scholarly journals Recent trends in daily rainfall extremes over Montenegro (1951–2010)

2015 ◽  
Vol 15 (9) ◽  
pp. 2069-2077 ◽  
Author(s):  
D. Burić ◽  
J. Luković ◽  
B. Bajat ◽  
M. Kilibarda ◽  
N. Živković
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Large Scale ◽  
Winter Season ◽  
Daily Rainfall ◽  
Extreme Rainfall ◽  
Intense Rainfall ◽  
The North ◽  
Rainfall Extremes ◽  
The North Atlantic Oscillation

Abstract. More intense rainfall may cause a range of negative impacts upon society and the environment. In this study we analysed trends in extreme ETCCDI (Expert Team on Climate Change Detection and Indices) rainfall indices in Montenegro for the period between 1951 and 2010. Montenegro has been poorly studied in terms of rainfall extremes, yet it contains the wettest Mediterranean region known as Krivošije. Several indices of precipitation extremes were assessed including the number of dry days and rainfall totals in order to identify trends and possible changes. A spatial pattern relationship between extreme rainfall indices and the North Atlantic Oscillation has also been examined. The results generally suggest that the number of days with precipitation decreased while rainfall intensity increased, particularly in south-western parts of the country. A slight tendency towards intense rainfall events is suggested. The examined rainfall indices and North Atlantic Oscillation over Montenegro seemed to be directly linked to changes in one of the major large-scale circulation modes such as the NAO pattern that is particularly evident during the winter season.

scholarly journals Trends in compound extremes of air temperature and precipitation in Eastern Europe

2021 ◽  
Author(s):  
Elena Vyshkvarkova ◽  
Olga Sukhonos
Keyword(s):  
Eastern Europe ◽  
North Atlantic Oscillation ◽  
Air Temperature ◽  
North Atlantic ◽  
Large Scale ◽  
The North ◽  
Temperature And Precipitation ◽  
Atmosphere System ◽  
Daily Data ◽  
The North Atlantic Oscillation

Abstract The spatial distribution of compound extremes of air temperature and precipitation was studied over the territory of Eastern Europe for the period 1950–2018 during winter and spring. Using daily data on air temperature and precipitation, we calculated the frequency and trends of the four indices – cold/dry, cold/wet, warm/dry and warm/wet. Also, we studying the connection between these indices and large-scale processes in the ocean-atmosphere system such as North Atlantic Oscillation, East Atlantic Oscillation and Scandinavian Oscillation. The results have shown that positive trends in the region are typical of the combinations with the temperatures above the 75th percentile, i.e., the warm extremes in winter and spring. Negative trends were obtained for the cold extremes. Statistically significant increase in the number of days with warm extremes was observed in the northern parts of the region in winter and spring. The analysis of the impacts of the large-scale processes in oceans-atmosphere system showed that the North Atlantic Oscillation index has a strong positive and statistically significant correlation with the warm indices of compound extremes in the northern part of Eastern Europe in winter, while the Scandinavian Oscillation shows the opposite picture.

scholarly journals Impact of the North Atlantic Oscillation on Transatlantic Flight Routes and Clear-Air Turbulence

2016 ◽  
Vol 55 (3) ◽  
pp. 763-771 ◽  
Author(s):  
Jung-Hoon Kim ◽  
William N. Chan ◽  
Banavar Sridhar ◽  
Robert D. Sharman ◽  
Paul D. Williams ◽  
...  
Keyword(s):  
New York ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Large Scale ◽  
Jet Streams ◽  
Weather Patterns ◽  
Teleconnection Patterns ◽  
The North ◽  
Air Turbulence ◽  
The North Atlantic Oscillation

AbstractThe variation of wind-optimal transatlantic flight routes and their turbulence potential is investigated to understand how upper-level winds and large-scale flow patterns can affect the efficiency and safety of long-haul flights. In this study, the wind-optimal routes (WORs) that minimize the total flight time by considering wind variations are modeled for flights between John F. Kennedy International Airport (JFK) in New York, New York, and Heathrow Airport (LHR) in London, United Kingdom, during two distinct winter periods of abnormally high and low phases of North Atlantic Oscillation (NAO) teleconnection patterns. Eastbound WORs approximate the JFK–LHR great circle (GC) route following northerly shifted jets in the +NAO period. Those WORs deviate southward following southerly shifted jets during the −NAO period, because eastbound WORs fly closely to the prevailing westerly jets to maximize tailwinds. Westbound WORs, however, spread meridionally to avoid the jets near the GC in the +NAO period to minimize headwinds. In the −NAO period, westbound WORs are north of the GC because of the southerly shifted jets. Consequently, eastbound WORs are faster but have higher probabilities of encountering clear-air turbulence than westbound ones, because eastbound WORs are close to the jet streams, especially near the cyclonic shear side of the jets in the northern (southern) part of the GC in the +NAO (−NAO) period. This study suggests how predicted teleconnection weather patterns can be used for long-haul strategic flight planning, ultimately contributing to minimizing aviation’s impact on the environment.

