D26    A forward model for the assimilation of ZTD data in 3- or 4DVar systems.


Responsible partner
Due date
Type
Access
MetO
33
Report
Public

This report is part of work-package 4100, the purpose of which is
·        Enable assimilation of ground based GPS data into 4DVar data assimilation systems.
·       
Investigate impact of ground based GPS data when assimilated using 4DVar data assimilation systems.

·       
Capability for operational assimilation of GPS data in 4DVAR.

Methodology/Work Description:
It is foreseen that ground based GPS observations due to their high time resolution will have the highest impact when assimilated using 4DVar assimilation systems. At both DMI and the Met Office, a 3DVar assimilation system is currently in operational use and  4DVar versions are under development.

The operators enabling assimilation of ground based GPS observations in 4DVar shall be tested. Secondly a number of case studies shall be performed, in which 4DVar assimilation of
GPS data is compared to simulations based on 3DVar analyses.

The observation operator developed at the UK Met Office for  assimilation of ZTD data in 3- and 4DVar is described in this report:
A forward model for the assimilation of ZTD data in 3- or 4DVar systems. The report includes details on how corrections are done for the offsets between  the GPS antenna heights and the model orography (model heights).