The impact of assimilating ATOVS 1D-var retrievals over Siberia

English, S.J. ; Poulsen, C.A. ; RENSHAW, R.J.

Editeur
The Met.Office
Année de publication
1999

1D-var retrievals from ATOVS have been assimilated using 3D-var in an area 30E-130E 50N-70N (corresponding closely to Siberia). For short range forecasts (1-2 days) RMS errors for mean sea level pressure and 500 hPa height over Siberia and the north-west Pacific were reduced by 5-10%. Over the whole northern hemisphere RMS errors fell by around 1%. At longer ranges the impact over the test region was lower, falling to 2% by 3 days and to the hemisphere average of 1% at 4 and 5 days. This gives an estimated improvement in the NWP index of 0.4%. The radiances largely reinforced the existing mean analysis but mid-​tropospheric temperatures were 0.2K lower over most of the test area. The mean temperature at longer forecast range was also lower but by less than 0.1K and thus a considerable spin-down of mid-​tropospheric temperatures over northern Asia was slightly reduced. Because the entire retrieved profile was assimilated the direct assimilation of radiances in 3D-var, anticipated for later in 1999, is expected to benefit similarly from the assimilation of radiances in this region. It gives encouragement for further improvement in the impact of radiances in the northern hemisphere especially when we begin testing the assimilation over all land regions during 2000.

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