Impact trials for the assimilation of SSM/I wind speeds in the global NWP model
Ridley [J.K.] ; Ballard, S. P.
Impact trials on the assimilation of SSM/I surface wind speed (WS) have been undertaken to determine if this new data source should be considered for assimilation in the operational suite at the Met Office. The trials were for March and June 1999 and were based on the data assimilation scheme as operational from March to July 1999. Assimilation of SSM/I WS observations, only available over the ocean, produced a positive impact against the analysis in the Southern Hemisphere (SH) and a slightly negative impact in the Northern Hemisphere (NH). Since the magnitude of the impact is related to the number of observations assimilated, it was concluded that the observations were being over fitted in the NH. Consequently the density of observations used in the NH reduced by a factor 4 compared with the SH. The impact against observations is neutral. The analysis increments to WS, mostly in the Southern Hemisphere, mainly impacted the surface pressure field.
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