North Atlantic Oscillation Values Research Articles

The Interconnection between Climate Cycles and Geohazards in Urban Areas of the Tourist Island of Mallorca, Spain

The island of Mallorca has experienced major interventions and transformations of the territory, with unprecedented urban development related to growing tourism activity. In this paper, we present a spatio-temporal analysis—by using spectral analysis techniques—of climate cycles on the island of Mallorca (Spain) and their correlation with the occurrences of landslides and flash floods. Both geohazards are closely related to wet periods, which are controlled by different, well-known natural cycles: ENSO, the NAO, sunspot, etc. Geostatistical methods are used to map the distribution of rainfall, as well as a spatial representation of the spectral confidence of the different natural cycles, to define the hazardous areas on the island. The cycles with the greatest influence on rainfall in Mallorca are El Niño–Southern Oscillation (ENSO) (5.6 y and 3.5 y), the North Atlantic Oscillation (NAO) (7.5 y), and Quasi-Biennial Oscillation (QBO). Recorded events of both rockfalls and flash floods exhibit a strong correlation with the climate indices of QBO, ENSO, the NAO, and sunspot activity. This correlation is particularly pronounced with QBO, as this cycle has a higher frequency than the others, and QBO is observed as part of the other cycles in the form of increases and decreases during periods of higher ENSO, NAO, and sunspot values. However, the impact of flash floods is also significant in the southeast part of the island, despite its lower levels of rainfall. The most dangerous episodes are related to ENSO (6.4 y) and the NAO. The validation of the methodology employed is strengthened by incorporating information from the flash flood data, as it offers comprehensive coverage of the entire island, compared to the landslide database, which is confined to the Serra de Tramuntana region. The study reveals that the city of Palma and the municipality of Calvià, as well as the central and eastern urban areas of the island, are the most vulnerable regions to intense rainfall and its consequences.

ПОЯВИ ЛЬОДОВИХ ЯВИЩ НА ВОДОСХОВИЩАХ ДНІПРОВСЬКОГО КАСКАДУ ТА МОЖЛИВОСТІ ЇХ ДОВГОСТРОКОВОГО ПРОГНОЗУВАННЯ

Long-term forecasting of the appearance dates of ice phenomena on the Dnipro Cascade reservoirs, especially with the forecast lead time at least 1 month, has important practical and scientific significance. So, it is on the basis of this characteristic of the ice regime that the terms and depths of autumn operation of each of the six Dnipro reservoirs are determined. Along with this, there are no methods for long-term forecasting of the appearance date of ice phenomena on the Dnipro Cascade reservoirs. Obviously, this is due to the fact that the problem of developing reliable long-term forecasts of the ice regime of water bodies is one of the most difficult in hydrometeorology, which has not yet received a fully satisfactory solution. The objective of this of the research is to find connections between quantitative indicators of atmospheric processes in the North Atlantic and the appearance dates of ice phenomena on the Dnipro Cascade reservoirs, and to evaluate the possibilities of using the obtained results for operational long-term forecasting. In long-term forecasting of ice regime is used the statistical, correlational, regression analysis as well as the atmospheric indicators as predictors. Therefore, the minimum atmospheric pressure in the center of the Icelandic minimum, the North Atlantic Oscillation (NAO) pattern and the Scandinavian Oscillation (SCAND) pattern were used in the research. These indicators characterize the atmospheric processes of the North Atlantic. Materials of the Department of Meteorological Forecasts of the Ukrainian Hydrometeorological Center (Kyiv) and the National Oceanic & Atmospheric Administration USA (archival synoptic maps, the values of NAO and SCAND patterns) were used as initial data. The obtained results show that such indicators of the atmospheric processes of the North Atlantic as the minimum atmospheric pressure in the center of the Icelandic minimum, NAO and SCAND patterns undoubtedly have a fairly significant influence on the formation of the appearance dates of ice phenomena on the Dnipro Cascade reservoirs, but such an influence is not predominant and such indicators can only be partially used as predictors for long-term forecasting. Therefore, to obtain more acceptable results, it is necessary to expand the search for predictors of atmospheric processes both in space and time.

