Origin and impact of initialisation shocks in coupled atmosphere-ocean forecasts

Mulholland, D., Laloyaux, P., Haines, K. ORCID: https://orcid.org/0000-0003-2768-2374 and Balmaseda, M. A. (2015) Origin and impact of initialisation shocks in coupled atmosphere-ocean forecasts. Monthly Weather Review, 143 (11). pp. 4631-4644. ISSN 0027-0644 doi: 10.1175/MWR-D-15-0076.1

Abstract/Summary

Current methods for initialising coupled atmosphere-ocean forecasts often rely on the use of separate atmosphere and ocean analyses, the combination of which can leave the coupled system imbalanced at the beginning of the forecast, potentially accelerating the development of errors. Using a series of experiments with the European Centre for Medium-range Weather Forecasts coupled system, the magnitude and extent of these so-called initialisation shocks is quantified, and their impact on forecast skill measured. It is found that forecasts initialised by separate ocean and atmospheric analyses do exhibit initialisation shocks in lower atmospheric temperature, when compared to forecasts initialised using a coupled data assimilation method. These shocks result in as much as a doubling of root-mean-square error on the first day of the forecast in some regions, and in increases that are sustained for the duration of the 10-day forecasts performed here. However, the impacts of this choice of initialisation on forecast skill, assessed using independent datasets, were found to be negligible, at least over the limited period studied. Larger initialisation shocks are found to follow a change in either the atmospheric or ocean model component between the analysis and forecast phases: changes in the ocean component can lead to sea surface temperature shocks of more than 0.5K in some equatorial regions during the first day of the forecast. Implications for the development of coupled forecast systems, particularly with respect to coupled data assimilation methods, are discussed.

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/40638
Identification Number/DOI	10.1175/MWR-D-15-0076.1
Refereed	Yes
Divisions	Science > School of Mathematical, Physical and Computational Sciences > National Centre for Earth Observation (NCEO) Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
Publisher	American Meteorological Society
Download/View statistics	View download statistics for this item