 |
| Titel |
Initial state perturbations in ensemble forecasting |
| VerfasserIn |
L. Magnusson, E. Källén, J. Nycander |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1023-5809
|
| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 15, no. 5 ; Nr. 15, no. 5 (2008-10-21), S.751-759 |
| Datensatznummer |
250012761
|
| Publikation (Nr.) |
 copernicus.org/npg-15-751-2008.pdf |
|
|
|
|
|
| Zusammenfassung |
| Due to the chaotic nature of atmospheric dynamics, numerical weather
prediction systems are sensitive to errors in the initial conditions. To
estimate the forecast uncertainty, forecast centres produce ensemble
forecasts based on perturbed initial conditions. How to optimally perturb the
initial conditions remains an open question and different methods are in use.
One is the singular vector (SV) method, adapted by ECMWF, and another is the
breeding vector (BV) method (previously used by NCEP). In this study we
compare the two methods with a modified version of breeding vectors in a
low-order dynamical system (Lorenz-63). We calculate the Empirical Orthogonal
Functions (EOF) of the subspace spanned by the breeding vectors to obtain an
orthogonal set of initial perturbations for the model. We will also use
Normal Mode perturbations. Evaluating the results, we focus on the fastest
growth of a perturbation. The results show a large improvement for the BV-EOF
perturbations compared to the non-orthogonalised BV. The BV-EOF technique
also shows a larger perturbation growth than the SVs of this system, except
for short time-scales. The highest growth rate is found for the second BV-EOF
for the long-time scale. The differences between orthogonal and
non-orthogonal breeding vectors are also investigated using the ECMWF
IFS-model. These results confirm the results from the Loernz-63 model
regarding the dependency on orthogonalisation. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|