WMOD00430

• Title: A Diagnostic Technique for Targeting During Airborne Seeding Experiments in Wintertime Storms over the Sierra Nevada
• Date: 7/7/1988
• Weather Modification - Doc Type: Report

822 JOURNAL OF APPLIED METEOROLOGY VOLUME 27
5 (0) (d) 5
4 4
3 3
2 2
30 January 1986 ~
uac - u 0
0
(e) "
'.
_-1Jl '--'2 ......'4"
8- - ""'/-?--
4 - - - 4
--6- --
E
~ 3
3
I-
:I: 2
(!) 2
w
:I: 1
0 0
5 (c) (f) 5
4 ;;;;,-0 4
3 3
2 --... c... 2
2 (p~
3 February 1986 3 February 1986
v com ponen! vac-v
0 0
40 60 80 100 0 20 40 60 80 100
DISTANCE (km)

FIG. 8. (a) Calculated (solid) and aircraft measured (dashed) u-component of the wind (m S-I) on 30 January 1986; (b)
as in a, but for v-component; (c) as in a, but for v-component on 3 February; (d) graphical subtraction (measured-
calculated) of fields in panel a; (e) graphical subtraction of fields in panel b; (f) graphical subtraction of fields in panel c.

periments, errors in the u-component were less than 4
m S-I throughout the 100 km domain from the base
of the Sierra Nevada to the crestline. In most locations
within this region, errors were <2 m S-I. The primary
exception to the quoted error values occurred in regions
of strong vertical shear. The magnitude of the velocities
within shear zones was normally reproduced closely,
but the location of the shear zone was sometimes dis-
placed upward or downward a few hundred meters in
altitude. This displacement typically resulted in a nar-
row region of larger errors. Such a region is evident
between 4 and 5 km altitude in Figs. 8a and d. The
largest error in any experiment (-10 m S-I) occurred
within such a shear zone. In almost all cases, these
zones of higher shear were above the seeding altitude
and had no effect on the calculated particle trajectories.
The v-component of the wind typically was maxi-
mum within the core of the barrier jet (Parish 1982)
approximately I km above the lower Sierra Nevada
foothills. Figure 8b shows a typical barrier jet profile

measured by the aircraft and calculated for targeting.
Figure 8e shows the error analysis of these fields. Under
conditions when the barrier jet decreased linearly to-
ward the barrier crest, errors in the calculated v-com-
ponent were minimized. This was the case on 30 Jan-
uary, where errors were generally 2-4 m S-l throughout
the seeded volume. Contrast this profile with that mea-
sured on 3 February 1986 (Fig. 8c). In this case, the
jet extended further into the lower foothills than would
have been anticipated based on a linear interpolation
between the Sheridan and Kingvale soundings. As a
result, a narrow core oflarger errors (Fig. 8f) was located
over the lower foothills. Errors in the v-component
were generally highest in this region.
The target was designed so that the sampling site,
Kingvale, would be at the center of the area on the
ground where seeding effects should have occurred.
However, errors in the calculated wind field would shift
the center of the predicted fallout area away from the
target. An estimate of the magnitude of this shift was