The influence of ocean-surface-velocity-dependent wind stress on the dynamics of the Southern Ocean: The near-inertial and the sub-inertial response.

Rath, Willi (2013) The influence of ocean-surface-velocity-dependent wind stress on the dynamics of the Southern Ocean: The near-inertial and the sub-inertial response. Open Access (PhD/ Doctoral thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 113 pp.

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Abstract

This thesis examines the consequences of the ocean-surface-velocity dependence of the wind stress (SVD) for the dynamics of the Southern Ocean. It does so by comparing the output from eddying ocean-model experiments that only differ in the way the wind stress is parameterized. The thesis consists of three separate research papers. The first paper assesses the influence of SVD on the near-inertial variability. It is shown that SVD leads to a substantial reduction of horizontally averaged near-inertial energy (NIE) and of horizontally averaged wind power input (WPI) into the near-inertial frequency band. The observed reduction of NIE and near-inertial WPI is explained by the fact that SVD, to leading order, adds a linear damping term to the momentum equation governing near-inertial oscillations in the mixed-layer. This damping term is inversely proportional to the mixed-layer depth and hence the effect of SVD on near-inertial oscillations is found to be largest if the mixed-layer is shallow. The second paper assesses the influence of SVD on sub-inertial time scales. It is found that SVD also substantially reduces sub-inertial WPI and mesoscale eddy kinetic energy (EKE). The largest effect of SVD on sub-inertial WPI and EKE is found along the path of the Antarctic Circumpolar Current (ACC). SVD is found to generally damp the amplitude of monthly to inter-annual variability in the model, without affecting the time-dependence of the wind stress, of WPI, and of the strength of the ACC. SVD is, however, found to have only a minor impact on the path and strength of the ACC. The third paper connects to the first one by focussing on the spatial and temporal distribution of NIE and near-inertial WPI in the Southern Ocean. The modelled near-inertial WPI is found to be mainly governed by the variability of the wind-stress at the local inertial frequency (IWSV). This relationship is used to indirectly examine the temporal evolution of near-inertial WPI on time scales much longer than those which can be directly examined with the model. It is found that from 1979 to 2011 IWSV over the Southern Ocean has increased substantially. Furthermore, the inter-annual variability of IWSV in the Southern Ocean is shown to be largely governed by the Southern Annular Mode.

Document Type: Thesis (PhD/ Doctoral thesis)
Thesis Advisors: Greatbatch, Richard John and Brandt, Peter
Keywords: Near-Inertial Oscillations; Ocean Modelling; Wind Forcing; Traegheitswellen; Ozeanmodelle; Wind-Antrieb
Research affiliation: OceanRep > SFB 754 > A2
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-TM Theory and Modeling
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-PO Physical Oceanography
OceanRep > SFB 754
Open Access Journal?: Yes
Date Deposited: 09 Jan 2014 10:36
Last Modified: 10 Mar 2017 08:30
URI: http://oceanrep.geomar.de/id/eprint/22949

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