Analysis supported by NSF-AGS-0910737 and DOWs by NSF-AGS-0801041. We thank Curtis Alexander, Paul Robinson, and Rachel Humphrey.
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DOWs have 3-dB beamwidths of ~0.9°, oversampled at 0.3°–0.4°, gating at 25 m (RSDOW) and 30 m (DOW7).
P1 crew discovered the resident ~100 s after the event, sitting on the rubble of the transported/destroyed house, suffering from lacerations and a broken collarbone; the crew assisted in her extraction.
The National Weather Service (NWS) rated the tornado EF2.
P1 hosts an R. M. Young 5103 propeller-type anemometer.
Reported DOW observations height adjusted +3 m, accounting for antenna height AGL.
RSDOW data were objectively analyzed onto a Cartesian grid using a Barnes scheme (Barnes 1964), grid spacing (radius of influence) of 5 (10) m and 2 (3) m in the horizontal and vertical directions, respectively. Tornado translational motion was subtracted from Vd. Tornado centers were vertically aligned, eliminating tilting errors, but not correcting for flow asymmetries. Vertical winds (w) were derived by the upward integration of the continuity equation, assuming w(z = 0) = 0 m s−1 and free slip.
Errors in vortex center location were <7 m.
It is likely that Vg > Vd because Vd only captures the component of motion toward–away from the radar.
P1 drove into the western side of the tornado after the tornado center had moved east of the road.
P1 is visible as moving ground clutter in the lowest RSDOW sweeps.
Radar measurements are instantaneous and represent reflectivity-weighted averages of scatterer (rain/debris, with associated terminal/centrifuging velocities) motion, usually determined using pulse-pair or spectrally based signal processing techniques, over spatial volumes not equal to 3-s air parcel trajectories.
Since the observations were close to the surface, dirt, gravel, and/or grass likely were appreciable scatter types in the radar sample volumes. The in situ P1 crew did not report airborne debris hitting their vehicle.
The surface roughness length was approximated as 0.1 m, characteristic of “openly rough” terrain (Davenport et al. 2000).
Here, Sc = rcΓ∞/ϒ, where rc is a characteristic radius of Vt(max), Γ∞ is the ambient angular momentum, and ϒ is the depleted angular momentum flux in the surface layer.
Note that So characterizes the flow in which the tornado forms. Both So and Sc are difficult to define in nature since flow parameters are not easily defined. In addition, So cannot be approximated in the current study since the analysis domain is too small to define the large-scale flow in which the tornado is embedded.
Assuming rc = 60 m, Γ∞ = 3.0 × 103 m2 s−1, and ϒ = 1.0 × 103 m5 s−2.
Values of parameters composing Sc are uncertain, but reasonable choices yield Sc ≫ 1.