WMOD00491

• Title: A Multisensor, Three-Dimensional Analysis of a Meso-High's Development
• Weather Modification - Doc Type: Report

Table 1. - Effect of lifting profile on total cloud depth, number of
clouds and rainfall

e

L1 fti ng
rate
(cm S-1)

Top of 1200 G.m.t. case
lifting Total No. of Total
(kPa) depth (km) clouds rain (11IIl)

1800 G.m.t. case
Total No. of Tota 1
depth (km) clouds rain [(I1IIl)

o
20
20
20

o
12.5
17.6
21.1

o
2
3
3

70
50
20

o
50.8
62.8
85.7

8.6
18.4
19.0
22.8

1
3
4
4

47.'3
74~3
62.:8
74.18
1

e

total cloud depth diagnosed for the 1800 G.m.t.
sounding occurred when the height of lifting was
increased from 70 to 20 kPa (see figure 4). The
atmosphere at 1200 G.m.t. was much more sensitive
to the change of lifting with height, having a
69-percent increase in total cloud depth. Similar
large increases occurred in the rainfall for the
1200 G.m.t. case, as shown in table 1.

Differences in stability and moisture profiles of
the 1200- and'1800-G.m.t. soundings show the rela-
tive importance of representative soundings in the
evaluation of lifting effect on the release of
available potential instability and the stabilizing
effects of local subsidence. The 1200 G.m.t.
sounding was more stable than the 1800 G.m.t.
sounding; consequently, the effect of vertical
motion on the stability of this sounding was larger
than that of the 1800 G.m.t. sounding. The 1200
G.m.t. sounding had insufficient releasible insta-
bility to produce clouds without lifting. However,
the unstable 1800 G.m.t. sounding produced deep
convection (cloudtop height of 11.1 km without
lifting - see figure 4).

When shallow lifting was applied to the 1200 G.m.t.
sounding, the model simulation produced deep con-
vection with a cloud top at 10.6 km. All subsequent
cloud development was suppressed by the strong sub-
sidence warming produced in compensation for the
initial cloud's vertical mass flux. Similarly,
suppressed clouds were produced in the simulation
using the 1800-G.m.t. soundings (see figures 4).
The tops of the radar echoes between 1900 and
2330 G.m.t. associated with the cumulonimbus cluster
that produced the arc cloud were at 10 to 13 km m.s.l.,
and the echo tops of the smaller cumulonimbus cloud
of the arc were at 5 to 7 km m.s.l.. These are in
good agreement with the model-diagnosed cloudtop
heights.

The effect of changing the lifting profile's upper
limit from 70 to 20 kPa is shown in figures
4 and 5. With shallow lifting there is no cooling
to compensate for the strong subsidence warming
induced by the first cloud at upper levels. Con-
sequently, cloud development is strongly suppressed.
As the depth of the lifting is raised to 20 kPa, its
compensating cooling permits deeper convection; how-
ever, in these simulations the secondary convection
remains at the cumulus congestus level of intensity.
The effects of lifting and compensating subsidence
are shown on the SKEW-T diagrams for each lifting
case (see figures 4 and 5).

e

16.0

14.0

12.0

:;::
:><:::

10.0

{-o
:r:
L9
~ 8.0

6.0

"

"

"

4.0

."

'-

'-

2.0

........... ................:
. ....... . . ......... :
'1

o . 0 I I --,-----.--
0.0 0.5 1.0
MAGNITUDE Of LIfT lKMl
I
Figure 3. - Three lifting profi;les used in model
simulations to test effect ofilifting profile
shape on model results. All experiments used a
20-cms-1 lifting rate at 80 t685 kPa; however,
the top of the lifting was in~reased from 70
(dotted line) to 50 kPa (dashed line) to 20 kPa
(solid line). :

5. CONCLUSIONS

The meso-high arc cloud is assofiated with strong
vertical lifting (3-6 ms-1) pro1duced by outflow
of moist downdraft air from cumulonimbus clouds.
The shape and magni tude of the :, ifti ng prof i1 e
associated with the meso-high arc cloud are import-
ant in determining the effect df lifting on the
release of available potential instability and
resulting cloud development.

Early detection of meso-high a~'c clouds, using
satellite imagery and radar, wi,ll improve the
analysis and forecasting of convective development.
Careful integration of mesoscale triggering effects