Parametrization of unresolved processes - can the principle of maximum entropy help us out? (Wim Verkleij, KNMI)

No matter how high the resolution of weather and climate models becomes, the need to represent, in one form or another, all processes that are not resolved explicitly will stay with us in the foreseeable future. Just think of the fact that in the atmosphere the ultimate sink of the kinetic energy of moving air is at spatial scales of the order of a millimeter or less. And there are many other processes whose intricacy makes it impossible to model them explicitly and deterministically.

To take these unresolved processes into account, parametrizations have
been devised such as the eddy viscosity proposed by Smagorinsky in his
1963 paper on one of the first general circulation models of the
atmosphere. Although these and other parametrization schemes work
reasonably well, there is a large heuristic element in their design and
a corresponding need to tune their parameters. One particular problem is
that they do not adjust themselves automatically to a change in model
resolution.

By representing the unresolved processes by a probability density
function and determining its explicit form by applying the principle of
maximum entropy, it is possible to derive parametrization schemes in a
rather systematic way. The resulting schemes have some interesting
properties such as the absence of tunable parameters. A simple
two-dimensional fluid system will be used to illustrate how this works
in practice.

Aanmelden bij de KNMI-Colloquia mailinglist? Klik hier.

Subscribe to our mailinglist KNMI-Colloquia? Do it here.