Transports across sections (key_ diadct)

A module is available to compute the transport of volume, heat and salt through sections. This diagnostic is actived with key_ diadct.

Each section is defined by the coordinates of its 2 extremities. The pathways between them are contructed using tools which can be found in NEMOGCM/TOOLS/SECTIONS_DIADCT and are written in a binary file section_ijglobal.diadct_ORCA2_LIM which is later read in by NEMO to compute on-line transports.

The on-line transports module creates three output ascii files:

- volume_transport for volume transports ( unit: $ 10^{6} m^{3} s^{-1}$ )

- heat_transport for heat transports ( unit: $ 10^{15} W $ )

- salt_transport for salt transports ( unit: $ 10^{9}Kg s^{-1}$ )

Namelist variables in namdct control how frequently the flows are summed and the time scales over which they are averaged, as well as the level of output for debugging:

&namdct        ! transports through sections
    nn_dct      = 15       !  time step frequency for transports computing
    nn_dctwri   = 15       !  time step frequency for transports writing
    nn_secdebug = 112      !      0 : no section to debug
                           !     -1 : debug all section
                           !  0 < n : debug section number n

nn_dct: frequency of instantaneous transports computing

nn_dctwri: frequency of writing ( mean of instantaneous transports )

nn_debug: debugging of the section

To create a binary file containing the pathway of each section

In NEMOGCM/TOOLS/SECTIONS_DIADCT/run, the file list_sections.ascii_global contains a list of all the sections that are to be computed (this list of sections is based on MERSEA project metrics).

Another file is available for the GYRE configuration ( list_sections.ascii_GYRE).

Each section is defined by:

long1 lat1 long2 lat2 nclass (ok/no)strpond (no)ice section_name

- long1 lat1 , coordinates of the first extremity of the section;

- long2 lat2 , coordinates of the second extremity of the section;

- nclass the number of bounds of your classes (e.g. 3 bounds for 2 classes);

- okstrpond to compute heat and salt transport, nostrpond if no;

- ice to compute surface and volume ice transports, noice if no.

The results of the computing of transports, and the directions of positive and negative flow do not depend on the order of the 2 extremities in this file.

If nclass =/ 0,the next lines contain the class type and the nclass bounds:

long1 lat1 long2 lat2 nclass (ok/no)strpond (no)ice section_name








where classtype can be:

- zsal for salinity classes

- ztem for temperature classes

- zlay for depth classes

- zsigi for insitu density classes

- zsigp for potential density classes

The script job.ksh computes the pathway for each section and creates a binary file section_ijglobal.diadct_ORCA2_LIM which is read by NEMO.

It is possible to use this tools for new configuations: job.ksh has to be updated with the coordinates file name and path.

Examples of two sections, the ACC_Drake_Passage with no classes, and the ATL_Cuba_Florida with 4 temperature clases (5 class bounds), are shown:

-68. -54.5 -60. -64.7 00 okstrpond noice ACC_Drake_Passage

-80.5 22.5 -80.5 25.5 05 nostrpond noice ATL_Cuba_Florida







To read the output files

The output format is :

date, time-step number, section number, section name, section slope coefficient, class number, class name, class bound 1 , classe bound2, transport_direction1 , transport_direction2, transport_total

For sections with classes, the first nclass-1 lines correspond to the transport for each class and the last line corresponds to the total transport summed over all classes. For sections with no classes, class number 1 corresponds to total class and this class is called N, meaning none.

transport_direction1 is the positive part of the transport ( > = 0 ).

transport_direction2 is the negative part of the transport ( < = 0 ).

The section slope coefficient gives information about the significance of transports signs and direction:

section slope coefficient section type direction 1 direction 2 total transport
0. horizontal northward southward postive: northward
1000. vertical eastward westward postive: eastward
=/0, =/ 1000. diagonal eastward westward postive: eastward

Gurvan Madec and the NEMO Team
NEMO European Consortium2017-02-17