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Extratropical low‐frequency variability as a low‐dimensional problem I: A simplified model
Author(s) -
D'Andrea Fabio,
Vautard Robert
Publication year - 2001
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49712757413
Subject(s) - parametrization (atmospheric modeling) , baroclinity , extratropical cyclone , closure (psychology) , empirical orthogonal functions , scale (ratio) , forcing (mathematics) , flow (mathematics) , climate model , scale model , reference model , mathematics , function (biology) , term (time) , geostrophic wind , stochastic modelling , projection (relational algebra) , mean flow , statistical physics , meteorology , climatology , turbulence , geology , mathematical analysis , computer science , climate change , physics , statistics , geometry , software engineering , aerospace engineering , quantum mechanics , evolutionary biology , market economy , economics , radiative transfer , algorithm , oceanography , engineering , biology
It is shown that the low‐frequency and large‐scale variability of an intermediate complexity reference model can be reproduced faithfully by a simplified model of 10 independent variables and 10 equations. The reference model is quasi‐geostrophic and baroclinic. The low‐order model is based on the truncated projection of the reference‐model equations on the empirical orthogonal functions of its output. A closure term is shown to be essential for good performance of the low‐order model. This closure term is meant to reproduce all the neglected scales and all the scale interactions, mainly baroclinic eddy forcing, that drive the large‐scale flow. The closure is built as an empirically defined function of the large‐scale flow of the model, relying on an extensive previously computed library of tendency differences between the full and truncated model. Two other parametrization schemes, a time‐mean and a stochastic one, are tested; comparisons of these two with the former underline the importance of the flow dependence of the formulation. The low‐order and reference models exhibit the same climate, as well as the same low‐frequency variability and weather regimes.