[ecco-support] Access to ECCOV4

[Fenty, Ian G (329C)]

Guancheng,

Just a clarification if you are using the ECCO v4-r2 solution, we call that the “ECCO Central Production version 4, release 2” state estimate.  Our ECCO2 solutions use a higher resolution, 18 km eddy-permitting grid.

As to your problem, our state estimates will close heat and salt budgets on the native model grid.  It looks like you are trying to close the MLS budget using only Ekman and geostrophic transports estimated using wind stress and SSH gradients.  

Using the method you described it is very unlikely that you would exactly close the MLS budget for several reasons.  First, actual salinity fluxes in the MLS include eddy advection and MLS depth changes.  Second, you are using monthly-mean wind stress and SSH gradients while salinity fluxes in the model are driven by time-varying wind stress and SSH gradients.  Third, you are looking at the ‘interp_monthly’ fields which are not on the native model grid.  'interp' fields are on an interpolated lat-lon grid.

My suggestion is that you work backwards.  At first, use the native model grid and fluxes on the native model grid and use the output flux terms and surface forcing and prove to yourself that you can close the MLS budget.  

To proceed, examine the individual advective and diffusive flux terms across the faces of the model grid cells.  The units of the flux terms are in g/kg m3/s because they are volume fluxes.  g/kg (m/s) m^2 or S*U*A, with S being g/kg, U being (m/s) equivalent velocity, and A (m^2) being the area of the face of the grid cell through which the flux is considered.

For each surface cell there are 5 advective terms, one for each face:

2 terms for the 'x' dimension lateral faces: ADVx_SLT,   "U Comp. Advective Flux of Salinity"
2 terms for the 'y' dimension lateral faces: ADVy_SLT,   "V Comp. Advective Flux of Salinity"
1 terms for the 'z' dimension bottom faces: ADVr_SLT,   "Vertical Advective Flux of Salinity"

and 6 diffusive terms, the bottom face now has an additional term:

2 terms for the 'x' dimension lateral faces: DFx_SLT,   "U Comp. Diffusive Flux of Salinity"
2 terms for the 'y dimension lateral faces: DFy_SLT,   "V Comp. Diffusive Flux of Salinity"
1 terms for the 'z' dimension bottom faces: DFrE_SLT,   "Vertical Advective Flux of Salinity (explicit part)"
1 terms for the 'z' dimension bottom faces: DFrI_SLT,   "Vertical Advective Flux of Salinity (implicit part)"

If a grid cell below the surface is considered, then you need to consider the additional advective and diffusive fluxes in the 'z' dimension across the top face as well.

To fully close the budget for grid cells at the surface you must also consider the air-sea freshwater flux term, oceFWflux.

While doing that it may be helpful to examine the 3-day T and S average tendency terms which are included in our output.

ftp://mit.ecco-group.org/ecco_for_las/version_4/release2/nctiles_tendencies/README

Stend    : "Salinity Tendency"
Sdi      : "Salinity Tendency Due To Diffusion"
Sad      : "Salinity Tendency Due To Advection"
Sforc    : "Salinity Tendency Due To Forcing"
SALT     : "Salinity Snapshots"

The total salinity tendency variable “Stend” is the sum of the individual tendency terms.  We also provide 3-daily snapshots of salinity so you can verify that salinity evolves as expected.

After you have convinced yourself that you can exactly close the salt budget, then you can attempt to reconcile the advective fluxes into the Ekman and geostrophic transports.  These diffusive fluxes can be thought of as parameterizing eddy fluxes which are not accounted for in the approximation that dS/dt is due to only Ekman and geostrophic fluxes.

-Ian

On 4/5/17, 12:45 AM, "ecco-support-bounces at mit.edu on behalf of Ligc" <ecco-support-bounces at mit.edu on behalf of liguancheng15 at mails.ucas.ac.cn> wrote:

    
    Dear Sir/Medam,
          Firstly, thank you for your reply so much! Now,please allow me to introduce my method and questions.
     I used the Budget equation of the mixed layer salinity to calculate the MLS variability around North Pacific using by ECCO2 original data (from ECCO v4-r2/ interp_monthly).The left term is the
     rate of change of the MLS, and the right terms represent the freshwater flux (E-P), advection of the MLS by Ekman and geostrophic transports, the entrainment of the MLS. Among these variables，Ekman Velocity was estimated from wind stress data and geostrophic
     Velocity from free surface height Anomalies using by the related formula. 
     I tried to calculate all of these terms at each lon-lat grid by using the original variables, but i found that the total range at the right hand is a bit more widely than the left, which may
     be resulted by the wrong or larger result of the advection of MLS because other term is fitted with the conclusion of other articles well，including the freshwater flux is the leading dominant term in this area.
      So i was wondering if there's any available variable or method to test my results. And, i want to know about how to calculate advective flux of Salinity in a better way.
      Moreover, Could you tell me how to get the ADVe_SLT and ADvn_SLT in this dataset, because i can not figure out the source of 'm^3' in these unit. I am looking forward for your helpless if it
     is convenient.
    Thank you for your patient reading! I really appreciate you help!
    
    
    Best regards,
    Guancheng