Opened 5 years ago

Closed 3 years ago

#1753 closed Defect (fixed)

Fix ssh incrementation in VVL code (Met Office)

Reported by: drew Owned by: mathiot
Priority: high Milestone:
Component: OCE Version: trunk
Severity: minor Keywords: NEMOVAR SSH VVL
Cc: Branch review:
MP ready?: Task progress:

Description

Context

Code improvements and revisions required for FOAM assimilation system in GO6

Analysis

Initial attempts to increment ssh directly as a change to the surface eta resulted in the introduction of fresh-water blotches into the ocean, presumably due to increased volume added with no heat/content change.

Fix

Chris Harris has devised a scheme to implement the ssh change though out the water column through changes to e3t. Associated changes to heat and salt content have also been added.

Commit History (2)

ChangesetAuthorTimeChangeLog
8791charris2017-11-23T12:11:00+01:00

#1753 Branch for fix to SSH assimilation with vvl

6689flavoni2016-06-13T16:24:43+02:00

#1753, commit mesh_mask.nc all fields in double precision now

Attachments (10)

iSSH_20050102.png (151.5 KB) - added by drew 5 years ago.
SLA increment for 2nd day
aSSS_20050102.png (169.1 KB) - added by drew 5 years ago.
Difference in SSS when adding ssh increment
aSST_20050102.png (232.7 KB) - added by drew 5 years ago.
Difference in SST when adding SLA increment
stats_sprof_tab_000.png (66.2 KB) - added by drew 5 years ago.
Hovmuller stats for run with VVL causing freshwater blotches.
stats_sprof_hov_001.png (108.3 KB) - added by drew 5 years ago.
Hovmuller stats for GO5 run
stats_sprof_hov_000.png (109.1 KB) - added by drew 5 years ago.
Hovmuller stats for run with VVL causing freshwater blotches.
slafb_1995_crop.png (143.1 KB) - added by drew 5 years ago.
Binned obs minus background stats for 1995/03 in mi-am200.
FOAMSLA-6.png (1.6 MB) - added by drew 5 years ago.
Increments for March 16 of mi-am700 run
FOAMSLA-7.png (1.8 MB) - added by drew 5 years ago.
Model Tendency for 16 March of mi-am700 run.
stats_sprof_pro_000.png (50.3 KB) - added by drew 5 years ago.
Profile stats for run with trasbc changes (black) and without (blue)

Change History (25)

comment:1 Changed 5 years ago by drew

Here is a Met Office intranet accessible html formatted version of an early email detailing the problem

comment:2 Changed 5 years ago by drew

  • Cc mattmartin charris removed
  • Owner changed from NEMO team to drew
  • Type changed from Bug to Defect

comment:3 Changed 5 years ago by drew

Under the original ssh incrementation code

freshwater blotches developed in the southern ocean — and probably elsewhere. This is manifest in my mi-am200/½ set of runs for which I will now show some evidence from mi-am201.

Last edited 5 years ago by drew (previous) (diff)

Changed 5 years ago by drew

SLA increment for 2nd day

Changed 5 years ago by drew

Difference in SSS when adding ssh increment

Changed 5 years ago by drew

Difference in SST when adding SLA increment

comment:4 Changed 5 years ago by drew

Here is the sea level anomaly increment on the 2nd day of one of the offending runs

SLA increment for 2nd day

While here is the corresponding difference in SSS when adding that increment

Difference in SSS when adding ssh incrementDifference in SST when adding SLA increment

There are also changes to the temperature, but it is harder to associate that directly to the sea level anomaly increment

Last edited 5 years ago by drew (previous) (diff)

comment:5 Changed 5 years ago by drew

Some fairly obvious freshening when volume is added through the ssh. Likely associated with no change in salt content. Not as clear what is happening with heat content. Freshening also was obvious in mean profile bias. Shown below are the mean and rmse bias for the new VVL code followed by bias in GO5.

Hovmuller stats for run with VVL causing freshwater blotches. Hovmuller stats for GO5 run

Last edited 5 years ago by drew (previous) (diff)

Changed 5 years ago by drew

Hovmuller stats for run with VVL causing freshwater blotches.

Changed 5 years ago by drew

Hovmuller stats for GO5 run

Changed 5 years ago by drew

Hovmuller stats for run with VVL causing freshwater blotches.

comment:6 Changed 5 years ago by drew

In an attempt to counteract this, salt and heat content changes were introduced to balance the volume change.

While the freshwater blotches disappeared — or at least were reduced in this revision.  The SSH mean bias in the North Pacific was greatly reduced in this revision — which was subsequently associated with an inability of the model to retain the sea level increment. 

comment:7 Changed 5 years ago by drew

A Met Office intranet review of what happen when implemented in mi-am700/½ set of runs is documented here

which I will summarize below.

Changed 5 years ago by drew

Binned obs minus background stats for 1995/03 in mi-am200.

Changed 5 years ago by drew

Increments for March 16 of mi-am700 run

Changed 5 years ago by drew

Model Tendency for 16 March of mi-am700 run.

comment:8 Changed 5 years ago by drew

Dan Lea observed that the obs-bkg for analysis runs had large error in the Pacific — here for mi-am700 run in March 1995.

Binned obs minus background stats for 1995/03 in mi-am200.

Further, plotting the increments and model tendency for 16 March

Increments for March 16 of mi-am700 run Model Tendency for 16 March of mi-am700 run.

showed that the correction to this error was present in the increments plots, but did not carry forward into the model tendency for the day (i.e. the increment was not retained).

It was thought this may be due to the creation of spurious model convergence/divergence in the process of pushing the increment — applied at the surface — down through the water column through the adjustment of e3t in the VVL code. Therefore, Chris Harris further revised the sshwzv.F90 code to recast the ssh incrementation as a increment on the full column e3t in a manner similar to what is done for the addition of freshwater.

  • The code is functional at
Last edited 5 years ago by drew (previous) (diff)

comment:9 Changed 5 years ago by drew

Additional changes to trasbc.F90 to properly conserve heat and salt content where added correctly at

comment:11 Changed 5 years ago by drew

To date, there seems to be little difference between adding the trasbc changes or not. Perhaps Ana has more comprehensive evidence.
Profile stats for run with trasbc changes (black) and without (blue)
Salinity profile obs minus background stats for run with trasbc changes [6608] and without [6660].
Note: A transition was made in mid-run between [6620] and [6660] of run with trasbc (black). Will be replaced with cleaner comparison.

Last edited 5 years ago by drew (previous) (diff)

Changed 5 years ago by drew

Profile stats for run with trasbc changes (black) and without (blue)

comment:12 Changed 5 years ago by nicolasmartin

  • Keywords SSH added; sshinc removed

comment:13 Changed 3 years ago by nemo

  • Milestone 2016 WP deleted
  • Severity set to minor

Looks like an internal issue within the Met Office.

comment:14 Changed 3 years ago by nemo

  • Owner changed from drew to mathiot
  • Status changed from new to assigned

Reassigned to UKMO officer as the current owner does no longer have the permissions to close tickets.

comment:15 Changed 3 years ago by mathiot

  • Resolution set to fixed
  • Status changed from assigned to closed
  • Version changed from release-3.6 to trunk

Has been included in the 2017 merge @ revision 9023

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