Using thisobs%use_global_obs=0

In the domain-localized filters (LESTK, LETKF, LSEIK, LNETF) observations are assimilated that are located within the localization around some grid point. When a model uses parallelization with domain-decomposition some of these observations might belong to a different process-domain. In the default mode (thisobs%use_global_obs=1) PDAF-OMI gathers all globally available observations so that each process has access to all observations. It can be more efficient to restrict the observations on a process-domain to those observations that are located inside the domain or within the localization radius arond it. Then, in the local analyses a smaller number of observation have to be checked for their distance. Setting thisobs%use_global_obs=0 activates this feature. However, it needs additional preparations to make PDAF-OMI aware of the limiting coordinates of a process sub-domain.

In order to make use of the restricted observations, one has to provide PDAF-OMI with the limiting coordinates of a process-subdomain. There are two routines that can to this task:

• PDAFomi_set_domain_limits
• PDAFomi_get_domain_limits_unstrc

One of these routines should be called in init_pdaf to set the domain information.

PDAFomi_set_domain_limits

In this routine one provide the limiting coordinates of the process domain so that PDAF-OMI can store the information.

The interface is

  SUBROUTINE PDAFomi_set_domain_limits(lim_coords)

    REAL, INTENT(in) :: lim_coords(2,2)     !< geographic coordinate array (1: longitude, 2: latitude)
                                            !< ranges: longitude (-pi, pi), latitude (-pi/2, pi/2)

here lim_coords are

• (1,1) coordinate of the western edge of the domain
• (1,2) coordinate of the eastern edge of the domain
• (2,1) coordinate of the northern edge of the domain
• (2,2) coordinate of the southern edge of the domain

thus, (:,1) specifies the north-western corner of the sub-domain and (:,2) the souther-estern corner.

If the model grid is not decomposed in cardinal directions, but e.g. rotated, the coordinates should specife the extrema. Thus, lim_coords(1,1) would be the coordinate of the northernmost grid point of a domain.

PDAFomi_get_domain_limits_unstrc

This routine is find the extreme coordinates for a model domain. The routine is provided with the coordinates of all grid pints of a domain and then find the limiting coordinates. It is designed for unstructured grid and we have only tested it with the ocean model FESOM. (The tricky part is when a process-domain crosses the date line).

The interface is

  SUBROUTINE PDAFomi_get_domain_limits_unstr(verbose, npoints_p, coords_p)

    INTEGER, INTENT(in) :: verbose          !< verbosity flag (1: write output)
    INTEGER, INTENT(in) :: npoints_p        !< number of process-local grid points
    REAL, INTENT(in) :: coords_p(:,:)       !< geographic coordinate array, dimension (2, npoints_p 
                                            !<   (row 1: longitude, 2: latitude)
                                            !<   ranges: longitude (-pi, pi), latitude (-pi/2, pi/2)

This function only supports geographic coordinates given in radians.