Richardson Number?

[Peter W Hughes]

Could someone explain the importance of the Richardson number to me in
regard to ocean Circulation?

any help much apreciated

[W.J.Jenkins]

There are a number of Richardson numbers, but they all relate the
relative importance of stratification (buoyancy production) to
available turbulent energy. The gradient Richardson Number is defined
as

g (d Rho/d z)
Rg = -----------------
Rho (d U /d z)^2

where Rho is the density, g is the gravitational constant, and U
is the horizontal velocity. In some senses it is a measure of how
difficult it is to overcome the vertical stability, and how much
energy is available to do it. Laboratory experiments indicate that
Rg < 0.25 is unstable, so vertical mixing will start for low Rg.

In some numerical models, investigators define a vertical turbulent
diffusivity which is inversely related to Rg.

--
W.J. Jenkins email: wjen...@whoi.edu
MS #25 phone: 508-289-2554
Woods Hole Oceanographic Institution fax: 508-457-2193
Woods Hole, MA 02543 www: http://hil.whoi.edu

[Brian D. May]

W.J.Jenkins (wjen...@whoi.edu) wrote:
: available turbulent energy. The gradient Richardson Number is defined
: as

: g (d Rho/d z)
: Rg = -----------------
: Rho (d U /d z)^2

Minor correction ...

Assuming z increases upwards,

g (d Rho/d z)
Rg = - ---------------- ,

Rho (d U /d z)^2

and for a stable environment

d Rho
----- < 0 .
d z

Brian

--
Brian May
Department of Oceanography email: bm...@phys.ocean.dal.ca
Dalhousie University phone: (902) 494-7007 (work)
Halifax, Nova Scotia phone: (902) 462-3364 (home)
B3H 4J1 Canada fax: (902) 494-2885