Relationship between cold season air temperature in the Baltic sea region and the Arctic sea ice extent

The variability of the atmospheric circulation described by the AO and NAO indices has a significant impact on the fluctuations of climate parameters in the Baltic Sea region. Many research show, that a decline in Arctic Sea ice extent increases the likelihood of negative phases of the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) in winter, and in the future could lead to more frequent relatively cold weather events during winter months in Baltic Sea region. This research is important for understanding possible teleconnections between Arctic Sea ice and atmospheric circulation (AO and NAO). In addition, this research helps to better understand the dynamics of Arctic Sea ice extent and Baltic Sea region air temperature, as well as AO and NAO circulation impact on the air temperature in the Baltic Sea region. A statistically significant decrease in the Arctic Sea ice extent and a statistically significant increase in the air temperature in the Baltic Sea region have been determined. The obtained results show that the expansion of the Arctic Sea ice in January-February with a delay of one month determines the AO and NAO values (correlation coefficients vary from 0.32 to 0.55). This means that if Arctic Sea ice decreases during winter months, AO and NAO indices are more likely to become negative as well. However, as the obtained correlations are not very strong, the results are insufficient to confirm the hypothesis that the Arctic Sea ice extent impacts negative AO and NAO phases likelihood and requires further research. A strong correlation between the Baltic Sea region air temperature and the values of AO/NAO indices has been established. The obtained results show that the Baltic Sea region air temperature variability in December-March is greatly influenced by the AO and NAO phases. Keywords: teleconnections, Arctic Sea ice, AO, NAO, Baltic Sea region, air temperature.

‘HESS-BREZOWSKY’ ATMOSPHERIC CLASSIFICATION TYPES ASSOCIATED WITH NAO AND AO PHASES IN THE NORTHERN PART OF MOLDOVA

The North Atlantic Oscillation (NAO) and that Artic (AO), respectively, are by considerable importance to make the short-time weather forecast (until three days), followed by those of middle range and long time (until two weeks). To analyzing the ‘Hess-Brezowsky’ weather patterns associated with the NAO and AO during 19 years (2000 to 2018), has highlighted some aspects over the weather kind in the north part of Moldova. The zonal air-masses’ movements such as northwestern and western, both of them into the anti-cyclonic and cyclonic regime, were deployed in a predominately positive phase of NAO and AO. In the case of NWA type, NAO was 0.17 and AO 0.60, and for WA, NAO was 0.12 and AO 0.71. From NWZ, the NAO shown values around of 0.03 and AO 0.08. Exceptionally, NAO was into a negative phase in the case of WZ, with a value of around -0.13. Instead, for WZ, the AO was positive, with a yearly average of 0.08. Such air-masses movements are associated with a mild weather pattern, especially during the wintertime. Then, over the southern part of Europe, it’s set up the ‘Omega’ ridge. In doing so, the amounts of the precipitations are low at the studied area’s level. By a more significant interest is the southwesterly air-masses movement into a cyclonic regime (SWZ) who shown values of NAO of -0.16 and 00.26 for AO. Also, negative values for NAO were in the case of TRM (Trough over Central Europe), with -0.04 and HNFZ (High over Scandinavia-Iceland, Trough over Central Europe), with -0.64. For the same synoptically contexts (TRM and HNFZ), the AO was of -0.23, respectively, -1.31. Associated with the negative phases of NAO and AO, the planetary waves have shown an undulatory tendency. In such a case, there are development areas with extreme weather. For the studied region, the negative phases of NAO and AO were associated with severe weather events, such as blizzards, storms, and floods.

A 2,000-year Bayesian NAO reconstruction from the Iberian Peninsula

The North Atlantic Oscillation (NAO) is the major atmospheric mode that controls winter European climate variability because its strength and phase determine regional temperature, precipitation and storm tracks. The NAO spatial structure and associated climatic impacts over Europe are not stationary making it crucial to understanding its past evolution in order to improve the predictability of future scenarios. In this regard, there has been a dramatic increase in the number of studies aimed at reconstructing past NAO variability, but the information related to decadal-scale NAO evolution beyond the last millennium is scarce and inconclusive. We present a new 2,000-year multi-annual, proxy-based reconstruction of local NAO impact, with associated uncertainties, obtained by a Bayesian approach. This new local NAO reconstruction is obtained from a mountain lacustrine sedimentary archive of the Iberian Peninsula. This geographical area is not included in previous NAO reconstructions despite being a widely used region for instrumental-based NAO measurements. We assess the main external forcings (i.e., volcanic eruptions and solar activity) on NAO variability which, on a decadal scale, show that a low number of sunspots correlate to low NAO values. By comparison with other previously published NAO reconstructions in our analyses we can test the stationarity of the solar influence on the NAO signal across a latitudinal gradient based on the position of the employed archives for each NAO reconstruction. Inconclusive results on the volcanic forcing on NAO variability over decadal time-scales indicates the need for further studies. Moreover, we highlight the potential role of other North Atlantic modes of variability (i.e., East Atlantic pattern) on the non-stationary behaviour of the NAO throughout the Common Era, likely via solar forcing.

