Jason Milbrandt Recherche en Prévision Numérique [RPN] Meteorological Research Division, Environment Canada GEM Workshop, June 12, 2007 Multi-Moment Cloud Microphysics Package A New Multi-Moment Cloud Microphysics Package for the GEM-LAM
Why develop a new cloud scheme for GEM? Computer resources increasing High-resolution NWP grids are becoming mainstream Important to predict cloud processes as well as possible GEM-LAM-2.5 has systematic problems with the precipitation forecasts
1.Background on bulk schemes 2.Description of the new microphysics package 3.Some advantages of the multi-moment approach OUTLINE
One of the goals of NWP model: Predict the effects of the clouds
MODEL GRID: (hypothetical NWP model) PARTLY CLOUDY (RH < 100%) CLOUDY (RH = 100%) CLOUD- FREE CPSEXPLICIT SCHEME
Single cloudy grid element: CLOUDY (RH = 100%) EXPLICIT SCHEME
INPUT: w, T, p, q v Single cloudy grid element – interaction with NWP model:
MICROPHYSICAL PROCESSES in the cloudy grid element
Single cloudy grid element – interaction with NWP model: Changes to w, T, p, q v and q c, q r, q i,... Advection and Turbulent Mixing MICROPHYSICAL PROCESSES OUTPUT: Latent heating Hydrometeors (cloud, rain, ice,…) q c, q r, q i,... INPUT: w, T, p, q v q c, q r, q i,...
Single cloudy grid element: Slight magnification = cloudy (saturated) air
Single cloudy grid element: Extreme magnification
1 m 3 (unit volume) [e.g. Cloud droplets] (not to scale)
N (D)N (D) D [ m] 100 [m -3 m -1 ] m 3 (unit volume) [e.g. Cloud droplets] (not to scale)
(Example of observed cloud droplet spectrum) N (D)N (D) D [ m] 100 [m -3 m -1 ] m 3 (unit volume) [e.g. Cloud droplets] (not to scale)
DISCRETE SIZE BINS SPECTRAL METHOD Representing the size spectrum N (D)N (D) D [ m] 100 [m -3 m -1 ] m 3 (unit volume) [e.g. Cloud droplets] (not to scale)
1 m 3 (unit volume) BULK METHOD N (D)N (D) D [ m] 100 [m -3 m -1 ] ANAYLTICAL FUNCTION [e.g. Cloud droplets] (not to scale) Representing the size spectrum
Gamma Distribution Function: * Q = q (mass content) INCREASING VALUES (of, N 0 and ) log N(D) D [mm] Varying : (N 0 and constant) Varying : (Q * and N 0 constant) Varying N 0 : ( and constant)
BULK METHOD Size Distribution Function: p th moment: N (D)N (D) D Hydrometeor Category x Total number concentration, N Tx Radar reflectivity factor, Z x Mass mixing ratio, q x Example of Moments:
BULK METHOD Size Distribution Function: p th moment: Total number concentration, N Tx Radar reflectivity factor, Z x Mass mixing ratio, q x Example of Moments: Predict changes to specific moment(s) e.g. q x, N Tx,... Implies changes to values of parameters i.e. N 0x, x,...
* (May contain traces of supercooled water) T < 0 C *
T < 0 C = ICE CRYSTAL (May contain traces of supercooled water)
T < 0 C = ICE CRYSTAL = SNOW CRYSTAL / AGGRETATE (May contain traces of supercooled water)
T < 0 C = ICE CRYSTAL = SNOW CRYSTAL / AGGREGATE = GRAUPEL (May contain traces of supercooled water)
T < 0 C = ICE CRYSTAL = SNOW CRYSTAL / AGGREGATE = GRAUPEL = HAIL (May contain traces of supercooled water)
= ICE CRYSTAL = SNOW CRYSTAL / AGGREGATE = GRAUPEL = HAIL = LIQUID WATER T < 0 C
ICE SNOW GRAUPEL HAIL LIQUID WATER PARTITIONING THE HYDROMETEOR SPECTRUM
ICE SNOW CLOUD GRAUPEL HAIL RAIN PARTITIONING THE HYDROMETEOR SPECTRUM
ICE SNOW CLOUD GRAUPEL HAIL RAIN BULK METHOD PARTITIONING THE HYDROMETEOR SPECTRUM
Full TRIPLE-MOMENT Version: Six hydrometeor categories: –2 liquid: cloud and rain –4 frozen: ice, snow, graupel and hail ~50 distinct microphysical processes Warm-rain scheme based on Cohard and Pinty (2000a) Ice-phase based on Murakami (1990), Ferrier (1994), Meyers et al. (1997), Reisner et al. (1998), etc. Predictive equations for Z x added for triple-moment* * Milbrandt and Yau (2005a,b) [J. Atmos. Sci.] Milbrandt-Yau Cloud Scheme *
