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  • Springer  (1)
  • Wiley  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Stochastic environmental research and risk assessment 14 (2000), S. 213-242 
    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract.  The North Atlantic Oscillation (NAO) is the most important mode of variability in the northern hemisphere (NH) atmospheric circulation. Put simply, the NAO measures the strength of the westerly winds blowing across the North Atlantic Ocean between 40°N and 60°N. The NAO is not a regional, North Atlantic phenomenon, however, but rather is hemispheric in extent. Based on 60 years of data from 1935 to 1995, Hurrell (1996) estimates that the NAO accounts for 31% of the variance in hemispheric winter surface air temperature north of 20°N. The present article provides an overview of the NAO, its role in the atmospheric circulation, its close relationship to the Arctic Oscillation of Thompson and Wallace (1998), and its influence on the underlying North Atlantic Ocean. Some discussion is also given on the dynamics of the NAO, the possible role of ocean surface temperature, and recent evidence that the stratosphere plays an important role in modulating the NAO.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2024-02-07
    Description: In austral winter, biological productivity at the Angolan shelf reaches its maximum. The alongshore winds, however, reach their seasonal minimum suggesting that processes other than local wind‐driven upwelling contribute to near‐coastal cooling and upward nutrient supply, one possibility being mixing induced by internal tides (ITs). Here, we apply a three‐dimensional ocean model to simulate the generation, propagation, and dissipation of ITs at the Angolan continental slope and shelf. Model results are validated against moored acoustic Doppler current profiler and other observations. Simulated ITs are mainly generated in regions with a critical/supercritical slope typically between the 200‐ and 500‐m isobaths. Mixing induced by ITs is found to be strongest close to the coast and gradually decreases offshore thereby contributing to the establishment of cross‐shore temperature gradients. The available seasonal coverage of hydrographic data is used to design simulations to investigate the influence of seasonally varying stratification characterized by low stratification in austral winter and high stratification in austral summer. The results show that IT characteristics, such as their wavelengths, sea surface convergence patterns, and baroclinic structure, have substantial seasonal variations and additionally strong spatial inhomogeneities. However, seasonal variations in the spatially averaged generation, onshore flux, and dissipation of IT energy are weak. By evaluating the change of potential energy, it is shown, nevertheless, that mixing due to ITs is more effective during austral winter. We argue that this is because the weaker background stratification in austral winter than in austral summer acts as a preconditioning for IT mixing.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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