Source locations of microseisms in the North Atlantic from Matched Field Processing using full Green's Functions.

2021 ◽  
Author(s):  
Sven Schippkus ◽  
Céline Hadziioannou
Keyword(s):  
Wave Propagation ◽  
Travel Time ◽  
North Atlantic ◽  
Seismic Noise ◽  
Green's Functions ◽  
Green’S Functions ◽  
Regional Scale ◽  
Matched Field Processing ◽  
The North ◽  
The North Atlantic

<p>Precise knowledge of the sources of seismic noise is fundamental to our understanding of the ambient seismic field and its generation mechanisms. Two approaches to locating such sources exist currently. One is based on minimizing the misfit between estimated Green's functions from cross-correlation of seismic noise and synthetically computed correlation functions. This approach is computationally expensive and not yet widely adopted. The other, more common approach is Beamforming, where a beam is computed by shifting waveforms in time corresponding to the slowness of a potentially arriving wave front. Beamforming allows fast computations, but is limited to the plane-wave assumption and sources outside of the array.</p><p>Matched Field Processing (MFP) is Beamforming in the spatial domain. By probing potential source locations directly, it allows for arbitrary wave propagation in the medium as well as sources inside of arrays. MFP has been successfully applied at local scale using a constant velocity for travel-time estimation, sufficient at that scale. At regional scale, travel times can be estimated from phase velocity maps, which are not yet available globally at microseism frequencies.</p><p>To expand MFP’s applicability to new regions and larger scales, we replace the replica vectors that contain only travel-time information with full synthetic Green's functions. This allows to capture the full complexity of wave propagation by including relative amplitude information between receivers and multiple phases. We apply the method to continuous recordings of stations surrounding the North Atlantic and locate seismic sources in the primary and secondary microseism band, using pre-computed databases of Green's functions for computational efficiency. The framework we introduce here can easily be adapted to a laterally homogeneous Earth once such Green’s function databases become available, hopefully in the near future.</p>

scholarly journals Influence of the North Atlantic oscillation on the atmospheric levels of benzo[a]pyrene over Europe

2021 ◽  
Author(s):  
Pedro Jiménez-Guerrero ◽  
Nuno Ratola
Keyword(s):  
Spatial Pattern ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Transport Model ◽  
Regional Scale ◽  
The South ◽  
Climatic Fluctuations ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

AbstractThe atmospheric concentration of persistent organic pollutants (and of polycyclic aromatic hydrocarbons, PAHs, in particular) is closely related to climate change and climatic fluctuations, which are likely to influence contaminant’s transport pathways and transfer processes. Predicting how climate variability alters PAHs concentrations in the atmosphere still poses an exceptional challenge. In this sense, the main objective of this contribution is to assess the relationship between the North Atlantic Oscillation (NAO) index and the mean concentration of benzo[a]pyrene (BaP, the most studied PAH congener) in a domain covering Europe, with an emphasis on the effect of regional-scale processes. A numerical simulation for a present climate period of 30 years was performed using a regional chemistry transport model with a 25 km spatial resolution (horizontal), higher than those commonly applied. The results show an important seasonal behaviour, with a remarkable spatial pattern of difference between the north and the south of the domain. In winter, higher BaP ground levels are found during the NAO+ phase for the Mediterranean basin, while the spatial pattern of this feature (higher BaP levels during NAO+ phases) moves northwards in summer. These results show deviations up to and sometimes over 100% in the BaP mean concentrations, but statistically significant signals (p<0.1) of lower changes (20–40% variations in the signal) are found for the north of the domain in winter and for the south in summer.

scholarly journals The onset of the North Atlantic Igneous Province in a rifting perspective

2009 ◽  
Vol 146 (3) ◽  
pp. 309-325 ◽  
Author(s):  
J. HANSEN ◽  
D. A. JERRAM ◽  
K. McCAFFREY ◽  
S. R. PASSEY
Keyword(s):  
North Atlantic ◽  
Regional Scale ◽  
The North ◽  
Time Space ◽  
Lithospheric Extension ◽  
Igneous Province ◽  
The North Atlantic ◽  
North Atlantic Igneous Province ◽  
North Atlantic Area ◽  
Atlantic Area

AbstractThe processes that led to the onset and evolution of the North Atlantic Igneous Province (NAIP) have been a theme of debate in the past decades. A popular theory has been that the impingement on the lower lithosphere of a hot mantle plume (the ‘Ancestral Iceland’ plume) initiated the first voluminous outbursts of lava and initiated rifting in the North Atlantic area in Early Palaeogene times. Here we review previous studies in order to set the NAIP magmatism in a time–space context. We suggest that global plate reorganizations and lithospheric extension across old orogenic fronts and/or suture zones, aided by other processes in the mantle (e.g. local or regional scale upwellings prior to and during the final Early Eocene rifting), played a role in the generation of the igneous products recorded in the NAIP for this period. These events gave rise to the extensive Paleocene and Eocene igneous rocks in W Greenland, NW Britain and at the conjugate E Greenland–NW European margins. Many of the relatively large magmatic centres of the NAIP were associated with transient and geographically confined doming in Early Paleocene times prior to the final break-up of the North Atlantic area.

