The Representation of Atmospheric Blocking and the Associated Low-Frequency Variability in Two Seasonal Prediction Systems

Athanasiadis, Panos; Bellucci, Alessio; Hermanson, Leon; Scaife, Adam A.; MacLachlan, Craig; Arribas, Alberto; Materia, Stefano; Borrelli, Andrea; Gualdi, Silvio

doi:10.1175/jcli-d-14-00291.1

Cited by 31 publications

(28 citation statements)

References 47 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The Aleutian low in the north Pacific typically deepens in response to El Niño as part of the Pacific North American teleconnection pattern which is highly predictable in the forecasting system used here (Athanasiadis et al ., ). As expected, a very deep Aleutian low also occurred during winter 2015/2016 (Figure ), with anomalies exceeding −10 hPa in the north Pacific corresponding to the very strong El Niño.…”

Section: Extratropical Circulationmentioning

confidence: 97%

Predictability of European winter 2015/2016

Scaife

Comer

Dunstone

et al. 2017

Atmospheric Science Letters

Self Cite

View full text Add to dashboard Cite

We present a case study of long range forecasts for Northern Hemisphere winter 2015/2016. This winter produced the strongest El Niño event since 1997/1998 and equatorial Pacific sea surface temperature anomalies exceeded 3 ∘ C. Other factors relevant to the Northern Hemisphere extratropical atmosphere circulation included a strong westerly phase of the Quasi-Biennial Oscillation (QBO) and very strong winds in the stratospheric polar night jet in early winter. At the surface, intense cyclonic extratropical circulation anomalies occurred in early winter in both the North Pacific and North Atlantic, consistent with known teleconnections to these phases of El Niño-Southern Oscillation, the QBO and the polar night jet. The midlatitude flow was very westerly in early winter and less westerly and sometimes northerly in late winter, when sudden stratospheric warming events also occurred. We show that initialised climate predictions were able to capture the winter mean flow pattern at seasonal lead times from well before the start of winter. In this special case, not only the winter mean flow pattern, but also some aspects of the sub-seasonal evolution were skilfully predicted. We show that the winter of 1982/1983 was closely analogous to winter 2015/2016 in both the predictable driving factors and the forecast winter circulation. This case study adds to the evidence that the north Atlantic circulation can be predictable on seasonal timescales and advance warning of the increased risk of intense rainfall and storminess which caused extreme flooding in the UK in December was possible in this case.

show abstract

Section: Extratropical Circulationmentioning

confidence: 97%

Predictability of European winter 2015/2016

Scaife

Comer

Dunstone

et al. 2017

Atmospheric Science Letters

Self Cite

View full text Add to dashboard Cite

show abstract

“…The GloSea5 system produces skilful forecasts of the winter North Atlantic Oscillation (NAO) from initial conditions in early November and in recent years, multiple seasonal forecast systems have been shown to produce skilful predictions of the winter NAO at this lead time (Athanasiadis et al, 2014;Butler et al, 2016;Baker et al, 2018). Figure 3 shows ensemble hindcasts of the winter NAO at the standard and higher resolutions.…”

Section: Prediction Skill Of the Naomentioning

confidence: 99%

Does increased atmospheric resolution improve seasonal climate predictions?

Scaife

Camp

Comer

et al. 2019

Atmospheric Science Letters

Self Cite

View full text Add to dashboard Cite

We assess the impact of atmospheric horizontal resolution on the prediction skill and fidelity of seasonal forecasts. We show the response to an increase of atmospheric resolution from 0.8 to 0.3° horizontal grid spacing in parallel ensembles of forecasts. Changes in the prediction skill of major modes of tropical El Nino Southern Oscillation (ENSO) and extratropical North Atlantic Oscillation (NAO) variability are small and not detected and there is no discernible impact on the weak signal‐to‐noise ratio in seasonal predictions of the winter NAO at this range of resolutions. Although studies have shown improvements in the simulation of tropical cyclones as model resolution is increased, we find little impact on seasonal prediction skill of either their numbers or intensity. Over this range of resolutions it appears that the benefit of increasing atmospheric resolution to seasonal climate predictions is minimal. However, at yet finer scales there appears to be increased eddy feedback which could strengthen weak signals in predictions of the NAO. Until prediction systems can be run operationally at these scales, it may be better to use additional computing resources for other enhancements such as increased ensemble size, for which there is a clear benefit in extratropical seasonal prediction skill.

