Monday, 30 July 2001
The Met Office 3D-Var stratosphere-troposphere data assimilation system
In November 2000, a new stratosphere-troposphere data assimilation system was implemented at the Met Office. The new system uses a 3-D variational analysis scheme, and replaces the system based on the Analysis Correction scheme which was originally implemented in October 1991. In conjunction with the change of assimilation method, the stratospheric system now also includes the direct assimilation of radiance measurements from the TOVS and ATOVS instruments, rather than temperature retrievals. The model configuration was changed to use a new set of 40 levels; the tropospheric levels are now the same as in the standard operational 30-level global forecast model but there are additional levels in the stratosphere and lower mesosphere. It is anticipated that such a set of levels will allow improvements to the assimilation of satellite soundings. Further research will be carried out to assess the benefits of the additional stratospheric levels with the intention of extending the standard global model when computer resources permit.