Three-category ice scheme WP 3.4.1 Three-category ice scheme Thorsten Reinhardt, Deutscher Wetterdienst Thorsten.Reinhardt@dwd.de

Motivation: In convective precipitation events, which are intended to be simulated explicitly in LMK, there occur not only unrimed or slightly rimed ice particles, but also more densely rimed particles like graupel or hailstones which have different properties compared to snow. At same mass concentration Graupel has a larger sedimentation flux Graupel grows less efficiently by vapour deposition and riming Graupel melts less fast than snow. For this reason, we want to consider in the LMK microphysics parameterization - besides snow - also graupel as an additional precipitation ice particle category.

Precipitation ice particles in LM microphysics parameterization: Up to now: Snow Now additionally: Graupel

Initiation of graupel: from freezing of raindrops from conversion of snow to graupel due to riming (if a cloud water threshold of 0.2 g/kg is exceeded) Additional conversion rates (formulated analogous to those of snow): water vapor deposition / sublimation riming collision with cloud ice particles (aggregation) melting

Additional Changes: For autoconversion from cloud water to rain a threshold of 0.2 g/kg is introduced. Coefficients for deposition and melting depend now from pressure and temperature; rates re-fitted Sublimation of cloud ice according to sublimation rate Sublimation of snow/graupel considered also at T>0 ºC.

Idealized simulation: 2-d warm bubble (after 72 min) Standard scheme Graupel scheme yellow: cloud ice red: snow green: graupel light blue: cloud water dark blue: rain (units: g/kg) Mesh size: 2 km

Real 3-d simulations with LMK: Cross-sections of hydrometeor distribution Stratiform snowfall event (left) & convective event (right) Graupel scheme simulates snow/graupel in a plausible way.

IMPROVE-2 Testcase Observation. Cloud water content (and also graupel, not shown) in modified version (increased snow-graupel conversion) agrees better with observation, but modified version seems to overpredict graupel in LMK real-weather simulations Graupel scheme Graupel scheme modified g/kg Mesh size: 1km

Cloud water content: IMPROVE-2 Case Observation 2-moment scheme Graupel scheme LM 3.13 Graupel scheme modified x=1km g/kg

LMK Testsuite July to September 2004 Synop verification reveals: Graupel testsuite scores are quite similar to parallel testsuite without graupel Total precipitation slightly (few percent) reduced Positive frequency bias for precipitation (especially 0.1-2 mm/h) is reduced

Outlook: • Testing whether a graupel category with more hail-like properties instead of those of low-density graupel might be more appropriate • Evaluation of simulated cloud microphysical quantities against cloudnet data Graupel scheme is standard for ongoing LMK testsuites now.