North Atlantic SST variability and high impact storms affecting the Iberian Peninsula

2020 ◽  
Author(s):  
Fátima Ferreira ◽  
Margarida L. R. Liberato ◽  
Alexandre M. Ramos ◽  
Raquel Nieto
Keyword(s):  
Iberian Peninsula ◽  
North Atlantic ◽  
Decadal Variability ◽  
High Impact ◽  
Average Intensity ◽  
Weather Extremes ◽  
The North ◽  
Sst Variability ◽  
Extreme Precipitation Events ◽  
The North Atlantic

<p>The Iberian Peninsula has experienced on recent years an increasing number of high impact cyclones (e.g. Klaus, 23-24 January 2009 and Xynthia, 27-28 February 2010; Liberato et al. 2011; 2013) associated with extreme precipitation events, flooding and damage to infrastructure. Recent examples are cyclones Elsa and Fabien, on December 2019, which forced more than 250 people to be evacuated from their homes in Mondego region villages, in central Portugal, due to rising river waters and infrastructure disruption .</p><p>However until now not enough evidence has been gathered to confirm a general and significant increase in the frequency and intensity of these events in the north-eastern Atlantic. In fact, according to Karremann et al. (2016) the maximum in recent years is comparable to other stormy periods in the 1960s and 1980s, suggesting that their frequency of occurrence undergoes strong multi-decadal variability.</p><p>In this study a high impact extratropical cyclones dataset developed in the framework of project “WEx-Atlantic - Weather Extremes in the Euro Atlantic Region: Assessment and Impacts” is used to assess the variability in frequency and intensity of these events over the last decades in the Iberian Peninsula. A ranking of daily precipitation days for the Iberian Peninsula taking into account not only the area affected but also its average intensity (Ramos et al. 2014) is also used. Additionally, a spatio-temporal variability of sea surface temperature (SST) is performed in the North Atlantic, using ECMWF ERA5 reanalysis data for the period 1979-2019. Finally the relevance of the North Atlantic SST variability on the intensity of these extreme events affecting the Iberian Peninsula on recent winter seasons is discussed.  </p><p><strong>Acknowledgements</strong></p><p>The authors would like to acknowledge the financial support by Fundação para a Ciência e a Tecnologia, Portugal (FCT), through projects PTDC/CTA-MET/29233/2017 and UIDB/50019/2020 – IDL. A.M. Ramos is supported by Scientific Employment Stimulus 2017 from FCT (CEECIND/00027/2017).</p><p><strong>References</strong></p><p>Karremann et al. (2016) Atmos. Sci. Let., 17: 354-361 DOI: 10.1002/asl.665</p><p>Liberato et al. (2011) Weather, 66: 330-334 DOI: 10.1002/wea.755</p><p>Liberato et al. (2013) Nat. Hazards Earth Syst. Sci., 13: 2239-2251 DOI: 10.5194/nhess-13-2239-2013</p><p>Ramos et al. (2014) Atmos. Sci. Let., 15: 328–334, DOI: 10.1002/asl2.507</p>

Near-surface wind speeds in ERA5: Climatology, decadal variability and long-term trends

2021 ◽  
Author(s):  
Terhi K. Laurila ◽  
Victoria A. Sinclair ◽  
Hilppa Gregow
Keyword(s):  
Iberian Peninsula ◽  
North Atlantic ◽  
Decadal Variability ◽  
Surface Wind ◽  
Northern Europe ◽  
Near Surface ◽  
Wind Speeds ◽  
The North ◽  
The North Atlantic

<p>The knowledge of long-term climate and variability of near-surface wind speeds is essential and widely used among meteorologists, climate scientists and in industries such as wind energy and forestry. The new high-resolution ERA5 reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF) will likely be used as a reference in future climate projections and in many wind-related applications. Hence, it is important to know what is the mean climate and variability of wind speeds in ERA5.</p><p>We present the monthly 10-m wind speed climate and decadal variability in the North Atlantic and Europe during the 40-year period (1979-2018) based on ERA5. In addition, we examine temporal time series and possible trends in three locations: the central North Atlantic, Finland and Iberian Peninsula. Moreover, we investigate what are the physical reasons for the decadal changes in 10-m wind speeds.</p><p>The 40-year mean and the 98th percentile wind speeds show a distinct contrast between land and sea with the strongest winds over the ocean and a seasonal variation with the strongest winds during winter time. The winds have the highest values and variabilities associated with storm tracks and local wind phenomena such as the mistral. To investigate the extremeness of the winds, we defined an extreme find factor (EWF) which is the ratio between the 98th percentile and mean wind speeds. The EWF is higher in southern Europe than in northern Europe during all months. Mostly no statistically significant linear trends of 10-m wind speeds were found in the 40-year period in the three locations and the annual and decadal variability was large.</p><p>The windiest decade in northern Europe was the 1990s and in southern Europe the 1980s and 2010s. The decadal changes in 10-m wind speeds were largely explained by the position of the jet stream and storm tracks and the strength of the north-south pressure gradient over the North Atlantic. In addition, we investigated the correlation between the North Atlantic Oscillation (NAO) and the Atlantic Multi-decadal Oscillation (AMO) in the three locations. The NAO has a positive correlation in the central North Atlantic and Finland and a negative correlation in Iberian Peninsula. The AMO correlates moderately with the winds in the central North Atlantic but no correlation was found in Finland or the Iberian Peninsula. Overall, our study highlights that rather than just using long-term linear trends in wind speeds it is more informative to consider inter-annual or decadal variability.</p>

