Geoscience Reference
In-Depth Information
0
100
200km
Mature
element
Cloud boundary
Old element
16
12
Motion
8
New
element
Melting band
4
Stable layer
0
Gust
front
Squall-
line
Anvil region
Convective-scale
motions
Mesoscale downdraughts
Heavy squall-line
precipitation
Lighter
precipitation
Mesoscale updraughts
Figure 11.12
Cross-section of a tropical squall-line cloud cluster showing locations of precipitation and
ice particle melting. Dashed arrows show the air motion generated by the squall-line convection and the
broad arrows the mesoscale circulation.
Source: After Houze; from Houze and Hobbs (1982). By permission of Academic Press.
10
25
7.16ins
18.2cm
2.18
5.5
0.39
1.0
0.00
0.0
0.00
0.0
0.31
0.76
3.91
9.9
5.92
14.9
23.12
58.7
44.51
113.0
35.43
90.0
18.07
45.8
8
20
6
15
4
10
2
5
0
0
O
N
D
J
F
M
A
M
J
J
A
S
Disturbance
lines
Little dry
season
Steady (monsoon) rain
Disturbance lines
Dry but humid
Harmattan
Dry but humid
Disturbance lines
Figure 11.13
Daily rainfall at Kortright (Freetown), Sierra Leone, October 1960 to September 1961.
Source: After Gregory (1965).
vast extent and the penetration of its influence
beyond tropical latitudes (
Figure 11.14
). However,
such seasonal shifts of the surface winds occur in
many regions that are not traditionally considered
as monsoonal. Although there is an overlap
between these traditional regions and those
experiencing over 60 percent frequency of winds
from the prevailing octant, it is obvious that a
variety of unconnected mechanisms can lead to
seasonal wind shifts. Nor is it possible to establish
a simple relationship between seasonality of rainfall
(
Figure 11.15
) and seasonal wind shift. Areas
traditionally designated as 'monsoonal' include
some of the tropical and near-tropical regions
experiencing a summer rainfall maximum and
most of those having a double rainfall maximum.
It is clear that a combination of criteria is necessary
for an adequate definition of monsoon areas.
In summer, the Equatorial Trough and the
subtropical anticyclones are everywhere displaced
