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14.9
27.2
A
7.1
B
12.7
26.1
F
C
E
19.0
D
5.6
10.8
9.2
G
26.5
H
27.3
I
4.7
7.1
J
K
Figure 14.5 Calculation of
area-average precipitation
using the Theissen Method.
(From Sumner, 1988,
published with permission.)
15.0
24.2
25.8
18.5
(a)
(b)
Direction of
storm movement
Frontal
Cyclonic
Figure 14.6 (a) Typical
arrangement of elliptical
storms in different
meteorological conditions;
(b) characteristic
precipitation field in a basic
single cell storm.
Intensity
Convective
being the asymptotic limit of an ellipse). There are usually bands of precipitation
(clusters of intense cells) in frontal systems, spiral bands of storms in tropical
cyclones, and individual intense cells in convective conditions (Fig. 14.6a).
Thus, on average, the characteristic form of a basic single cell storm deduced
from surface gauge observations has an outer boundary which is approximately
elliptical in shape, with a series of successively smaller ellipses inside corresponding
to increasing intensity. The rate of change in intensity rises toward the middle of the
storm, i.e., the slope of the upper surface of the intensity pattern is concave upward,
steeper toward the center of the storm and dying out gradually and intermittently
toward the edges of the storm (Fig. 14.6b).
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