scholarly journals Dynamics of the Northern Annular Mode at Weekly Time Scales

2015 ◽  
Vol 72 (12) ◽  
pp. 4569-4590 ◽  
Author(s):  
Gwendal Rivière ◽  
Marie Drouard
Keyword(s):  
Wave Propagation ◽  
North America ◽  
North Atlantic ◽  
North Pacific ◽  
Low Frequency ◽  
Northern Annular Mode ◽  
The North ◽  
Momentum Fluxes ◽  
The North Atlantic ◽  
The North Pacific

Abstract Rapid onsets of positive and negative tropospheric northern annular mode (NAM) events during boreal winters are studied using ERA-Interim datasets. The NAM anomalies first appear in the North Pacific from low-frequency Rossby wave propagation initiated by anomalous convection in the western tropical Pacific around 2 weeks before the peak of the events. For negative NAM, the enhanced convection leads to a zonal acceleration of the Pacific jet, while for positive NAM, the reduced convection leads to a poleward-deviated jet in its exit region. The North Atlantic anomalies, which correspond to North Atlantic Oscillation (NAO) anomalies, are formed in close connection with the North Pacific anomalies via downstream propagation of low-frequency planetary-scale and high-frequency synoptic waves, the latter playing a major role during the last onset week. Prior to positive NAM, the generation of synoptic waves in the North Pacific and their downstream propagation is strong. The poleward-deviated Pacific jet favors a southeastward propagation of the waves across North America and anticyclonic breaking in the North Atlantic. The associated strong poleward eddy momentum fluxes push the Atlantic jet poleward and form the positive NAO phase. Conversely, prior to negative NAM, synoptic wave propagation across North America is significantly reduced and more zonal because of the more zonally oriented Pacific jet. This, together with a strong eddy generation in the North Atlantic, leads to equatorward eddy momentum fluxes, cyclonic wave breaking, and the formation of the negative NAO phase. Even though the stratosphere may play a role in some individual cases, it is not the main driver of the composited tropospheric NAM events.

Seismic P- and S-wave velocity Tomography in Scandinavia

2020 ◽  
Author(s):  
Nevra Bulut ◽  
Valerie Maupin ◽  
Hans Thybo
Keyword(s):  
Travel Time ◽  
North Atlantic ◽  
Upper Mantle ◽  
Body Waves ◽  
Significant Heterogeneity ◽  
Finite Frequency ◽  
S Wave ◽  
The North ◽  
The North Atlantic ◽  
High Topography

&lt;p&gt;The causes of the high topography in Scandinavia along the North Atlantic passive continental margins are enigmatic, and two end-member models have been proposed. One opinion is that the high topography has been maintained since the Caledonian orogeny, because isostatic rebound has compensated for most of the erosion over &gt;400 My. The other opinion is that the topography is Cenozoic and that it is related to plate tectonic or deep thermal / geodynamic processes. Onshore uplift is related to simultaneous offshore subsidence, and the rapid topographic changes may be the combined result of a series of complementary processes.&lt;/p&gt;&lt;p&gt;Here, we provide new evidence for the upper mantle structure by calculating a tomographic model for Fennoscandia (Scandinavia and Finland) by teleseismic inversion of finite-frequency P- and S- wave travel-time residuals. We use seismic signals from earthquakes at epicentral distances between 30&amp;#176; and 104&amp;#176; and with magnitudes larger than 5.5, gathered on 200 broad-band seismic stations installed by the ScanArray project in Norway, Sweden and Finland, which operated during 2012-2017, together with data from earlier projects and stationary stations..&lt;/p&gt;&lt;p&gt;We measure relative travel-time residuals of direct body waves in high- and low-frequency bands, and carry out an appropriate frequency-dependent crustal correction. The average residuals vary over the region, and show clear trends depending on location and and back-azimuthal directions. This demonstrates the presence of significant heterogeneity of seismic velocities in the upper mantle across the region. Based on the travel-time residuals&lt;strong&gt;,&lt;/strong&gt; we carry out finite-frequency body-wave tomographic inversion to determine the P and S wave seismic velocity structure of the upper-mantle. By use of &amp;#8220;relative kernels&amp;#8221; we reduce problems related to station coverage with asynchronous datasets, which allows the use of data from different deployments for the inversion. The resulting seismic model is compared to the existing and past topography in order to contribute to the understanding of mechanisms responsible for the topographic changes in the Fennoscandian region, which we relate to the general tectonic and geological evolution of the North Atlantic region. The models provide basis for deriving high-resolution models of temperature and compositional anomalies that may contribute to the understanding of the observed, enigmatic topography.&lt;/p&gt;

scholarly journals Deep drilling results of Leg 47b (Galicia Bank area) in the framework of the early evolution of the North Atlantic Ocean

1980 ◽  
Vol 294 (1409) ◽  
pp. 51-61 ◽  
Keyword(s):  
Atlantic Ocean ◽  
Continental Margin ◽  
North Atlantic ◽  
Lower Cretaceous ◽  
North Atlantic Ocean ◽  
Regional Scale ◽  
Upper Jurassic ◽  
Borehole Data ◽  
The North ◽  
The North Atlantic

