Revised observation uncertainties for bending angle assimilation
Presenter:
Neill Bowler
Met Office
Met Office
Talk
The method of Desroziers et al. (2005) has been used to estimate new observation uncertainties for GNSS-RO at the Met Office. The current set of observation uncertainties depend on the absolute value of latitude and height only. New uncertainties have been diagnosed, and dependence has been seen on temperature and water vapour, as well as the traditional quantities.
Testing the new uncertainties in the NWP system, good results were observed using observation uncertainties which depend on latitude, height and satellite identifier. However, this is unsatisfying since there is no causal link between latitude and the source of errors in the observations. After examining a number of quantities, the average temperature between the surface and 20km was chosen to replace latitude. This naturally varies with season, so no variation with calendar date is required. Some modest attempts have been made at understanding the origin of the additional benefit when using the new observation uncertainties.
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