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Fig. 5. Vertical cross-section of CReSS model-simulated vertical velocity at y = 26 km in Fig.
4. Contours are as in Fig. 4. Vectors indicate the speed and direction of wind flow along the
vertical cross-section.
Figure 5 shows a vertical cross-section of the simulated storm along the y = 26 km transect in
Fig. 4. The strong updraft extended upward to 12 km ASL, with a maximum updraft speed
of 24 m s -1 at 4 km ASL. Three downdraft cores flanked the strong updraft core. A weak
compensating downdraft was located to the west of the strong updraft at approximately 6
km ASL. A second strong downdraft (6 m s -1 ) formed at 8 km ASL, and was associated with
a high graupel mixing ratio (data not shown). A third strong downdraft was simulated at
heights above 11 km ASL in the non-precipitating region. This downdraft was likely related
to gravity wave dynamics.
Four pseudo-radars are assumed to observe this simulated three-dimensional wind field
(the locations of these pseudo-radars are shown in Fig. 1). The wind components are
bilinearly interpolated from the model grid to sampling locations along the radar beams.
Radial velocity is calculated from the three wind components interpolated to each radar grid
point. The maximum range of detection is set to 70 km for all four pseudo-radars, as shown
in Fig. 1. Each radar sweep observes a total of 90 azimuthal angles, with a gate spacing of
100 m and an azimuthal resolution of 1°. The radial velocities along each radar beam in the
volume scan (see Fig. 2) are interpolated back onto the Cartesian coordinate system using a
Cressman scheme with an influence radius R of 1.0 km. Some upper-level velocities will be
lost because the highest elevation angle was less than 30° (Fig. 2). The robustness of the
variational analysis method to noise is shown by adding random errors (mean 0 m s -1 ,
variance 1 m 2 s -2 ) to the radial velocities after interpolation back to the Cartesian coordinate
system.
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