Changes between Version 17 and Version 18 of GeneralImplementationConcept

Timestamp:

May 19, 2011, 8:56:05 AM (14 years ago)

Author:

lnerger

Comment:

--

GeneralImplementationConcept

@@ -30 +30 @@
 
 There are two possibilities to build a data assimilation system 
- 1. '''Offline mode:''' [[BR]] The model is executed separately from the assimilation/filter code. Output files from the model are used as inputs for the assimilation program.
  1. '''Online mode:''' [[BR]] The model code is extended by calls to PDAF core routines. A single executable is compiled. While running this single executable the necessary ensemble integrations and the actual assimilation is performed.
+ 1. '''Offline mode:''' [[BR]] The model is executed separately from the assimilation/filter program. Output files from the model are used as inputs for the assimilation program.
 PDAF supports both the online and offline modes. Generally, we recommend to use the online mode because it is more efficient on parallel computers. However, the required coding is simpler for the offline than the online mode.
+
+The better efficiency of the online mode of the data assimilation system is caused by several factors:
+ * The initialization phase of the model program is only executed once
+ * The output files are limited to the necessary outputs for the estimated forecast and analysis states and/or ensembles. In contrast for the offline mode restart files have to be written and read for each forecast/assimilation cycle.
+ * The assimilation system for the online mode can make efficient use of a large number of processors by executing a single program containing the full assimilation system. In contrast, in the offline mode, separate programs for the forecasts and the assimilation have to be run, each of these use typically less processors.
 
 The implementation concepts of the online and offline modes of PDAF are described on separate pages: