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Model Best-fit Pressure Comparison - Feb/March 2010

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Introduction Stats vs Press Zonal Conclusions

Model best-fit pressure

The aim of this investigation is to compare the model best-fit pressure statistics from the Met Office and ECMWF global models.

The Met Office model best-fit pressure is defined as the model pressure (hPa) with the smallest vector difference between the AMV and model background wind. Some filtering is then applied to the data to remove cases where there is no good agreement between the AMV and the model (at any height) or where the best-fit pressure is not well constrained e.g. secondary/broad minima. A full description is given in the 3rd NWP SAF analysis report with one alteration; vertical interpolation is performed between model levels to find the minimum vector difference.

The ECMWF calculation of model best-fit pressure is identical except in the case where there are multiple minima which fulfil the criteria. In the ECMWF formulation the closest one minima to the originally assigned height is chosen, whereas the Met Office formulation will choose the first (i.e. lowest) minima.


Details of plotted data
General
  • This study covers the period February - March 2010
  • All data is in BUFR format.
  • A QI threshold of 80 is applied to all geostationary AMVs and a QI threshold of 60 is applied to all polar AMVs. The QI used is the EUMETSAT quality indicator without first guess check.
  • Latitude bands are NH (north of 20N), Tropics (20S-20N) and SH (south of 20S).
Plots
  • Pressure differences are calculated as (observed pressure - model bestfit pressure) hPa
  • The zonal plots have been binned in boxes 50 hPa by 2 degrees latitude.
  • The bestfit pressure plots as a function of pressure are plotted in 100 hPa intervals e.g. 1050, 950, 850..
Channels
  • For the Met Office these are given on the plots.
  • For ECMWF the channel numbers are:

    Meteosat-9
    • 301 IR 10.8um
    • 202 VIS 0.81
    • 302 VIS 0.75
    • 105 WV 6.2 (clear sky)
    • 205 WV 7.3 (clear sky)
    • 100 WV 6.2 (cloudy)
    • 200 WV 7.3 (cloudy)

    GOES-11 and GOES-12
    • 101 IR1 10.7
    • 102 VIS 0.65
    • 105 WV 7.4 (clear sky)
    • 201 IR 3.9
    • 205 WV 7.0 (clear sky)
    • 300 WV 6.8 (cloudy)
    • 305 WV 6.8 (clear sky)