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A new ice microphysical processes for a commonly used bulk parameterization of cloud and precipitation. Song-You Hong (Yonsei Univ) Jimy Dudhia (NCAR) Shu-Hua Chen (U.C. Davis). Background A revised cloud scheme Idealized case experiment Heavy rainfall case experiment
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A new ice microphysical processes for a commonly used bulk parameterization of cloud and precipitation Song-You Hong (Yonsei Univ) Jimy Dudhia (NCAR) Shu-Hua Chen (U.C. Davis)
Background A revised cloud scheme Idealized case experiment Heavy rainfall case experiment Ice cloud – radiation interaction Conclusion List of presentation A tip for the MRFPBL
The highest level for the PBL is the half of the total number of vertical layers KLPBL = KL/2 (currently in WRF & MM5) The PBL mixing is ill-posed with many layers near the surface as done for the air pollution application Correction : In the “mrfpbl.F”, change KLPBL = 1 (modified one)
Community model: NCAR, NCEP, FSL, AFWA, NSSL, and University communities Real time fcsts : NCAR (22km, 10km), NSSL(34km), AWFA(45km), Italy (20km) MRF PBL, Kain-Fritsch cumulus RRTM, Dudhia Radiation Lin or NCEP simple ice microphysics WRF (Weather and Research Forecasting Model) http://wrf-model.org
- Hong et al. (1998), NCEP RSM cloud physics - NCEP cloud microphysics v1.0 (Hong et al. 1998, with some modifications) - NCEP cloud microphysics v1.1 (Jimy’s bug fix in computing Vr, Vs) - > solves the too much precip. - NCEP cloud microphysics v1.2 (Hong et al. 2002, the new scheme) NCEP Cloud Microphysics
NCEP (Hong) Cloud schemes NCEP CLOUD 3 (simple ice) and CLOUD 5 (mixed phase) qv (qci,qrs) (qc,qi,qr,qs) Modifications after Dudhia (1989) and Rutledge and Hobbs (1983)
Lin et al. (1983) and Rutledge and Hobbs (1983) -> core part of microphyscs A typical problem -> too much cirrusdue to Ni from Fletcher Different assumptions in microphysics ( Meyers et al. 1992, Kruger et al. 1995, Reisner et al. 1998, Rotstayn et al. 2000, Ryan 2001 ) Sedimentation of ice crystals (Manning and Davis, 1997, Wang 2001) Background
Ice crystal property (Mass, Diameter, Mixing ratio, Ice number)
Rotstayn 2000 Ryan 1996 Ryan 2000 Observed and formulated Ni
Fletcher : D89, RH83 - qicrit has small range of T : 0.1 and 1 gkg-1 for –27 and –32C This study - qicrit=0.18gkg-1, at T=-40C, P=300 mb
RH83,D89 This study Comparison of deposition rate of water vapor onto ice as a function of cloud temperature, with the assumption that cloud ice mixing ratio is 0.1 gkg-1 and the air is supersaturated with respect to ice by 10 %.
LW radiation : RRTM SW radiation : Dudhia Vertical diffusion : MRF Cumulus scheme : Kain-Fritsch Microphysics : NCEP (HONG) simple ice Grid size : 45 km, 15 km Time step : 120 s, 60 s Initial time : 1200 UTC 23 June 1997 Integration : 48 hrs Initial and BDY : NCEP GDAS WRF version 1.1-beta
Exp1 : Dudhia microphysics (OLD) Exp2 : Dudhia + sedimentation of qi Exp3 : New microphysics Exp4 : New + sedimentation of qi (NEW) Sensitivity Experiments
Cloud and Precipitation after 30 min. qci Lin HDC3 qrs
Exp1 Exp4 Exp3 Exp2 Exp3,4 Exp1, 2 qci qrs Fig. 3. Profiles of domain-averaged (a) cloud/ice water and (b) snow/rain water mixing ratio (gkg-1) for the Exp1 (thin solid line), Exp2 (dotted line), Exp3 (dashed line), and Exp4 (thick solid line) experiments.
(a) (b) A A heavy rainfall case : 1997.6.25
OBS EXP1 EXP2 EXP3 EXP4 45-km experiment : 24-hr precipitation (mm) > 90 mm
Volume-averaged qci Domain averaged 300 hPa T Exp1 Exp1 Exp2 Exp3 Exp2 Exp4 Exp3 ANAL Exp4
Exp1 : Dudhia microphysics (too much cloud ice -> warm bias) NORA : Exp1 but without radiation feedback due to ice cloud) NOLW : Exp1 but without LW radiation feedback due to ice cloud) NOSW : Exp1 but without SW radiation feedback due to ice cloud) Ice cloud - radiation feedback
Volume-averaged qci Domain averaged 300 hPa T NOSW EXP1 EXP1 NOSW ANAL NOLW NORA NORA NOLW
Ice cloud - radiation feedback More cloud ice Less SW heating More LW heating Tropospheric cooling Upper level heating Less SFC buoyancy Less cloud ice Less explicit rain Less implicit rain Less Precipitation, Warmer Troposphere
New scheme produces better cloudiness (remove high cloud bias) New scheme alleviates the discontinuity problem of small and large ice particles Reduction of ice clouds induces more surface precipitation Combined effects of improved microphysics and the inclusion of sedimentation of ice crystals are attributed to the improvement of precipitation, cloudiness, and large-scale features Sedimentation of HD1990 dominates the effects of detailed ice-microphysical processes Concluding Remarks
Thank you Regional climate Seasonal prediction Climate mechanism Severe weather NWP