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G REGORY T HOMPSON, R OY M . R ASMUSSEN, AND K EVIN M ANNING

Explicit Forecasts of Winter Precipitation Using an Improved Bulk Microphysics Scheme. Part Ⅰ: Description and Sensitivity Analysis. G REGORY T HOMPSON, R OY M . R ASMUSSEN, AND K EVIN M ANNING February 2004 Monthly Weather Review 519~542. 1.Introduction.

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G REGORY T HOMPSON, R OY M . R ASMUSSEN, AND K EVIN M ANNING

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  1. Explicit Forecasts of Winter Precipitation Using an Improved Bulk Microphysics Scheme.Part Ⅰ: Description and Sensitivity Analysis GREGORY THOMPSON, ROY M. RASMUSSEN, AND KEVIN MANNING February 2004 Monthly Weather Review 519~542

  2. 1.Introduction • Explicit bin-resolving cloud models(Rasmussen et al 2002, hereafter RG) • Bulk microphysics parameterization • 利用Reisner et al.(hereafter RRB)作為修正基準 • 目的：改善顯示(explicit)的即時過冷水滴預報，藉以防止飛機積冰(aircraft icing)的現象發生 Note : 利用bulk model來替代explicit model，節省計算時間

  3. 2.Description of the bulk microphysics parameterization • Initiation of cloud ice • Autoconversion • Treatment of graupel • Intercept parameter of the snow size distribution • Intercept parameter of the rain size distribution

  4. Initiation of cloud ice Fletcher 1962 Cooper 1986 Meyers 1992

  5. Note : 在最近的研究指出ice的形成Si >5%，T<-5℃

  6. Autoconversion Kessler 1969 Qr is rain content,Db=0.3, Nb is cloud droplet concentration, Qc is the cloud water content Berry 1968 (Berry and Reinhardt 1974) υ is a gamma distribution parameter

  7. Treatment of graupel 改進冰雹形成中兩個最大量： Rutledge and Hobbs 1983

  8. Intercept parameter of snow size • 因為固定的截斷參數(N0,S)使得過多的雲水被消耗 • 發展一個跟混和比和single moment相關的關係式(Swann 1998) • 平均粒子直徑跟溫度一起增加，且N0,S和λ減小時，溫度也會增加(Houze et al. 1979) Houze et al 1979

  9. 灰粗線/虛線是利用Houze et al.1979 細實線/虛線是Reisner et al.1998

  10. Intercept parameter of rain size distribution • Droplet size drizzle drops rain (雨滴的形成過程) • 在大部分的single moment scheme中，都是假設雨水突然由雲水形成而且呈現Marshall-Pamler size distibution and intercept parameter(8106(m-4)) • 考慮drizzle to rain

  11. 大雨滴 小雨滴 粗實線是利用上頁公式畫出來的終端速度和雨混和比圖，虛線是利用N0,r= 8106(m- 4)做出來的圖

  12. 3.Approach • Mesoscale model (MM5) • 2-D idealized configuration • 120points, spacing 10km • 39σp level, flow is 15ms-1 • Bell-shaped mountain 1km high with 100km half-width

  13. 敏感度實驗的設定

  14. 4.Sensitivity tests

  15. CONTROL experiment

  16. b.Bin model Initial cloud ice是利用Cooper(1986)

  17. c.Ice initial:Meyers and Fletcher experiment • Fletcher experiment減少了cloud ice 在鋒值的數量 • Meyers experiment增加了cloud ice 的數量

  18. d.Autoconversion:Kessler1, Kessler5, Berry, and BandR Kessler1(qco=0.110-3) Kessler5(qco=0.5 10-3) Berry(1986) BandR(Berry and Reinhardt autoconversion 1974)

  19. e.CCN spectra:Maritime, Continent1, and Continent2 experiment Maritime(Nc=50cm-3) Continent1(Nc=200cm-3) Continent2(Nc=500cm-3)

  20. f.Treatment of graupel: Graupel1 and Graupel2 experiment Graupel1:original exponential distribution, No,g=4 106m-4, and Reisner rimed snow-to-graupel conversion Graupel2:Riming growth of snow must be 3 times larger then depositional growth before creating graupel

  21. g.Version2 • 把Fletcher, Kessler5, Graupel1一起使用 • 可以得到一個非常接近Graupel1的結果，所以在這三組實驗中以Graupel1比較敏感

  22. h.Snow intercept parameter:SON and SONV experiment SON(No,s=2 107m-4) SONV(No,s=f(T))

  23. i.Rain intercept parameter:RON and RONV RON(No,r=11010m-4) RONV(No,r=f(qr)) Note : combine SNOV

  24. j.Final experiment BandR, Graupel2, SONV, RONV一起使用

  25. k.Deeper/colder cloud system • CCT=-25℃ • CCT=-60℃ • Seeder and feeder system

  26. CCT=-25℃

  27. CCT=-60℃

  28. Seeder and feeder system 上層都是由冰晶跟雪組成的溫度較低的雲 下層是混和雲 在經過兩小時之後上層的雲開始影響下層 在下層會有一些過冷毛雨被冰覆蓋落在地面

  29. Conclusion • Primary ice nucleation using Copper(1986), replaces the Fletcher(1962) curve • Autoconversion using Walko et al.(1995), replaces the Kessler scheme • A generalized gamma distribution for graupel (eq. 8) replaces the exponential distribution; the intercept parameter depends on mixing ratio (eq. 10) instead of constant; and riming growth of snow must exceed depositional growth of snow by a factor 3 before rimed snow transfers graupel • The intercept parameter of snow size distribution depends on temperature replacing the mixing ratio dependency • The intercept parameter for rain size distribution depend on mixing ratio, thereby simulating the fall velocity of drizzle drops as well as raindrops

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