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Aktionsprogramm 2003
-Thorsten Reinhardt, DWD
Sensitivity Tests Regarding Assumed Graupel Particle Properties
Motivation:
Gilmore et al (MWR 2004) found high sensitivity to assumed graupel/hail particle properties in simulations of idealized convection.
Can in LMK graupel particle properties changed to more hail-likeproperties help to reduce problem of underestimation of convection?
Aktionsprogramm 2003
-Thorsten Reinhardt, DWD
Aktionsprogramm 2003
-Thorsten Reinhardt, DWD
Sensitivity Tests Regarding Assumed Graupel Particle Properties
• Intercept parameter N0 in particle size distribution N0 = 4*104 m-4, N0 = 4*105 m-4, N0 = 4*106 m-4 (currently: N0 = 4*106 m-4)
• Graupel density rho 0,2 g/cm3, rho = 0,4 g/cm3, rho = 0,9 g/cm3
(currently: rho 0,2 g/cm3)
)exp()(0
DDf N
Both variations change graupel properties toward those of hail-like particles.
Aktionsprogramm 2003
-Thorsten Reinhardt, DWD
Idealized Convection(dx=2.8 km,3d Weisman-Klemp warm bubble, strong vertical (unidirectional) wind shear,
--> symmetric cell-splitting)
Total precipitation (TotP, in Gg), total graupel precipitation (TotG, in Gg),maximum precipitation (MaxP, in mm), maximum graupel precipitation (MaxG, in mm),after 2 hours.
Aktionsprogramm 2003
-Thorsten Reinhardt, DWD
Standard LME schemeno graupel (snow only)
Graupel (as currently used)N0 = 4*106 m-4
rho 0,2 g/cm3
Hail-like graupelN0 = 4*104 m-4
rho = 0,9 g/cm3
precipitation after 2 h in mm precipitation after 2 h in mm precipitation after 2 h in mm
Idealized Convection(dx=2.8 km,3d Weisman-Klemp warm bubble, strong vertical (unidirectional) wind shear,
--> symmetric cell-splitting)
Aktionsprogramm 2003
-Thorsten Reinhardt, DWD
LMK Simulation of 7th Aug 2004 Weather Situation
Mean total precipitation (MeanP, in mm), mean total graupel precipitation (MeanG, in mm), maximum precipiation (MaxP, in mm), maximum graupel precipiation (MaxG, in mm), after 23 hours.
Aktionsprogramm 2003
-Thorsten Reinhardt, DWD
rho 0,2 g/cm3
N0 = 4*106 m-4
rho 0,9 g/cm3
N0 = 4*104 m-4
LM schemeno graupel
radar
Aktionsprogramm 2003
-Thorsten Reinhardt, DWD
Conclusion
• In LMK simulations of idealized strong convection simulated precipitation can be highly sensitive to the assumed graupel particle properties.
• This sensitivity was much weaker in simulations of real weather situations.
• Changing graupel properties toward those of more hail-like properties does not cure problem of underestimated convection in LMK.
• Therefore a change in the parameterization of the graupel category in the microphysics scheme was not introduced.
