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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-like

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Sensitivity tests regarding assumed graupel particle properties
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-like

properties help to reduce problem of underestimation of convection?


Sensitivity tests regarding assumed graupel particle properties1
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)

Both variations change graupel properties toward those of hail-like particles.


Idealized Convection Properties

(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.


Idealized Convection Properties

(dx=2.8 km,3d Weisman-Klemp warm bubble, strong vertical (unidirectional) wind shear,

--> symmetric cell-splitting)

precipitation after 2 h in mm

precipitation after 2 h in mm

precipitation after 2 h in mm

Standard LME scheme

no graupel (snow only)

Hail-like graupel

N0 = 4*104 m-4

rho = 0,9 g/cm3

Graupel (as currently used)

N0 = 4*106 m-4

rho  0,2 g/cm3


LMK Simulation of 7th Aug 2004 Weather Situation Properties

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.


rho Properties 0,2 g/cm3

N0 = 4*106 m-4

LM scheme

no graupel

rho  0,9 g/cm3

N0 = 4*104 m-4

radar


Conclusion
Conclusion Properties

  • 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.


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