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

O’Reilly, Christopher H.; Heatley, James; MacLeod, Dave; Weisheimer, Antje; Palmer, Tim; Schaller, Nathalie; Woollings, Tim

doi:10.1002/2017gl073736

Cited by 45 publications

(83 citation statements)

References 41 publications

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“…15 for moving 31-year windows. The variability in correlation closely follows the variability in PNA skill demonstrated in seasonal hindcast experiments of the PNA by O'Reilly et al (2017). In the mid-century period, the ensemble mean correlation disappears, owing to the weakness in the observed ENSO teleconnection to the North Pacific.…”

Section: Implications For Extratropical North Pacific Predictabilitymentioning

confidence: 68%

“…O'Reilly et al (2017) showed that in Northern Hemisphere seasonal hindcast experiments the skill of the PNA varies dramatically over the 20th century, closely following the observed relationship between ENSO and the PNA. The drop in skill over the North Pacific in the mid-20th century also corresponds to a period of reduced skill in over the Euro-Atlantic sector O'Reilly et al 2017). Understanding the nature of the interdecadal variability in the ENSO teleconnection to the North Pacific is therefore crucial in determining how seasonal forecast skill has varied in the past and may possibly change going forwards.…”

Section: Introductionmentioning

confidence: 97%

“…Significant recent developments have resulted in increased skill of seasonal forecast systems for the extratropics in the Northern Hemisphere winter Dunstone et al 2016). O'Reilly et al (2017) showed that in Northern Hemisphere seasonal hindcast experiments the skill of the PNA varies dramatically over the 20th century, closely following the observed relationship between ENSO and the PNA. The drop in skill over the North Pacific in the mid-20th century also corresponds to a period of reduced skill in over the Euro-Atlantic sector O'Reilly et al 2017).…”

Section: Introductionmentioning

confidence: 99%

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Interdecadal variability of the ENSO teleconnection to the wintertime North Pacific

O’Reilly

2018

Clim Dyn

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The El Niño/Southern Oscillation (ENSO) strongly influences the large-scale atmospheric circulation over the extratropical North Pacific during boreal winter, which has an important impact on North American winter climate. This study analyses the interdecadal variability of the ENSO teleconnection to the wintertime extratropical North Pacific, over the period 1900-2010, using a range of observationally derived datasets and an ensemble of atmospheric model simulations. The observed teleconnection strength is found to vary substantially over the 20th century. Specifically, 31-year periods in the early-century (1912-1942), mid-century (1946-1976) and the late-century are identified in the observations when the ENSO teleconnection to the North Pacific circulation are found to be particularly strong, weak and strong respectively. The ENSO teleconnection to the North Pacific in the atmospheric model ensemble is weak in the mid-century period and substantially stronger in the late-century, closely following the variability in the observed ENSO-North Pacific teleconnection. In the earlycentury, however, the atmospheric model also exhibits a weak teleconnection to the North Pacific, unlike in observations. In a subset of the model realisations that exhibit similar ENSO-North Pacific teleconnection as in observations during the early-century period there are large differences in extratropical circulation but not in equatorial Pacific precipitation anomalies, in contrast to the late-century period. This suggests that the high correlation in the early century period is largely due to internal extratropical variability. The important implications of these results for seasonal predictability and the assessment of seasonal forecasting systems are discussed.

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Section: Implications For Extratropical North Pacific Predictabilitymentioning

confidence: 68%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Interdecadal variability of the ENSO teleconnection to the wintertime North Pacific

O’Reilly

2018

Clim Dyn

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“…The dashed grey lines depict return level uncertainties calculated from ERA-Interim only NAO phase; however the loss during the negative phase is also lower than for the mean across all years and ensembles. Studies have shown that the NAO in seasonal forecasts can be predicted with significant skill (e.g., Scaife et al, 2014;O'Reilly et al, 2017). As a result, this would mean that a seasonal forecast exhibiting extreme NAO values for a season bears the potential of either above or below average windstorm damage.…”

Section: Estimated Damage Linked With Large-scale Driver Indicesmentioning

confidence: 99%

Loss potentials based on an ensemble forecast: How likely are winter windstorm losses similar to 1990?

Walz

Leckebusch

2019

Atmospheric Science Letters

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In this paper we investigate the feasibility and added value of using the seasonal hindcasts of the ECMWF System 4 as a hazard event set for European winter windstorms damage calculations. The windstorms are identified for every ensemble member and every year by an objective windstorm tracking algorithm. The damages are calculated directly from the obtained wind footprints via the open source natural catastrophe damage model CLIMADA for Germany, the UK, France and Spain and compared to the loss from ERA‐Interim. The results show that the ensembles of losses in System 4 nicely capture the inter‐annual loss variability of the reanalysis. Due to more than 1,500 years of “virtual reality” windstorm data from the hindcasts, the return levels of extreme losses can be estimated fairly accurately. Based on System 4, the losses in the scale of 1990 (January, February, March and December including the prominent windstorm Daria) represent a 20‐year event in Germany whereas they represent a 100‐year event for the UK. Thus, a considerably shorter return period compared to return periods calculated from ERA‐Interim alone. Further we investigate the link between the annual losses and large‐scale drivers derived from mean‐sea‐level‐pressure (MSLP) data in System 4. We can show that within System 4 there is a significant link between increased loss potentials for strongly positive North Atlantic Oscillation (NAO) phases for Germany and the UK as well as a reduced loss potential for Spain. The link between the other analysed indices is weak bar the East Atlantic (EA) pattern index. Thus, if the NAO in System 4 is correct we can assume that the windstorms in System 4 are useable. If this premise is given our study shows that the loss estimates and ultimately the return levels of losses from System 4 can be used in an operational way.

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“…Since the sensitivities were estimated from a control integration of a coupled model and were treated as being constant in time, further improvements of the method could include sensitivities depending on the atmospheric state, for instance, for phases of either low or high NAO states, which have shown to impact the predictability of the NAO (O'Reilly et al, ).…”

Section: Discussionmentioning

confidence: 99%

Seasonal Prediction of Northern European Winter Air Temperatures From SST Anomalies Based on Sensitivity Estimates

Köhl

Vlasenko

2019

Geophysical Research Letters

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The climate over Europe is significantly affected by the state of the atmospheric circulation over the North Atlantic, which in turn is influenced by various slowly varying components of the climate system. Linear models are employed to investigate how much of the European winter air temperature variability can directly be predicted from the sea surface temperature. By comparing relations from a statistical model to those from an adjoint to a linearized climate model we evaluate the ability of the lagged maximum covariance analysis to reconstruct the dynamical relation between sea surface temperature (SST) and atmosphere temperature. Applied to specific SST conditions, both approaches allow prediction of a similar and significant fraction of the air temperature variability from SST. For a 1‐month lag, extreme air temperature responses are significant and found to be associated with an omega‐blocking pattern over Scandinavia.

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

Cited by 45 publications

References 41 publications

Interdecadal variability of the ENSO teleconnection to the wintertime North Pacific

Interdecadal variability of the ENSO teleconnection to the wintertime North Pacific

Loss potentials based on an ensemble forecast: How likely are winter windstorm losses similar to 1990?

Seasonal Prediction of Northern European Winter Air Temperatures From SST Anomalies Based on Sensitivity Estimates

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