WMOD00291

• Title: Bulk Parameterization of the Snow Field in a Cloud Model
• Date: 6/6/1983
• Weather Modification - Doc Type: Report

1082

JOURNAL OF CLIMATE AND APPLIED METEOROLOGY

VOLUME 22

portion of the mature stage. Surface rain and gust
front formation. have occurred .in these cases. The
precipitation fields in all cases show hail in the upper
levels melting to rain in the lower levels (Fig. 6b). A
very large area (volume) of hail exists in Case 3. Note
that the snow is melted or evaporated before reaching
the ground and is, for the most part, limited to the
higher levels (above 6 km).
At 42 min (Fig. 6b), Cases 1 and 2, with active rain
processes, are much more alike than Cases 1 and 3,
both of which have active snow processes. Hail is
being regenerated in Cases I and 2 due to an invig-
oration of the updraft. This renewed hail generation
occurs mainly in the region of the cloud between 4
and 5 km AGL due to the contact freezing of rain
being recycled by the invigorated updraft during the
time period between 36 and 42 min. The outflow
from the precipitation-induced downdraft is the pri-
mary cause of the updraft surge and hail increase.
Cloud ice covers a large region in Case 2 with a max-
imum value of 3.6 X 10-3 g g-l. Maximum values
of cloud ice in Cases 1 and 3 are near 10-3 g g-l. The
presence of a snow field in Cases 1 and 3 and the lack
of snow in Case 2 causes this difference. Rain has
reached the surface in Case 3.
At 48 min (Fig. 6b), secondary cloud formation is
evident in all three cases, the more vigorous cell on
the right (lower upwind) side. The most vigorous
growth of secondary cells is in Case 3.

The earlier formation and fallout of precipitation
in Cases 1 and 2 compared to that in Case 3 have
profound dynamic effects on the later stages of the
simulations. Although not clearly evident in Fig. 6,
the precipitation-induced downdraft in Case 3, while
occurring later than in Cases I and 2, is more intense.
The cascade of precipitation is also more intense and
occurs over a shorter time span in Case 3. As is
pointed out in Orville and Chen (1982), the timing
of precipitation fallout has a strong modulating effect
on storm intensity. Similar to their results, the earlier
formation and fallout of precipitation in Cases I and
2 actually weaken subsequent storm development
(the generation of daughter clouds or cells). This
would be even more evident in the current results
had the integrations been continued beyond 48 min.

b. Total production of rain, hail and snow

The net production of rain, hail and snow, inte-
grated over the entire domain and accumulated to
the time indicated, are shown in Figs. 7a-c for the
three cases. The time evolution of the domain totals
of cloud water, cloud ice, rain, snow and hail for the
three cases are shown in Fig. 8. [The unit kT in Figs.
7, 8, 10, 11 and 12 is equal to 109 g.] Figs. 7b and
8 in conjunction with the cloud outlines in Figs. 6a
and 6b show the two cells or surges in growth of the
hail content for Cases I and 2. The two maxima occur

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TIME (MINUTESl- TIME (MINUTESl- TIME (MINUTESl-

FIG. 7. The accumulated net production of (a) rain, (b) hail and (c) snow versus time for the three cases.
The units of production are kT km-I (109 g km-I).