Data Structure, Access

Downloading files

To download: go to the pages of links to the individual ensemble members, e.g.:

• SODA3.3.1 forced by NASA MERRA2 {available now}
• SODA3.4.1 forced by ECMWF ERA-Int
• SODA3.5.1 forced by ECMWF ERA20C
• SODA3.6.1 forced by CORE2
• SODA3.7.1 forced by JMA JRA55
• SODA3.8.1 forced by NCAR 20CRv2

File naming conventions

• 3.X indicates which meteorological forcing set used
  • 3.X=3.3 indicates MERRA2
  • 3.X=3.4 indicates ERA_int ,
  • 3.X=3.5 indicates ERA20C ,
• x indicates the particular experiment number.
• x=0 indicates the simulation
• x=1init indicates then initial assimilation reanalysis prior to bias correction
• x=1 indicates the final assimilation reanalysis
• Z indicates the time averaging and sampling interval
  • Z=mn indicates monthly average,
  • Z=5dy indicates 5-day average.
  • Z=10dy indicates 10-day interval (for increments).
• V indcates which set of variables is included, and on what vertical grid.
  • V=ocean indicates that the file constains 3D fields of temperature, salinity, and velocity (specified at 50 levels), and a series of 2D fields, including such variables as surface stress, mixed layer depth, and SSH.
  • V=isopycn indicates that the file contains temperature and salinity remapped to constant potential density surfaces.
  • V=ice indicates the file contains a series of sea ice-related fields.
  • V=transp indicates the file contains 3D vector volume transport.
  • V=increm indicates that the file constaint the 3D temperature and salinity increments (e.g. [H^-1(T^o-HT^f)]) computed by the data assimilation.
• G indicates the horizontal grid on which the data is presented.
  • G missing the reanalysis has been remapped onto a uniform 1/2x1/2 Mercator coordinate horizontal grid with 720x330 grid points, and with the first point at (74.75S, 0.25E).
  • G=or the reanalysis has been provided on the original model grid with 1440x1070 grid points in the horizontal and with the first point at (86.55S, 279.875W).
  • G=1x1 indicates a field on a uniform 1x1 degree mercator coordinate grid.
• YYYY indicates the date.
• YYYY = year (4 digits) for monthly files (so each file contains 12 month times).
• YYYY = year_mo_dy (4y,2m,2d digits) for 5dy files (so each file contains a single 5dy time).

Native and remapped grids

The native interlaced horizonal velocity and conserved tracer (e.g. temperature and salinity) grids form a tripolar Arakawa-B grid, varying from 0.1°x0.25° at high latitude to 1/4°x1/4° in the tropics (quasi-isotropic grid spacing increases from ~11.7km at 65 latitude to ~28.0km at the Equator, 1440x1070 grid points). The netcdf variable ordering is: {time, depth, latitude, longitude} written out surface to bottom (positive down), south to north (velocity begins at 79.968°S while tracers begin at 80.021°S), and west to east (velocity begins at 279.75°E while tracers begin at 279.875°E).

The vertical grid consists of 50 levels at telescoping depths (z* coordinate). Horizontal velocity and tracers are specified at : {5.03355m, 15.10065, 25.21935, 35.35845, 45.57635, 55.86325, 66.26175, 76.80285, 87.57695, 98.62325, 110.0962, 122.1067, 134.9086, 148.7466, 164.0538, 181.3125, 201.2630, 224.7773, 253.0681, 287.5508, 330.0078, 382.3651, 446.7263, 524.9824, 618.7031, 728.6921, 854.9935, 996.7153, 1152.376, 1319.997, 1497.562, 1683.057, 1874.788, 2071.252, 2271.323, 2474.043, 2678.757, 2884.898, 3092.117, 3300.086, 3508.633, 3717.567, 3926.813, 4136.251, 4345.864, 4555.566, 4765.369, 4975.209, 5185.111, 5395.023}.

