[ecco-support] ECCO Mixed Layer Depths criteria

Mon May 1 13:19:11 EDT 2017

Don’t know what criterion was used for ECCOv4
For cube92, the default parameters were used:

C     hMixCriteria:: criteria for mixed-layer diagnostic
C     dRhoSmall   :: parameter for mixed-layer diagnostic
C     hMixSmooth  :: Smoothing parameter for mixed-layer diag (default=0=no smoothing)
      hMixCriteria        = -.8 _d 0
      dRhoSmall           = 1. _d -6
      hMixSmooth          = 0. _d 0
C--   First method :
C     where the potential density (ref.lev=surface) is larger than
C       surface density plus Delta_Rho = hMixCriteria * Alpha(surf)
C     = density of water which is -hMixCriteria colder than surface water
C     (see Kara, Rochford, and Hurlburt JGR 2000 for default criterion)

See model/src/calc_oce_mxlayer for other options.

Another available definition (when using KPP scheme)
is KPPhbl, which is the “mixing” layer depth.
The daily maximum of KPPhbl is a very good proxy for
mixed layer depth most places, except seasonally-sea-ice-covered and polar-winter regions.
(Kara’s criterion is also problematic for polar regions, which tend to be salt-stratified.)

On May 1, 2017, at 9:50 AM, Martha Buckley <marthabuckley at gmail.com<mailto:marthabuckley at gmail.com>> wrote:

One follow up question regarding mixed layer depths in ECCO.

What is the criteria for the variable "MXLDEPTH" in the ecco v4 product.  I think I recall being told it is the density equivalent of 0.8C.  Two questions:
(1) Is this the criteria that was used?  It the criteria applied to model profiles at the model timestep?
(2) If so, isn't this criteria a bit large?  0.125 kg/m^3 or 0.5C seem common MLD criteria when applying criteria to monthly-averaged data.  However, criteria that are smaller (~0.03 kg/m^3 or ~0.2 C) are typically applied when using raw observational profiles.

I know that the MLD criteria is somewhat arbitrary, but I want an idea of the rational for the chosen criteria.
Thanks!
Martha

On Fri, Apr 28, 2017 at 6:04 PM, HONG ZHANG <hong.zhang at ucla.edu<mailto:hong.zhang at ucla.edu>> wrote:

-------- Forwarded Message --------
Subject:        Re: [ecco-support] ECCO2 Mixed Layer Depths Concerns
Date:   Fri, 28 Apr 2017 12:48:59 -0700
From:   HONG ZHANG <hong.zhang at ucla.edu><mailto:hong.zhang at ucla.edu>
To:     Dimitris Menemenlis <dmenemenlis at gmail.com><mailto:dmenemenlis at gmail.com>, Moisan, John R. (WFF-610W) <john.r.moisan at nasa.gov><mailto:john.r.moisan at nasa.gov>
CC:     Daria Halkides <halkides at esr.org><mailto:halkides at esr.org>

On 4/28/17 9:37 AM, Dimitris Menemenlis wrote:
Daria or Hong, would you have looked at MXLDEPTH depth in the “cube92” solution?
ftp://ecco2.jpl.nasa.gov/data1/cube/cube92/lat_lon/quart_90S_90N/MXLDEPTH.nc/

John, why not use the ECCO-V4, which is data-constrained?
http://www.ecco-group.org/products.htm
ECCO v4 is on a 1-degree grid, which is closer to your desired 2x2 degree grid.

Dimitris Menemenlis

On Apr 26, 2017, at 9:41 AM, Moisan, John R. (WFF-610W) <john.r.moisan at nasa.gov<mailto:john.r.moisan at nasa.gov>> wrote:

Hello ECCO2’ers,

I would like to make use of the Mixed-Layer Depth model outputs from the global model runs 1992-present (Nov. 2016) to drive some simple 1D biogeochemical models for CDOM.  I have binned to model outputs from the jpg site into monthly 2x2 deg. grids.  One thing of concern that I have is the trends in the global MLDs (see attached figure), which are more extreme in the SO.  Is there an issue with maintaining correct ocean boundary layers, esp. in the SO for this model?  Has this been observed yet?

Hi John,
You're right, MLD from cube92 run has bias in late stage
because it's a free run for the later period.
As Dimitris said, you can look at other ECCO product provided at the website.
Please see attached fig showing MLD from ECCOv4 and ECCO llc270 for an example,
where red line is for ECCOv4 (1992-2012) and blue line for ECCO llc270 (2001-2015) in upper plot
also MLD for cube92 is also shown in lower plot for reference.

cheers
Hong

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--
Martha W. Buckley
marthabuckley at gmail.com<mailto:marthabuckley at gmail.com>
http://sites.google.com/site/marthabuckley/home
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