Presentation on theme: "Acknowledge: Mike Ek provides most of slides here"— Presentation transcript:
1Acknowledge: Mike Ek provides most of slides here Land Surface ModelingHelin WeiAcknowledge: Mike Ek provides most of slides here
2Outline • Role of Land Surface Models (LSMs) • Requirements and Noah LSM- atmospheric forcing, valid physics, land data sets/parameters, initial land states, cycled land states- Noah LSM• Recent upgrades of Noah in the NCEP GFS• Validation• Future upgrade
3Role of Land Models• Traditionally, from a coupled (atmosphere-ocean-land-ice) Numerical Weather Prediction (NWP) and climate modeling perspective, a land-surface model provides quantities to a parent atmospheric model:- Surface sensible heat flux,- Surface latent heat flux (evapotranspiration)- Upward longwave radiation (or skin temperature and surface emissivity),Upward (reflected) shortwave radiation (or surface albedo, including snow effects),Surface momentum exchange.
4Atmospheric Energy Budget …to close the surface energy budget, & provide surface boundary conditions to NWP and climate models.seasonal storage
5Water Budget (Hydrological Cycle) • Land models close the surface water budget, and provide surface boundary conditions to models.
6LoCo: Local land-atmospheric modeling • NEAR-SURFACE LOCAL COUPLING METRIC: Evaporative fraction change with changing soil moisture for both bare soil & vegetated surface = function of near- surface turbulence, canopy control, soil hydraulics & soil thermodynamics,• Utilize GHP/CEOP reference site data sets (“clean” fluxnet),• Extend to coupling with atmos. boundary- layer and entrainment processes,• Link with approaches by Santanello et al.From “GEWEX Imperatives: Plans for 2013 and Beyond”6
7Land-Atmosphere Interaction Betts et al(1996)Diurnal time-scalesSeasonalCentury
8History of Land Modeling (e.g. at NCEP) 1960s (6-Layer PE model): land surface ignoredAside from terrain height and surface friction effects1970s (LFM): land surface ignoredLate 1980s (NGM): first simple land model introduced (Tuccillo)Single layer soil slab (“force-restore” model: Deardorff)No explicit vegetation treatmentTemporally fixed surface wetness factorDiurnal cycle is treated (as is PBL) with diurnal surface radiationSurface albedo, skin temperature, surface energy balanceSnow cover (but not depth)Early1990s (Global Model): OSU land model (Mahrt& Pan, 1984)Multi-layer soil column (2-layers)Explicit annual cycle of vegetation effectsSnow pack physics (snowdepth, SWE)Mid-90s (Meso Model): OSU/Noah LSM replaces Force-RestoreMid 2000s (Global Model): Noah replaces OSU (Ek et al 2003)Mid 2000s (Meso Model: WRF): Unified Noah LSM with NCAR2000s-10s: Noah “MP” with explicit canopy, ground water,CO2
9Outline • Role of Land Surface Models (LSMs) • Requirements and Noah LSM- atmospheric forcing, valid physics, land data sets/parameters, initial land states, cycled land states- Noah LSM• Recent upgrades of Noah in the NCEP GFS• Validation• Future upgrade
10Land Model Requirements • To provide proper boundary conditions, land model must have:Necessary atmospheric forcing to drive the land model,Appropriate physics to represent land-surface processes (for relevant time/spatial scales),- Corresponding land data sets and associated parameters, e.g. land use/land cover (vegetation type), soil type, surface albedo, snow cover, surface roughness, etc., andProper initial land states, analogous to initial atmospheric conditions, though land states may carry more “memory” (e.g. especially in deep soil moisture), similar to ocean SSTs.
11Weather & Climate a “Seamless Suite” Static vegetation, e.g. climatology or realtime observationsDynamic vegetation, e.g. plant growthDynamic ecosystems,e.g. changing land cover• Products and models are integrated & consistent throughout time & space, as well as across forecast application & domain.Land modelingexample:
12Land Model Requirements • To provide proper boundary conditions, land model must have:Necessary atmospheric forcing to drive the land model,Appropriate physics to represent land-surface processes (for relevant time/spatial scales),- Corresponding land data sets and associated parameters, e.g. land use/land cover (vegetation type), soil type, surface albedo, snow cover, surface roughness, etc., andProper initial land states, analogous to initial atmospheric conditions, though land states may carry more “memory” (e.g. especially in deep soil moisture), similar to ocean SSTs.
