1. Workshop: Aspects of regional modelling – at GKSS Contributions by Hans von Storch, Frauke Feser, Insa Meinke and Burkhardt Rockel Ouranos, Montreal 7.9.2004

2. Issues Generation of gravity waves Experiments with digital filtering and pre- filtering by subtraction of 2d polynomials An example of divergence in terms of cloudiness Castro’s hypothesis – in large area simulations, lateral control is insufficient to maintain large scale states.

3. Generation of gravity waves? v u SLP Intensity of temporal variance on time scales between 2 and 6 hours No SN = no spectral nudging SN = with spectral nudging No SN SN

4. Experiments with digital filtering and pre-filtering by subtraction of 2d polynomials With representing a fitted polynomial of order k, and filtered components representing large, medium and small spatial scales:

5. Subtraction of Polynomials of order k=1 and K=2

6. Digital filters The filters are almost isotropic digital filters, obtained by solving an optimization problem

7. 10m wind speed fields (m/s) for the storm ’Anatol’ on December 3rd, 1999, 6 p.m., of a LAM simulation: (a) Unfiltered, (b) low-pass filtered, (c) bandpass filtered, and (d) high-pass filtered data. After subtraction of fitted polynomial of 2nd order.

8. Precipitation fields (mm) for the storm ’Anatol’ accumulated for December 3rd, 1999, of a LAM simulation: (a) Unfiltered, (b) low-pass filtered, (c) band-pass filtered, and (d) high-pass filtered data.

9. Mean sea level pressure (hPa) for the storm ’Anatol’ for December 3rd, 1999, 6 p.m. of a LAM simulation: (a) Unfiltered, (b) low-pass filtered, (c) band-pass filtered, and (d) high-pass filtered data.

10. An example of divergence in terms of cloudiness

12. Castro’s hypothesis – in large area simulations, lateral control is insufficient to maintain large scale states. Castro, C.L., and R.A. Pielke, Sr., 2004: Dynamical Downscaling: Assessment of value restored and added using the Regional Atmospheric Modelling System. submitted

13. NCEP small 50 km 500 hPa height, 0000 UTC, 12 May 1993 Lateral constraint too weak to maintain large-scale in the interior if flushing time too long (Example: May 1993; strongly non-zonal flow) - Castro and Pielke, 2004.  small -- large integration area

14. The finding of Castro & Peilke is not specific to RAMS – but emerges also in CLM (Rockel, pers. comm) CLM NCEP 13. May 1993, 00 UTC

15. The Rinke & Dethloff study on regional modelling of the Arctic atmosphere Rinke, A., and K. Dethloff, 2000: On the sensitivity of a regional Arctic climate model to initial and boundary conditions. Clim. Res. 14, 101-113. Ensemble standard deviation 500 hPa height [m²/s²] Institut für Küstenforschung I f K The problem of regional noise

16. Institut für Küstenforschung I f K standard obs spectral nudging wind speed Weisse and Feser (2002) The problem of regional noise