These images are based upon the randomly selected time step 18UTC on 2008-04-04. The layer is always the one at the lowest altitude because only this is subjected to downscaling.

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

Downscaled data

Due to the existence of a Schomburg rule for temperature, it can be subjected to full downscaling (fig. 3,5,5.1). Figures 2,4,4.1 deal with results from mere interpolation.

Fig. 2: Temperature after spline interpolation. Fig. 3: Temperature after full downscaling.

Fig. 4: Temperature after spline interpolation and subsequent upscaling back to the coarse grid. Fig. 5: Temperature after full downscaling and subsequent upscaling back to the coarse grid.

Fig. 4.1: Temperature bias after spline interpolation, on the coarse grid. Fig. 5.1: Temperature bias after full downscaling, on the coarse grid. The axis limits have changed.

Compared to the usual differences of 10 K within such a temperature field (fig. 1), the biases cover a mere 6*10^–5 K. This hints at numerical fluctuations around a bias of 0 K.