A critical assessment of the long-term changes in the wintertime surface Arctic Oscillation and Northern Hemisphere storminess in the ERA20C reanalysis

Bloomfield, Hannah; Shaffrey, Len; Hodges, Kevin I.; Vidale, Pier Luigi

doi:10.1088/1748-9326/aad5c5

Cited by 36 publications

(38 citation statements)

References 53 publications

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“…We show that the disagreement is linked to the assimilation of marine surface winds, which is only performed in the ECMWF reanalyses. Our results have implication beyond wind applications and may explain several issues identified in previous analysis, such as reported drifts and discontinuities of ocean heat content (Laloyaux et al, 2016), trends in Arctic mean sea level pressure (MSLP; Bloomfield et al, 2018), and disagreeing long-term trends in cyclones and wind storms (Befort et al, 2016). Moreover, trends in wind speeds are expected to impact other societally relevant fields such as energy, the water cycle (McVicar et al, 2012), and food chains in the oceans (Kahru et al, 2010).…”

Section: 1029/2018jd030083mentioning

confidence: 59%

“…The trends may be spurious and due to evolving wind measurement techniques. Moreover, Bloomfield et al () report a spurious MSLP trend over the Arctic, which hints to a disagreement between the assimilated MSLP and wind speed data. The trends also disagree with land‐based wind measurements, which feature downward trends in the last couple of decades.…”

Section: Resultsmentioning

confidence: 99%

“…Moreover, focusing on the Arctic Oscillation, a recent study finds that the ERA20C Arctic MSLP disagrees with the HadSLP2 observational data set (Bloomfield et al, ). While no trend is found in the observations, ERA20C features a significant downward trend in the Arctic, which increases the meridional pressure gradient over large parts of the Atlantic and the northern North Pacific.…”

Section: Discussion—are These Trends Real?mentioning

confidence: 97%

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Inconsistent Wind Speed Trends in Current Twentieth Century Reanalyses

et al. 2019

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Reanalysis data underpin much research in atmospheric and related sciences. While most reanalysis only cover the last couple of decades, National Oceanic and Atmospheric Administration (20CR) and European Centre for Medium‐Range Weather Forecasts (ERA20C and CERA20C) also developed reanalyses for the entire twentieth century that theoretically allow investigation of multidecadal variability. However, the approaches adopted to handle the massively evolving number of observations can cause spurious signals. Here we focus on wind speeds, as its assimilation is a key difference among these two products. We show that ERA20C and CERA20C feature significant trends in the North Atlantic and North Pacific wind speeds of up to 3 m/s per century. We show that there is a good relation between the trends in the reanalysis and assimilated wind speeds. In contrast, 20CR and the European Centre for Medium‐Range Weather Forecasts free model run ERA20CM do not show positive trends in the same regions. As a consequence, conclusions drawn from any single twentieth century reanalysis should be treated cautiously in particular in sectors with a strong wind dependency (e.g., wind energy).

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Section: 1029/2018jd030083mentioning

confidence: 59%

Section: Resultsmentioning

confidence: 99%

Section: Discussion—are These Trends Real?mentioning

confidence: 97%

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Inconsistent Wind Speed Trends in Current Twentieth Century Reanalyses

et al. 2019

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“…This gridded product has a spatial resolution of 2°latitude × 2°longitude, and extends from 1920 to 2014. Long-term SLP trends over the NH extratropics in winter are considered more reliable in the 20CR than the ECMWF 20th Century Reanalysis (Poli et al, 2016) as documented by Bloomfield et al (2018). Long-term SLP trends over the NH extratropics in winter are considered more reliable in the 20CR than the ECMWF 20th Century Reanalysis (Poli et al, 2016) as documented by Bloomfield et al (2018).…”

Section: Observational Data Setsmentioning

confidence: 99%

Human Influence on Winter Precipitation Trends (1921–2015) over North America and Eurasia Revealed by Dynamical Adjustment

Guo

Deser

Terray

et al. 2019

Geophysical Research Letters

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Detecting and attributing a human influence on observed rainfall trends is a major challenge due to the presence of large amplitude internal variability on all time scales and by limited temporal and spatial data coverage. Here we apply a “dynamical adjustment” methodology to a gridded archive of monthly precipitation to estimate an anthropogenic influence on long‐term (1920–2015) trends over North America and Eurasia during winter (November–March). This empirical approach aims to remove atmospheric circulation influences from precipitation variability and trends, thereby revealing the thermodynamically induced component as a residual. The geographical pattern and amplitude of this observed thermodynamic residual precipitation trend are in good agreement with anthropogenically forced trends obtained from ensembles of historical climate model simulations. Such consistency helps to reconcile observations and models and provides compelling evidence for a human influence on century‐scale precipitation trends over North America and Eurasia during the cold season.

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“…Benchmarking a 100-year event for example is thus quite difficult and associated with very large uncertainties. As recent studies have shown there is also a spurious trend in this reanalysis data set (Befort et al, 2016;Bloomfield et al, 2018). The lack of observations is often tackled by producing probabilistic event sets based on alteration of observed events (e.g., Schwierz et al, 2010).…”

Section: Introductionmentioning

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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A critical assessment of the long-term changes in the wintertime surface Arctic Oscillation and Northern Hemisphere storminess in the ERA20C reanalysis

Cited by 36 publications

References 53 publications

Inconsistent Wind Speed Trends in Current Twentieth Century Reanalyses

Inconsistent Wind Speed Trends in Current Twentieth Century Reanalyses

Human Influence on Winter Precipitation Trends (1921–2015) over North America and Eurasia Revealed by Dynamical Adjustment

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

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