13Unified NCEP-NCAR Noah land model Four soil layers (10, 30, 60, 100 cm thick).Linearized (non- iterative) surface energy budget; numerically efficient.Soil hydraulics and parameters follow Cosby et al.Jarvis-Stewart “big- leaf” canopy cond.Direct soil evaporation.Canopy interception.Vegetation-reduced soil thermal conductivity.Patchy/fractional snow cover effect on surface fluxes; coverage treated as function of snowdepth & veg typeFreeze/thaw soil physics.Snowpack density and snow water equivalent.Veg & soil classes parameters.
14Prognostic Equations Soil Moisture (Θ): • “Richard’s Equation”; DΘ (soil water diffusivity) and KΘ (hydraulic conductivity), are nonlinear functions of soil moisture and soil type (Cosby et al 1984); FΘ is a source/sink term for precipitation/evapotranspiration.Soil Temperature (T):• CT (thermal heat capacity) and KT (soil thermal conductivity; Johansen 1975), non-linear functions of soil/type; soil ice = fct(soil type/temp./moisture).Canopy water (Cw):• P (precipitation) increases Cw, while Ec (canopy water evaporation) decreases Cw.
16Surface Water Budget S = change in land-surface water P = precipitationR = runoffE = evapotranspirationP-R = infiltration of moisture into the soil• S includes changes in soil moisture, snowpack (cold season), and canopy water (dewfall/frostfall and intercepted precipitation, which are small).• Evapotranspiration is a function of surface, soil and vegetation characteristics: canopy water, snow cover/ depth, vegetation type/cover/density & rooting depth/ density, soil type, soil water & ice, surface roughness.• Noah model provides: S, R and E.
17Potential Evaporation open water surface(Penman) = slope of saturation vapor pressure curveRn-G = available energy = air densitycp = specific heatCh = surface-layer turbulent exchange coefficientU = wind speede = atmos. vapor pressure deficit (humidity) = psychrometric constant, fct(pressure)
18Surface Latent Heat Flux (Evapotranspiration)Canopy WaterEvap. (LEc)Transpiration(LEt)Bare SoilEvaporation (LEd)canopy watercanopysoil• LEc is a function of canopy water % saturation.• LEt uses Jarvis (1976)-Stewart (1988) “big-leaf”canopy conductance.• LEd is a function of near-surface soil % saturation.• LEc, LEt, and LEd are all a function of LEp.
19Surface Latent Heat Flux (cont.) Canopy Water Evaporation (LEc):• Cw, Cs are canopy water & canopy water saturation, respectively, a function of veg. type; nc is a coeff.Transpiration (LEt):• gc is canopy conductance, gcmax is maximum canopy conductance and gS, gT, ge, gΘ are solar, air temperature, humidity, and soil moisture availability factors, respectively, all functions of vegetation type.Bare Soil Evaporation (LEd):• Θd, Θs are dry (minimum) & saturated soil moisture contents, =fct(soil type); nd is a coefficient (nom.=2).smax
20Latent Heat Flux over Snow Shallow/Patchy Snow Snowcover<1 LE (shallow snow)<LE (deep snow)Sublimation (LEsnow)LEsnow = LEpLEsnow = LEpsnowpackLEns < LEpLEns = 0soilShallow/Patchy Snow Snowcover<1Deep snowSnowcover=1• LEns = “non-snow” evaporation (evapotranspiration terms).• 100% snowcover a function of vegetation type, i.e. shallower for grass & crops, deeper for forests.
21Surface Sensible Heat Flux soilcanopysnowpackbare soil(from canopy/soilsnowpack surface), cp = air density, specific heatCh = surface-layer turbulent exchange coeff.U = wind speedTsfc-Tair = surface-air temperature difference• “effective” Tsfc for canopy, bare soil, snowpack.
22(to canopy/soil/snowpack surface) Ground Heat Fluxsoilcanopysnowpackbare soil(to canopy/soil/snowpack surface)KT = soil thermal conductivity (function of soil type: larger for moister soil, larger for clay soil; reduced through canopy, reduced through snowpack)z = upper soil layer thicknessTsfc-Tsoil = surface-upper soil layer temp. difference• “effective” Tsfc for canopy, bare soil, snowpack.
