WRF Physics Options - dtcenter.org · 2006-08-22 · PBL Scheme Options PBL schemes can be used for...
Transcript of WRF Physics Options - dtcenter.org · 2006-08-22 · PBL Scheme Options PBL schemes can be used for...
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WRF Physics Options
Jimy Dudhia
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WRF Physics
Turbulence/Diffusion (diff_opt, km_opt)Radiation
Longwave (ra_lw_physics)Shortwave (ra_sw_physics)
SurfaceSurface layer (sf_sfclay_physics)Land/water surface (sf_surface_physics)
PBL (bl_physics)Cumulus parameterization (cu_physics)Microphysics (mp_physics)
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Radiation
Atmospheric temperature tendencySurface radiative fluxes
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ra_lw_physics=1
RRTM schemeSpectral schemeK-distributionLook-up table fit to accurate calculationsInteracts with cloudsOzone/CO2 from climatology
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ra_lw_physics=99
GFDL longwave scheme used in Eta/NMMCan only be called with Ferrier microphysicsSpectral scheme from global modelAlso uses tablesInteracts with cloudsOzone/CO2 from climatology
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ra_sw_physics=1
MM5 shortwave (Dudhia)Simple downward calculationClear-sky scatteringWater vapor absorptionCloud albedo and absorption
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ra_sw_physics=2
Goddard shortwaveSpectral methodInteracts with cloudsOzone effects
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ra_sw_physics=99
GFDL shortwaveUsed in Eta/NMM modelCan only be used with Ferrier microphysicsOzone effectsInteracts with clouds
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nrads/nradl
Radiation time-step recommendationNumber of fundamental steps per radiation callOperational setting should be 3600/dtHigher resolution could be used, e.g. 1800/dt
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Surface schemes
Surface layer of atmosphere diagnostics (exchange/transfer coeffs)Land Surface: Soil temperature /moisture /snow prediction /sea-ice temperature
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sf_sfclay_physics=1
Monin-Obukhov similarity theoryTaken from standard relations used in MM5 MRF PBLProvides exchange coefficients to surface (land) schemeShould be used with bl_pbl_physics=1 or 99
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sf_sfclay_physics=2
Monin-Obukhov similarity theoryModifications due to JanjicTaken from standard relations used in NMM model, including Zilitinkevichthermal roughness lengthShould be used with bl_pbl_physics=2
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sf_sfclay_physics=3
GFS Monin-Obukhov similarity theoryFor use with NMM-LSMShould be used with bl_pbl_physics=3
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sf_surface_physics=1
5-layer thermal diffusion model from MM5Predict ground temp and soil tempsThermal properties depend on land useNo effect for waterProvides heat and moisture fluxes for PBL
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sf_surface_physics=99
NMM Land Surface Model (NCEP Noah)Vegetation effects includedPredicts soil temperature and soil moisture in four layersPredicts snow cover and canopy moistureHandles fractional snow cover and frozen soilDiagnoses skin temp and uses emissivityProvides heat and moisture fluxes for PBL
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sf_surface_physics=3
RUC Land Surface Model (Smirnova)Vegetation effects includedPredicts soil temperature and soil moisture in six layersMulti-layer snow modelProvides heat and moisture fluxes for PBL
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LANDUSE.TBL
LANDUSE.TBL file (ascii) has land-use properties (vegetation, urban, water, etc.)24 USGS categories from 30” global datasetEach type is assigned summer/winter value
AlbedoEmissivityRoughness length
Other table properties (thermal inertia, moisture availability, snow albedo effect) are used by 5-layer modelOther tables (VEGPARM.TBL, etc.) are used by NoahRUC LSM has internal values
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Initializing LSMs
• Noah and RUC LSM require additional fields for initialization• Soil temperature• Soil moisture• Snow liquid equivalent
• Best source is a consistent model-derived dataset• Eta/GFS/AGRMET/NNRP for Noah (although some have limited
soil levels available)• RUC for RUC
• Optimally the resolution, land-use, soil texture, should match the data source model, otherwise there will be a spin-up issue
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Planetary Boundary Layer
Boundary layer fluxes (heat, moisture, momentum)Vertical diffusion
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bl_pbl_physics=1
YSU PBL scheme (Hong and Noh)Parabolic non-local-K mixing in dry convective boundary layerDepth of PBL determined from thermal profileExplicit treatment of entrainmentVertical diffusion depends on Ri in free atmosphere
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bl_pbl_physics=2
Mellor-Yamada-Janjic (Eta/NMM) PBL1.5-order, level 2.5, TKE predictionLocal TKE-based vertical mixing in boundary layer and free atmosphere
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bl_pbl_physics=3
GFS PBL1st order Troen-MahrtClosely related to MRF PBLNon-local-K vertical mixing in boundary layer and free atmosphere
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bl_pbl_physics=99
MRF PBL scheme (Hong and Pan 1996)Non-local-K mixing in dry convective boundary layerDepth of PBL determined from critical RinumberVertical diffusion depends on Ri in free atmosphere
