In POP tvag output data file, there is a variable named SFWF_WRST and represents for Virtual Salt Flux due to weak restoring.

float SFWF_WRST(time, nlat, nlon) ;
    SFWF_WRST:long_name = "Virtual Salt Flux due to weak restoring" ;
    SFWF_WRST:units = "kg/m^2/s" ;
    SFWF_WRST:coordinates = "TLONG TLAT time" ;
    SFWF_WRST:grid_loc = "2110" ;
    SFWF_WRST:cell_methods = "time: mean" ;
    SFWF_WRST:_FillValue = 9.96921e+36f ;
    SFWF_WRST:missing_value = 9.96921e+36f ;