24NEMS/GFS Modeling Summer School 13-type SIB used in the OPS GFS (global 1-degree)1: broadleaf-evergreen trees : broadleaf-deciduous trees : broadleaf and needleleaf trees4: needleleaf-evergreen trees 5: needleleaf-deciduous trees (larch) 6: broadleaf trees with groundcover7: groundcover only (perennial) 8: broadleaf shrubs with perennial groundcover9: broadleaf shrubs with bare soil : dwarf trees and shrubs with groundcover (tundra)11: bare soil : cultivations (the same parameters as for type 7) : glacial iceNEMS/GFS Modeling Summer School
25NEMS/GFS Modeling Summer School 9-type Zolber used in the OPS GFS (global 1-degree)1: loamy sand : silty clay loam : light clay4: sandy loam : sandy clay : clay loam7: sandy clay loam : loam : loamy sandNEMS/GFS Modeling Summer School
26Land surface model physics parameters (examples) Surface momentum roughness dependent on vegetation/land-use type.Stomatal control dependent on vegetation type, direct effect on transpiration.Depth of snow (snow water equivalent, or s.w.e.) for deep snow and assumption of maximum snow albedo is a function of vegetation type.Heat transfer through vegetation and into the soil a function of green vegetation fraction (coverage) and leaf area index (density).Soil thermal and hydraulic processes highly dependent on soil type (vary by orders of magnitude).
27Initial Land StatesValid land state initial conditions are necessary for NWP and climate models, & must be consistent with the land model used in a given weather or climate model, i.e. from same cycling land model.Land states spun up in a given NWP or climate model cannot be used directly to initialize another model without a rescaling procedure because of differing land model soil moisture climatologies.May Soil Moisture Climatology from 30-year NCEP Climate Forecast System Reanalysis (CFSR), spun up from Noah land model coupled with CFS.
28Initial Land States (cont.) • In addition to soil moisture: the land model provides surface skin temperature, soil temperature, soil ice, canopy water, and snow depth & snow water equivalent.National Ice Center snow coverAir Force Weather Agency snow cover & depth
29Initial Land States (cont.) • In seasonal (and longer) climate simulations, land states are “cycled” so that there is an evolution in land states in response to atmospheric forcing and land model physics.• Land data set quantities may be observed and/or simulated, e.g. green vegetation fraction & leaf area index, and even land-use type (evolving ecosystems).
30Noah Land Model Connections in NOAA’s NWS Model Production Suite ClimateCFSOceansHYCOMWaveWatch III2-Way CoupledHurricane GFDLHWRFMOM4GLDAS1.7B Obs/DaySatellites99.9%DispersionARL/HYSPLITGlobalForecastSystemRegional NAMWRF NMM(including NARR)Global DataAssimilationUncoupled“NLDAS”(drought)Severe WeatherRegional DataAssimilationWRF NMM/ARWWorkstation WRFShort-RangeEnsemble ForecastNorth American Ensemble Forecast SystemWRF: ARW, NMMETA, RSMForecastAir QualityGFS, Canadian Global ModelNAM/CMAQNOAH Land Surface ModelNCEP-NCAR unifiedRapid Updatefor Aviation (ARW-based)
31NCEP-NCAR unified Noah land model • Surface energy (linearized) & water budgets; 4 soil layers.• Forcing: downward radiation, precip., temp., humidity, pressure, wind.• Land states: Tsfc, Tsoil*, soil water* and soil ice*, canopy water*, snow depth/density* *prognostic• Land data sets: green vegetation frac., veg. type, soil type, snow-free albedo & maximum snow albedo.• Noah coupled with NCEP models: North American Mesoscale model (NAM; short-range), Global Forecast System (GFS; medium-range), Climate Forecast System (CFS; seasonal), and uncoupled NCEP modeling systems, i.e. NLDAS & GLDAS.
