Workshop: Aspects of regional modelling – at GKSS

Contributions by Hans von Storch, Frauke Feser, Insa Meinke and

Burkhardt Rockel

Ouranos, Montreal 7.9.2004

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.

Generation of gravity waves?

v

uSLP

Intensity of temporal variance on time scales between 2 and 6 hours

No SN = no spectral nudging SN = with spectral nudging

No SN No SNSN SN

Experiments with digital filtering and pre-filtering by

subtraction of 2d polynomials

),( yxPkf

),(),,(),,( yxFyxFyxF sf

mf

lf

),(),(),(),(),( yxFyxFyxFyxPyxf sf

mf

lf

kf

With representing a fitted polynomial of order k,

and filtered components representing large, medium and small spatial scales:

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

Digital filters

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

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.

Precipitation fields (mm) for the storm ’Anatol’ accumulated for December3rd, 1999, of a LAM simulation: (a) Unfiltered, (b) low-pass filtered, (c)band-pass filtered, and (d) high-pass filtered data.

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.

An example of

divergence in terms of cloudiness

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

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

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

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]

Inst

itu

t fü

r K

üst

enfo

rsch

un

g

I f K

The problem of regional noise

Inst

itu

t fü

r K

üst

enfo

rsch

un

g

I f K

standard

obs

spectral nudging

wind speed

Weis

se a

nd F

ese

r (2

002

)

The problem of regional noise