Hydrological, Socioeconomic and Ecological Impacts of the North Atlantic Oscillation in the Mediterranean Region

2011 ◽  
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Mediterranean Region ◽  
Ecological Impacts ◽  
The North ◽  
The North Atlantic ◽  
The Mediterranean ◽  
The North Atlantic Oscillation

scholarly journals Mechanisms of Winter Precipitation Variability in the European–Mediterranean Region Associated with the North Atlantic Oscillation

2020 ◽  
Vol 33 (16) ◽  
pp. 7179-7196
Author(s):  
Richard Seager ◽  
Haibo Liu ◽  
Yochanan Kushnir ◽  
Timothy J. Osborn ◽  
Isla R. Simpson ◽  
...  
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Mediterranean Region ◽  
Mean Flow ◽  
The North ◽  
Precipitation Anomalies ◽  
The Mean ◽  
The North Atlantic ◽  
The Mediterranean ◽  
The North Atlantic Oscillation

AbstractThe physical mechanisms whereby the mean and transient circulation anomalies associated with the North Atlantic Oscillation (NAO) drive winter mean precipitation anomalies across the North Atlantic Ocean, Europe, and the Mediterranean Sea region are investigated using the European Centre for Medium-Range Weather Forecasts interim reanalysis. A moisture budget decomposition is used to identify the contribution of the anomalies in evaporation, the mean flow, storm tracks and the role of moisture convergence and advection. Over the eastern North Atlantic, Europe, and the Mediterranean, precipitation anomalies are primarily driven by the mean flow anomalies with, for a positive NAO, anomalous moist advection causing enhanced precipitation in the northern British Isles and Scandinavia and anomalous mean flow moisture divergence causing drying over continental Europe and the Mediterranean region. Transient eddy moisture fluxes work primarily to oppose the anomalies in precipitation minus evaporation generated by the mean flow, but shifts in storm-track location and intensity help to explain regional details of the precipitation anomaly pattern. The extreme seasonal precipitation anomalies that occurred during the two winters with the most positive (1988/89) and negative (2009/10) NAO indices are also explained by NAO-associated mean flow moisture convergence anomalies.

North Atlantic Oscillation-related impacts on precipitation over the Italian Peninsula during the 1979-2020 period

2021 ◽  
Author(s):  
Paula Lorenzo Sánchez ◽  
Leonardo Aragão
Keyword(s):  
High Resolution ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Mediterranean Region ◽  
Italian Peninsula ◽  
The North ◽  
Nao Index ◽  
The North Atlantic ◽  
The Mediterranean ◽  
Resolution Dataset

<p>The North Atlantic Oscillation (NAO) has been widely recognized as one of the main patterns of atmospheric variability over the northern hemisphere, helping to understand variations on the North Atlantic Jet (NAJ) position and its influence on storm-tracks, atmospheric blocking and Rossby Wave breaking. Among several relevant teleconnection patterns identified through different timescales, the most prominent ones are found for northern Europe during winter months, when positive (negative) phases of NAO are related to wetter (drier) conditions. Although it is not well defined yet, an opposite connection is observed for the Mediterranean region, where negative NAO values are often associated with high precipitation. Therefore, the main goal of this study is to identify which regions and periods of the year are the most susceptible to abundant NAO-related precipitation throughout the Italian Peninsula. For doing so, the last 42 years period (1979-2020) was analysed using the Fifth Generation ECMWF Atmospheric ReAnalysis of the Global Climate (ERA5). The NAO index was calculated using the Mean Sea Level Pressure (MSLP) extracted from the nearest gridpoints to Reykjavik, Ponta Delgada, Lisbon and Gibraltar, with a time resolution of one hour and horizontal spatial resolution of 0.25ºx0.25º. Both NAO index and MSLP time series were validated for different timescales (hourly, daily, monthly and seasonal) using the Automated Surface Observing System data and the Climatic Research Unit (CRU) high-resolution dataset (based on measured data). High correlations, ranging from 0.92 to 0.98, were found for all stations, timescales and evaluated parameters. To quantify the influence of NAO over the Mediterranean region, the monthly averaged ERA5 ‘total precipitation’ data over the Italian Peninsula [35-48º N; 5-20º E] were used. As expected, the results concerning NAO x Precipitation presented the best correlations when analysed monthly, confirming some of the already known NAO signatures over the Italian Peninsula: higher correlations during winter and over the Tyrrhenian coast, and lower correlations during summer and over the Apennines, the Adriatic Sea and the Ionian Sea. On the other hand, the precipitation over the Alps and the Tunisian coast presented a remarkable signature of positive NAO values that, despite a lower statistical significance (85-90%), is in agreement with recent findings of observational studies. In addition, significant negative correlations were identified for the spring and autumn months over the Tyrrhenian area. Among those, the high correlations found during May are particularly interesting, as they follow the behaviour described in recent studies performed using the same high-resolution dataset (ERA5), which have identified an increased number of cyclones over the Mediterranean during this month. This connection suggests that NAO could also be used to explore the potential penetration of the North Atlantic depressions into the Mediterranean Basin. </p><p>Keywords: NAO; Teleconnections; ERA5; ReAnalysis; Mediterranean; Climatology.</p>

scholarly journals Cyclones causing wind storms in the Mediterranean: characteristics, trends and links to large-scale patterns

2010 ◽  
Vol 10 (7) ◽  
pp. 1379-1391 ◽  
Author(s):  
K. M. Nissen ◽  
G. C. Leckebusch ◽  
J. G. Pinto ◽  
D. Renggli ◽  
S. Ulbrich ◽  
...  
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Positive Phase ◽  
East Atlantic ◽  
The North ◽  
The North Atlantic ◽  
Wind Storms ◽  
The Mediterranean ◽  
Wind Events ◽  
The North Atlantic Oscillation

