Initialization and ensemble generation for decadal climate predictions: A comparison of different methods.

Polkova, Iuliia , Brune, Sebastian , Kadow, Christopher , Romanova, Vanya, Gollan, Gereon , Baehr, Johanna , Glowienka-Hense, Rita, Greatbatch, Richard John , Hense, Andreas , Illing, Sebastian, Köhl, Armin, Kröger, Jürgen, Müller, Wolfgang A. , Pankatz, Klaus and Stammer, Detlef (2019) Initialization and ensemble generation for decadal climate predictions: A comparison of different methods. Open Access Journal of Advances in Modeling Earth Systems, 11 . pp. 149-172. DOI 10.1029/2018MS001439.

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Abstract

Five initialization and ensemble generation methods are investigated with respect to their impact on the prediction skill of the German decadal prediction system "Mittelfristige Klimaprognose" (MiKlip). Among the tested methods, three tackle aspects of model‐consistent initialization using the ensemble Kalman filter (EnKF), the filtered anomaly initialization (FAI) and the initialization method by partially coupled spin‐up (MODINI). The remaining two methods alter the ensemble generation: the ensemble dispersion filter (EDF) corrects each ensemble member with the ensemble mean during model integration. And the bred vectors (BV) perturb the climate state using the fastest growing modes. The new methods are compared against the latest MiKlip system in the low‐resolution configuration (Preop‐LR), which uses lagging the climate state by a few days for ensemble generation and nudging toward ocean and atmosphere reanalyses for initialization. Results show that the tested methods provide an added value for the prediction skill as compared to Preop‐LR in that they improve prediction skill over the eastern and central Pacific and different regions in the North Atlantic Ocean. In this respect, the EnKF and FAI show the most distinct improvements over Preop‐LR for surface temperatures and upper ocean heat content, followed by the BV, the EDF and MODINI. However, no single method exists that is superior to the others with respect to all metrics considered. In particular, all methods affect the Atlantic Meridional Overturning Circulation in different ways, both with respect to the basin‐wide long‐term mean and variability, and with respect to the temporal evolution at the 26° N latitude.

Document Type: Article
Keywords: decadal prediction system; initialization methods; ensemble generation methods
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-OD Ocean Dynamics
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1029/2018MS001439
ISSN: 1942-2466
Projects: MiKlip, MODINI
Date Deposited: 14 Jan 2019 07:59
Last Modified: 18 Mar 2019 13:57
URI: http://oceanrep.geomar.de/id/eprint/45302

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