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Surface pressure bias on 2008-04-07, 05UTC

These images are based upon the randomly selected time step 05UTC on 2008-04-07. The layer is always the one at the lowest altitude because only this is subjected to downscaling.

Coarse sfc pressure from COSMO-DE
Fig. 1: Pressure as supplied by the COSMO model: The coarse data.

Downscaled data

Due to the existence of a Schomburg rule for pressure, it can be subjected to full downscaling (fig. 3,5,5.1). Figures 2,4,4.1 deal with results from mere interpolation.
Fine sfc pressure after downscaling w\o rules Fine sfc pressure after downscaling with rules
Fig. 2: Pressure after spline interpolation. Fig. 3: Pressure after full downscaling.

Coarse sfc pressure after downscaling w\o rules and susequent upscaling Coarse sfc pressure after downscaling with rules and susequent upscaling
Fig. 4: Pressure after spline interpolation and subsequent upscaling back to the coarse grid. Fig. 5: Pressure after full downscaling and subsequent upscaling back to the coarse grid.

sfc pressure bias from downscaling w\o rules sfc pressure bias from downscaling with rules
Fig. 4.1: Pressure bias after spline interpolation, on the coarse grid. Fig. 5.1: Pressure bias after full downscaling, on the coarse grid. The axis limits have changed.

While common fluctuations within the pressure field hardly ever exceed 10^4 Pa = 100 hPa, the bias fluctuations are much smaller, on the scale of 10^–3 Pa. This encourages the interpretation that the calculated bias is 0 plus some numerical fluctuations.

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