scholarly journals On the Interpretation of the North Atlantic Averaged Sea Surface Temperature

2020 ◽  
Vol 33 (14) ◽  
pp. 6025-6045
Author(s):  
Jing Sun ◽  
Mojib Latif ◽  
Wonsun Park ◽  
Taewook Park
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Atlantic ◽  
Climate Models ◽  
Ocean Dynamics ◽  
Sea Surface ◽  
The North ◽  
Sst Variability ◽  
The North Atlantic ◽  
Different Time Scales

AbstractThe North Atlantic (NA) basin-averaged sea surface temperature (NASST) is often used as an index to study climate variability in the NA sector. However, there is still some debate on what drives it. Based on observations and climate models, an analysis of the different influences on the NASST index and its low-pass filtered version, the Atlantic multidecadal oscillation (AMO) index, is provided. In particular, the relationships of the two indices with some of its mechanistic drivers including the Atlantic meridional overturning circulation (AMOC) are investigated. In observations, the NASST index accounts for significant SST variability over the tropical and subpolar NA. The NASST index is shown to lump together SST variability originating from different mechanisms operating on different time scales. The AMO index emphasizes the subpolar SST variability. In the climate models, the SST-anomaly pattern associated with the NASST index is similar. The AMO index, however, only represents pronounced SST variability over the extratropical NA, and this variability is significantly linked to the AMOC. There is a sensitivity of this linkage to the cold NA SST bias observed in many climate models. Models suffering from a large cold bias exhibit a relatively weak linkage between the AMOC and AMO and vice versa. Finally, the basin-averaged SST in its unfiltered form, which has been used to question a strong influence of ocean dynamics on NA SST variability, mixes together multiple types of variability occurring on different time scales and therefore underemphasizes the role of ocean dynamics in the multidecadal variability of NA SSTs.

The ability of the adjoint technique to recover decadal variability of the North Atlantic circulation

2013 ◽  
Vol 69 ◽  
pp. 166-180 ◽  
Author(s):  
Michael Brüdgam ◽  
Carsten Eden ◽  
Lars Czeschel ◽  
Johanna Baehr
Keyword(s):  
North Atlantic ◽  
Decadal Variability ◽  
The North ◽  
The North Atlantic

scholarly journals Reconciling two alternative mechanisms behind bi-decadal variability in the North Atlantic

2015 ◽  
Vol 137 ◽  
pp. 237-249 ◽  
Author(s):  
Pablo Ortega ◽  
Juliette Mignot ◽  
Didier Swingedouw ◽  
Florian Sévellec ◽  
Eric Guilyardi
Keyword(s):  
North Atlantic ◽  
Decadal Variability ◽  
The North ◽  
The North Atlantic

scholarly journals Understanding Precipitation Changes in Iberia in Early Spring: Weather Typing and Storm-Tracking Approaches

2006 ◽  
Vol 7 (1) ◽  
pp. 101-113 ◽  
Author(s):  
Daniel Paredes ◽  
Ricardo M. Trigo ◽  
Ricardo Garcia-Herrera ◽  
Isabel Franco Trigo
Keyword(s):  
Iberian Peninsula ◽  
North Atlantic ◽  
Large Scale ◽  
Western Mediterranean ◽  
Early Spring ◽  
The North ◽  
Western Mediterranean Basin ◽  
The North Atlantic ◽  
Circulation Changes ◽  
Precipitation Trends

