scholarly journals Prediction of North Atlantic Oscillation Index with Convolutional LSTM Based on Ensemble Empirical Mode Decomposition

Atmosphere ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 252 ◽  
Author(s):  
Shijin Yuan ◽  
Xiaodan Luo ◽  
Bin Mu ◽  
Jing Li ◽  
Guokun Dai
Keyword(s):  
North Atlantic Oscillation ◽  
Empirical Mode Decomposition ◽  
North Atlantic ◽  
Ensemble Empirical Mode Decomposition ◽  
Machine Learning Algorithms ◽  
Index Data ◽  
The North ◽  
Nao Index ◽  
Mode Decomposition ◽  
The North Atlantic

The North Atlantic Oscillation (NAO) is the most significant mode of the atmosphere in the North Atlantic, and it plays an important role in regulating the local weather and climate and even those of the entire Northern Hemisphere. Therefore, it is vital to predict NAO events. Since the NAO event can be quantified by the NAO index, an effective neural network model EEMD-ConvLSTM, which is based on Convolutional Long Short-Term Memory (ConvLSTM) with Ensemble Empirical Mode Decomposition (EEMD), is proposed for NAO index prediction in this paper. EEMD is applied to preprocess NAO index data, which are issued by the National Oceanic and Atmospheric Administration (NOAA), and NAO index data are decomposed into several Intrinsic Mode Functions (IMFs). After being filtered by the energy threshold, the remaining IMFs are used to reconstruct new NAO index data as the input of ConvLSTM. In order to evaluate the performance of EEMD-ConvLSTM, six methods were selected as the benchmark, which included traditional models, machine learning algorithms, and other deep neural networks. Furthermore, we forecast the NAO index with EEMD-ConvLSTM and the Rolling Forecast (RF) and compared the results with those of Global Forecast System (GFS) and the averaging of 11 Medium Range Forecast (MRF) model ensemble members (ENSM) provided by the NOAA Climate Prediction Center. The experimental results show that EEMD-ConvLSTM not only has the highest reliability from evaluation metrics, but also can better capture the variation trend of the NAO index data.

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 Coupled decadal variability of the North Atlantic Oscillation, regional rainfall and karst spring discharges in the Campania region (southern Italy)

2012 ◽  
Vol 16 (5) ◽  
pp. 1389-1399 ◽  
Author(s):  
P. De Vita ◽  
V. Allocca ◽  
F. Manna ◽  
S. Fabbrocino
Keyword(s):  
Time Series ◽  
North Atlantic Oscillation ◽  
Air Temperature ◽  
North Atlantic ◽  
Karst Spring ◽  
The North ◽  
Nao Index ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract. Thus far, studies on climate change have focused mainly on the variability of the atmospheric and surface components of the hydrologic cycle, investigating the impact of this variability on the environment, especially with respect to the risks of desertification, droughts and floods. Conversely, the impacts of climate change on the recharge of aquifers and on the variability of groundwater flow have been less investigated, especially in Mediterranean karst areas whose water supply systems depend heavily upon groundwater exploitation. In this paper, long-term climatic variability and its influence on groundwater recharge were analysed by examining decadal patterns of precipitation, air temperature and spring discharges in the Campania region (southern Italy), coupled with the North Atlantic Oscillation (NAO). The time series of precipitation and air temperature were gathered over 90 yr, from 1921 to 2010, using 18 rain gauges and 9 air temperature stations with the most continuous functioning. The time series of the winter NAO index and of the discharges of 3 karst springs, selected from those feeding the major aqueducts systems, were collected for the same period. Regional normalised indexes of the precipitation, air temperature and karst spring discharges were calculated, and different methods were applied to analyse the related time series, including long-term trend analysis using smoothing numerical techniques, cross-correlation and Fourier analysis. The investigation of the normalised indexes highlighted the existence of long-term complex periodicities, from 2 to more than 30 yr, with differences in average values of up to approximately ±30% for precipitation and karst spring discharges, which were both strongly correlated with the winter NAO index. Although the effects of the North Atlantic Oscillation (NAO) had already been demonstrated in the long-term precipitation and streamflow patterns of different European countries and Mediterranean areas, the results of this study allow for the establishment of a link between a large-scale atmospheric cycle and the groundwater recharge of carbonate karst aquifers. Consequently, the winter NAO index could also be considered as a proxy to forecast the decadal variability of groundwater flow in Mediterranean karst areas.

