Noise-induced phenomena in environmental systems - Noise-induced Phenomena in the Environmental Sciences - page 110

0.9

30N

0.8

20N

0.7

0.6 10N

0.5

EQ

0.4

10S

0.3

0.2

20S

0.1
0

30S

(a) (b)

40S

<

20W 10W 0 10E 20E 30E 40E 50E 20W 10W 0 10E 20E 30E 40E 50E

>

40N

0.8 30N

0.7

20N

0.6

10N

0.5

EQ

0.4

10S

0.3

20S

0.2

30S

0.1
<

(c) (d)

40S

20W 10W 0 10E 20E 30E 40E 50E 20W 10W 0 10E 20E 30E 40E 50E

Figure 4.4. Equilibrium vegetation distribution from a coupled atmosphere-
vegetation model. Dark shaded areas correspond to forest cover. Light gray areas
correspond to sparse vegetation and desert conditions. (a) Simulation starting from
desert (i.e., unvegetated) conditions in the whole African continent; (b) simulation
starting with forest vegetation across the whole continent; (c) map of the difference
between (b) and (a); (d) difference between equilibrium vegetation (obtained with
fluctuating SST and initial desert conditions) and the equilibrium state in (a) (after
Zeng and Neelin , 2000 ).

v

1

0.8

FOREST

FOREST_INTERANNUAL

0.6

0.4 DESERT_INTERANNUAL

0.2

DESERT

0

t
Figure 4.5. Average vegetation cover in the Sahel region as a function of time.
Calculated with model simulations using different initial conditions (after Zeng and
Neelin , 2000 ).

(yrs)

50 150 200

0 100