Time-variable 4DVAR surface forcing adjustment

[arango]

The 4DVAR surface forcing adjustment was revised to include minimization at other times in addition to initialization. A new input parameter (nSFF) was introduced to allow minimization at other times during strong constraint data assimilation. Here, nSFF is the number of time-steps between adjustment of surface fields. This required several changes to the IO NetCDF files involved in 4DVAR data assimilation. All the changes are internal to ROMS.

Several new arrays with an additional dimension (nFrec) are introduced during the minimization. The number of forcing record to process are:

nFrec = 1 + ntimes / nSFF      (integer operation)

nSFF is either a multiple of ntimes or greater than ntimes. Therefore, there are three posibilities:

(1) If  NSFF > NTIMES,       nFrec = 1  (constant adjustment)
(2) If  NSFF = NTIMES,       nFrec = 2  (initial and final)
(3) If  NSFF < NTIMES,       nFrec > 2  (adjustment every NSFF steps)

We will continue looking and testing this capability.