Predicting beach rotation using multiple atmospheric indices

Shoreline change in the form of beach rotation can occur at event to decadal timescales, especially in semi-sheltered embayments with bi-directional wave climates, leading to enhanced coastal vulnerability under predictions of increased sea level rise. Previous studies have shown that phases of winter-averaged atmospheric indices in the North Atlantic correlate with variations in average winter wave height and dominant direction; however, predictions of a localised wave climate and beach rotation from individual climate indices has exhibited limited skill. Here we show that the combination of two major north Atlantic climate indices, the North Atlantic Oscillation (NAO) and West Europe Pressure Anomaly (WEPA), improves the prediction of a wave power directionality index (WDI), known to correlate with beach rotation along the length of a headland bound gravel embayment. Results using a combination of NAO and WEPA, improves predictions of WDI with an associated R2 of 0.66, when compared to 0.23 and 0.31 for NAO and WEPA individually. Hindcast (WDIWW3) and index predicted (WDIPred) values of the WDI were shown to validate against measured beach rotation from 2008 to 2018 and modelled inshore potential longshore energy fluxes from 1980 to 2018. A long-term historic time series of WDIPred (1906–present) was then hindcast using records of NAO and WEPA. Qualitative validation of long-term beach rotation in response to the WDIPred is achieved with proxy records of beach change in the form of oblique and aerial photography and topographic maps. Low frequency (~60 years) beach rotation is shown to follow phases of the detrended cumulative WDIPred values, over the period of 1906 to 2018, linked to the multi-decadal fluctuations in detrended cumulative values of NAO and WEPA. When examined in the context of millennial-scale proxy NAO records, it is clear the recent centurial-scale analysis does not capture past variability and duration. This work has shown that: (1) potential future season ahead forecasts of atmospheric indices may skilfully predict beach rotation in many regions with bi-directional wave climates; and (2) historical analysis highlights the potential past phases of extreme coastal realignment. These new insights will lead to proactive and informed management from local authorities and coastal engineers.

Atmospheric indices allow anticipating the incidence of jellyfish coastal swarms

Jellyfish swarms affect littoral ecosystems, are unpleasant for bathers and jeopardize coastal socio-economic sectors. Anticipating the incidence of jellyfish swarms could be useful for implementing preventive management measures. Macroclimatic indices are good candidates for this type of anticipation since they are macro-ecologically related to oceanographic characteristics that affect marine species after a certain time lag. An increase of jellyfish swarms has been recently reported in the Mediterranean Sea. From 2005 to 2018, jellyfish swarms in the littoral of the province of Malaga (Spain, northwest coast of the Alboran Sea), mainly formed by the mauve stinger (Pelagia noctiluca), were frequent during summer. We recorded data on jellyfish swarm incidence in the province of Malaga from 2005 to 2018 using the reports in local newspapers, searches in Google Search Engine, and a citizen science application for mobile phones as information sources. With this information, we classified the period in years of low, medium and high incidence of jellyfish swarms. Then, we tested if the known effects of the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) in winter on the sea surface temperature (SST) during the year, which in turn affects the proliferation of jellyfish, could explain the inter-annual variation in this incidence. Our hypothesis significantly explained the variation in the medium versus low incidence of jellyfish swarms, with medium incidence in the summers of higher SST. This suggests that medium incidence of jellyfish swarms was caused by the proliferation of jellyfish. This also suggests that years of medium incidence of jellyfish in the beach during summer could be anticipated by computing the average AO and NAO values of the previous winter. Years of high incidence of swarms could not be explained by this process. We speculate that they may be caused by a change in the distribution of the swarms rather than by proliferation. Jellyfish may be pushed from the pelagic western anticyclonic gyre of the Alboran Sea to the northern coast by eddies that are formed when, as recent literature has shown, this gyre is weakened by westerly winds and the Atlantic jet. Citizen science has contributed useful data to build macroecological models that may result in better management plans based on scientific data.

