Added standard_name to eastward/northward velocity components

[arango]

Added the standard_name attribute to the eastward and northward, rotated, velocity components at RHO-point. Recall that these components can be computed only at the interior RHO-points and set to zero at the boundaries.

  float ubar_eastward(ocean_time, eta_rho, xi_rho) ;
  ubar_eastward:long_name = "eastward vertically integrated momentum component at RHO-points" ;
  ubar_eastward:units = "meter second-1" ;
  ubar_eastward:time = "ocean_time" ;
  ubar_eastward:standard_name = "barotropic_eastward_sea_water_velocity" ;
  ubar_eastward:grid = "grid" ;
  ubar_eastward:location = "face" ;
  ubar_eastward:coordinates = "lon_rho lat_rho ocean_time" ;
  ubar_eastward:field = "ubar_eastward, scalar, series" ;
  ubar_eastward:_FillValue = 1.e+37f ;

  float vbar_northward(ocean_time, eta_rho, xi_rho) ;
  vbar_northward:long_name = "northward vertically integrated momentum component at RHO-points" ;
  vbar_northward:units = "meter second-1" ;
  vbar_northward:time = "ocean_time" ;
  vbar_northward:standard_name = "barotropic_northward_sea_water_velocity" ;
  vbar_northward:grid = "grid" ;
  vbar_northward:location = "face" ;
  vbar_northward:coordinates = "lon_rho lat_rho ocean_time" ;
  vbar_northward:field = "vbar_northward, scalar, series" ;
  vbar_northward:_FillValue = 1.e+37f ;

  float u_eastward(ocean_time, s_rho, eta_rho, xi_rho) ;
  u_eastward:long_name = "eastward momentum component at RHO-points" ;
  u_eastward:units = "meter second-1" ;
  u_eastward:time = "ocean_time" ;
  u_eastward:standard_name = "eastward_sea_water_velocity" ;
  u_eastward:grid = "grid" ;
  u_eastward:location = "face" ;
  u_eastward:coordinates = "lon_rho lat_rho s_rho ocean_time" ;
  u_eastward:field = "u_eastward, scalar, series" ;
  u_eastward:_FillValue = 1.e+37f ;

  float v_northward(ocean_time, s_rho, eta_rho, xi_rho) ;
  v_northward:long_name = "northward momentum component at RHO-points" ;
  v_northward:units = "meter second-1" ;
  v_northward:time = "ocean_time" ;
  v_northward:standard_name = "northward_sea_water_velocity" ;
  v_northward:grid = "grid" ;
  v_northward:location = "face" ;
  v_northward:coordinates = "lon_rho lat_rho s_rho ocean_time" ;
  v_northward:field = "v_northward, scalar, series" ;
  v_northward:_FillValue = 1.e+37f ;

This facilitates the plotting vectors with third-party software like ncWMS, NcML, etc. Many thanks to Rich Signell and ​Francisco López for bringing this to my attention.