Diagnostic-Dispersion DOUBLE-MOMENT Version: Identical to full version except: Diagnostic- x relations added for double-moment* Milbrandt-Yau Cloud Scheme * Recall: Size Distribution Function:
CURRENT VERSIONS AVAILABLE FOR GEM: GEM_v3.2.2 / PHY_4.4 available upon request** GEM_v3.3.0 / PHY_4.5 part of official RPN/CMC library Single-moment version –Six hydrometeor categories –Single-moment (Q x ) for each Double-moment version –Six hydrometeor categories –double-moment (Q x,, N x ) for each –fixed- x Milbrandt-Yau Cloud Scheme **(also available for MC2_v4.9.8)
UPCOMING VERSION AVAILABLE FOR GEM: Prototype cloud scheme for the 2010 Winter Olympics “Olympic” version * CLOUDdouble-moment(Q c, N c ) RAINdouble-moment(Q r, N r ) [diagnostic- r ] ICE/SNOWdouble-moment(Q i, N i ) [hybrid category] GRAUPELsingle-moment(Q g ) HAILdouble-moment(Q h, N h ) [diagnostic- h ] Milbrandt-Yau Cloud Scheme * To be implemented in GEM-LAM 2.5 km AUTUMN 2007
Prognostic N c Double-Moment “CLOUD” Category: Condensation rate based on saturation adjustment N c initialization is air-mass (CCN) dependent Advantages of multi-moment approach:
CCN-dependent N c nucleation: MARITIME CONTINENTAL SUPERSATURATION (%) 10 1 N CCN (cm -3 ) 10 2 Advantages of multi-moment approach:
Q c (Cloud Mixing Ratio)
N c (Cloud Number Concentration)
D c (Cloud Mean-Mass Diameter)
The warm-rain coalescence process Radius [cm] Bin-resolving coalescence model S OURCE: Berry and Reinhardt (1974) RAIN CLOUD DRIZZLE Mass Density [g m -3 (lnr) -1 ] Time [min] Advantages of multi-moment approach:
0.1–1 mm RAIN DRIZZLE STRATIFORM RAIN Q r Mass Content [g m -3 ] D r Mean Diameter [mm] Advantages of multi-moment approach:DRIZZLE vs. RAIN
z [km] Q [g m -3 ] D m [mm] N T [m -3 ]Z e [dBZ] Contours every 5 min Mass Content Total Number Concentration Equivalent Reflectivity Mean-Mass Diameter 5 min 10 min 15 min 20 min INITIAL Analytic bin model calculation: (1D column) Advantages of multi-moment approach:SEDIMENTATION
= mass-weighted fall velocity SM = number-weighted fall velocity DM = reflectivity-weighted fall velocity TM SEDIMENTATION: Bulk scheme
SINGLE-moment scheme (SM): ANALYTIC BIN model (ANA): z [km] Q [g m -3 ] D m [mm] N T [m -3 ]Z e [dBZ] z [km] Q [g m -3 ] D m [mm] N T [m -3 ]Z e [dBZ] 5 min 10 min 15 min 20 min INITIAL
DOUBLE-moment scheme, FIXED DISPERSION ( = 0): ANALYTIC BIN model (ANA): z [km] Q [g m -3 ] D m [mm] N T [m -3 ]Z e [dBZ] z [km] Q [g m -3 ] D m [mm] N T [m -3 ]Z e [dBZ] 5 min 10 min 15 min 20 min INITIAL
ANALYTIC BIN model (ANA): DOUBLE-moment scheme, DIAGNOSTIC DISPERSION, = f (D m ): z [km] Q [g m -3 ] D m [mm] N T [m -3 ]Z e [dBZ] z [km] Q [g m -3 ] D m [mm] N T [m -3 ]Z e [dBZ] 5 min 10 min 15 min 20 min INITIAL
TRIPLE-moment scheme: ANALYTIC BIN model (ANA): z [km] Q [g m -3 ] D m [mm] N T [m -3 ]Z e [dBZ] z [km] Q [g m -3 ] D m [mm] N T [m -3 ]Z e [dBZ] 5 min 10 min 15 min 20 min INITIAL
Mass Content Bulk schemes: Analytic model: z [km] Q [g m -3 ] 5 min 10 min 15 min 20 min INITIAL Q [g m -3 ] z [km] DOUBLE- MOMENT Fixed SINGLE- MOMENT DOUBLE- MOMENT Diagnosed Q [g m -3 ] TRIPLE- MOMENT Prognosed Advantages of multi-moment approach:SEDIMENTATION
mm SNOW (large crystals / aggregates) Q s Mass Content [g m -3 ] D s Mean Diameter [mm] (equivalent sphere) Advantages of multi-moment approach:MASS ≠SIZE
SUMMARY Efficient single-moment and double-moment versions of the Milbrandt-Yau scheme are available for GEM-LAM Single-moment version will be proposed as the operational scheme for GEM-LAM_2.5 by fall 2007 New version (“semi-double-moment”) will be developed and tested for implementation by spring 2007 Large-scale version (diagostic cloud-fraction; fewer prognostic variables) to be developed soon For code, support, bug reports, or question:
MERCI