Anthropogenic food resources, sardine decline and environmental conditions have triggered a dietary shift of an opportunistic seabird over the last 30 years on the northwest coast of Spain

Human activities and environmental conditions are the main drivers of ecosystem change. One major alteration near the western Iberian coast has been the collapse of the Atlanto-Iberian sardine Sardina pilchardus stock, with important cascading effects on marine top predators. We investigated the effect of long-term changes in fishery landings, sardine availability and environmental conditions on the diet of the yellow-legged gull Larus michahellis in the northwest coast of Spain, over the last 30 years (1987–2017). Dietary trends of gulls were investigated through the analysis of 5010 pellets that revealed a sharp decline of fish and refuse and a shift to a crustacean-based diet. General additive mixed models showed that both total fish and sardine occurrences in gull pellets were negatively associated with total fishery landings and positively associated with sardine landings, suggesting fish depletion and higher fishing efficiency (i.e. reduced discards) during the study period. The winter North Atlantic Oscillation (NAO) index was also positively related with sardine occurrence in gull pellets, possibly due to low sardine abundance and rough conditions in years with very low NAO values. The refuse decline was most probably caused by the closure of open-air landfills, implemented under the European Union Landfill Directive. Our results suggest that changes in fishing practices and waste disposal were the main factors responsible for the sharp decline of fish and refuse in yellow-legged gull diet.

Detrended cross-correlation patterns between North Atlantic oscillation and precipitation

In this study, the long-range relationships between North Atlantic Oscillation (NAO) and precipitation data obtained from Climate Prediction Centre (CPC) Merged Analysis of Precipitation (CMAP) from 1979 to 2016 are investigated using Detrended Fluctuation Moving Average Cross-Correlation Analysis (DMCA). In the atmosphere, teleconnections through strong convective processes sporadically affect various climatic regimes in Europe, Mediterranean basin, North Africa, Middle East, and Caucasus. The NAO is one of the teleconnection processes and results in heavy rainfall in the Mediterranean basin during its negative phase while it gives rise to rain in Europe during its positive phase. The DMCA technique shows that the NAO fluctuation series exhibit different long-range cross-correlation coefficients, ρDMCA(s) with “s” being the moving average time window length, between the precipitation values and NAO. Large ρDMCA(s) coefficients with time window(s) larger than 12 months were obtained particularly over the Mediterranean basin, near the North Pole including northern Europe. Furthermore, the ρDMCA(s) coefficients were grouped into clusters using K-mean method to distinguish the similar patterns. The 1st cluster refers to the negative phase of the NAO indicating warm-rainy conditions and dry spells, which is especially evident in the Mediterranean basin. The 2nd cluster represents the long-range cross-correlation with respect to the positive phase of NAO and precipitation values, particularly for the Western and Northern Europe. Conversely, the 3rd cluster is evaluated as power law of long-range cross-correlations between the precipitation and NAO with respect to the different time scale processes.

Forest fires in Finland - the influence of atmospheric oscillations

In Finland, in the period 1996–2017, 28,434 forest fires were recorded (an average of 1,292.5 per year), and the total burned area was 11,922 ha (an average of 541.9 ha per year). In both cases, a statistically non-significant downward trend was recorded. Forest fires in Finland do not represent a particularly significant problem, primarily due to climatic characteristics, well-organized fire protection, and low density of population. The research of climate influence included the Atlantic Multidecadal Oscillation (AMO), the North Atlantic Oscillation (NAO), and the Arctic Oscillation (AO). The statistically significant values (p ≤ .05) of Pearson correlation coefficient were recorded for the August values of NAO and the surface area of burned forest (−0.44), the June values of NAO and the average surface area of forest burned per fire (−0.51) and the May AO values and the average surface area of forest burned per fire (−0.45). For the June values of NAO and the average surface area of forest burned per fire, the Lomb periodogram shows four significant peaks, and the match is at two, at 2.4 and 3.4 years, which supports the hypothesis of the connection between NAO and forest fires in Finland.

