Cosmo implementations at cnmca tests with different dinamycal options
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COSMO implementations at CNMCA: tests with different dinamycal options. Lucio TORRISI Italian Met. Service CNMCA – Pratica di Mare (Rome) l.torrisi@meteoam.it. Overview. COSMO implementations at CNMCA New reference atmosphere impact 7km RK/LF comparison RKold (previous to 4.9) RK4.9

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Cosmo implementations at cnmca tests with different dinamycal options
COSMO implementations at CNMCA: tests with different dinamycal options

Lucio TORRISI

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

l.torrisi@meteoam.it


Overview
Overview dinamycal options

  • 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


Cosmo implementations at cnmca tests with different dinamycal options

CNMCA NWP System dinamycal options

  • compressible equations

  • explicit convection

2.8 km

  • hydrostatic equations

  • parameterized convection

14 km

  • compressible equations

  • parameterized convection

7 km


New reference atmosphere
New reference atmosphere dinamycal options

Zaengl (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.


Cosmo implementations at cnmca tests with different dinamycal options

New reference atmosphere dinamycal options


Cosmo implementations at cnmca tests with different dinamycal options

Pressure bias problem (1) dinamycal options

  • 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.


Cosmo implementations at cnmca tests with different dinamycal options

7km RKold/LF comparison dinamycal options


Cosmo implementations at cnmca tests with different dinamycal options

7km RKold/LF comparison dinamycal options


Cosmo implementations at cnmca tests with different dinamycal options

7km LF: MSLP bias dinamycal options


Cosmo implementations at cnmca tests with different dinamycal options

7km LF/RKold: MSLP bias dinamycal options


Cosmo implementations at cnmca tests with different dinamycal options

7km RK4.9/LF comparison dinamycal options

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


7km rk4 9 lf comparison
7km RK4.9/LF comparison dinamycal options


Cosmo implementations at cnmca tests with different dinamycal options

7km RK4.9/LF comparison dinamycal options


7km rk4 9 lf comparison1
7km RK4.9/LF comparison dinamycal options


7km rk4 9 lf comparison2
7km RK4.9/LF comparison dinamycal options


Cosmo implementations at cnmca tests with different dinamycal options

7km LF/RK: MSLP bias dinamycal options

LF

RK4.9

RKold


14km rk4 9 lf comparison
14km RK4.9/LF comparison dinamycal options


Rk lf comparison
RK/LF comparison dinamycal options

  • 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.


Rk4 9 iva eva comparison
RK4.9 IVA/EVA comparison dinamycal options

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)


Cosmo implementations at cnmca tests with different dinamycal options

7km RK4.9 IVA/EVA comparison dinamycal options


Cosmo implementations at cnmca tests with different dinamycal options

7km RK4.9 IVA/EVA comparison dinamycal options


Cosmo implementations at cnmca tests with different dinamycal options

7km RK4.9 IVA/EVA comparison dinamycal options


Cosmo implementations at cnmca tests with different dinamycal options

7km RK4.9 IVA/EVA comparison dinamycal options


Cosmo implementations at cnmca tests with different dinamycal options

2.8km RK4.9 IVA/EVA compar. dinamycal options


Conclusion
Conclusion dinamycal options

  • 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).



Cosmo implementations at cnmca tests with different dinamycal options

Pressure bias problem (2) dinamycal options

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


Cosmo implementations at cnmca tests with different dinamycal options

Pressure bias problem (3) dinamycal options

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