scholarly journals Rainfall-triggered landslides in the Lisbon region over 2006 and relationships with the North Atlantic Oscillation

2008 ◽  
Vol 8 (3) ◽  
pp. 483-499 ◽  
Author(s):  
J. L. Zêzere ◽  
R. M. Trigo ◽  
M. Fragoso ◽  
S. C. Oliveira ◽  
R. A. C. Garcia
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Rainfall Threshold ◽  
Antecedent Rainfall ◽  
Landslide Activity ◽  
The North ◽  
Nao Index ◽  
Landslide Event ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract. Landslides occurred in the Lisbon area during the last 50 years were almost always induced by rainfall and have been used to establish rainfall thresholds for regional landslide activity. In 2006, three new rainfall-triggered landslide events occurred in the study area, namely on the 20 March, the 25–27 October, and the 28 November. Landslide events occurred in March and October 2006 include shallow translational slides and few debris flows, and the corresponding absolute antecedent rainfall was found to be above the threshold for durations ranging from 4 to 10 days. These events also fit the combined threshold of daily precipitation and 5 days calibrated antecedent rainfall values. Likewise the landslide event that took place in late November 2006 includes some slope movements with deeper slip surfaces, when compared with landslides dating from March and October. Moreover, the corresponding absolute antecedent rainfall was also found to be above the 40-day period rainfall threshold. Here we characterize in detail the short and long-term atmospheric circulation conditions that were responsible for the intense rainfall episodes that have triggered the corresponding landslide events. It is shown that the three rainfall episodes correspond to considerably different synoptic atmospheric patterns, with the March episode being associated to an intense cut-off low system while the October and November episodes appear to be related to more typical Atlantic low pressure systems (and associated fronts) travelling eastwards. Finally, we analyse the role played by the North Atlantic Oscillation (NAO) during those months marked by landslide activity. It is shown that the NAO index was consistently negative (usually associated with above average precipitation) for the months prior to the landslide events, i.e. between October 2005 and March 2006, and again between August and October 2006.

scholarly journals Coral calcification responses to the North Atlantic Oscillation and coral bleaching in Bermuda

PLoS ONE ◽  
2020 ◽  
Vol 15 (11) ◽  
pp. e0241854
Author(s):  
Travis A. Courtney ◽  
Theodor Kindeberg ◽  
Andreas J. Andersson
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Coral Bleaching ◽  
Inverse Correlation ◽  
Life History Strategies ◽  
Coral Calcification ◽  
The North ◽  
Nao Index ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

The North Atlantic Oscillation (NAO) has been hypothesized to drive interannual variability in Bermudan coral extension rates and reef-scale calcification through the provisioning of nutritional pulses associated with negative NAO winters. However, the direct influence of the NAO on Bermudan coral calcification rates remains to be determined and may vary between species and reef sites owing to implicit differences in coral life history strategies and environmental gradients across the Bermuda reef platform. In this study, we investigated the connection between negative NAO winters and Bermudan Diploria labyrinthiformis, Pseudodiploria strigosa, and Orbicella franksi coral calcification rates across rim reef, lagoon, and nearshore reef sites. Linear mixed effects modeling detected an inverse correlation between D. labyrinthiformis calcification rates and the winter NAO index, with higher rates associated with increasingly negative NAO winters. Conversely, there were no detectable correlations between P. strigosa or O. franksi calcification rates and the winter NAO index suggesting that coral calcification responses associated with negative NAO winters could be species-specific. The correlation between coral calcification rates and winter NAO index was significantly more negative at the outer rim of the reef (Hog Reef) compared to a nearshore reef site (Whalebone Bay), possibly indicating differential influence of the NAO as a function of the distance from the reef edge. Furthermore, a negative calcification anomaly was observed in 100% of D. labyrinthiformis cores in association with the 1988 coral bleaching event with a subsequent positive calcification anomaly in 1989 indicating a post-bleaching recovery in calcification rates. These results highlight the importance of assessing variable interannual coral calcification responses between species and across inshore-offshore gradients to interannual atmospheric modes such as the NAO, thermal stress events, and potential interactions between ocean warming and availability of coral nutrition to improve projections for future coral calcification rates under climate change.

