WORKING GROUP 4: 3D-VAR Data Assimilation
2. Overview of area of focus, objectives and strategies
We are developing advanced 3D- variational
(3D-Var) data assimilation tools for the WRF model. The analysis
system must be able to properly resolve all variables and scales of
importance of the assimilation system. This formidable problem
will be addressed incrementally by analyzing scales and variables,
which we currently know how to do and developing techniques to perform
the analysis at smaller scales and with additional analysis variables.
We have designed the framework of a basic 3D-Var analysis scheme
capable of analyzing most standard meteorological data, and more
recently (V2.0) included a number of of non-traditional data types e.g.
SSM/I radiances and radar radial velocity. The WRF assimilation
research will strive to develop the "forward models" (and their
adjoints) by which the WRF model fields can be transformed and
interpolated to the observation locations and values for each of these
data, and for these operators to be portable to alternative
assimilation algorithms (e.g alternative 3D-Var systems, 4D-Var,
ensemble-based DA, etc.).
The 3D-Var system is being developed in four major stages.
a) The basic system (June 2003)
The basic system contained the necessary infrastructure, but not all the complexities (e.g. radiance assimilation, anisotropic recursive filters) of subsequent “research” and “advanced” versions. The characteristics of the basic 3D-Var system were:
b) Upgraded basic version (June 2004)
This version has been released in May 2004 as part of the WRFV2.0 package. It incorporates the following additional capabilities:
b) Research version (June 2005)
c) Advanced Version (2006)
The advanced version will incorporate new developments from the WRF team to create an improved 3DVAR system.
3. Process for inclusion of new capabilities in the WRF 3D-Var repository
The development of WRF 3D-Var is a joint effort across a number of international organisations. To avoid duplication of work, and to coordinate multiple code changes, the following procedure has been adopted:
a) Change proposed with draft of methodology and impact in initial tests (if any).
b) If approved for potential inclusion, reviewer assigned and schedule for development decided.
c) “Contributed” code tested in “repository” system (including standard tests and additional tests which show the new capability in action).
d) Developer/reviewer present results to working group.
e) When approved, change is added to repository (including change file describing code changes and impacts).
basic" version of WRF 3DVAR has been released in May 2004. This version
is intended for use by knowledgeable, friendly users. While the
release has no known errors, it is known that deficiencies exist e.g.
radiance assimilation is not yet included, and background errors are
currently only climatological estimates. The developers would
appreciate notification of any problems with the WRF 3D-Var code, but
cannot promise prompt response or solution to the problems.
Work is now focusing on the “research” version of 3/4D-Var described above.
5. Links, Documentation