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Seabirds as Indicators of Oceanographic Changes
Published in Jaime A. Ramos, Leonel Pereira, Seabird Biodiversity and Human Activities, 2022
The NAO index frames a north-south shift in atmospheric mass (pressure) between the Arctic and the subtropical Atlantic. This is known to influence patterns of wind intensity and direction, precipitation, air and sea temperature and current strength and upwelling intensity (Stenseth et al. 2003). In the North Atlantic region, a positive NAO index is characterised by prevailing westerly winds moving northwards, with increased frequency of stormy weather and precipitation both at-sea and inland. Contemporaneously, the southern area of the North Atlantic and Mediterranean Sea should experience the opposite climatological and oceanographic conditions, with fewer storms and dry weather. During a negative phase of NAO, there is a shift in these patterns, with the northern section of the Atlantic and Arctic Oceans experiencing fewer storms (Stenseth et al. 2002). Variability in NAO has been shown to be correlated with changes in local oceanographic regimes, such as values of SST, patterns of marine productivity, abundance and availability of prey, and subsequently with various seabird measures (Oro 2014). Yet, there is also some evidence supporting the idea that the NAO might not always be correlated with trends in SST and for instance, SST explained most of the variation in adult survival of Common Guillemot (Uria aalge) in the Arctic Ocean (Sandvik et al. 2012).
Floods in the Iberian Peninsula
Published in Zbigniew W. Kundzewicz, Changes in Flood Risk in Europe, 2019
Gerardo Benito, Maria J. Machado
The position of the zonal circulation in Western Europe can be characterized by the North Atlantic Oscillation index (NAO), measured by pressure differences between Iceland and the subtropical Atlantic (from the Azores across to the Iberian Peninsula; Walker & Bliss, 1932; van Loon & Rogers, 1978). Connections have been observed between this pressure difference and the distribution of winter rainfall and discharge in the Atlantic basins of the Iberian Peninsula (Trigo et al., 2004; López et al., 2010), and in particular with flooding on the Guadiana and Guadalquivir rivers (Ortega & Garzón, 2004; Benito et al., 2005). Periods with the NAO in a negative phase are associated with wetter conditions in the western Mediterranean and northern Africa (Wanner et al., 1994; Rodríguez-Puebla et al., 2001) and cold air in northern Europe. Furthermore, a study of the wintertime (DJF) correlation between the NAO index and the streamflow of Iberian Atlantic rivers (Trigo et al., 2004) points towards a southward increase of the sensitivity of the basins to the NAO with a correlation value of –0.79 for the Guadiana River, followed by the Tagus (–0.77) and Duero (–0.76). Recent studies have shown that the NAO index decreases during secular maxima of solar activity and increases during periods of decreased solar activity (Kirov & Georgieva, 2002). Since the NAO is a natural mode of atmospheric variability, it is uncertain how anthropogenic climate change might influence modes of the NAO (Corti et al. 1999; Hurrell et al., 2003), and subsequently the winter rainfall excess and flooding over NAO sensitive areas of the Iberian Peninsula.
Arctic Oscillation
Published in Yeqiao Wang, Atmosphere and Climate, 2020
North Atlantic Oscillation (NAO) is a seesaw-like dipole oscillation along the Atlantic sector and defined by the difference of air pressure between Iceland and the Azores.[12,13] NAO was discovered in the 1920s by Walker[14] and has been studied extensively.115- Since the NAO index correlates well with the AOI,[16- some studies focused on the physical reality of the AO and the connection between AO and NAO.
Introducing driving-force information increases the predictability of the North Atlantic Oscillation
Published in Atmospheric and Oceanic Science Letters, 2019
Xinnong PAN, Geli WANG, Peicai YANG
The North Atlantic Oscillation (NAO) acts as one of the most dominant modes of global climate variability, affecting the weather patterns over the North Atlantic Ocean, North America, Europe, and even the entire Northern Hemisphere (Wallace and Gutzler 1981; Hurrell 1995; Li, Sun, and Jin 2013; Jajcay et al. 2016; Delworth et al. 2016). On the one hand, the NAO is believed to be generated by internal atmospheric processes (i.e. eddy–mean-flow interaction of the atmosphere (Barnes and Hartmann 2010) and atmospheric responses to external forces, i.e. oceanic forcing (Rodwell, Rowell, and Folland 1999; Keenlyside et al. 2008)); whilst on the other hand, the NAO is considered as a forcing agent for the interannual and multidecadal variability of sea surface temperature and oceanic circulation (Nicolay et al. 2009; Li, Sun, and Jin 2013).
North Atlantic weather regimes in δ18O of winter precipitation: isotopic fingerprint of the response in the atmospheric circulation after volcanic eruptions
Published in Tellus B: Chemical and Physical Meteorology, 2019
Hera GuðlaugsdÓttir, Jesper Sjolte, ÁrnÝ Erla Sveinbjörnsdóttir, Martin Werner, Hans Christian Steen-Larsen
In this study, we establish the water isotopic fingerprint associated with each of the four major modes of North Atlantic (NA) climate variability. The dominating weather regimes in the NA are the positive and negative phases of the North Atlantic Oscillation (NAO), defined as deviations from the mean (normalized) zonal pressure difference between the Icelandic Low and the Azores High. Pressure differences between these centres control the strength of the zonal wind flow (the westerlies) over the NA and therefore the climate and weather around the NA. The other two weather regimes are the AtR, also known as the positive phase of the East Atlantic (EA) pattern, and the ScB. These regimes tend to be in anti-phase with each other where the pressure centres are located just south of Greenland and over central Europe/Scandinavia. During either AtR or ScB, the wind flow is more meridional compared to during NAO and therefore also the storm track. These four weather regimes have been identified as being part of the climate variability recorded in the stable isotopes of Greenland ice cores (Ortega et al., 2014; Rimbu et al., 2017). By using the output of an isotope-enabled general circulation model (ECHAM5-wiso) and observations, Comas-Bru et al. (2016) found that the EA pattern was generally uncorrelated with δ18O in precipitation over Europe. However, they found that the polarity of the EA pattern influenced the δ18O–NAO relationship. Especially when both NAO and EA pattern were positive, NAO + and AtR occurring simultaneously, the jet stream migrated northward.
Spatio-temporal variability of drought and effect of large scale climate in the source region of Yellow River
Published in Geomatics, Natural Hazards and Risk, 2019
Yadi Wang, Quan Quan, Bing Shen
NAO is the main source region of inter-annual climatic variation in the Northern Hemisphere (Hurrell and Van Loon 1997); it influences the westerlies, thereby affecting vapour transmission and radiation above the Tibet Plateau. Therefore, NAO influences precipitation in the study area and changes in SPEI. In the middle latitude, NAO and AO reflect the strength of the westerlies, which cause important and extensive impacts on climatic changes in the Northern Hemisphere. Fluctuations in NAO and AO significantly influence climatic factors, such as air temperature, precipitation, and snow cover. Cross wavelet analysis revealed that the occurrence and periods of signals of NAO and AO in high-energy and low-energy regions are similar and that NAO has stronger impacts than AO.