7.2 Wind Pattern on Earth
N
t
.0
.. 0 '
.0".0 '
.0'
Coral Sea
0 '"
~bO ... O,O 7 March
COJ .... ·o
o tropical
depression
01
02
. 3
207
Fig. 7.4: Path of tropical cyclone Justin along the east coast of Australia, for the
period 7~24 March, 1997 (adapted from Bureau of Meteorology, 1998)
Guinea. On this figure, the categories of cyclone severity at particular locations
of the cyclone's eye are given. It should be noted that there are five categories of
cyclone, increasing from 1 to 5. Associated central pressure, Pc, wind velocities
and typical effects are described in Table 7.1.
A tropical cyclone is an almost circular vortex with a centre of extremely
low pressure into which winds are spiralling at high speed (Fig. 7.5, see colour
plate p.564). At the centre of a t.ropical cyclone is the 'eye' in which calm
conditions prevail and the pressure reaches its lowest value, PC) known as t.he
central pressure. The central pressure can be convert.ed to maximum sustained
wind by the approximate relationship (Young and Holland, 1996):
(
) 0.644
Vmax = 1.74 Po - Pc
,
(7.7)
where Vmax is the speed in mis, Po is the ambient pressure, usually taken as
Po = 1010hPa, and Pc is the pressure at the cyclone centre. Barometric pressure
in the tropical cyclone centre commonly falls to 950 mb or lower.
Wind velocity within the cyclone increases from zero at the cyclone eye, to
its maximum value, Vm.ax, some distance (20~40 km) from the eye, and then
slowly decreases as the distance from the eye increases. The strongest winds are
typically found in the front right (left) quadrant for cyclones in the Northern
N
t
.0
.. 0 '
.0".0 '
.0'
Coral Sea
0 '"
~bO ... O,O 7 March
COJ .... ·o
o tropical
depression
01
02
. 3
207
Fig. 7.4: Path of tropical cyclone Justin along the east coast of Australia, for the
period 7~24 March, 1997 (adapted from Bureau of Meteorology, 1998)
Guinea. On this figure, the categories of cyclone severity at particular locations
of the cyclone's eye are given. It should be noted that there are five categories of
cyclone, increasing from 1 to 5. Associated central pressure, Pc, wind velocities
and typical effects are described in Table 7.1.
A tropical cyclone is an almost circular vortex with a centre of extremely
low pressure into which winds are spiralling at high speed (Fig. 7.5, see colour
plate p.564). At the centre of a t.ropical cyclone is the 'eye' in which calm
conditions prevail and the pressure reaches its lowest value, PC) known as t.he
central pressure. The central pressure can be convert.ed to maximum sustained
wind by the approximate relationship (Young and Holland, 1996):
(
) 0.644
Vmax = 1.74 Po - Pc
,
(7.7)
where Vmax is the speed in mis, Po is the ambient pressure, usually taken as
Po = 1010hPa, and Pc is the pressure at the cyclone centre. Barometric pressure
in the tropical cyclone centre commonly falls to 950 mb or lower.
Wind velocity within the cyclone increases from zero at the cyclone eye, to
its maximum value, Vm.ax, some distance (20~40 km) from the eye, and then
slowly decreases as the distance from the eye increases. The strongest winds are
typically found in the front right (left) quadrant for cyclones in the Northern