Geoscience Reference
In-Depth Information
window and so are data from the adjacent azimuth centered 0.5
o
off from the previous. This
produces more radials of data (spaced by 0.5
o
as opposed to 1
o
) increasing resolution to
facilitate recognition of small phenomena such as tornado vortices (Brown et al., 2002, and
2005). The contrast between the routine and enhanced resolution of a tornado vortex
signature is evident in the example in Fig. 9. The reflectivity field (top figures in dBZ as
indicated by the color bars) displays a “hook echo” associated with low level circulation.
The crisp pattern (top right) is the result of the enhanced resolution.
The velocity field (bottom in Fig. 9) displays three circular features (“balls”) in its center: the
lighter green and red adjacent to it in azimuth indicate cyclonic circulation (mesocyclone).
Its diameter is about four km and it is estimated from the distance between maximum
inbound (green) and outbound (red) velocities. The sharp discontinuity in the center (light
green ~ -30 m s
-1
to > 30 m s
-1
) is the tornado vortex signature (TVS). The transition between
the red “ball” and the green one farther in range marks the zero radial velocity suggesting
converging flow (i.e., red and green velocities pushing air toward each other) near ground.
Bottom right: same as in the left but the resolution in azimuth is enhanced to 0.5
o
. The TVS is
better defined and so are other small scale features.
Fig. 9. Top Left: Z, resolution 1 km x 1
o
. Right: resolution 250 m x 0.5
o
. Bottom Left: V field,
resolution 250 m x 1
o
. Right: resolution 250 m x 0.5
o
. X, Y sizes are 25 by 20 km; radar is at x=
4 km and y = -25 km with respect to each image left corner. (Courtesy, S. Torres).