Abstract. A climatology of cyclones with a focus on their relation to wind storm tracks in the Mediterranean region (MR) is presented. Trends in the frequency of cyclones and wind storms, as well as variations associated with the North Atlantic Oscillation (NAO), the East Atlantic/West Russian (EAWR) and the Scandinavian variability pattern (SCAND) are discussed. The study is based on the ERA40 reanalysis dataset. Wind storm tracks are identified by tracking clusters of adjacent grid boxes characterised by extremely high local wind speeds. The wind track is assigned to a cyclone track independently identified with an objective scheme. Areas with high wind activity – quantified by extreme wind tracks – are typically located south of the Golf of Genoa, south of Cyprus, southeast of Sicily and west of the Iberian Peninsula. About 69% of the wind storms are caused by cyclones located in the Mediterranean region, while the remaining 31% can be attributed to North Atlantic or Northern European cyclones. The North Atlantic Oscillation, the East Atlantic/West Russian pattern and the Scandinavian pattern all influence the amount and spatial distribution of wind inducing cyclones and wind events in the MR. The strongest signals exist for the NAO and the EAWR pattern, which are both associated with an increase in the number of organised strong wind events in the eastern MR during their positive phase. On the other hand, the storm numbers decrease over the western MR for the positive phase of the NAO and over the central MR during the positive phase of the EAWR pattern. The positive phase of the Scandinavian pattern is associated with a decrease in the number of winter wind storms over most of the MR. A third of the trends in the number of wind storms and wind producing cyclones during the winter season of the ERA40 period may be attributed to the variability of the North Atlantic Oscillation.

scholarly journals Asian Jet Waveguide and a Downstream Extension of the North Atlantic Oscillation

2004 ◽  
Vol 17 (24) ◽  
pp. 4674-4691 ◽  
Author(s):  
Masahiro Watanabe
Keyword(s):  
East Asia ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Wave Train ◽  
East Asian ◽  
The North ◽  
The North Atlantic ◽  
The Mediterranean ◽  
The North Atlantic Oscillation ◽  
Asian Jet Waveguide

Abstract Anomalous atmospheric fields associated with the North Atlantic Oscillation (NAO) are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the NAO is a regional phenomenon. Analyses on the interannual time scale reveal that the NAO signal is relatively confined to the Euro–Atlantic sector in December while it extends toward East Asia and the North Pacific in February. The difference is most clearly seen in the meridional wind anomaly, which shows a wave train along the Asian jet, collocated with an anomalous vorticity source near the jet entrance. Diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi-stationary Rossby waves trapped on the Asian jet waveguide, and effectively excited by the anomalous upper-level convergence over the Mediterranean Sea. It is found that, when the NAO accompanies the Mediterranean convergence (MC) anomaly, most frequently seen in February, the NAO indeed has a much wider horizontal structure than the classical picture, rather similar to the Arctic Oscillation. In such cases interannual variability of the NAO is tied to the East Asian climate variability such that the positive NAO tends to bring a surface warming over East Asia. Similar results are obtained from an analysis of individual NAO events based on low-pass-filtered daily fields, which additionally identified that the downstream extension occurs at the decay stage of the NAO event and the MC anomaly appears to be induced by the Ekman pumping associated with the NAO. The signal of the MC anomaly can be detected even at 5 days before the peak of the NAO, suggesting that the NAO influence to East Asia is predictable to some extent; therefore, monitoring the developing NAO event is useful to the medium-range weather forecast in East Asian countries.

Influence of climate drivers and the North Atlantic Oscillation on beech growth at marginal sites across the Mediterranean

2015 ◽  
Vol 66 (3) ◽  
pp. 229-242 ◽  
Author(s):  
K Chen ◽  
I Dorado-Liñán ◽  
L Akhmetzyanov ◽  
G Gea-Izquierdo ◽  
T Zlatanov ◽  
...  
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
The North ◽  
The North Atlantic ◽  
The Mediterranean ◽  
The North Atlantic Oscillation

scholarly journals A summer climate regime over Europe modulated by the North Atlantic Oscillation

2011 ◽  
Vol 15 (1) ◽  
pp. 57-64 ◽  
Author(s):  
G. Wang ◽  
A. J. Dolman ◽  
A. Alessandri
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Winter Precipitation ◽  
Maximum Temperature ◽  
Functional Responses ◽  
Summer Climate ◽  
The North ◽  
The North Atlantic ◽  
The Mediterranean ◽  
The North Atlantic Oscillation

Abstract. Recent summer heat waves in Europe were found to be preceded by precipitation deficits in winter. Numerical studies suggest that these phenomena are dynamically linked by land-atmosphere interactions. However, there exists as yet no complete observational evidence that connects summer climate variability to winter precipitation and the relevant circulation patterns. In this paper, we investigate the functional responses of summer mean and maximum temperature (June–August, Tmean and Tmax) as well as soil moisture proxied by the self-calibrating Palmer drought severity index (scPDSI) to preceding winter precipitation (January–March, PJFM) for the period 1901–2005. All the analyzed summer fields show distinctive responses to PJFM over the Mediterranean. We estimate that 10 ~ 15% of the interannual variability of Tmax and Tmean over the Mediterranean is statistically forced by PJFM. For the scPDSI this amounts to 10 ~ 25%. Further analysis shows that these responses are highly correlated to the North Atlantic Oscillation (NAO) regime over the Mediterranean. We suggest that NAO modulates European summer temperature by controlling winter precipitation that initializes the moisture states that subsequently interact with temperature. This picture of relations between European summer climate and NAO as well as winter precipitation suggests potential for improved seasonal prediction of summer climate for particular extreme events.

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