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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 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 • RK4.9_EVA • MSLP bias distribution • 14 km RK4.9_EVA/LF comparison • 2.8 km RKold/RKold_EVA comparison • Conclusion
CNMCA NWP System • compressible equations • explicit convection 2.8 km • hydrostatic equations • parameterized convection 14 km • compressible equations • parameterized convection 7 km
New reference atmosphere 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.
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 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 LF RK4.9 RKold
RK/LF comparison • 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 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)
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).
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