Calculate emps with ANHA4 Output

This section describes the steps to calculate evaporation minus precipitation (emps) term in MY_TRC with ANHA4 forcing fields. This approache was tested with forcing files from ANHA4-EXH001 and EXH005.

The equation for emps is [Schmitt, 1989]:

\[\mathrm{emps(:, :) = -\frac{iocesafl(:, :)*soce}{rday*(isssalin(:, :)+1.0E^{-16})}}\]
  • iocesafl is the salt flux at ocean surface, defined in icemod files.
  • isssalin is Sea surface salinity, defined in icemod files.
  • soce is 34.7, rday is 3600*24, they are constants.

In NEMO 3.4, the “p” part of emps indlues both precipitation and sea-ice melt but does not take runoff into account. In Kyle’s research, emps was calculated for estimating the dilution of tracers (combined with runoff) and the parameterization of isotopic fractionation. By definition, net precipitation minus emps is the sea-ice melt water.

Use namelist/&namdta_dyn

A simple way to read iocesafl and isssalin in the model is using the file channels in namelist/&namdta_dyn. sn_emp can be used, and since ANHA4-EXH001/EXH005 does not have “key_eiv”, here we also choose sn_eiw.

In namelist, add the following

&namdta_dyn        !   offline dynamics read in files                ("key_offline")
!            !  file name  ! frequency (hours) ! variable  ! time interp. !  clim  ! 'yearly'/ ! weights  ! rotation !
!            !             !  (if <0  months)  !   name    !   (logical)  !  (T/F) ! 'monthly' ! filename ! pairing  !
    sn_emp  = 'ANHA4-EXH001_icemod',    120    , 'iocesafl',    .true.    , .false.,   'fday'  , ''       , ''
    sn_eiw  = 'ANHA4-EXH001_icemod',    120    , 'isssalin',    .true.    , .false.,   'fday'  , ''       , ''

Then copy datdyn.F90 from OFF_SRC and on row 295, add the following:

emp(:, :) = -1.0*emp(:, :)*34.7/(3600.0*24*(aeiw(:, :)+1.0e-16))
emps(:,:) = emp(:,:)


      1. Schmitt, P. S. Bogden, and C. E. Dorman. Evaporation minus precipitation and density fluxes for the North Atlantic. J. Phys. Oceanogr., 19(9):1208–1221, 1989.