Geoscience Reference
In-Depth Information
NE Trades
Meso scale
convective cell
10-10
2
km
Equator
0°
Individual
convective
elements
1-10 km
Cloud cluster
10
2
- 10
3
km
SE Trades
Subtropical highs
30°S
30°S
Cloud cluster
O
utflo
w
Outflow region
12 km
Hadley cell
(Mesoscale
convective elements
containing
individual cells)
Convective layer
1km
Trade Wind
bound
ary la
yer
Fractional inflow
of moist air
0°
5°
30°
Figure 11.3
The mesoscale and synoptic structure of the equatorial trough zone (ITCZ), showing a model
of the spatial distribution (above) and of the vertical structure (below) of convective elements which form
the cloud clusters.
Source: From Mason (1970). By permission of the Royal Meteorological Society.
Table 11.1
Annual frequencies and usual seasonal occurrence of tropical cyclones (maximum
sustained winds exceeding 25m s
-1
), 1958-1977
Location
Annual frequency
Main occurrence
Western North Pacific
26.3
July-October
Eastern North Pacific
13.4
August-September
Western North Atlantic
8.8
August-October
Northern Indian Ocean
6.4
May-June; October-November
Northern Hemisphere total
54.6
Southwest Indian Ocean
8.4
January-March
Southeast Indian Ocean
10.3
January-March
Western South Pacific
5.9
January-March
Southern Hemisphere total
24.5
Global total
79.1
Source: After Gray (1979).
Note: Area totals are rounded.