Characteristics of North European winter lightning related to a high positive North Atlantic Oscillation index

2020 ◽  
Author(s):  
Ivana Kolmašová ◽  
Kateřina Rosická ◽  
Ondřej Santolík
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Large Scale ◽  
Winter Season ◽  
Winter Climate ◽  
The North ◽  
Nao Index ◽  
The North Atlantic ◽  
Icelandic Low ◽  
Azores High

<p>The variability of winter climate in the North Atlantic region is predominantly driven by a large scale alternation of atmospheric masses between the Icelandic Low and Azores High pressure systems called the North Atlantic Oscillation (NAO) and characterized by the NAO index. The calculation of the NAO index is based on the difference between sea-level pressure strengths of the Azores High and the Icelandic Low. Unusually high positive values of the NAO index were observed to manifest themselves by above-average precipitation and severe winter storms over British Isles and other parts of northwestern and northern Europe.</p><p>In the last two decades, the winter season 2014/2015 exhibited the highest positive monthly NAO indexes. During this winter, newspapers in the UK, Germany, Poland, and Scandinavia reported extremely strong storms which caused huge power outages, damages of buildings, and collapses of traffic which paralyzed the daily life. As winter thunderstorms are also characterized by a higher production of very energetic lightning, we use the World Wide Lightning Location Network (WWLLN) data and investigate properties of lightning which occurred in the north European region from October 2014 to March 2015.  The dataset consists of more than 90 thousand lightning detections. We focus on spatial and temporal distribution of lightning strokes, their energies and multiplicity.</p><p>We have found that the diurnal distribution of lightning was random from November till February, while the afternoon peak typical for summer storms was noticeable only in October and March. The median energy of lightning strokes observed in October, November and March reached only about 10-20% of the median energy of strokes detected in December, January and February. The most energetic strokes were concentrated above the ocean close to the western coastal areas and appeared exclusively at night and in the morning hours.</p>

Assessing the influence of the North Atlantic Oscillation on a migratory demersal predator in the Alboran Sea

2015 ◽  
Vol 96 (7) ◽  
pp. 1499-1505 ◽  
Author(s):  
José Carlos Báez
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Large Scale ◽  
Regime Shift ◽  
Close Association ◽  
Alboran Sea ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation ◽  
Alborán Sea

This study analysed the regime shift of tope shark and the overlapping taxa Raja spp. in the Alboran Sea. Tope shark and Raja spp. landings are both significantly correlated with the North Atlantic Oscillation (NAO). A significant negative correlation was found between Raja spp. landings and tope shark landings. This finding suggests that climatic oscillations affect regime shifts between these taxa in the Alboran Sea. Studies are scarce on the dependence of deep-sea communities on biological and physical processes occurring in near-shore pelagic environments mediated by large-scale atmospheric phenomena. Similar to previous studies on the Mediterranean Sea, a close association was found between landings of deep-water animals and the NAO. The main conclusion is that the regime shift of tope shark and the overlapping taxa Raja spp. is mediated by a negative NAO and accumulated snow.

scholarly journals The North Atlantic Oscillation Response to Large-Scale Atmospheric Anomalies in the Northeastern Pacific

