ENSO Predictions with Coupled Ocean Atmosphere Models
335
16.6 Summary
In the first part of this paper the El Nifio/Southem Oscillation phenomenon was
described, and it was shown that the ENSO cycle is predictable on lead times up to
one year. This is an important issue, since the climatic and economic impacts are
tremendous.
Different types of ENSO prediction models were presented in the second part of
the paper, and their specific strong and weak points were discussed. Nowadays the
forecast skill obtained with coupled general circulation models is comparable to
the skill achievable with much simpler and much more economical models like statistical methods or hybrid coupled models. However, coupled general circulation
models show the highest potential for further improvements, and therefore further
research should be devoted to these complicated and expensive models.
It is evident from the results found by different groups that data assimilation
techniques may help to compensate for model errors or for wind forcing errors during the initialization phase. However, the main goal must be to improve the performance of the models in order to achieve higher forecast skills. An interesting and
very promising approach is the coupled initialization of an ENSO forecast system.
In this case the coupling shock at the beginning of a forecast can be avoided. Preliminary results further indicate that the low frequency component of the wind
fields, essential for ENSO initializations, was better extracted from the wind data
than in the case ofuncoupled initialization.
This paper also indicates that the question of forecast verification needs to be
addressed in more detail. In one example it was shown that the interpretation of the
results critically depends on the definition ofthe skill measure.
Correcting known systematic errors of a forecast system is necessary to make the
final product more understandable for people who are not familiar with the scientific issues of ENSO predictions.
335
16.6 Summary
In the first part of this paper the El Nifio/Southem Oscillation phenomenon was
described, and it was shown that the ENSO cycle is predictable on lead times up to
one year. This is an important issue, since the climatic and economic impacts are
tremendous.
Different types of ENSO prediction models were presented in the second part of
the paper, and their specific strong and weak points were discussed. Nowadays the
forecast skill obtained with coupled general circulation models is comparable to
the skill achievable with much simpler and much more economical models like statistical methods or hybrid coupled models. However, coupled general circulation
models show the highest potential for further improvements, and therefore further
research should be devoted to these complicated and expensive models.
It is evident from the results found by different groups that data assimilation
techniques may help to compensate for model errors or for wind forcing errors during the initialization phase. However, the main goal must be to improve the performance of the models in order to achieve higher forecast skills. An interesting and
very promising approach is the coupled initialization of an ENSO forecast system.
In this case the coupling shock at the beginning of a forecast can be avoided. Preliminary results further indicate that the low frequency component of the wind
fields, essential for ENSO initializations, was better extracted from the wind data
than in the case ofuncoupled initialization.
This paper also indicates that the question of forecast verification needs to be
addressed in more detail. In one example it was shown that the interpretation of the
results critically depends on the definition ofthe skill measure.
Correcting known systematic errors of a forecast system is necessary to make the
final product more understandable for people who are not familiar with the scientific issues of ENSO predictions.