Predictability and Non-Gaussian Characteristics of the North Atlantic Oscillation

Önskog, Thomas; Franzke, Christian; Hannachi, Abdel

doi:10.1175/jcli-d-17-0101.1

Cited by 11 publications

(5 citation statements)

References 55 publications

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“…As the influence of the westerly winds weakened during the MCA in Iberia, Nieto‐Moreno et al () assume that the concurrent intensification of upwelling in the Alboran Sea was related to Mediterranean strengthening of cyclonic circulation (cyclogenesis) rather than by the westerly wind system. The westerlies must have been shifted northward during the MCA, which typically occurs at times of the positive phase of the North Atlantic Oscillation (NAO+) at this latitude (Moreno et al, ; Önskog et al, ). A NAO reconstruction by Baker et al () from a speleothem in Scotland confirms that NAO+ conditions prevailed during the MCA (Figures and ).…”

Section: Discussionmentioning

confidence: 99%

The Medieval Climate Anomaly in the Mediterranean Region

Lüning¹,

Schulte

Garcés‐Pastor

et al. 2019

Paleoceanog and Paleoclimatol

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The Medieval Climate Anomaly (MCA) is a preindustrial phase of pronounced natural climate variability with a core period from 1000 to 1200 CE. The paper presents a synthesis that integrates palaeotemperature records from the Greater Mediterranean Region encompassing the past 1,500 years based on multiproxy data from 79 published land and marine sites. MCA warming dominated the Western Mediterranean (Iberia, NW Africa) as well as the northern land areas of the Central and Eastern Mediterranean region. MCA cooling prevailed in the Canary Current Upwelling System, southern Levant, and some sea areas of the Central and Eastern Mediterranean. Previous palaeoreconstructions suggest persistent positive Atlantic Multidecadal Oscillation (AMO+) and North Atlantic Oscillation (NAO+) conditions during the MCA, while the Little Ice Age was dominated by an AMO− and NAO− regime. During the past 150 years, AMO+ conditions are typically associated with warming episodes in the Mediterranean area. A similar relationship appears to have also been established during the MCA as the majority of all Mediterranean land sites experienced warm climate conditions. In contrast, the NAO typically leads to a characteristic west‐east temperature dipole pattern in the basin, as documented for the last decades. During NAO+ conditions the Western Mediterranean is generally warm (and dry), while large parts of the Central and Eastern Mediterranean are cold. Similar trends seem to have been developed during the MCA when the NAO+ regime led to consistent warming in the Western Mediterranean, while a significant number of sites with MCA cooling existed in the Central and Eastern Mediterranean.

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Section: Discussionmentioning

confidence: 99%

The Medieval Climate Anomaly in the Mediterranean Region

Lüning¹,

Schulte

Garcés‐Pastor

et al. 2019

Paleoceanog and Paleoclimatol

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“…Finally, Önskog et al. (2018) confirmed the decorrelation time scale of around 10 days but in addition found long‐range dependence in the daily NAO index. These studies do not, however, analyze NAO + and NAO − events separately, and therefore they do not find the important differences in preconditioning between NAO + and NAO − events, as we do here.…”

Section: Discussionmentioning

confidence: 84%

Asymmetries in Circulation Anomalies Related to the Phases of the North Atlantic Oscillation on Synoptic Time Scales

Schmith

Olsen

Yang

et al. 2022

Geophysical Research Letters

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The North Atlantic Oscillation (NAO) index is often characterized by independent positive and negative NAO events with a characteristic spatial pattern and a typical lifetime of around 1 week. These events are separated by periods of near‐neutral NAO conditions. Here, we challenge this view by showing in reanalysis and observed data that the strength and spatial shape of NAO events depends on the NAO index prior to the window of 1 week and this dependency is most pronounced for negative NAO events. The influence is seen in the mean sea level pressure, and in other important features, including blocking frequency and jet stream characteristics, and also in air surface temperature and precipitation in parts of Europe. This new appreciation is important for efforts to improve methods for subseasonal‐to‐seasonal predictions of NAO.

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“…Negative NAO events are associated with increased occurrence of blocking episodes (Woollings et al., 2008) which are often hard to predict. Asymmetries between positive and negative NAO forecasts indicates a violation of linearity/Gaussianity, and may arise due to the effects of skew (Stephenson et al., 2004), flow‐dependent predictability (Ferranti et al., 2015; Frame et al., 2013; Matsueda & Palmer, 2018), or non‐linearities and state dependence (Önskog et al., 2018, 2020) such as that expected from regime dynamics (Strommen, 2020). Our results suggest that taking into account such asymmetries may help shed light on the “paradox.”…”

Section: Discussionmentioning

confidence: 99%