Geophysical fluid dynamics: whence, whither and why?

Abstract

A contribution to the special feature 'Perspectives in astrophysical and geophysical fluids' . GKV, This article discusses the role of geophysical fluid dynamics (GFD) in understanding the natural environment, and in particular the dynamics of atmospheres and oceans on Earth and elsewhere. GFD, as usually understood, is a branch of the geosciences that deals with fluid dynamics and that, by tradition, seeks to extract the bare essence of a phenomenon, omitting detail where possible. The geosciences in general deal with complex interacting systems and in some ways resemble condensed matter physics or aspects of biology, where we seek explanations of phenomena at a higher level than simply directly calculating the interactions of all the constituent parts. That is, we try to develop theories or make simple models of the behaviour of the system as a whole. However, these days in many geophysical systems of interest, we can also obtain information for how the system behaves by almost direct numerical simulation from the governing equations. The numerical model itself then explicitly predicts the emergent phenomenathe Gulf Stream, for example-something that is still usually impossible in biology or condensed matter physics. Such simulations, as manifested, for example, in complicated general circulation models, have in some ways been extremely successful and one may reasonably now ask whether understanding a complex geophysical system is necessary for predicting it. In what follows we discuss such issues and the roles that GFD has played in the past and will play in the future.

Generalized quasilinear approximation of the interaction of convection and mean flows in a thermal annulus

“…Such an undertaking via direct solution of the partial differential equations (often termed Direct Numerical Simulation or DNS) is currently beyond the capability of numerical models, even utilising state-ofthe art high performance computation on massively parallel architectures [2,3]. A major problem for such schemes is that, for the rotating and stratified systems that are typical of geophysical and astrophysical flows, the large scales influence and are in turn influenced by the smaller scales (which are typically difficult to model) [4]. For this reason, much effort has been dedicated to deriving alternative approaches to DNS that in some way takes into account the small-scale interactions in the large-scale dynamics (and the corresponding effect of large scales on the small scale turbulence).…”

Hierarchical Modeling of Solar System Planets with Isca

“…In this paper we describe the use of Isca to construct models of varying complexity for three Solar System planets, Earth, Mars, and Jupiter. Hierarchical modeling of Earth's atmosphere and climate is a well established field, with notable contributions and endorsements by Schneider and Dickinson [73] and Hoskins [74]; reinforced by Held [75]; discussed by Vallis [76]; and reviewed by Maher et al [10]. Hierarchical modeling is, in our view, even more important if we wish to understand and simulate (not always the same thing) planets other than our own, for the reasons discussed in the Introduction.…”

Is Computational Oceanography Coming of Age?

“…We still require idealized models; in particular, we need a hierarchy of models that span the gap between geophysical fluid dynamics problems and realistic simulations of the circulation. This hierarchy will ensure that the increasing OGCM realism does not outpace understanding of the basic physics (Held 2005;Vallis 2016;Coveney et al 2016;Emanuel 2020).…”