2013 ◽  
Vol 70 (9) ◽  
pp. 2854-2874 ◽  
Author(s):  
Marie Drouard ◽  
Gwendal Rivière ◽  
Philippe Arbogast
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Wave Breaking ◽  
Large Scale ◽  
Wave Train ◽  
Low Frequency ◽  
The North ◽  
Northeastern Pacific ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract Ingredients in the North Pacific flow influencing Rossby wave breakings in the North Atlantic and the intraseasonal variations of the North Atlantic Oscillation (NAO) are investigated using both reanalysis data and a three-level quasigeostrophic model on the sphere. First, a long-term run is shown to reproduce the observed relationship between the nature of the synoptic wave breaking and the phase of the NAO. Furthermore, a large-scale, low-frequency ridge anomaly is identified in the northeastern Pacific in the days prior to the maximum of the positive NAO phase both in the reanalysis and in the model. A large-scale northeastern Pacific trough anomaly is observed during the negative NAO phase but does not systematically precede it. Then, short-term linear and nonlinear simulations are performed to understand how the large-scale ridge anomaly can act as a precursor of the positive NAO phase. The numerical setup allows for analysis of the propagation of synoptic waves in the eastern Pacific in the presence of a large-scale ridge or trough anomaly and their downstream impact onto the Atlantic jet when they break. The ridge acts in two ways. First, it tends to prevent the downstream propagation of small waves compared to long waves. Second, it deflects the propagation of the wave trains in such a way that they mainly propagate equatorward in the Atlantic. The two modes of action favor the anticyclonic wave breaking and, therefore, the positive NAO phase. With the trough, the wave train propagation is more zonal, disturbances are more meridionally elongated, and cyclonic wave breaking is more frequent in the Atlantic than in the ridge case.

scholarly journals Stochastic Forcing of Ocean Variability by the North Atlantic Oscillation

2009 ◽  
Vol 39 (1) ◽  
pp. 162-184 ◽  
Author(s):  
Kettyah C. Chhak ◽  
Andrew M. Moore ◽  
Ralph F. Milliff
Keyword(s):  
North Atlantic Oscillation ◽  
Ocean Circulation ◽  
Rossby Wave ◽  
North Atlantic ◽  
Large Scale ◽  
Western Boundary ◽  
Stochastic Forcing ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract At middle and high latitudes, the magnitude of stochastic wind stress forcing of the ocean by atmospheric variability on synoptic time scales (i.e., “weather” related variability) is comparable to that of the seasonal cycle. Stochastic forcing may therefore have a significant influence on the ocean circulation, climate, and ocean predictability. Here, the influence of stochastic forcing associated with the North Atlantic Oscillation on the subtropical gyre circulation of the North Atlantic is explored in an eddy-permitting quasigeostrophic framework. For the North Atlantic winds used in this study, the root-mean-square of the annual average Ekman pumping velocity of the seasonal cycle between 35° and 52°N is 1.3 × 10−7 m s−1, while the wintertime standard deviation of the stochastic component of the North Atlantic Oscillation over the same latitude band is 2.2 × 10−7 m s−1. Significant stochastically induced variability in the ocean circulation occurs near the western boundary region and along the western margins of the abyssal plains associated with vortex stretching, energy release from the mean flow, and the generation of topographic Rossby waves. Variability arises from a combination of two effects, depending on the measure of variance used: growth of unstable modes of the underlying circulation and modal interference resulting from their nonnormal nature, which dominates during the first 10 days or so of perturbation growth. Near the surface, most of the variability is associated with large-scale changes in the barotropic circulation, although more than 20% of the energy and enstrophy variability is associated with small-scale baroclinic waves. In the deep ocean, much of the stochastically induced variability is apparently due to topographic Rossby wave activity along the continental rise and ocean ridges. Previous studies have demonstrated that rectification of topographic Rossby wave–induced circulations in the western North Atlantic may contribute to the western boundary current recirculation zones. The authors suggest that a source of topographic Rossby wave energy, significant enough to rectify the mean ocean circulation, may arise from stochastic forcing by large-scale atmospheric forcing, such as the North Atlantic Oscillation and other atmospheric teleconnection patterns.

scholarly journals Bivariate Modelling of a Teleconnection Index and Extreme Rainfall in a Small North Atlantic Island

Climate ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 86
Author(s):  
Luis Angel Espinosa ◽  
Maria Manuela Portela ◽  
João Dehon Pontes Filho ◽  
Martina Zelenakova
Keyword(s):  
Climate Variability ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Extreme Rainfall ◽  
Small Island ◽  
Return Periods ◽  
Rainfall Events ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

