Etudes et évaluation de processus océaniques par des hiérarchies ...
Etudes et évaluation de processus océaniques par des hiérarchies ... Etudes et évaluation de processus océaniques par des hiérarchies ...
144 CHAPITRE 4. ETUDES DE PROCESSUS OCÉANOGRAPHIQUES 4.8 Estimation of friction laws and parameters in gravity currents by data assimilation in a model hierarchy tel-00545911, version 1 - 13 Dec 2010
4.8. ESTIMATION OF FRICTION LAWS AND PARAMETERS IN GRAVITY CURRENTS BY DATA Noname manuscript No. (will be inserted by the editor) Estimation of Friction Parameters in Gravity Currents by Data Assimilation in a Model Hierarchy A. Wirth Received: date / Accepted: date tel-00545911, version 1 - 13 Dec 2010 Abstract This paper is the last in a series of three investigating the friction laws and their parametrisation in idealised gravity currents in a rotating frame. Results on the dynamics of a gravity current (Wirth, Ocean Dyn. 59, 551, 2009) and on the estimation of friction laws by data assimilation (Wirth & Verron Ocean Dyn. 58, 247, 2008) are combined to estimate the friction parameters and discriminate between friction laws in non-hydrostatic numerical simulations of gravity current dynamics, using data assimilation and a reduced gravity shallow water model. I demonstrate, that friction parameters and laws in gravity currents can be estimated using data assimilation. The results clearly show that friction follows a linear Rayleigh law for small Reynolds numbers and the estimated value agrees well with the analytical value obtained for non-accelerating Ekman layers. A significant and sudden departure towards a quadratic drag law at an Ekman layer based Reynolds number of around 800 is shown, in agreement with classical laboratory experiments. The drag coefficient obtained compare well to friction values over smooth surfaces. I show that data assimilation can be used to determine friction parameters and discriminate between friction laws and that it is a powerful tool in systematically connection models within a model hierarchy. Keywords ocean dynamics · gravity current · friction laws · parameter estimation · data assimilation PACS 65N35 · 76M22 · 86A05 1 Introduction The realism todays and tomorrows numerical models of the ocean dynamics is and will be governed by the accuracy of the parametrisations of the processes not explicitly A. Wirth LEGI / MEOM CNRS BP 53, 38041 Grenoble Cedex 9, France E-mail: achim.wirth@hmg.inpg.fr
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144 CHAPITRE 4. ETUDES DE PROCESSUS OCÉANOGRAPHIQUES<br />
4.8 Estimation of friction laws and <strong>par</strong>am<strong>et</strong>ers in<br />
gravity currents by data assimilation in a mo<strong>de</strong>l<br />
hierarchy<br />
tel-00545911, version 1 - 13 Dec 2010
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