show abstract

“…Various seasonal forecast systems now provide skilful forecasts out to a few months ahead (e.g. MacLachlan et al, 2015;Athanasiadis et al, 2014), allowing for some form of skilful dynamical hydrological forecast. As well as using a climate model output, others are investigating statistical relationships between large-scale North Atlantic climate indices (such as the North Atlantic Oscillation, NAO) and seasonal rainfall or river flow anomalies (Lavers et al, 2010a, b;McGregor and Phillips, 2004;Svensson and Prudhomme, 2005;Wedgbrow et al, 2002;Wilby, 2001;Svensson et al, 2015), and these can provide increased skill when large-scale patterns dominate regional rainfall .…”

Section: Introductionmentioning

confidence: 99%

A national-scale seasonal hydrological forecast system: development and evaluation over Britain

Bell

Davies

Kay

et al. 2017

Hydrol. Earth Syst. Sci.

Self Cite

View full text Add to dashboard Cite

Abstract. Skilful winter seasonal predictions for the North Atlantic circulation and northern Europe have now been demonstrated and the potential for seasonal hydrological forecasting in the UK is now being explored. One of the techniques being used combines seasonal rainfall forecasts provided by operational weather forecast systems with hydrological modelling tools to provide estimates of seasonal mean river flows up to a few months ahead.The work presented here shows how spatial information contained in a distributed hydrological model typically requiring high-resolution (daily or better) rainfall data can be used to provide an initial condition for a much simpler forecast model tailored to use low-resolution monthly rainfall forecasts. Rainfall forecasts ("hindcasts") from the GloSea5 model (1996 to 2009) are used to provide the first assessment of skill in these national-scale flow forecasts. The skill in the combined modelling system is assessed for different seasons and regions of Britain, and compared to what might be achieved using other approaches such as use of an ensemble of historical rainfall in a hydrological model, or a simple flow persistence forecast. The analysis indicates that only limited forecast skill is achievable for Spring and Summer seasonal hydrological forecasts; however, Autumn and Winter flows can be reasonably well forecast using (ensemble mean) rainfall forecasts based on either GloSea5 forecasts or historical rainfall (the preferred type of forecast depends on the region). Flow forecasts using ensemble mean GloSea5 rainfall perform most consistently well across Britain, and provide the most skilful forecasts overall at the 3-month lead time. Much of the skill (64 %) in the 1-month ahead seasonal flow forecasts can be attributed to the hydrological initial condition (particularly in regions with a significant groundwater contribution to flows), whereas for the 3-month ahead lead time, GloSea5 forecasts account for ∼ 70 % of the forecast skill (mostly in areas of high rainfall to the north and west) and only 30 % of the skill arises from hydrological memory (typically groundwater-dominated areas). Given the high spatial heterogeneity in typical patterns of UK rainfall and evaporation, future development of skilful spatially distributed seasonal forecasts could lead to substantial improvements in seasonal flow forecast capability, potentially benefitting practitioners interested in predicting hydrological extremes, not only in the UK but also across Europe.

show abstract

The Representation of Atmospheric Blocking and the Associated Low-Frequency Variability in Two Seasonal Prediction Systems

Cited by 31 publications

References 47 publications

Predictability of European winter 2015/2016

Predictability of European winter 2015/2016

Does increased atmospheric resolution improve seasonal climate predictions?

A national-scale seasonal hydrological forecast system: development and evaluation over Britain

Contact Info

Product

Resources

About