Habitat‐ and species‐mediated short‐ and long‐term distributional changes in waterbird abundance linked to variation in European winter weather

AbstractAimMany species are showing distribution shifts in response to environmental change. We explored (a) the effects of inter‐annual variation in winter weather conditions on non‐breeding distributional abundance of waterbirds exploiting different habitats (deep‐water, shallow water, farmland) and (b) the long‐term shift in the population centroid of these species and investigate its link to changes in weather conditions.LocationEurope.MethodsWe fitted generalized additive mixed Models to a large‐scale, 24‐year dataset (1990–2013) describing the winter distributional abundance of 25 waterbird species. We calculated the annual and long‐term (3‐year periods) population centroid of each species and used the winter North Atlantic Oscillation (NAO) index to explain the inter‐annual and long‐term shifts in their location.Results(a) Year‐to‐year southwestwards shifts in the population centroids of deep‐ and shallow‐water species were linked to negative NAO values. Shallow‐water species shifted northeastwards associated with positive NAO values and the distance shifted increased with increasing NAO. Deep‐water species shifted northeastwards up to zero NAO indices, but showed no further increase at higher NAO values. (b) Deep‐water species showed long‐term northeastwards shifts in distributional abundance throughout the 1990s and the 2000s. Shallow‐water species, on the other hand, shifted northeastwards during the 1990s and early 2000s, but southwestwards thereafter. There were no significant links between the NAO and year‐to‐year movements or long‐term shifts in farmland species’ population centroid.Main ConclusionsWe provide evidence for a link between both year‐to‐year and long‐term changes in waterbird winter distributional abundances at large geographical scales to short‐ and long‐term changes in winter weather conditions. We also show that species using shallow water, deep‐water and farmland habitats responded differently, especially at high NAO values. As well as important ecological implications, these findings contribute to the development of future conservation measures for these species under current and future climate change.

Factors behind the variability of phosphorus accumulation in Finnish lakes

Phosphorus retention (TPacc) is one of the major water quality regulators in lakes. The current study aimed at ascertaining the specific lake characteristics regulating TPacc. Moreover, we were interested whether NAO (North Atlantic Oscillation), a proxy of climatic forcing, can explain variability in TPacc, additionally to that ascribed to lake characteristics. Sediment cores were obtained from 21 Finnish lakes, subject to radiometric dating and measurements of TP concentrations. Principal components (PCs) were generated using lake characteristics that are usually included into the modelling of TPacc (e.g. lake area, lake depth, catchment area, P inflow) but also the parameters that the classical models usually missed (e.g. anoxic factor). We used significant principal components (PCs), specific combinations of lake characteristics and monthly NAO values as predictors of TPacc. Lake characteristics explained the bulk of TPacc variability. The most influential factors (positive drivers) behind TPacc included PC1 (representing mainly deep lakes), PC2 (small lakes with high levels of anoxia and water column stability), PC3 (productive lakes with large catchment area and short water residence time), PC4 (lakes with high water column stability, low anoxic factor and relatively high sediment focusing) and PC5 (lakes with high levels of P inflow, anoxia and long water residence time). Additionally, we found a potential negative effect of NAO in October on the annual TPacc. This NAO was significantly positively related to temperatures in surface and near-bottom water layer (also their difference) in autumn, suggesting the possible implications for the internal P dynamics. Increased mineralization of organic matter is the most likely explanation for the reduced TPacc associated with NAO-driven water temperature increase. The analysis presented here contributes to the knowledge of the factors controlling P retention. Moreover, this spatially and temporally comprehensive sediment data can potentially be a valuable source for modelling climate change implications.

Winter North Atlantic Oscillation impact on European precipitation and drought under climate change

The North Atlantic Oscillation (NAO) is responsible for the climatic variability in the Northern Hemisphere, in particular, in Europe and is related to extreme events, such as droughts. The purpose of this paper is to study the correlation between precipitation and winter (December–January–February–March (DJFM)) NAO both for the historical period (1951–2000) and two future periods (2001–2050 and 2051–2100). NAO is calculated for these three periods by using sea level pressure, while precipitation data from seven climate models following the representative concentration pathway (RCP) 8.5 are also used in this study. An increasing trend in years with positive DJFM NAO values in the future is defined by this data, along with higher average DJFM NAO values. The correlation between precipitation and DJFM NAO is high, especially in the Northern (high positive) and Southern Europe (high negative). Therefore, higher precipitation in Northern Europe and lower precipitation in Southern Europe are expected in the future. Cross-spectral analysis between precipitation and DJFM NAO time series in three different locations in Europe revealed the best coherence in a dominant cycle between 3 and 4 years. Finally, the maximum drought period in terms of consecutive months with drought is examined in these three locations. The results can be used for strategic planning in a sustainable water resources management plan, since there is a link between drought events and NAO.

