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Semi-implicit semi-Lagrangian methods for numerical weather ...

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<strong>Semi</strong>-Implicit<br />

<strong>Semi</strong>-<br />

<strong>Lagrangian</strong><br />

Time-<br />

Stepping<br />

Methods and<br />

Regularized<br />

Fluid<br />

Equations in<br />

Numerical<br />

Weather<br />

Prediction<br />

Sebastian<br />

Reich<br />

Numerical<br />

Weather<br />

Prediction<br />

Basic Facts<br />

Unified Model<br />

Towards a<br />

New Dynamic<br />

Core<br />

Model System and<br />

Basic Ideas<br />

Results<br />

General<br />

Methodology<br />

Concluding<br />

Remarks<br />

Improved Regularization<br />

Linear Waves<br />

On a linearized equation level both discretizations behave<br />

the same <strong>for</strong> waves provided that [Frank et al 2004]<br />

<br />

f ∆t<br />

gH∆t<br />

γ = , α = .<br />

2 2<br />

However, the geostrophic mode is distorted.<br />

Balanced Regularization<br />

Improved regularization [Wood, Stani<strong>for</strong>th, Reich, 2005]:<br />

(1 + γ 2 − α 2 ∇ 2 <br />

) ˜h − h = α 2<br />

<br />

∇ 2 h − f<br />

g (vx<br />

<br />

− uy)

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