32Outline • Role of Land Surface Models (LSMs) • Requirements and Noah LSM- atmospheric forcing, valid physics, land data sets/parameters, initial land states, cycled land states- Noah LSM• Recent upgrades of Noah in the NCEP GFS• Validation• Future upgrade
33GFS : Land Model Upgrade Noah LSM (new) versus OSU LSM (old): 2 soil layers (10, 190 cm)No frozen soil physicsOnly one snowpack state (SWE)Surface fluxes not weighted by snow fractionVegetation fraction never less than 50 percentSpatially constant root depthRunoff & infiltration do not account for subgrid variability of precipitation & soil moisturePoor soil and snow thermal conductivity, especially for thin snowpackNoah LSM (vegetation, snow, ice)4 soil layers (10, 30, 60, 100 cm)Frozen soil physics includedAdd glacial ice treatmentTwo snowpack states (SWE, density)Surface fluxes weighted bysnow cover fractionImproved seasonal cycle of vegetationSpatially varying root depthRunoff and infiltration account for sub-grid variability in precipitation & soil moistureImproved thermal conduction in soil/snowHigher canopy resistanceImproved evaporation treatment over bare soil and snowpackNoah LSM replaced OSU LSM in operational NCEP medium-rangeGlobal Forecast System (GFS) in late May 2005
34Mean GFS surface latent heat flux: 09-25 May 2005: Upgrade to Noah LSM significantly reduced the GFS surface latent heat flux(especially in non-arid regions)Pre-May 05 GFS: with OSU LSMPost-May 05 GFS: with new Noah LSM
35May 2011, the new thermal roughness scheme was implemented to deal with the daytime cold skin temp bias over semi-arid region during the warm season
37Outline • Role of Land Surface Models (LSMs) • Requirements and Noah LSM- atmospheric forcing, valid physics, land data sets/parameters, initial land states, cycled land states- Noah LSM• Recent upgrades of Noah in the NCEP GFS• Validation• Future upgrade
38grid2obs for 2m-T Rh, and 10-m wind from Fanglin Yang http://www. emc
392m-T Rh, and 10-m wind comparisons between GFS and NAM http://www. emc Red: OBS Blue: GFS Green: NAMApril, 2013
40SURFX (Surface Flux) Network NOAA/ATDD, Tilden Meyers et al Compare monthly diurnal composites of modeloutput versus observations from flux sites toassess systematic model biases. From Mike EKSURFX (Surface Flux) NetworkNOAA/ATDD, Tilden Meyers et al
43Downward Solar Upward Longwave Downward Longwave Reflected Solar Ft. Peck, Montana(grassland)Upward LongwaveSURFACE ENERGY BUDGET TERMSJanuary 2008monthly averages:model vs obsDownward LongwaveReflected SolarSensible Heat FluxLatent Heat FluxGround Heat Flux
44Outline • Role of Land Surface Models (LSMs) • Requirements and Noah LSM- atmospheric forcing, valid physics, land data sets/parameters, initial land states, cycled land states- Noah LSM• Recent upgrades of Noah in the NCEP GFS• Validation• Future upgrade
45NEMS/GFS Modeling Summer School Future improvementsMore land surface data assimilation (soil moisture, snow, etc)Replace land surface characteristic data by more recent and high-resolution onePhysics upgrades :-Noah MP: urbanization, dynamic vegetation, ground water, carbon cycle, multi-layer snow model)-River routingNEMS/GFS Modeling Summer School
4613-type SIB used in the OPS GFS (global 1-degree) 1: broadleaf-evergreen trees!2: broadleaf-deciduous trees : broadleaf and needleleaf trees!4: needleleaf-evergreen trees5: needleleaf-deciduous trees (larch) : broadleaf trees with groundcover7: groundcover only (perennial) : broadleaf shrubs with perennial groundcover9: broadleaf shrubs with bare soil : dwarf trees and shrubs with groundcover (tundra)11: bare soil : cultivations (the same parameters as for type 7)13: glacial ice20-type IGBP used in the test (global 1-km)1:Evergreen Needleleaf Forest2:Evergreen Broadleaf Forest3:Deciduous Needleleaf Forest4:Deciduous Broadleaf Forest5:Mixed Forests6:Closed Shrublands7:Open Shrublands8:Woody Savannas9:Savannas10:Grasslands11:Permanent wetlands12:Croplands13:Urban and Built-Up14:Cropland/natural vegetation mosaic15:Snow and Ice16:Barren or Sparsely Vegetated17:Water18:Wooded Tundra19:Mixed Tundra20:Bare Ground Tundra
479-type Zolber used in the OPS GFS (global 1-degree) loamy sandsilty clay loamlight claysandy loamsandy clayclay loamsandy clay loamloam19-type STASGO used in the test (global 1-km)1: sand2: loamy sand3: sandy loam4: silt loam5: silt6:loam7:sandy clay loam8:silty clay loam9:clay loam10:sandy clay11: silty clay12: clay13: organic material14: water15: bedrock16: other (land-ice)17: playa18: lava19: white sand