Variability in seasonal forecast skill of Northern Hemisphere winters over the twentieth century

O'Reilly, Christopher H., Heatley, James, MacLeod, Dave ORCID: https://orcid.org/0000-0001-5504-6450, Weisheimer, Antje, Palmer, Tim N., Schaller, Nathalie and Woollings, Tim 2017. Variability in seasonal forecast skill of Northern Hemisphere winters over the twentieth century. Geophysical Research Letters 44 (11) , pp. 5729-5738. 10.1002/2017GL073736

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Abstract

Seasonal hindcast experiments, using prescribed sea surface temperatures (SSTs), are analyzed for Northern Hemisphere winters from 1900 to 2010. Ensemble mean Pacific/North American index (PNA) skill varies dramatically, dropping toward zero during the mid-twentieth century, with similar variability in North Atlantic Oscillation (NAO) hindcast skill. The PNA skill closely follows the correlation between the observed PNA index and tropical Pacific SST anomalies. During the mid-century period the PNA and NAO hindcast errors are closely related. The drop in PNA predictability is due to mid-century negative PNA events, which were not forced in a predictable manner by tropical Pacific SST anomalies. Overall, negative PNA events are less predictable and seem likely to arise more from internal atmospheric variability than positive PNA events. Our results suggest that seasonal forecasting systems assessed over the recent 30 year period may be less skillful in periods, such as the mid-twentieth century, with relatively weak forcing from tropical Pacific SST anomalies.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Earth and Environmental Sciences
Publisher:	Wiley Open Access
ISSN:	0094-8276
Date of Acceptance:	21 May 2017
Last Modified:	28 May 2024 16:00
URI:	https://orca.cardiff.ac.uk/id/eprint/168329

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