Life history tactics shape amphibians’ demographic responses to the North Atlantic Oscillation

Over the last three decades, climate abnormalities have been reported to be involved in biodiversity decline by affecting population dynamics. A growing number of studies have shown that the North Atlantic Oscillation (NAO) influences the demographic parameters of a wide range of plant and animal taxa in different ways. Life history theory could help to understand these different demographic responses to the NAO. Indeed, theory states that the impact of weather variation on a species' demographic traits should depend on its position along the fast-slow continuum. In particular, it is expected that NAO would have a higher impact on recruitment than on adult survival in slow species, while the opposite pattern is expected occur in fast species. To test these predictions, we used long-term capture-recapture datasets (more than 15,000 individuals marked from 1965 to 2015) on different surveyed populations of three amphibian species in Western Europe: Triturus cristatus, Bombina variegata, and Salamandra salamandra. Despite substantial intraspecific variation, our study revealed that these three species differ in their position on a slow-fast gradient of pace of life. Our results also suggest that the differences in life history tactics influence amphibian responses to NAO fluctuations: Adult survival was most affected by the NAO in the species with the fastest pace of life (T.cristatus), whereas recruitment was most impacted in species with a slower pace of life (B.variegata and S.salamandra). In the context of climate change, our findings suggest that the capacity of organisms to deal with future changes in NAO values could be closely linked to their position on the fast-slow continuum.

Relationship Between the North Atlantic Oscillation and Spring Migration Phenology of Broad-Winged Hawks (Buteo platypterus) At Hawk Mountain Sanctuary, 1998–2013

Abstract Climatic factors influence migration behavior in both short- and long-distance migratory birds. The Broad-winged Hawk (Buteo platypterus) is a long-distance migrant that exhibits a regular calendar-like migration pattern, with some interannual variability during both the northbound and southbound migrations. We examined the relationship between the North Atlantic Oscillation (NAO) and the timing of spring migration in Broad-winged Hawks based on standardized migration count data collected at Hawk Mountain Sanctuary from 1998 to 2013. A strong negative correlation was found between a higher April NAO index and earlier passage dates for the first 50% (r = −0.723, P < 0.01) and 95% (r = −0.565, P = 0.02) and mean passage date (r = −0.730, P < 0.01) of the hawks passing the watchsite. The April NAO values may serve as a useful indicator of the conditions encountered by Broad-winged Hawks during their northbound migration and our analyses suggest a possible climatic effect on their migration t...

A switch in the Atlantic Oscillation correlates with inter-annual changes in foraging location and food habits of Macaronesian shearwaters (Puffinus baroli) nesting on two islands of the sub-tropical Atlantic Ocean

Changes in oceanographic conditions, shaped by changes in large-scale atmospheric phenomena such as the North Atlantic Oscillation (NAO), alters the structure and functioning of marine ecosystems. Such signals are readily captured by marine top predators, given that their use of foraging habitats and diets change when the NAO changes. In this study we assessed sexual, seasonal and annual (2010/11–2012/13) differences in diet, trophic and isotopic niche (using δ15N and δ13C values of whole blood, 1st primary, 8th secondary and breast feathers), foraging locations and oceanographic variation within foraging areas for Macaronesian shearwaters' (Puffinus baroli) during two years of contrasting NAO values, and between two sub-tropical islands 330km apart in the North Atlantic Ocean, Cima Islet and Selvagem Grande. These two locations provide contrasting oceanographic foraging regimes for the birds, because the second colony is much closer to the African coast (375 vs 650km), and, therefore, to the upwelling area of the Canary Current. There was a marked environmental perturbation in 2010/2011, related with a negative NAO Index and lower marine productivity (lower concentration of Chlorophyll a). This event corresponded to the Macaronesian shearwaters feeding farther north and west, which was readily seen in change of both δ15N and δ13C values, and in a higher intake of cephalopods. Diet and stable isotopes did not differ between sexes. Regurgitation analysis indicate a dominance of cephalopods in both islands, but prey fish were important for Selvagem Grande in 2012 and cephalopods for Cima Islet in 2011. Both δ15N and δ13C values were significantly higher for Cima Islet than for Selvagem Grande, irrespective of year, season and tissue sampled. SIBER analysis showed smaller isotopic niches for the breeding period. Our study suggests that during years of poor environmental conditions Macaronesian shearwaters shift their foraging location to more pelagic waters, take more cephalopods and overall present a narrower isotopic niche.