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nphs
Time steps between PBL/turbulence/LSM callsTypical value is 10 for efficiencyAlso used for microphysics
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PBL Scheme Options
PBL schemes can be used for most grid sizes when surface fluxes are presentAssumes that PBL eddies are not resolvedWith PBL scheme, lowest full level should be .99 or .995 (not too close to 1)At grid size dx << 1 km, this assumption breaks downCan use 3d tke diffusion, but, this is not yet coupled to the actual surface fluxesCurrently 3d tke can only be used with constant specified surface fluxes
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Cumulus Parameterization
Atmospheric heat and moisture/cloud tendenciesSurface rainfall
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cu_physics=1
New Kain-Fritsch As in MM5 and Eta/NMM test versionIncludes shallow convectionLow-level vertical motion in trigger functionCAPE removal time scale closureMass flux type with updrafts and downdrafts, entrainment and detrainmentIncludes cloud detrainment
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cu_physics=2
Betts-Miller-JanjicAs in NMM model (Janjic 1994)Adjustment type schemeBM saturated profile modified by cloud efficiency, so post-convective profile can be unsaturated in BMJNo explicit updraft or downdraft
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cu_physics=3
Grell-Devenyi EnsembleMultiple-closure (e.g. CAPE removal, quasi-equilibrium)Multi-parameter (e.g maximum cap, precipitation efficiency)Explicit updrafts/downdraftsMean feedback of ensemble is appliedWeights can be tuned (spatially, temporally) to optimize scheme (training)
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cu_physics=4
Simpified Arakawa-Schubert (SAS) GFS schemeQuasi-equilibrium schemeRelated to Grell scheme in MM5Downdrafts and single, simple cloud
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ncnvc
Time steps between cumulus parameterization callsTypically 10 - same as NPHS
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Cumulus scheme
Recommendations about useFor dx ≥ 10 km: probably need cumulus schemeFor dx ≤ 3 km: probably do not need scheme
However, there are cases where the earlier triggering of convection by cumulus schemes help
For dx=3-10 km, scale separation is a ?No schemes are specifically designed with this range of scales in mind
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Microphysics
Atmospheric heat and moisture tendenciesMicrophysical ratesSurface rainfall
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Ferrier
Qi/Qs/Qg
Qv
Qc
Qr
Kessler WSM3
Lin et al./WSM6WSM5
Illustration of Microphysics Processes
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mp_physics=1
Kessler schemeWarm rain – no iceIdealized microphysicsTime-split rainfall
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mp_physics=2
Purdue Lin et al. scheme5-class microphysics including graupelIncludes ice sedimentation and time-split fall terms
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mp_physics=3
WSM 3-class schemeFrom Hong, Dudhia and Chen (2004)Replaces NCEP3 scheme3-class microphysics with iceIce processes below 0 deg CIce number is function of ice contentIce sedimentation and time-split fall terms
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mp_physics=4
WSM 5-class schemeAlso from Hong, Dudhia and Chen (2004)Replaces NCEP5 scheme5-class microphysics with iceSupercooled water and snow meltIce sedimentation and time-split fall terms
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mp_physics=5Ferrier (current NAM) scheme
Designed for efficiency Advection of total condensateCloud water, rain, & ice (cloud ice, snow/graupel) from storage arrays –assumes fractions of water & ice within the column are fixed during advection
Supercooled liquid water & ice meltVariable density for precipitation ice (snow/graupel/sleet) – “rime factor”
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mp_physics=6
WSM 6-class schemeFrom Hong and Lim (2006, JKMS)6-class microphysics with graupelIce number concentration as in WSM3 and WSM5Modified accretionTime-split fall terms with melting
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mp_physics=8
Thompson et al. graupel schemeFrom Thompson et al. (2004, MWR)Newer version of Reisner2 scheme6-class microphysics with graupelIce number concentration also predicted (double-moment ice)Time-split fall terms
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mp_physics=98,99
NCEP3,NCEP5Old options from Version 1.3 still available for comparisonOriginally from Regional Spectral ModelTo be phased out later
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mp_zero_out
Microphysics switch (also mp_zero_out_thresh)1: all values less than threshold set to zero (except vapor)2: as 1 but vapor also limited ≥ 0Note: this option will not conserve total waterNMM: Recommend mp_zero_out=0
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nphs
Time steps between microphysics callsSame as parameter for turbulence/PBL/LSMTypical value is 10 for efficiency
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Microphysics Options
Recommendations about choiceProbably not necessary to use a graupel scheme for dx > 10 km
Updrafts producing graupel not resolvedCheaper scheme may give similar results
When resolving individual updrafts, graupel scheme should be usedAll domains use same option
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Physics Interactions
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shallow cumulus
or downdrafts
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End