Changes between Initial Version and Version 1 of U_next_observation

Timestamp:

Jan 19, 2015, 9:54:56 PM (10 years ago)

Author:

lnerger

Comment:

--

U_next_observation

@@ +1 @@
+= U_next_observation =
+
+The page document the user-supplied call-back routine `U_next_observation`.
+
+The routine `U_next_observation` is a call-back routine that has to be provided by the user. In the simplified interface the predefined name of the routine is `next_observation_pdaf`, but in the full interface, the user can choose the name of the routine. At the beginning of a forecast phase, `U_next_observation` is called once by either `PDAF_get_state` ot `PDAF_assimilate_X` (with X being the name of a filter algorithm) to get the number of time steps to be computed in the forecast phase. 
+
+The interface is the following:
+{{{
+SUBROUTINE U_next_observation(stepnow, nsteps, doexit, timenow)
+}}}
+with
+ * `stepnow` : `integer, intent(in)`[[BR]] Number of the current time step
+ * `nsteps` : `integer, intent(out)`[[BR]] Number of time steps until next observations are available
+ * `doexit` : `integer, intent(out)`[[BR]] Whether to exit forecasting (1 for exit); only relevant for the 'flexible' implementation variant.
+ * `timenow` : `real, intent(out)`[[BR]] Current model (physical) time at the beginning of the current forecast phase; only relevant for the 'flexible' implementation variant.
+
+Notes:
+ * The routine is called by all processes in a parallel program
+ * The variable `timenow` is only passed through PDAF to other user-supplied routines. It can be useful, e.g. to reset model forcing, which is time-specific
+
+Some hints: 
+ * If the time interval between successive observations is known, `nsteps` can be simply initialized by dividing the time interval by the size of the time step
+ * At the first call to `U_next_observation` the variable `timenow` can be initialized with the current model time. At the next call a forecast phase has been completed. Thus, the new value of `timenow` follows from the time interval for the previous forecast phase.