Decadal Relationship between European Blocking and the North Atlantic Oscillation during 1978–2011. Part I: Atlantic Conditions

2015 ◽  
Vol 72 (3) ◽  
pp. 1152-1173 ◽  
Author(s):  
Dehai Luo ◽  
Yao Yao ◽  
Aiguo Dai
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Western Europe ◽  
Storm Track ◽  
Western Atlantic ◽  
Atlantic Sector ◽  
The North ◽  
Nao Index ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract Both the positive and negative phases of the North Atlantic Oscillation (NAO+ and NAO−, respectively) and atmospheric blocking in the Euro-Atlantic sector reflect synoptic variability over the region and thus are intrinsically linked. This study examines their relationship from a decadal change perspective. Since the winter-mean NAO index is defined as a time average of instantaneous NAO indices over the whole winter, it is unclear how the activity of European blocking (EB) events can be related to the variation of the positive mean NAO index. Here, this question is examined by dividing the winter period 1978–2011 into two decadal epochs: 1978–94 (P1) with an increasing and high NAO index and 1995–2011 (P2) with a decreasing and low NAO index. Using atmospheric reanalysis data, it is shown that there are more intense and persistent EB events in eastern Europe during P1 than during P2, while the opposite is true for western Europe. It is further shown that there are more NAO+ (NAO−) events during P1 (P2). The EB events associated with NAO+ events extend more eastward and are associated with stronger Atlantic mean zonal wind and weaker western Atlantic storm track during P1 than during P2, but EB events associated with NAO− events increase in western Europe under opposite Atlantic conditions during P2. Thus, the increase in the number of individual NAO+ (NAO−) events results in more EB events in eastern (western) Europe during P1 (P2). The EB change is also associated with the increased frequency of NAO− to NAO+ (NAO+ to NAO−) transition events.

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>

scholarly journals The Role of the North Atlantic Oscillation in Shaping Regional-Scale Peak Seasonal Precipitation across the Indian Subcontinent

2011 ◽  
Vol 15 (2) ◽  
pp. 1-13 ◽  
Author(s):  
Shouraseni Sen Roy
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Indian Subcontinent ◽  
Regional Level ◽  
The North ◽  
Nao Index ◽  
The North Atlantic ◽  
The North Atlantic Oscillation ◽  
The Impact

Abstract The present study focuses on the impact of the North Atlantic Oscillation (NAO) in shaping the regional-level precipitation during the peak months of the two main rainy seasons over the Indian subcontinent. Monthly precipitation data from 1871 to 2005 were collected for 30 homogenous regions across the subcontinent. Regression analysis was used to analyze the strength of the relationship between NAO on regional-level precipitation patterns. The results of the study showed distinct spatial variations in the response of regional-level rainfall to the monthly NAO index. There were greater variations in the strength of the regression coefficients for peak monsoon rainfall (PMR) compared to the peak winter rainfall (PWR) season. During the latter half of the year, the association between PMR and the NAO index was predominantly negative. In general, the role of NAO was more pronounced across most of the regions in the peninsular India.

Effect of the North Atlantic Oscillation on recruitment of Atlantic cod (Gadus morhua)

2004 ◽  
Vol 61 (9) ◽  
pp. 1558-1564 ◽  
Author(s):  
K Brander ◽  
R Mohn
Keyword(s):  
North Atlantic Oscillation ◽  
North Sea ◽  
North Atlantic ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
The North ◽  
Nao Index ◽  
The North Sea ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

