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Explicit Forecasts of Winter Precipitation using an improved bulk microphysics scheme

Explicit Forecasts of Winter Precipitation using an improved bulk microphysics scheme. Gregory Thompson and Roy Rasmussen. Collaborators : Bill Hall, Matt Garvert, Brian Colle, Axel Seifert, Istvan Geresdi,…. Mount Washington, Oregon. Funded by FAA to support aircraft icing research.

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Explicit Forecasts of Winter Precipitation using an improved bulk microphysics scheme

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  1. Explicit Forecasts of Winter Precipitationusing an improved bulk microphysics scheme Gregory Thompson and Roy Rasmussen Collaborators: Bill Hall, Matt Garvert, Brian Colle, Axel Seifert, Istvan Geresdi,… Mount Washington, Oregon Funded by FAA to support aircraft icing research WMO Cloud Modeling Workshop Hamburg, Germany 12-16 July 2004

  2. Outline • 2D simulations • idealized flow simulations using 2-d version of MM5 (PSU/NCAR) • 18 sensitivity experiments plus 4 different cloud depths • bulk scheme tuned to Geresdi’s bin/explicit model • key results from sensitivity experiments • 3D case studies • one of numerous cases from variety of field projects • different precip formation mechanisms • different geographic regions (continental/maritime) • Future work • verification data • other bulk species (aggregates) or 2-moments? • WRF model simulations WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  3. Idealized 2-D simulations original R-G sounding increase moisture to create deeper and colder clouds modified sounding WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  4. MM5 microphysics testing in 2-d WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  5. 2-D sensitivity experiments • primary ice initiation • autoconversion (cloud to rain) • CCN spectra (maritime v. continental) • graupel • gamma vs. exp size distribution • rimed snow to graupel conversion • snow size distribution • y-intercept constant • y-intercept depends on mass • y-intercept depends on temp • rain size distribution • cloud depth increased to lower temps WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  6. Bin versus Control and Final bulk schemes WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  7. Key results of 2D bulk micro experiments 1. The choice of ice initiation schemes is relatively unimportant for deep, precipitating snow clouds but more important for shallow, warm clouds having cloud-top temperatures greater than –13°C. WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  8. Key results of 2D bulk micro experiments 2. The assumed snow size distribution and associated snow diffusional growth have major impacts on the mass of supercooled cloud water and formation of freezing drizzle. snow depositional growth M-P y-intercept WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  9. Key results of 2D bulk micro experiments Snow depositional growth 3. The assumed graupel size distribution and method of transforming rimed snow into graupel have major impacts on the mass of supercooled cloud water and formation of freezing drizzle. Snow riming growth relative ratio 1:3 1:1 WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  10. Key results of 2D bulk micro experiments 4. A proper simulation of drizzle using a single-moment scheme and exponential size distribution requires an increase in the rain intercept parameter, thereby reducing rain terminal velocities to values more characteristic of drizzle. orig. rain graupel snow new rain WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  11. 2-D Workshop case3 WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  12. 1990 Feb 13-14 (WISP) shallow, post-frontal, upslope cloud w/widespread FZDZ. 1998 Jan 30 (NASA-SLDRP) shallow stratoCu, primarily CLW w/slight FZDZ. 1998 Feb 04-05 (SLDRP) deep and dynamic snowstorm w/classic FZRA. 2001 Feb 01-02 (IMPROVE-1) deep PacNW frontal system, abundant precip. 2001 Nov 28 (IMPROVE-2) deep PacNW frontal system plus orographics. 2001 Dec 13-14 (IMPROVE-2) deep PacNW frontal system plus orographics. Case Studies WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  13. 30 Jan 1998 – NASA Twin Otter flight Canada Lake Erie Pennsylvania Ohio WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  14. 30 Jan 1998 – Cleveland, OH sounding WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  15. 30 Jan 1998 – cloud-top temperature WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  16. 30 Jan 1998 – liquid water content >95% of water mass in drops less than 30 microns WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  17. Future: • Expand analysis/verification: • how to verify snow/graupel mixing ratios • surface precipitation • composite pattern, lots of cases • include AIRS2 and other cases? WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  18. Future: • Expand analysis/verification: • how to verify snow/graupel mixing ratios • surface precipitation • composite pattern, lots of cases • include AIRS2 and other cases? • Comparisons to other models: • bin/explicit model of Geresdi • THIS WORKSHOP WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  19. Future: • Expand analysis/verification: • how to verify snow/graupel mixing ratios • surface precipitation • composite pattern, lots of cases • include AIRS2 and other cases? • Comparisons to other models: • bin/explicit model of Geresdi • THIS WORKSHOP • Put into WRF model: • std-version + 2-moment • Hall/Seifert modifications WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  20. Future: • Expand analysis/verification: • how to verify snow/graupel mixing ratios • surface precipitation • composite pattern, lots of cases • include AIRS2 and other cases? • Comparisons to other models: • bin/explicit model of Geresdi • THIS WORKSHOP • Put into WRF model: • std-version + 2-moment • Hall/Seifert modifications • Other micro species: • aggregate category? • drizzle category? • hail category? WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

  21. Thompson, Rasmussen, & Manning, 2004: Explicit forecasts of winter precipitation using an improved bulk microphysics scheme. Part I: Description and sensitivity analysis. Mon. Wea. Rev., 132, 519-542. Thompson, Bernstein, & Rasmussen, 2004: Explicit forecasts of winter precipitation using an improved bulk microphysics scheme. Part II: Case studies. Mon. Wea. Rev., in preparation. JAS - IMPROVE special issue (late 2004). Microphysics: more detailed reports WMO Cloud Modeling Workshop, 12-16 July 2004, Hamburg, Germany

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