Decadal predictability of North Atlantic blocking and the NAO

Athanasiadis, Panos; Yeager, Stephen; Kwon, Young‐Oh; Bellucci, Alessio; Smith, David W.; Tibaldi, S.

doi:10.1038/s41612-020-0120-6

Cited by 80 publications

(79 citation statements)

References 79 publications

(155 reference statements)

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“…Essentially, this additional criterion requires that a band of westerlies must be present in the latitudinal band between 15° and 30° south of the grid‐point where blocking is evaluated. This criterion has been employed in D12 but suppressed in most subsequent studies (e.g., Davini et al ., 2017; Athanasiadis et al ., 2020; Schiemann et al ., 2020, and references therein) which were based on the algorithm described in D12 or the very similar one introduced by Scherrer et al . (2006).…”

Section: Methodsmentioning

confidence: 99%

“…Essentially, this additional criterion requires that a band of westerlies must be present in the latitudinal band between 15 • and 30 • south of the grid-point where blocking is evaluated. This criterion has been employed in D12 but suppressed in most subsequent studies (e.g., Davini et al, 2017;Athanasiadis et al, 2020;Schiemann et al, 2020, and references therein) which were based on the algorithm described in D12 or the very similar one introduced by Scherrer et al (2006). Therefore for our results to be compatible and comparable with those from previous studies that employed the same blocking detection scheme, and because the focus of this study is on HLB, we did not include in our algorithm the third criterion introduced by D12.…”

Section: Data and Blocking Identification Methodsmentioning

confidence: 99%

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Reconciling different methods of high‐latitude blocking detection

Tyrlis

Bader

Manzini

et al. 2021

Quart J Royal Meteoro Soc

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Blocking is associated with outbreaks of easterlies induced by a continuum of features including anticyclones, cyclones or both. Blocking identification methods disagree on the levels of high‐latitude blocking (HLB) activity. We investigate the cause of the disagreement in HLB activity over the Northern Hemisphere obtained by two 2D methods: the PV–θ index and the Absolute Geopotential Height (AGH) reversal method. Although both classify as absolute field methods, the former yields nearly twice the winter HLB activity of the latter method. We show that this discrepancy is caused by the addition of a poleward criterion in the AGH method that requires strong poleward westerlies. The additional criterion in the AGH method shifts the focus on the detection of blocking ridges and thus other blocking circulation patterns are under‐represented. Both methods agree on the climatology of midlatitude blocking because the poleward criterion has been tuned to capture the strong midlatitude blocking, but the discrepancy grows in high latitudes. HLBs are different because they occur on the northern flank of the westerlies and are associated with the equatorward displacement of the midlatitude jet. HLB anticyclones are weaker and do not induce strong poleward westerlies compared to their midlatitude counterparts. The implementation of a strict poleward criterion designed to identify midlatitude blocks rejects many HLBs. The use of the less strict cut‐off threshold (CT) of 0 m (°lat)−1 in the poleward criterion for latitudes higher than 60°N results in the convergence of climatology, interannual variability and trends of HLB between the two methods, especially during winter. The additional HLBs identified by the modified AGH algorithm develop from cyclonic wave breaking that is typical for oceanic blocking. The modified AGH method can be useful in detecting more robust HLB trends in climate model projections.

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Section: Methodsmentioning

confidence: 99%

Section: Data and Blocking Identification Methodsmentioning

confidence: 99%

Reconciling different methods of high‐latitude blocking detection

Tyrlis

Bader

Manzini

et al. 2021

Quart J Royal Meteoro Soc

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“…GCMs have historically been ineffective at predicting NAO dynamics within future scenarios (Smith et al, 2016); however, recent developments in high‐performance computing have enabled forecasting of NAOI effects at seasonal (Świerczyńska‐Chlaściak & Niedzielski, 2020) or decadal (Athanasiadis et al, 2020; Dunstone et al, 2016) timescales. Furthermore, with high‐resolution hydrometeorological datasets becoming more readily available (Sun et al, 2018), regression analyses between the NAOI and climate variables for forecasting purposes is more achievable.…”

Section: Introductionmentioning

confidence: 99%

Non‐stationary control of the NAO on European rainfall and its implications for water resource management

