[ecco-support] [EXTERNAL] Re: ecco-support Digest, Vol 99, Issue 13

[Zhang, Hong (US 398K)]

On Jun 29, 2024, at 4:13 PM, Wang, Ou (US 329B) <ou.wang at jpl.nasa.gov> wrote:

Hi Xinfeng,

In terms of z* and the real freshwater flux boundary condition, there is no change between v4r1 and v4r4. The smaller horizontal integral of the Eulerian vertical velocity We (i.e. WVELMASS) in Figure 6 of your paper is probably because you were looking at the time-mean value. I did a quick calculation of the horizontal integrals of WVELMASS for v4r1. The time-mean value is only a few percent of Sv's, one to two orders of magnitude smaller than that for a particular month.
Here is an earlier discussion of WVEL with Carl.
Hope it helps for this theme of discussion.

An interesting question, but your result and description is exactly what one would expect if I've
understood you.

Even the twenty year average wvel is noisy (see the Liang etal attachment) particularly at
depth. One slightly troubling numerical problem is that w is computed (as I understand it)
as the residual divergence of the horizontal velocity at any given time---and that's an intrinsically
noisy method.

Furthermore, in theory at hourly time steps, the internal wave field is in principle present (the
spatial resolution of 1 degree means that it wouldn't be realistic, but the physics should apply). That
field, and see some of the ECCO high resolution results in the other attachment) is known to be almost fully stochastic (tides
aside) and is described by a frequency/wavenumber spectrum (Garrett-Munk). An then at low latitudes,
the 1 degree resolution is probably sufficient to produce an eddy-like field, which is also stochastic.
An interesting question would be what would w look like if you could average for 50 or 500 years?


Carl



Hi Carl,
A quick question about Eulerian vertical velocity.
Normally we look at monthly/yearly/decadal mean WVEL
(like fig 18 in your BAMS paper for 20-yr mean WVEL).
But when we look at the hourly or daily mean,
it's surprised that WVEL field looks "messy" (or "grid noisy")
and larger by order of magnitude,
So WVEL must vary rapidly with time and place
and only after much cancellation does it look "normal" (as classical
gyre and upwelling).
Have you touched upon this phenomenon in your papers?
Or are you aware where it is discussed in the literature?

cheers
Hong



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