P. Malanotterizzoli et al., STOCHASTIC WAVE RADIATION BY THE GULF-STREAM - NUMERICAL EXPERIMENTS, Deep-sea research. Part 1. Oceanographic research papers, 42(3), 1995, pp. 389-423
The present work combines two ideas: (i) that transient Rossby waves a
re excited by meander growth and decay and radiate into the far field;
(ii) that the stochastic nature of meander growth, lifetimes and deca
ys is responsible for the observed high values of eddy variances. A si
mple barotropic model was used analytically through an asymptomatic th
eory and numerically to explore the fully nonlinear regime. Three ques
tions are addressed. First, in the fully nonlinear limit can a Rossby
wave radiation field be excited for which the predicted covariance dis
tributions compare well with the observed ones? Second, can the diverg
ence of the associated eddy Vorticity fluxes induce a mean recirculati
on similar to the deep recirculation gyre observed north of the stream
? Third, is the variable thickness of the deep layer due to the main t
hermocline depth change across the stream and the sloping bottom topog
raphy, crucial in driving the deep recirculation gyre? From the result
s obtained the following was concluded. Over a flat bottom, both theor
y and the numerical experiments predict a series of circulation cells
produced by the nonlinear interactions between the forced and free wav
e response of the flow. Realistic eddy variances due to Rossby wave ra
diation into the far field are predicted. However, the induced mean re
circulation is much too weak. A bowl-shaped topography that mimics the
variable thickness of the deep layer across the stream front was then
introduced. In this case, the mean cyclonic circulation follows the c
losed potential vorticity contours and compares well with that observe
d. However, this equivalent topography produces a very rapid energy de
cay away from the southern boundary by inhibiting wave radiation. The
fact that one or the other of the two results were achieved, but not b
oth simultaneously, is a clear indication of the limitations of the mo
del used in which the meandering stream is idealized as a southern bou
ndary forcing. A final, interesting result of these simulations is tha
t topographic Rossby waves are preferentially forced in regions where
the stream meanders over the sloping relief, corresponding to the regi
ons upstream of the Grand Banks and downstream of Cape Hatteras.