Semi-implicit predictor-corrector methods for atmospheric models Colm Clancy Janusz A. Pudykiewicz Atmospheric Numerical Weather Prediction Research, Environment Canada PDEs on the Sphere, 26th of September 2012
Motivation Development of a finite-volume atmospheric model on an icosahedral grid (Pudykiewicz 2006, 2011) Investigation of stable time integration schemes, beyond the traditional semi-implicit leapfrog Some recent work: Williams (2011), Durran & Blossey (2012), Kar (2012)
General ODE system
General ODE system ‘Traditional’ semi-implicit, (SILF):
Semi-implicit predictor-corrector approach Predictor stage, for : Corrector stage, for :
Implicit linear terms: Trapezoidal AM2*
Explicit nonlinear terms:
Many possible combinations… Examples:
Linear stability analysis
Reference semi-implicit
Shallow water tests Shallow water model of Pudykiewicz (2011) Iterative GCR(4) solver for Helmholtz equations (Smolarkiewicz and Margolin, 2000) No explicit diffusion Filter of Williams (2011) for the semi-implicit leapfrog Spatial resolution: grid 6 (40,962 nodes, ~112km). Reference: grid 7 (163,842 nodes, ~56km) with RK4 at 90s time-step
Sample results: Flow over isolated mountain
Williamson et al. (1992) – Mountain case
Williamson et al. (1992) – Mountain case
Williamson et al. (1992) – Mountain case
Sample results: Rossby-Haurwitz wave
Williamson et al. (1992) – RH wave case
Williamson et al. (1992) – RH wave case
Williamson et al. (1992) – RH wave case
Efficiency Predictor-corrector schemes: two elliptic solver calls per time-step Consider total number of iterations per step
Efficiency
Conclusions and further work Semi-implicit predictor-corrector schemes offer an accurate alternative to the traditional leapfrog: Stable No time filter necessary Efficiency not affected Future tests with a three-dimensional baroclinic model Comparison with other time integration methods
References Clancy & Pudykiewicz (2012); to appear in J. Comp. Phys. Durran & Blossey (2012); Mon. Weather. Rev. 140, 1307-1325 Kar (2012); Mon. Weather. Rev. 134, 2916-2926 Pudykiewicz (2006); J. Comp. Phys. 213, 358-390 Pudykiewicz (2011); J. Comp. Phys. 230, 1956-1991 Smolarkiewicz & Margolin (2000). Proc. ECWMF Workshop, 5-7 June 2000, 137-159 Williams (2011); Mon. Weather. Rev. 139, 1996-2007 Williamson et al. (1992); J. Comp. Phys. 102, 211-224
Many possible combinations…