Variability in storm climate along the Gulf of Cadiz: the role of large scale atmospheric forcing and implications to coastal hazards

In the context of increased coastal hazards due to variability in storminess patterns, the danger of coastal damages and/or morphological changes is related to the sum of sea level conditions, storm surge, maximum wave height and run up values. In order to better understand the physical processes that cause the variability of the above parameters a 44 years reanalysis record (HIPOCAS) was used. The HIPOCAS time-series was validated with real wave and sea-level data using linear and vector correlation methods. In the present work changes in the magnitude, duration, frequency and approach direction of the Atlantic storms over the Gulf of Cadiz (SW Iberian Peninsula) were identified by computing various storm characteristics such as maximum wave height, total energy per storm wave direction and storm duration. The obtained time-series were compared with large-scale atmospheric indices such as the North Atlantic Oscillation (NAO) and the East Atlantic pattern. The results show a good correlation between negative NAO values and increased storminess over the entire Gulf of Cadiz. Furthermore, negative NAO values were correlated with high residual sea level values. Finally, a joint probability analysis of storm and sea level analysis resulted in increased probabilities of the two events happening at the same time indicating higher vulnerability of the coast and increased coastal risks. The above results were compared with coastal inundation events that took place over the last winter seasons in the province of Cadiz.

North Atlantic Oscillation index stochastic modelling

The North Atlantic Oscillation (NAO) index plays a crucial role in the climatic evolution of the Northern Hemisphere. Predicting NAO evolution is very challenging due to the large number of physical processes that influence it. Quantitative surveys have tried to detect possible long-term trends or periodic features in the NAO evolution. In this study, we implement a stochastic model that is able to replicate the statistical characteristics of the NAO index, based on a non-homogeneous semi-Markov Model. For this purpose, we set up two states of the process, namely positive and negative NAO values. We also analyse positive and negative sequences of NAO values. The model characteristics are estimated using daily real values during the period 1950–2013 and we lastly implement a Monte Carlo procedure in order to simulate daily NAO values covering a 1-year time horizon. Next, this model is compared with a typical ARMA - GARCH model used in time series analysis, which appears to be underperforming, in contrast with the semi-Markov one.

Storminess interannual variability and coastal hazards over the south-western Spanish coast: links to large scale atmospheric forcing

In the context of increased coastal hazards through storminess variability, the danger of coastal damages and/or morphological changes is related to the sum of mean sea level conditions, storm surge and maximum wave height and run up values. In order to better understand the physical processes that cause the interannual variability of the above parameters a reanalysis record (HIPOCAS) of the last 44 years was used. The HIPOCAS time-series was validated with real wind, wave and sea-level data using linear and vector correlation methods. In the present work changes in the duration, frequency, chronology and approach direction of the Atlantic storms over the Spanish Gulf of Cadiz (SW Iberian Peninsula) were identified by computing various storm characteristics such as maximum wave height, total energy per storm and storm groupiness. The obtained time-series were compared with large-scale atmospheric indices such as the North Atlantic Oscillation (NAO) and the East Atlantic pattern (EA). The results show a good correlation between negative NAO values and increased storminess over the entire Gulf of Cadiz. Furthermore, negative NAO values were correlated with high mean sea level values and westerly and south-westerly wind events, indicating higher probability of coastal risks. The above results were compared with coastal inundation events that took place over the last winter seasons in the province of Cadiz.

Winter‐responding proxy temperature reconstructions and the North Atlantic Oscillation

AbstractInstrumental temperature data for the Northern Hemisphere (30°–90°N) clearly indicate that winter season variability is larger than equivalent measures for summer. This should not be surprising as temperatures in winter are dominated by variability caused by changes in atmospheric circulation features, whereas in summer variability is more dominated by local changes in cloudiness. Here we consider most of the few winter‐responding annually resolved proxy reconstructions of temperature from the northern North Atlantic and northwestern European regions. We find the expected out‐of‐phase relationship between northwest Europe and Greenland due to the North Atlantic Oscillation (NAO), which is stronger when the series from the two locations are formed from more than one series. On 30 year time scales this relationship between the two locations shows no century‐scale variations since 1250 CE (Common Era), the start of our reconstructions, in contrast to the strong positive NAO values before 1400 CE implied by the study of Trouet et al. (2009).