Abstract March monthly accumulated precipitation in the central and western regions of the Iberian Peninsula presents a clear continuous decline of 50% during the 1960–97 period. A finer analysis using daily data reveals that this trend is exactly confined to the month of March. However, this is merely the most visible aspect of a larger phenomenon over the North Atlantic/European sector. The European precipitation trends in March for the period 1960–2000 show a clear distribution of increasing precipitation in the northern regions (the British Isles and parts of Scandinavia) together with decreasing trends throughout the western Mediterranean Basin. Relevant circulation changes over the North Atlantic and European sectors explain these precipitation trends. First, a regional Eulerian approach by means of a weather-type (WT) classification shows that the major rainfall contributors in March display significantly decreasing frequencies for the Iberian Peninsula, in contrast to the corresponding “wet” weather types for the U.K./Ireland sector, which display increasing frequencies. Within a larger context, a Lagrangian approach, based on the analysis of storm tracks over Europe and the North Atlantic region, reveals dramatic changes in the location of cyclones in the last four decades that coincide with the corresponding precipitation trends in Europe. The North Atlantic Oscillation is suggested to be the most important large-scale factor controlling both the circulation changes and the precipitation trends over the Euro–Atlantic area in March. Finally, the potential impact of reduced precipitation for rivers and water resources in the Iberian Peninsula is considered.

scholarly journals Influence of the North Atlantic SST Variability on the Atmospheric Circulation during the Twentieth Century

2015 ◽  
Vol 28 (4) ◽  
pp. 1396-1416 ◽  
Author(s):  
Guillaume Gastineau ◽  
Claude Frankignoul
Keyword(s):  
Twentieth Century ◽  
North Atlantic ◽  
Lower Troposphere ◽  
Atlantic Multidecadal Oscillation ◽  
Early Winter ◽  
Tropical Forcing ◽  
The North ◽  
Sst Variability ◽  
Sst Anomaly ◽  
The North Atlantic

Abstract The ocean–atmosphere coupling in the North Atlantic is investigated during the twentieth century using maximum covariance analysis of sea surface temperature (SST) and 500-hPa geopotential height analyses and performing regressions on dynamical diagnostics such as Eady growth rate, wave activity flux, and velocity potential. The North Atlantic Oscillation (NAO) generates the so-called SST anomaly tripole. A rather similar SST anomaly tripole, with the subpolar anomaly displaced to the east and a more contracted subtropical anomaly, which is referred to as the North Atlantic horseshoe pattern, in turn influences the atmosphere. In the fall and early winter, the response is NAO like and primarily results from subpolar forcing centered over the Labrador Sea and off Newfoundland. In summer, the largest atmospheric response to SST resembles the east Atlantic pattern and results from a combination of subpolar and tropical forcing. To emphasize the interannual to multidecadal variability, the same analysis is repeated after low-pass filtering. The SST influence is dominated by the Atlantic multidecadal oscillation (AMO), which also has a horseshoe shape, but with larger amplitude in the subpolar basin. A warm AMO phase leads to an atmospheric warming limited to the lower troposphere in summer, while it leads to a negative phase of the NAO in winter. The winter influence of the AMO is suggested to be primarily forced by the Atlantic SSTs in the northern subtropics. Such influence of the AMO is found in winter instead of early winter because the winter SST anomalies have a larger persistence, presumably because of SST reemergence.

scholarly journals Predictability and Decadal Variability of the North Atlantic Ocean State Evaluated from a Realistic Ocean Model

2017 ◽  
Vol 30 (2) ◽  
pp. 477-498 ◽  
Author(s):  
Florian Sévellec ◽  
Alexey V. Fedorov
Keyword(s):  
Atlantic Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Atlantic ◽  
Decadal Variability ◽  
North Atlantic Ocean ◽  
Meridional Overturning Circulation ◽  
Sea Surface ◽  
The North ◽  
The North Atlantic

This study investigates the excitation of decadal variability and predictability of the ocean climate state in the North Atlantic. Specifically, initial linear optimal perturbations (LOPs) in temperature and salinity that vary with depth, longitude, and latitude are computed, and the maximum impact on the ocean of these perturbations is evaluated in a realistic ocean general circulation model. The computations of the LOPs involve a maximization procedure based on Lagrange multipliers in a nonautonomous context. To assess the impact of these perturbations four different measures of the North Atlantic Ocean state are used: meridional volume and heat transports (MVT and MHT) and spatially averaged sea surface temperature (SST) and ocean heat content (OHC). It is shown that these metrics are dramatically different with regard to predictability. Whereas OHC and SST can be efficiently modified only by basin-scale anomalies, MVT and MHT are also strongly affected by smaller-scale perturbations. This suggests that instantaneous or even annual-mean values of MVT and MHT are less predictable than SST and OHC. Only when averaged over several decades do the former two metrics have predictability comparable to the latter two, which highlights the need for long-term observations of the Atlantic meridional overturning circulation in order to accumulate climatically relevant data. This study also suggests that initial errors in ocean temperature of a few millikelvins, encompassing both the upper and deep ocean, can lead to ~0.1-K errors in the predictions of North Atlantic sea surface temperature on interannual time scales. This transient error growth peaks for SST and OHC after about 6 and 10 years, respectively, implying a potential predictability barrier.

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