General information about the grids as well as other model characteristics are available in the document: www.mom-ocean.org/web/docs/project/MOM5_elements.pdf. Code downloads are available through mom-ocean.org/web.

3D ocean 1/2°x1/2°x50lev files

Regridding from the original staggered ~1/4°x1/4° tripolar horizontal grid described above onto a single uniform 1/2°x1/2°x50lev Mercator grid is done using the GFDL Flexible Modeling System (FMS) 'regrid' routine with conservative remapping for temperature and salinity and nonconservative remapping for velocity. 3D arrays are thus 720x330x50 ≈ 12Mb with the starting point at: 0.5E, 74.75S, 5.033...m depth. Units are MKS. Projection onto isopycnal surfaces is carried out using the linear interpolation routines contained in GRADS. Many files are converted to calendar monthly averages, which is carried out post run-time either using GRADS routines or NCO routines. The ocean files [written in netcdf (NetCDF3)] contain seven two dimensional fields:

• ssh [= sea level + Pa/(rho0*g)]: MOM5 computes sea level from a complete conservation of mass equation (MOM5_elements.pdf section 38.2). This means sea level includes both steric (changes in column density) effects and eustatic (changes in column mass) effects. Currently SODA3 does not add mass due to continental ice melt, and does not include the impact of self-gravitation. Also note that the ocean bottom elevation in MOM5 is fixed and thus we do not include the effects of glacial isostatic adjustment or ocean loading.
• {mlt,mlp,mls}: mixed layer depth calculated either as the depth where temperature differs from surface (z=5m) temperature 0.2K, or as the depth where buoyancy is less than surface buoyancy by 0.0003 m/s^2, or where salinity differs from surface salinity by 0.01 psu. [m]
• anompb: bottom pressure minus change in hydrostatic pressure from z=0 to z=-H assuming a constant density rh0 [dbar=100hPa]
• {taux,tauy}: wind stress calculated from bulk formulas in the model, e.g. accounting for ocean motion. [N/m^2]

The ocean files also contain six three dimensional fields specified at the depths listed above.

• temp: potential temperature [°C]
• salt: SODA3 treats salinity as practical salinity (PSS-78) as expressed in Practical Salinity Units [psu]. The model uses preformed salinity as its salinity state variable and uses the TEOS10 equation of state. Absolute salinity is, on average, 0.4% larger than practical salinity.
• {u,v,w}: horizontal and vertical components of velicity. w is computed diagnostically from conservation of mass and is evaluated on a different grid. [m/s]
• prho: potential density computed from potential temperature, practical salinity, and pressure using the TEOS-10 formulas. [kg/m^3]

2D sea ice files

The sea ice files [written in netcdf (NetCDF3)] contain eight two-dimensional fields. Further description of the Sea Ice Simulator and its variables is provided at: www.gfdl.noaa.gov/sea-ice-simulator

• hi: sea ice thickness [m ice]
• mi: sea ice mass [kg/m^2]
• hs: snow thickness [m snow]
• {cn1,cn2,cn3,cn4,cn5}: sea ice concentration [0:1] in five ice thickness classes

3D ocean mass transport files

The mass transport files [written in netcdf (NetCDF3) on the original grid] contain two two-dimensional fields and two three-dimensional fields

• {mxvint,myvint}: (2D) total column vector horizontal mass transport across the face of a grid cell vertical column [10^9 kg/s ~ Sv]
• {mx,my}: (3D) vector horizontal mass transport across the face of each grid cell [10^9 kg/s ~ Sv]

Citing the data

When using the data set in a paper, please provide the SODA3 ensemble member (e.g. SODA3.3), the date/site the data were downloaded from, and cite the following reference:

Carton, J.A., G.A. Chepurin, and L. Chen, 2016: An updated reanalysis of ocean climate using the Simple Ocean Data Assimilation version 3 (SODA3), manuscript in preparation.