The variable link between PNA and NAO in observations and in multi-century CGCM simulations (original) (raw)
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The relationship between the North Atlantic oscillation and El Niño-Southern oscillation
Geophysical Research Letters, 1998
We have applied a multiresolution crossspectral analysis technique to resolve the temporal relationship between the NAO and ENSO. The study shows significant coherence between NAO and Nifio3 SST in about 70% of the warm ENSO events from 1900 to 1995, of which 33% and 37% are associated with a 5-to 6-year period (El) and a 2-to 4-year period (E2) oscillation terms in the spectral decomposition, respectively. The dominant teleconnection pattern associated with changes in the mean atmospheric circulation during the initial winter of a typical E1 and E2 events is the positive phase of the Pacific/North American (PNA) pattern. Non-coherence between the NAO and ENSO occurs during relatively weak Nifio3 SST anomaly, with a teleconnection pattern which shows a strong negative phase of the NAO and a pattern which resembles a weak eastward shifted negative phase of the PNA pattern.
Characteristics of the Recent Eastward Shift of Interannual NAO Variability
Journal of Climate, 2003
Recent observational studies have shown that the centers of action of interannual variability of the North Atlantic Oscillation (NAO) were located farther eastward during winters of the period 1978-97 compared to previous decades of the twentieth century. In this study, which focuses on the winter season (December-March), new diagnostics characterizing this shift are presented. Further, the importance of this shift for NAO-related interannual climate variability in the North Atlantic region is discussed. It is shown that an NAO-related eastward shift in variability can be found for a wide range of different parameters like the number of deep cyclones, near-surface air temperature, and turbulent surface heat flux throughout the North Atlantic region. By using a near-surface air temperature dataset that is homogenous with respect to the kind of observations used, it is shown that the eastward shift is not an artifact of changes in observational practices that took place around the late 1970s. Finally, an EOF-based Monte Carlo test is developed to quantify the probability of changes in the spatial structure of interannual NAO variability for a relatively short (20 yr) time series given multivariate ''white noise.'' It is estimated that the likelihood for differences in the spatial structure of the NAO between two independent 20-yr periods, which are similar (as measured by the angle and pattern correlation between two NAO patterns) to the observed differences, to occur just by chance is about 18%. From the above results it is argued that care has to be taken when conclusions about long-term properties of NAO-related climate variability are being drawn from relatively short recent observational data (e.g., 1978-97).
INTERANNUAL VARIABILITY OF THE LOCATION OF THE MAIN ATLANTIC PRESSURE SYSTEMS AND THE NAO INDEX
The North Atlantic Oscillation (NAO) is a major feature of the Northern Hemisphere climate system. The unprecedented trends it exhibited after the early 60's led some authors to propose human induced climate forcing as a possible cause. The various NAO indices are not able to distinguish the variability associated to the magnitude strengthening/weakening of the action centers and the variability associated with the movement of these centers. Using the NCEP/NCAR reanalysis for the years 1958 till 1998 the positions of the Iceland low-pressure and of the Azores high-pressure systems were tracked down. With the geographic position of these two action centers and the corresponding pressure values, an
Interrelationship between the North Atlantic Oscillation and Solar cycle
Understanding the influence of solar variability on the Earth's climate requires knowledge of solar variability, solar interactions, and the mechanisms explain the response of the Earth's climate system. The NAO (North Atlantic oscillation) is one of the most dominant modes of global climate variability. Like El Niño, La Niña, and the Southern Oscillation, it is considered as free internal oscillation of the climate system not subjected to external forcing. It is shown, to be linked to energetic solar eruptions. Surprisingly, it turns out that features of solar activity have been related to El Niño and La Niña, also have an significant impact on the NAO. The climate of the Atlantic sector exhibits considerable variability on a wide range of time scales. A substantial portion is associated with the North Atlantic Oscillation (NAO), a hemispheric meridional oscillation as atmospheric mass with centers of action near Iceland and over the subtropical Atlantic. NAO-has a related impacts on winter climate extend from Florida to Greenland and from northwestern Africa over Europe far into northern Asian region. In the present work solar cycle 22 was implemented via sun spots number and area and there interrelationship with NAO index and discussed their dependency which consequently that could be used to predict the behavior of NAO index in the next solar cycle as an indicator to climatic variability.
Climate Dynamics, 2002
The influence of zonal and meridional flow on surface temperature in the North Atlantic/European region is investigated. The degree to which the North Atlantic Oscillation (NAO) index reflects these two different flow types is considered, as is the relationship between the NAO index and surface temperature. Zonal and meridional circulation indices extending back to the early nineteenth or eighteenth centuries are based on surface pressure observations from the North Atlantic and Europe and on an empirical orthogonal function (EOF) analysis of European surface pressure from 1845-1995. The NAO index appears to integrate aspects of both zonal and meridional flow types. The pattern associated with the NAO index is composed of a quadrupole correlation pattern with surface temperature, showing positive correlations over Europe and the Sargasso Sea and negative correlations over northwest Africa and the Greenland/Labrador Sea region. Analysis indicates that the relationship between the NAO index and temperatures downstream of the Atlantic is associated with zonal flow, whereas the influence of the NAO on temperatures upstream is more closely linked to meridional flow patterns. Running correlations indicate that while there is no obvious link between the NAO index and the secular temperature trend, the second principal component of temperature is closely linked to atmospheric circulation, with a relationship which in winter has remained fairly steady through the twentieth century. Notwithstanding this, there have been changes in the strength of the correlation between tem-perature and circulation. These fluctuations in climatecirculation relationships should be further investigated and addressed in studies of climate change, especially in the calibration of paleoclimatic time series and downscaling models.
EPL (Europhysics Letters), 2013
We construct a network from climate records of the atmospheric temperature at the surface level, at different geographical sites in the globe, using reanalysis data from years 1948-2010. We find that the network correlates with the North Atlantic Oscillation (NAO), both locally in the North Atlantic, and through coupling to the Southern Pacific Ocean. The existence of tele-connection links between those areas and their stability over time allows us to suggest a possible physical explanation for this phenomenon.
North Atlantic Oscillation and Variations of Geomagnetic Field
Proceedings of the Bulgarian Academy of Sciences
The North Atlantic Oscillation is one of the most influential climatic modes in the Northern Hemisphere. However, the mechanism(s) standing behind its wide spectra of variations is still unknown despite its numerous investigations. This paper presents evidence for a synchronization between secular variations of geomagnetic field intensity and NAO long-term variability. Analysis of the connectivity between geomagnetic secular variations and the sea-level pressure – point by point, in a grid with resolution 10 [deg] in latitude and longitude – reveals that the strength of their relation is unevenly distributed over the Northern Hemisphere. Based on the machine learning analysis over the period 1900–2019, we found that there are two centres of significant geomagnetic-pressure relations – the weaker of them is placed slightly north of Iceland, and the stronger one is in a close proximity to Azores islands. The suggested mechanism for geomagnetic influence on the near surface climatic co...
Dynamics of Atmospheres and Oceans, 2008
In this paper we discuss the atmospheric dynamics of the North Atlantic Oscillation (NAO), the zonal index, and annular patterns of variability (also known as annular modes). Our goal is to give a unified treatment of these related phenomena, to make explicit how they are connected and how they differ, and to illustrate their dynamics with the aid of an idealized primitive equation model. Our focus is on tropospheric dynamics.