent toward the centerline.…”

“…2 Social media were used to collect imagery and video from amateur storm chasers and news crews. Azimuth and elevation grids were superimposed on select photographs and video frames using photogrammetric techniques that are well documented in the literature (e.g., Rasmussen et al 2003;Zehnder et al 2007;Wakimoto et al 2011;Atkins et al 2012). By measuring the azimuth angles of known landmarks in the photos, the grid uncertainty is estimated to be 0.1°.…”

“…It is possible to estimate the condensation funnel diameter (e.g., Wakimoto et al 2003;Atkins et al 2012) by triangulation in concurrent photos taken at two or more vantage points. Unfortunately, triangulation is not possible with the available photos of the Moore tornado.…”

“…It is particularly important to survey high-impact events as has been done in the past for the 3 May 1999 Moore-Bridge Creek, Oklahoma (Marshall 2002;Speheger et al 2002), 4 May 2007 Greensburg, Kansas (Marshall et al 2008b), 22 May 2011Joplin, Missouri (NOAA 2011, and 27 April 2011 Tuscaloosca-Birmingham, Alabama (Karstens et al 2013), tornadoes and many other historical cases. Much has been learned from these and other damage survey studies regarding the low-level tornado wind field (Karstens et al 2013) and attendant damage (Wurman and Alexander 2005), structure failure (Marshall 2002;Marshall et al 2008a), distribution of risk in the damage path (Abbey and Fujita 1975;Speheger et al 2002), nonlinear damage markings (Wakimoto et al 2003;Marshall et al 2008b), and the relationship between the condensation funnel, the damage path, and radar observations (Wakimoto et al 2003).…”

Reproducing tornadoes in laboratory using proper scaling

“…Wakimoto et al (2011) presented photogrammetric and radar analysis of this tornado and showed that the damaging wind in the region few hundred meters above the ground extended beyond the funnel cloud. Afterwards, Wakimoto et al (2012) published GBVTD analysis of June 5th, 2009 LaGrange, WY tornado combined with pictures of the funnel cloud in order to identify the relationship between the three velocity components, pressure gradients and the visual features of the tornado.…”