Reconstruction of the North Atlantic Oscillation variability and its response to anthropogenic forcing using data-driven stochastic models based on artificial neural networks

2021 ◽  
Author(s):  
Aleksei Seleznev ◽  
Andrey Gavrilov ◽  
Dmitry Mukhin ◽  
Alexander Feigin
2005 ◽  
Vol 18 (12) ◽  
pp. 2102-2118 ◽  
Author(s):  
Edwin P. Gerber ◽  
Geoffrey K. Vallis

Abstract Meridional dipoles of zonal wind and geopotential height are found extensively in empirical orthogonal function (EOF) analysis and single-point correlation maps of observations and models. Notable examples are the North Atlantic Oscillation and the so-called annular modes (or the Arctic Oscillation). Minimal stochastic models are developed to explain the origin of such structure. In particular, highly idealized, analytic, purely stochastic models of the barotropic, zonally averaged zonal wind and of the zonally averaged surface pressure are constructed, and it is found that the meridional dipole pattern is a natural consequence of the conservation of zonal momentum and mass by fluid motions. Extension of the one-dimensional zonal wind model to two-dimensional flow illustrates the manner in which a local meridional dipole structure may become zonally elongated in EOF analysis, producing a zonally uniform EOF even when the dynamics is not particularly zonally coherent on hemispheric length scales. The analytic system then provides a context for understanding the existence of zonally uniform patterns in models where there are no zonally coherent motions. It is also shown how zonally asymmetric dynamics can give rise to structures resembling the North Atlantic Oscillation. Both the one- and two-dimensional results are manifestations of the same principle: given a stochastic system with a simple red spectrum in which correlations between points in space (or time) decay as the separation between them increases, EOF analysis will typically produce the gravest mode allowed by the system’s constraints. Thus, grave dipole patterns can be robustly expected to arise in the statistical analysis of a model or observations, regardless of the presence or otherwise of a dynamical mode.


2021 ◽  
Author(s):  
Pedro Jiménez-Guerrero ◽  
Nuno Ratola

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.


1997 ◽  
Vol 42 (11) ◽  
pp. 927-931 ◽  
Author(s):  
Yonghong Zhou ◽  
Dawei Zheng ◽  
Benjamin Fong Chao

2014 ◽  
Vol 62 (3) ◽  
pp. 169-176 ◽  
Author(s):  
Miriam Fendeková ◽  
Pavla Pekárová ◽  
Marián Fendek ◽  
Ján Pekár ◽  
Peter Škoda

Abstract Changes in runoff parameters are very important for Slovakia, where stream-flow discharges, being supplied by precipitation and groundwater runoff, are preferentially influenced by climatic conditions. Therefore, teleconnections between runoff parameters, climate parameters and global atmospheric drivers such as North Atlantic Oscillation, Southern Pacific Oscillation, Quasi-biennial oscillation and solar activity were studied in the Nitra River Basin, Slovakia. Research was mostly based on records of 80 years (1931-2010) for discharges and baseflow, and 34 years for groundwater heads. Methods of autocorrelation, spectral analysis, cross-correlation and coherence function were used. Results of auto- correllograms for discharges, groundwater heads and base flow values showed a very distinct 11-year and 21-year periodicity. Spectrogram analysis documented the 11-year, 7.8-year, 3.6-year and 2.4-year periods in the discharge, precipitation and air temperature time series. The same cycles except of 11-years were also identified in the long-term series of the North Atlantic Oscillation and Southern Pacific Oscillation indices. The cycle from approximately 2.3 to 2.4-years is most likely connected with Quasi-biennial oscillation. The close negative correlation between the North Atlantic Oscillation winter index and the hydrological surface and groundwater parameters can be used for their prediction within the same year and also for one year in advance.


SOLA ◽  
2017 ◽  
Vol 13 (0) ◽  
pp. 209-213 ◽  
Author(s):  
Naoaki Saito ◽  
Shuhei Maeda ◽  
Tosiyuki Nakaegawa ◽  
Yuhei Takaya ◽  
Yukiko Imada ◽  
...  

2017 ◽  
Vol 205 ◽  
pp. 855-867 ◽  
Author(s):  
Andrew N. Commin ◽  
Andrew S. French ◽  
Matteo Marasco ◽  
Jennifer Loxton ◽  
Stuart W. Gibb ◽  
...  

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