Snow‐(N)AO relationship revisited over the whole twentieth century

Douville, Hervé; Peings, Yannick; Saint‐Martin, David

doi:10.1002/2016gl071584

Cited by 27 publications

(28 citation statements)

References 35 publications

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“…We would like to emphasise that whilst the inter‐decadal differences in NAO skill are, by themselves, only marginally statistically significant (Weisheimer et al, ), the variations in skill strongly co‐vary with statistics of the general circulation itself (examples of which can be found in e.g. Minobe, ; Hoerling et al, ; Derome et al, ; Fletcher and Saunders, ; Greatbatch and Jung, ; Douville et al, ; Hegerl et al, ; Huang et al, ) suggesting that such differences are indeed physically based. In particular, the temporal skill evolution of the NAO co‐varies with changes in the skill of the Pacific–North America (PNA) pattern that are highly statistically significant and relate to changes in the ENSO–North Pacific teleconnections (O'Reilly et al, ; O'Reilly, ).…”

Section: Discussionmentioning

confidence: 99%

How confident are predictability estimates of the winter North Atlantic Oscillation?

Weisheimer

Decremer

MacLeod

et al. 2019

Quart J Royal Meteoro Soc

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Atmospheric seasonal predictability in winter over the Euro-Atlantic region is studied with an emphasis on the signal-to-noise paradox of the North Atlantic Oscillation. Seasonal hindcasts of the ECMWF model for the recent period show, in agreement with other studies, that correlation skill over Greenland and parts of the Arctic is higher than the signal-to-noise ratio implies. This leads to the paradoxical situation where the real world appears more predictable than the models suggest, with the forecast ensembles being overly dispersive (or underconfident). However, it is demonstrated that these conclusions are not supported by the diagnosed relationship between ensemble mean root-mean-square error (RMSE) and ensemble spread which indicates a slight under-dispersion (overconfidence). Furthermore, long atmospheric seasonal hindcasts suggest that over the 110-year period from 1900 to 2009 the ensemble system is well calibrated (neither overnor under-dispersive). The observed skill changed drastically in the middle of the twentieth century and paradoxical regions during more recent hindcast periods were strongly under-dispersive during mid-century decades. Due to non-stationarities of the climate system in the form of decadal variability, relatively short hindcasts are not sufficiently representative of longer-term behaviour. In addition, small hindcast sample size can lead to skill estimates, in particular of correlation measures, that are not robust. It is shown that the relative uncertainty due to small hindcast sample size is often larger for correlation-based than for RMSE-based diagnostics. Correlation-based measures like the RPC are shown to be highly sensitive to the strength of the predictable signal, implying that disentangling of physical deficiencies in the models on the one hand, and the effects of sampling uncertainty on the other hand, is difficult. Given the current lack of a causal physical mechanism to unravel the puzzle, our hypotheses of non-stationarity and sampling uncertainty provide simple yet plausible explanations for the paradox.

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Section: Discussionmentioning

confidence: 99%

How confident are predictability estimates of the winter North Atlantic Oscillation?

Weisheimer

Decremer

MacLeod

et al. 2019

Quart J Royal Meteoro Soc

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“…However, due to the low observation density in the first half of the twentieth century and a drop of the global number of assimilated observations before the 1940s (Compo et al, 2011;Douville et al, 2017), the 20CR2 product is deemed probably unreliable for the early part of the record (Krueger et al, 2013). The 20CR2 reanalysis is produced by assimilating surface pressure observations along with a prescribed SST boundary condition.…”

Section: Data Setsmentioning

confidence: 99%

Recent Acceleration of Arabian Sea Warming Induced by the Atlantic‐Western Pacific Trans‐basin Multidecadal Variability

Sun

Kucharski

et al. 2019

Geophysical Research Letters

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Arabian Sea (AS) warming has been significantly accelerated since the 1990s, in particular in the spring season. Here we link the AS warming changes to the Atlantic multidecadal oscillation (AMO). A set of Atlantic pacemaker experiments with a slab mixed‐layer ocean model successfully reproduces the AS spring multidecadal variability and its connection with the AMO. An atmospheric teleconnection from the Atlantic to the AS in the preceding winter and associated thermodynamic air‐sea feedback is found to be important. The teleconnection can be reestablished by the atmospheric model when the AMO sea surface temperature (SST) and its trans‐basin footprint over the western Pacific are prescribed simultaneously. The western Pacific SST warming associated with the AMO positive phase induces a Gill‐type Rossby wave over the AS, showing anomalously low pressures and converging southerlies that weaken winter northerlies. Thus, the wind‐evaporation‐SST feedback results in and maintains the AS warm SST anomalies to the subsequent spring.

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“…For example, in Fletcher et al (), they reported on the response of a stratospheric resolving model to a snow perturbation; however, this model had a low decorrelation time in the stratosphere, with a decorrelation timescale of around 9–11 days between 100 hPa and 10 hPa, which is about a half of what is seen in ERA‐Interim and simulated by their other low‐top model (see their Figure 12). Furthermore, Peings et al () and Douville et al () found that the observed link is unstable during the twentieth century and proposed that the snow‐AO relation can be modulated by the QBO.…”

Section: Introductionmentioning

confidence: 99%

The Influence of Eurasian Snow Extent on the Northern Extratropical Stratosphere in a QBO Resolving Model

2018

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The European Centre/Hamburg version 6 atmospheric model with a well‐defined stratosphere and an internally generated Quasi‐biennial oscillation (QBO) was used to study the relationship between the autumn Eurasian snow extent and the wintertime climate of the northern hemisphere. A positive snow cover anomaly was imposed over Eurasia in early autumn and held constant until spring. One hundred years of the snow anomaly run was compared with a 100 year control run. A dynamical response to the snow anomaly is seen in the northern polar stratosphere and troposphere during autumn and early winter, in line with previous modeling studies, and the monthly progression of the atmospheric anomalies follows the size of the surface forcing. However, this response is weaker, and occurs earlier in season, than that seen in observations. Considering the effect of QBO, we find a stratospheric vortex weakening during the easterly phase; however, the effect is weaker than that seen in observations. The strongest response of the polar vortex is found when both factors—the snow anomaly and the QBO phase—are considered together, with the response being close to an additive combination of the responses to the individual forcings. Although our study confirms the ability of snow cover variability to significantly influence the large‐scale circulation, it also demonstrates that the inclusion of a well‐resolved stratosphere is not a sufficient condition for reproducing the intensity and timing of the circulation response appearing in observations.

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Snow‐(N)AO relationship revisited over the whole twentieth century

Cited by 27 publications

References 35 publications

How confident are predictability estimates of the winter North Atlantic Oscillation?

How confident are predictability estimates of the winter North Atlantic Oscillation?

Recent Acceleration of Arabian Sea Warming Induced by the Atlantic‐Western Pacific Trans‐basin Multidecadal Variability

The Influence of Eurasian Snow Extent on the Northern Extratropical Stratosphere in a QBO Resolving Model

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