Opened 4 years ago

Last modified 9 months ago

#1646 assigned Defect

pit falls of choosing parameters in the F-S sigma code

Reported by: jamesharle Owned by: jamesharle
Priority: low Milestone:
Component: OCE Version: release-4.0
Severity: minor Keywords: DOM SCO
Cc: jamesharle

Description (last modified by jamesharle)

Having had a look at the NOCL set up of a high resolution AMM60 configuraton I've come across a possible pit fall concerning the choice of parameters in the Furner-Siddorn vertical coordinates. See the attached figures of the top grid box depth (e3t) using the Siddorn-Furner sigma coords for hc=150 and hc=50 (50 being the default shipped with NEMO for the AMM12 domain). Spot the discontinuity!

From reading the code - it looks like the fixed surface grid box depth (rn_zs=1m in AMM60) and stretched coordinates come into play at depths > hc. Anything less than the hc depth and we're in pure sigma - so as AMM60 has only 50 wet vertical levels - top grid box (e3t) is going to just under 3m at depths approaching 150m (i.e. hc=150). And that's why hc = 50 looks as it should!

If hc < jpk you'd have the reverse scenario: a very sudden shallowing of the depth of the top grid box.

So I guess the guidance for this is to make hc = jpk (for rn_zs=1m)!

Or more generally hc = jpk * rn_zs

To avoid users selecting inappropriate combinations of these parameters, perhaps 'hc' should be set in the furner-siddorn subroutine and a WARNING issued if it differs from the one in the namelist?

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Attachments (2)

fs_hc_150.png (24.2 KB) - added by jamesharle 4 years ago.
fs_hc_50.png (12.9 KB) - added by jamesharle 4 years ago.

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Change History (9)

Changed 4 years ago by jamesharle

Changed 4 years ago by jamesharle

comment:1 Changed 4 years ago by jamesharle

  • Owner changed from NEMO team to jamesharle

comment:2 Changed 3 years ago by nicolasmartin

  • Keywords DOM added; zgr removed

comment:3 Changed 3 years ago by nicolasmartin

  • Keywords domzgr removed

comment:4 Changed 3 years ago by nicolasmartin

  • Keywords SCO added; sco removed

comment:5 Changed 2 years ago by clevy

  • Cc jamesharle added
  • Status changed from new to assigned

comment:6 Changed 2 years ago by nicolasmartin

  • Description modified (diff)

comment:7 Changed 9 months ago by jamesharle

  • Description modified (diff)
  • Severity set to minor
  • Version changed from release-3.6 to release-4.0
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