Lithologic and stratigraphic evidence from D.S.D.P. Site 398 (3910 m water depth, 1740m total penetration) and regional seismic reflexion data are placed in the context of the early tectonic evolution of the North Atlantic ocean. The morphology of the western Iberian continental margin is the result of two main tensional episodes dated Permo— Lias and Upper Jurassic - Lower Cretaceous, during which the initial basins between Grand Banks and Iberia were created by subsidence and tilting of continental blocks. A limited oceanic opening had probably occurred in Jurassic time between these two tensional episodes. There was no relative motion during Lower Cretaceous between North America and Iberia. One of the main results is that the 398 drillhole penetrated into the basement structure of a tilted block of the continental margin. Borehole data indicate an Uppermost Aptian age for the end of the Upper Jurassic - Lower Cretaceous tensional episode at the level of the site. The subsequent beginning of sea floor spreading in the Uppermost Aptian is associated with a change of sedimentary facies from graded sequences interbedded with slump beds or debris flows to dark, detritic shales. The continental margin had subsided on a regional scale since this time.

scholarly journals The Development of a Statistical Forecast Model for Changma

2013 ◽  
Vol 28 (6) ◽  
pp. 1304-1321 ◽  
Author(s):  
Seung-Eon Lee ◽  
Kyong-Hwan Seo
Keyword(s):  
Wave Propagation ◽  
North Atlantic ◽  
North Pacific ◽  
Forecast Model ◽  
Tropical Pacific ◽  
The North ◽  
Sst Anomaly ◽  
The North Atlantic ◽  
The North Pacific ◽  
The Tropical Pacific

Abstract Forecasting year-to-year variations in East Asian summer monsoon (EASM) precipitation is one of the most challenging tasks in climate prediction because the predictors are not sufficiently well known and the forecast skill of the numerical models is poor. In this paper, a statistical forecast model for changma (the Korean portion of the EASM system) precipitation is proposed that was constructed with three physically based predictors. A forward-stepwise regression was used to select the predictors that included sea surface temperature (SST) anomalies over the North Pacific, the North Atlantic, and the tropical Pacific Ocean. Seasonal predictions with this model showed high forecasting capabilities that had a Gerrity skill score of ~0.82. The dynamical processes associated with the predictors were examined prior to their use in the prediction scheme. All predictors tended to induce an anticyclonic anomaly to the east or southeast of Japan, which was responsible for transporting a large amount of moisture to the southern Korean Peninsula. The predictor in the North Pacific formed an SST front to the east of Japan during the summertime, which maintained a lower-tropospheric baroclinicity. The North Atlantic SST anomaly induced downstream wave propagation in the upper troposphere, developing anticyclonic activity east of Japan. Forcing from the tropical Pacific SST anomaly triggered a cyclonic anomaly over the South China Sea, which was maintained by atmosphere–ocean interactions and induced an anticyclonic anomaly via northward Rossby wave propagation. Overall, the model used for forecasting changma precipitation performed well (R = 0.85) and correctly predicted information for 16 out of 19 yr of observational data.

scholarly journals IWV retrieval from ground GNSS receivers during NAWDEX

2021 ◽  
Vol 55 ◽  
pp. 13-22
Author(s):  
Pierre Bosser ◽  
Olivier Bock
Keyword(s):  
Water Vapor ◽  
North Atlantic ◽  
Regional Scale ◽  
Satellite System ◽  
Tropospheric Delay ◽  
Spatial And Temporal Variability ◽  
Data Set ◽  
The North ◽  
The North Atlantic ◽  
Global Navigation Satellite

Abstract. A ground-based network of more than 1200 Global Navigation Satellite System (GNSS) Continuously Operating Reference Stations (CORS) was analysed using GIPSY-OASIS II software package for the documentation of time and space variations of water vapor in atmosphere during the North Atlantic Waveguide and Downstream impact EXperiment (NAWDEX) during fall 2016. The network extends throughout the North Atlantic, from the Caribbeans to Morocco through Greenland. This paper presents the methodology used for GNSS data processing, screening, and conversion of Zenith Tropospheric Delay (ZTD) estimates to Integrated Water Vapor content (IWV) using surface parameters from reanalysis. The retrieved IWV are used to evaluate the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalyses ERAI and ERA5. ERA5 shows an overall improvement over ERAI in representing the spatial and temporal variability of IWV over the study area. The mean bias is decreased from 0.31±0.63 to 0.19±0.56 kg m−2 (mean ±1σ over all stations) and the standard deviation reduced from 2.17±0.67 to 1.64±0.53 kg m−2 combined with a slight improvement in correlation coefficient from 0.95 to 0.97. At regional scale, both reanalyses show a general wet bias at mid and northern latitudes but a dry bias in the Caribbeans. We hypothesize this results from the different nature of data being assimilated over the tropical oceans. This GNSS IWV data set is intended to be used for a better description of the high impact weather events that occurred during the NAWDEX experiment.

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