TY - JOUR

T1 - Joint modelling of vertical profiles of large ocean currents

AU - Jonathan, P.

AU - Ewans, K.

AU - Flynn, J.

PY - 2012

Y1 - 2012

N2 - We present an empirical approach to modelling the vertical (vector) profile of large ocean currents, based on a conditional extremes model (Heffernan and Tawn, 2004) from the statistics literature. Observed vector currents at each of a number of water depths are expressed as components with respect to major- and minor-axis of current variation at that depth using Principal Components Analysis. Each current component is then independently decomposed into the sum of (deterministic periodic) tidal and (random) non-tidal currents using a local harmonic model. The marginal and dependence structure of extremes of hourly maxima and minima of non-tidal components is characterised using the conditional extremes model. We simulate under this model to estimate characteristics of extreme current profiles corresponding to arbitrary return periods, and quantify the uncertainty of those estimates. For a sample collected over a 2.5-year period in 250 m water on the outer shelf of North Western Australia, the model predicts monthly instantaneous extreme conditional profiles well. We also estimate marginal and conditional current profiles corresponding to a 10-year return period. © 2011 Elsevier Ltd.

AB - We present an empirical approach to modelling the vertical (vector) profile of large ocean currents, based on a conditional extremes model (Heffernan and Tawn, 2004) from the statistics literature. Observed vector currents at each of a number of water depths are expressed as components with respect to major- and minor-axis of current variation at that depth using Principal Components Analysis. Each current component is then independently decomposed into the sum of (deterministic periodic) tidal and (random) non-tidal currents using a local harmonic model. The marginal and dependence structure of extremes of hourly maxima and minima of non-tidal components is characterised using the conditional extremes model. We simulate under this model to estimate characteristics of extreme current profiles corresponding to arbitrary return periods, and quantify the uncertainty of those estimates. For a sample collected over a 2.5-year period in 250 m water on the outer shelf of North Western Australia, the model predicts monthly instantaneous extreme conditional profiles well. We also estimate marginal and conditional current profiles corresponding to a 10-year return period. © 2011 Elsevier Ltd.

KW - Current profile

KW - Extreme

KW - Joint modelling

KW - Current component

KW - Empirical approach

KW - Harmonic model

KW - Principal components analysis

KW - Return periods

KW - Vertical profile

KW - Water depth

KW - Western Australia

KW - Estimation

KW - Ocean currents

KW - Principal component analysis

KW - Uncertainty analysis

KW - continental shelf

KW - current velocity

KW - empirical analysis

KW - harmonic analysis

KW - oceanic current

KW - prediction

KW - principal component analysis

KW - tidal current

KW - water depth

KW - Australia

U2 - 10.1016/j.oceaneng.2011.12.010

DO - 10.1016/j.oceaneng.2011.12.010

M3 - Journal article

VL - 42

SP - 195

EP - 204

JO - Ocean Engineering

JF - Ocean Engineering

SN - 0029-8018

ER -