COSMO implementations at CNMCA: tests with different dinamycal options

11th COSMO General Meeting, Offenbach, 7-10 September 2009

COSMO implementations at CNMCA: tests with different

dinamycal options

Lucio TORRISI

Italian Met. Service CNMCA – Pratica di Mare (Rome)

[email protected]


Overview• COSMO implementations at CNMCA• New reference atmosphere impact • 7km RK/LF comparison

– RKold (previous to 4.9)– RK4.9– RK4.9_EVA– MSLP bias distribution

• 14 km RK4.9_EVA/LF comparison • 2.8 km RKold/RKold_EVA comparison • Conclusion


14 km

7 km

2.8 km

- hydrostatic equations- parameterized convection

- compressible equations- parameterized convection

- compressible equations- explicit convection

CNMCA NWP System


New reference atmosphereZaengl (2008) implemented in COSMO model a new reference atmosphere based on a temperature profile which starts with a prescribed sea-level temperature and exponentially approaches an isothermal stratosphere. In this way there is no limitation on vertical extent of model domain.


New reference atmosphere


Pressure bias problem (1) • This problem was pointed out in Torrisi (2005):

“Sensitivity experiments with the Runge Kutta time integration scheme”, presentation at COSMO GM in Zurich

1) RK/LF core - Objective verification showed a difference in MSLP bias behaviour between 7km RK (red line) and LF (green line) runs.

MSLP bias difference increases with forecast time. RK runs have a larger bias, typically positive, leading to a worse RMSE.


7km RKold/LF comparison


7km LF: MSLP bias


7km LF/RKold: MSLP bias


7km RK4.9/LF comparison

In COSMO 4.9 a more accurate discretization of the metric terms was introduced by G. Zaengl.


7km LF/RK: MSLP bias

RK4.9

RKold

LF


• Pressure forecast skill of RK dynamical core was clearly improved by the new discretization of the metric terms introduced in version 4.9 (7-14km)

• RK have a better MSLP RMSE than LF; the sign of bias is positive for LF and negative for RK

• Spatial distribution of RK MSLP bias confirms how this dynamical core is sensitive to the change in the discretization of the metric terms.

RK/LF comparison


RK4.9 IVA/EVA comparison

Vertical advection in COSMO• IVA - Vertically implicit centered diff.

2° order (and 3° order in the next future)

• EVA - Vertically explicit upwind scheme (3°/5° order)


7km RK4.9 IVA/EVA comparison


2.8km RK4.9 IVA/EVA compar.


Conclusion

• The new reference atmosfere has a neutral impact except for above 100 hPa.

• The pressure forecast skill of RK dynamical core is clearly improved by the new discretization of the metric terms introduced in version 4.9 (7-14km)

• The third order explicit vertical advection scheme has a slightly positive impact on wind and mean sea level pressure (higher accuracy, more consistent with explicit horizontal advection).


Thank you for your attention!


Pressure bias problem (2) 2) Domain size - Objective verification showed a difference in MSLP bias behaviour in 7km RK (and LF) runs having a different domain size (smaller one - red line, larger one -green line).

The larger domain, the greater MSLP bias


Pressure bias problem (3) 3) Model formulation - Objective verification showed a difference in MSLP bias behaviour between 14km COSMO LF/RK (blue line) and HRM (red line) runs.

HRM is the DWD regional hydrostatic model (LF time integration scheme) used in the CNMCA assimilation systems (3D-Var PSAS and LETKF).

MSLP bias difference increases with forecast time (COSMO larger positive bias)

COSMO

EURO-HRM

COSMO implementations at CNMCA: tests with different dinamycal options

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