316 Martin Fischer
~"r-------------------------------------~~--~~~~
25"
2C"
15"
'0"
. .
: .t~1~, _____ N1 __ N _O _-_ 4 ______ L -________________ ~
lOS iJf> . ' ~
0 ,
15S
205
25S
JOS L---~ 1~ ~--~"~OE~--~ 1 8~ O ----~1~~W~--~1~ 'O~W----~12~OW----~100~W ~--~~
Fig.16.7 The NINO-3 and NINOA index regions.
circulation model integration. This model integration successfully reproduced the
observed interannual ENSO related variability. In a second experiment with the
same boundary conditions but different initial conditions the low frequency interannual variability was equally well reproduced. The principal result from these
experiments is that the ENSO related variability is not governed by internal atmospheric instabilities. The low frequency variations in tropical Pacific SST, on the
other hand, can be reproduced by ocean models, provided the surface wind stress
variations are specified from observations (e.g. Latif 1987). Thus, low frequency
variations in both the atmosphere and the ocean are strongly controlled by changes
in the boundary conditions which demonstrates the coupled nature of ENSO (see
also Latif at al. 1997 and references therein).
Coupled ocean atmosphere models of different complexities also have been
used for ENSO predictions and predictability studies (e.g. Zebiak and Cane 1987,
Eckert and Latif 1997). These models generally simulate fairly robust ENSO
cycles which share many similarities with the observations. Predictability studies
with such models also indicate an ENSO predictability of about one to two years,
and thus confirm the results obtained from observational studies, and investigations
with uncoupled models.
16.2.3 The impact of ENSO 00 climate aod ecooomy
The impacts of ENSO are felt worldwide through a disruption of the atmosphere
general circulation pattems (Ropelewski and Halpert 1987), which leads to climate
changes in many regions of the world (Fig. 16.9) ENSO related climate variations
and the corresponding economic al impacts are correlated worldwide so that amplification effects play an important role. Severe droughts are observed during El
Nifio events in Northwest Australia, South East Asia and Northeast BraziI. Zimbabwe and the south of the United States are other regions where rainfall variations
are highly correlated with ENSO indices. The agriculture, and thus the crop yield is
directly and strongly affected in these regions. The variability of crop yield in Zim-
~"r-------------------------------------~~--~~~~
25"
2C"
15"
'0"
. .
: .t~1~, _____ N1 __ N _O _-_ 4 ______ L -________________ ~
lOS iJf> . ' ~
0 ,
15S
205
25S
JOS L---~ 1~ ~--~"~OE~--~ 1 8~ O ----~1~~W~--~1~ 'O~W----~12~OW----~100~W ~--~~
Fig.16.7 The NINO-3 and NINOA index regions.
circulation model integration. This model integration successfully reproduced the
observed interannual ENSO related variability. In a second experiment with the
same boundary conditions but different initial conditions the low frequency interannual variability was equally well reproduced. The principal result from these
experiments is that the ENSO related variability is not governed by internal atmospheric instabilities. The low frequency variations in tropical Pacific SST, on the
other hand, can be reproduced by ocean models, provided the surface wind stress
variations are specified from observations (e.g. Latif 1987). Thus, low frequency
variations in both the atmosphere and the ocean are strongly controlled by changes
in the boundary conditions which demonstrates the coupled nature of ENSO (see
also Latif at al. 1997 and references therein).
Coupled ocean atmosphere models of different complexities also have been
used for ENSO predictions and predictability studies (e.g. Zebiak and Cane 1987,
Eckert and Latif 1997). These models generally simulate fairly robust ENSO
cycles which share many similarities with the observations. Predictability studies
with such models also indicate an ENSO predictability of about one to two years,
and thus confirm the results obtained from observational studies, and investigations
with uncoupled models.
16.2.3 The impact of ENSO 00 climate aod ecooomy
The impacts of ENSO are felt worldwide through a disruption of the atmosphere
general circulation pattems (Ropelewski and Halpert 1987), which leads to climate
changes in many regions of the world (Fig. 16.9) ENSO related climate variations
and the corresponding economic al impacts are correlated worldwide so that amplification effects play an important role. Severe droughts are observed during El
Nifio events in Northwest Australia, South East Asia and Northeast BraziI. Zimbabwe and the south of the United States are other regions where rainfall variations
are highly correlated with ENSO indices. The agriculture, and thus the crop yield is
directly and strongly affected in these regions. The variability of crop yield in Zim-