Rust

Bloomfield

Cuthbert

et al. 2021

Hydrological Processes

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Water resource forecasting generally centres on understanding hydrological variability over coming months or years, so that water managers can prepare for extremes such as droughts or floods (Chang & Guo, 2020; Hao et al., 2018). Some forecasting systems seek to project further into the future to allow long-term planning of infrastructure and resilience to extremes and climate change (Svensson et al., 2015). These systems can rely directly or indirectly on outputs from Global Climate Models (GCMs; such as gridded reanalysis datasets) to forecast hydrological conditions (Bhatt & Mall, 2015; Ionita & Nagavciuc, 2020). In the North Atlantic region, in particular Western Europe, the North Atlantic Oscillation (NAO) is used as an indicator for hydrometeorological conditions given its leading control on winter rainfall totals (Hurrell & Deser, 2010; Scaife et al., 2008, 2014). A dipole of pressure anomalies over the North Atlantic, the NAO's positive phase (greater than average pressure gradient; NAO+) results in wetter conditions in northwest Europe with dryer conditions in southwest Europe (Rust et al., 2018; Trigo et al., 2004). Its negative phase (weaker than average pressure gradient; NAO−) results in the inverse effect on rainfall (Folland et al., 2015; and as shown by the correlation coefficients in Figure 1). Given this relationship, and, con

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“…Despite the recent improvements in forecasting the North Atlantic Oscillation (NAO) on interannual time‐scales (Dunstone et al ., 2016; Weisheimer et al ., 2019), which is intimately related to blocking at high latitudes (Woollings et al ., 2008), many authors report low or negligible year‐to‐year skill of atmospheric blocking (e.g., Prodhomme et al ., 2016). Athanasiadis et al . (2014; 2020) investigated the winter NAO and atmospheric blocking in seasonal (UKMO and CMCC) and decadal (CESM) prediction systems. While they find promising results when looking at the NAO and Greenland Blocking, the skill remains low for blocking over Central Europe.…”

Section: Introductionmentioning

confidence: 99%

The representation of winter Northern Hemisphere atmospheric blocking in ECMWF seasonal prediction systems

Davini

Weisheimer

Balmaseda

et al. 2021

Quart J Royal Meteoro Soc

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The simulation and prediction of winter Northern Hemisphere atmospheric blocking in the seasonal prediction systems from the European Centre for Medium‐Range Weather Forecasts (ECMWF) is analysed. Blocking statistics from the operational November‐initialised seasonal hindcasts are evaluated in three generations of models: System3, System4, and System5 (SEAS5). Improvements in the climatological representation of blocking are observed in the most recent model configurations, with reduced bias over North Pacific and Greenland. Minor progress is seen over the European sector, where SEAS5 still underestimates the observed blocking frequency. SEAS5 blocking interannual variability is underestimated too and is proportional to the climatological frequency, highlighting that a negative bias in the blocking frequency implies an underestimation of the interannual variance. SEAS5 predictive skill and signal‐to‐noise ratio remain low, but interesting positive results are found over Western and Central Europe. Improved forecasts with reduced ensemble spread are obtained during El Niño years, especially at low latitudes. Complementary experiments show that the statistics of blocking are improved following atmospheric and oceanic resolution increase. Conversely, they remain largely insensitive to coupled model sea‐surface temperature (SST) errors. On the other hand, the implementation of stochastic parameterisations tends to displace blocking activity equatorward. Finally, by comparing seasonal hindcasts with climate runs using the same model, we highlight that the largest contributors to the chronic underestimation of blocking are persistent errors in the atmospheric model. It is also shown that SST errors have a larger impact on blocking bias in climate runs than in seasonal runs, and that increased ocean model resolution contributes to improved blocking more effectively in climate runs. Seasonal forecasts can thus be considered a suitable test‐bed for model development targeting blocking improvement in climate models.

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Decadal predictability of North Atlantic blocking and the NAO

Cited by 80 publications

References 79 publications

Reconciling different methods of high‐latitude blocking detection

Reconciling different methods of high‐latitude blocking detection

Non‐stationary control of the NAO on European rainfall and its implications for water resource management

The representation of winter Northern Hemisphere atmospheric blocking in ECMWF seasonal prediction systems

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