These images are based upon the randomly selected time step 12UTC on 2008-05-03. Further 2 randomly selected time steps are also available:

• 2008-04-04, 18 UTC
• 2008-04-07, 05 UTC

In the latter case, numerical fluctuations take the shape of an area of elevated gravimetric humidity in the associated field.

Shown here is always the layer at the lowest altitude because only it is subjected to downscaling.

Fig. 1: Gravimetric humidity as supplied by the COSMO model: The coarse data.

Downscaled data

In the case of gravimetric humidity, there is no Schomburg rule, so the downscaling is limited to spline interpolation (cf. Fig. 2). Figures 3, 5, and 5.1 are missing for this reason.

Fig. 2: Gravimetric humidity after spline interpolation.

There is not much difference to be seen between figure 1 and 2. The smooth spline-interpolated field cannot introduce fine structures because it has no to access to fine data.

Fig. 4: Gravimetric humidity after spline interpolation and subsequent upscaling back to the coarse grid.

Fig. 4.1: Gravimetric humidity bias after spline interpolation, on the coarse grid.

As the bias is 10^7 times smaller than the ordinary fields above, it can safely be attributed to only numerical fluctuations.