This paper explores practical applications of bivariate modelling via copulas of two likely dependent random variables, i.e., of the North Atlantic Oscillation (NAO) coupled with extreme rainfall on the small island of Madeira, Portugal. Madeira, due to its small size (∼740 km2), very pronounced mountain landscape, and location in the North Atlantic, experiences a wide range of rainfall regimes, or microclimates, which hamper the analyses of extreme rainfall. Previous studies showed that the influence of the North Atlantic Oscillation (NAO) on extreme rainfall is at its largest in the North Atlantic sector, with the likelihood of increased rainfall events from December through February, particularly during negative NAO phases. Thus, a copula-based approach was adopted for teleconnection, aiming at assigning return periods of daily values of an NAO index (NAOI) coupled with extreme daily rainfalls—for the period from December 1967 to February 2017—at six representative rain gauges of the island. The results show that (i) bivariate copulas describing the dependence characteristics of the underlying joint distributions may provide useful analytical expressions of the return periods of the coupled previous NAOI and extreme rainfall and (ii) that recent years show signs of increasing climate variability with more anomalous daily negative NAOI along with higher extreme rainfall events. These findings highlight the importance of multivariate modelling for teleconnections of prominent patterns of climate variability, such as the NAO, to extreme rainfall in North Atlantic regions, especially in small islands that are highly vulnerable to the effects of abrupt climate variability.

scholarly journals Impact of Eurasian autumn snow on the winter North Atlantic Oscillation in seasonal forecasts of the 20<sup>th</sup> century

2021 ◽  
Author(s):  
Martin Wegmann ◽  
Yvan Orsolini ◽  
Antje Weisheimer ◽  
Bart van den Hurk ◽  
Gerrit Lohmann
Keyword(s):  
North Atlantic Oscillation ◽  
Snow Cover ◽  
North Atlantic ◽  
Climate Model ◽  
Winter Season ◽  
Reanalysis Data ◽  
Causal Connection ◽  
Seasonal Forecasts ◽  
The North ◽  
The North Atlantic Oscillation

Abstract. As the leading climate mode of wintertime climate variability over Europe, the North Atlantic Oscillation (NAO) has been extensively studied over the last decades. Recently, studies highlighted the state of the Eurasian cryosphere as a possible predictor for the wintertime NAO. However, missing correlation between snow cover and wintertime NAO in climate model experiments and strong non-stationarity of this link in reanalysis data is questioning the causality of this relationship. Here we use the large ensemble of Atmospheric Seasonal Forecasts of the 20th Century (ASF-20C) with the European Centre for Medium-Range Weather Forecasts model, focusing on the winter season. Besides the main 110-year ensemble of 51 members, we investigate a second, perturbed ensemble of 21 members where initial (November) land conditions over the Northern Hemisphere are swapped from neighboring years. The Eurasian snow/NAO linkage is examined in terms of a longitudinal snow depth dipole across Eurasia. Subsampling the perturbed forecast ensemble and contrasting members with high and low initial snow dipole conditions, we found that their composite difference indicates more negative NAO states in the following winter (DJF) after positive west to east snow cover gradients at the beginning of November. Surface and atmospheric forecast anomalies through the troposphere and stratosphere associated with the anomalous positive snow dipole consist of colder early winter surface temperatures over Eastern Eurasia, an enhanced Ural ridge and increased vertical energy fluxes into the stratosphere, with a subsequent negative NAO-like signature in the troposphere. We thus confirm the existence of a causal connection between autumn snow patterns and subsequent winter circulation in the ASF-20C forecasting system.

Spatial differences in the impact of the North Atlantic Oscillation on the flow of rivers in Europe

2011 ◽  
Vol 42 (1) ◽  
pp. 30-39 ◽  
Author(s):  
Dariusz Wrzesiński ◽  
Rafał Paluszkiewicz
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Winter Season ◽  
Winter Period ◽  
The North ◽  
The North Atlantic ◽  
Positive Correlations ◽  
The North Atlantic Oscillation ◽  
River Profiles ◽  
The Impact

The article presents regional differences in the impact that the North Atlantic Oscillation (NAO) exerts on the flow of European rivers. The impact is determined by temporal variations in the strength of relations expressed by coefficients of correlation between monthly or seasonal NAO indices and discharges recorded at 510 river profiles. The results of the correlation analysis were arranged using Ward’s method of hierarchical grouping. The classification of river profiles thus obtained made it possible to distinguish seven regions differing in the nature of the dependence between streamflow and the intensity of the NAO. The most statistically significant positive correlations are displayed by the rivers of Fennoscandia, Denmark and the northwest part of the British Isles in the winter period, while the most significant negative correlations (also in winter) are recorded for streams of the Mediterranean Basin, western France and the southeast of England. In the southeast part of the Baltic Sea drainage basin, significant positive correlations of streamflow with the NAO indices can be observed in the winter season and negative correlations are observed in spring.

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