We examine the effect of introducing an environmental factor — the North Atlantic Oscillation (NAO) index — into a stock–recruit relationship fitted to 13 North Atlantic cod (Gadus morhua) stocks and discuss the implications for management. The NAO has a significant effect on recruitment of four of the stocks (positive effect on recruitment in the North Sea, Baltic Sea, and Irish Sea; negative effect on recruitment at Iceland), and the pattern of positive and negative effects on all stocks is consistent with the geographic influence of the NAO on environmental variables. Observed variability in the NAO should be taken into account in interpreting the causes of past changes in cod stocks. The NAO index for the previous winter is available by April and thus may provide an early indication of the likely range of cod recruitment in the current year. In areas, such as the North Sea, where the effect is strong, medium- and long-term assessments of recruitment and yield of the cod stocks should consider likely future states of the NAO. The NAO can be used to represent environmental variability in stock projections and thereby provide a better basis for the estimation of risk.

scholarly journals Winter Lightning and North Atlantic Oscillation

2007 ◽  
Vol 135 (7) ◽  
pp. 2810-2815 ◽  
Author(s):  
Fernando de Pablo ◽  
Luis Rivas Soriano
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Lightning Activity ◽  
Lightning Flash ◽  
Eastern Area ◽  
The North ◽  
European Area ◽  
Nao Index ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract The relationship between the North Atlantic Oscillation (NAO) and total (in cloud and cloud to ground) lightning activity during the wintertime (December to March) is analyzed. Lightning data from the Optical Transient Detector were used and were studied in the North Atlantic and western European area. The southern half of the area analyzed (latitudes lower than ∼50°N) was observed to have an increased (decreased) lightning flash rate associated with negative (positive) NAO index values. The opposite relationship was found when the northern half (latitudes higher than ∼50°N) was considered. In both cases, the effect of the NAO on the lightning activity was stronger over the eastern area analyzed. Low (clearly <1) absolute values of the NAO index seem to be associated with minimum lightning activity.

Characteristics of the Atlantic Storm-Track Eddy Activity and Its Relation with the North Atlantic Oscillation

2007 ◽  
Vol 64 (2) ◽  
pp. 241-266 ◽  
Author(s):  
G. Rivière ◽  
I. Orlanski
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
High Frequency ◽  
Wave Breaking ◽  
Momentum Flux ◽  
Regional Model ◽  
The North ◽  
Nao Index ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract This study focuses on feedbacks of the high-frequency eddy activity onto the quasi-stationary circulation, particularly with regard to the North Atlantic Oscillation (NAO). The methodology consists of analyzing NCEP–NCAR reanalysis data and sensitivity runs from a high-resolution nonhydrostatic regional model. Consistent with recent studies, results show that the jet displacement characteristic of the NAO phenomenon depends strongly on the dynamics of the synoptic-scale waves and the way they break. Positive and negative phases of the NAO are closely related to anticyclonic and cyclonic wave breaking, respectively. Indeed, the high-frequency momentum flux whose sign is directly related to the type of wave breaking is correlated with the NAO index over the Atlantic. The peak of the momentum flux signal precedes that of the NAO by a few days suggesting that wave breaking is triggering NAO events. Two examples illustrate the significant impact of single storms, in particular those occurring in the east coast of the United States. The wave breaking at the end of their life cycle can suddenly change the NAO index in few days, and as the return to equilibrium takes generally a longer time, it can even affect the sign of the NAO during an entire month. An important issue determining the NAO phase is related to upstream effects. By considering a domain extending from the eastern Pacific to western Europe and by forcing the regional model with real data at the western boundary, sensitivity runs show that the right sign of the NAO index can be recovered. It indicates that waves coming from the eastern Pacific are crucial for determining the NAO phase. According to their spatial scales and frequencies when they reach the Atlantic domain, they can break one way or another and push the Atlantic jet equatorward or poleward. Synoptic waves with periods between 5 and 12 days break anticyclonically whereas those with periods between 2 and 5 days break both anticyclonically and cyclonically with a predominance for cyclonic wave breaking. Another crucial factor concerns surface effects. Cyclonic wave breaking in the upper levels is strongly connected with an explosive cyclonic development at the surface accompanied by strong surface moisture fluxes whereas such an explosive growth is not present in the anticyclonic wave breaking case. Finally, it is proposed that these results are not only useful for explaining the intraseasonal variations of the NAO but would serve also as a basis for understanding its interannual and interdecadal variations.

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