NCEP Land-Surface Modeling Michael Ek and the EMC Land-Hydrology Team Environmental Modeling Center (EMC) National Centers for Environmental Prediction (NCEP) 5200 Auth Road, Room 207 Suitland, Maryland 20732 USA National Weather Service (NWS) National Oceanic and Atmospheric Administration (NOAA) NWP Workshop on Model Physics, Suitland, Maryland, 26-28 July 2011 1
Noah Land Model Connections in NOAA s NWS Model Production Suite 1.7B Obs/Day Satellites 99.9% GLDAS Climate CFS MOM4 Hurricane GFDL HWRF Oceans HYCOM WaveWatch III Global Data Assimilation Regional Data Assimilation NCEP- NCAR unified Global Forecast System North American Ensemble Forecast System GFS, Canadian Global Model NOAH Land Surface Model Regional NAM WRF NMM (including NARR) Short-Range Ensemble Forecast WRF: ARW, NMM ETA, RSM Uncoupled NLDAS (drought) Dispersion ARL/HYSPLIT Severe Weather WRF NMM/ARW Workstation WRF Air Quality NAM/CMAQ Rapid Update for Aviation (ARW-based) 2 For eca st
NCEP-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 and snow density. *prognostic Land data sets: veg. type, green vegetation fraction, 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), & other NCEP modeling systems (i.e. NLDAS & GLDAS). 3
Land Data Sets (NAM, NLDAS) MAM Vegetation Type (1-km, MODIS) Soil Type (1-km, STATSGO/FAO) Snow-Free Albedo (1-km, MODIS) fixed climatologies or (near) realtime observations (e.g. green veg. fraction); some quantities may be assimilated (e.g. soil moist., snow). June Green Vegetation Fraction (1/8-deg, new NESDIS/AVHRR; new climo. & near realtime) Max.-Snow Albedo (5-km, MODIS) 4
Land Data Sets (GFS and CFS, GLDAS) Vegetation Type (1-deg, UMD) Soil Type (1-deg, Zobler) Max.-Snow Albedo (1-deg, Robinson) Jan July Jan July Green Vegetation Fraction (monthly, 1/8-deg, NESDIS/AVHRR) Snow-Free Albedo (seasonal, 1-deg, Matthews) 5
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), are nonlinear functions of soil moisture and soil type. Canopy water (Cw): Prognostic Equations P (precipitation) increases Cw, while Ec (canopy water evaporation) decreases Cw. 6
Atmospheric Energy Budget Noah land model closes the surface energy budget, & provides surface boundary conditions to NCEP models. seasonal storage 7
Surface Energy Budget Rn = Net radiation = S - S + L - L S = incoming shortwave (provided by atmos. model) S = reflected shortwave (snow-free albedo ( ) provided by atmos. model; modified by Noah model over snow) L = downward longwave (provided by atmos. model) L = emitted longwave = T 4 s ( =surface emissivity, =Stefan-Boltzmann const., T s =surface skin temperature) H = sensible heat flux LE = latent heat flux (surface evapotranspiration) G = ground heat flux (subsurface soil heat flux) SPC = snow phase-change heat flux (melting snow) Noah model provides:, L, H, LE, G and SPC. 8
Hydrological Cycle Noah land model closes the surface water budget, & provides surface boundary conditions to NCEP models. 9
Surface Water Budget S = change in land-surface water P = precipitation R = runoff E = evapotranspiration P-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. 10
Potential Evaporation open water surface (Penman) = slope of saturation vapor pressure curve Rn-G = available energy = air density cp = specific heat Ch = surface-layer turbulent exchange coefficient U = wind speed e = atmos. vapor pressure deficit (humidity) = psychrometric constant, fct(pressure) 11
Surface Latent Heat Flux (Evapotranspiration) canopy water canopy Canopy Water Evap. (LEc) Transpiration (LEt) Bare Soil Evaporation (LEd) soil 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. 12
Surface 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, gcmin is minimum canopy conductance and gs, gt, g e, 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, respectively, a fct of soil type; nd is a coeff. 13
Latent Heat Flux over Snow LE (shallow snow) < LE (deep snow) Sublimation (LEsnow) LEsnow = LEp LEsnow = LEp LEns < LEp snowpack LEns = 0 soil Shallow/Patchy Snow Snowcover<1 Deep snow Snowcover=1 LEns = non-snow evaporation (evapotranspiration terms). 100% snowcover a function of vegetation type, i.e. shallower for grass & crops, deeper for forests. 14 Soil ice = fct(soil type, soil temp., soil moisture).
Surface Sensible Heat Flux (from canopy/soil snowpack surface) canopy bare soil snowpack soil, cp = air density, specific heat Ch = surface-layer turbulent exchange coeff. U = wind speed Tsfc-Tair = surface-air temperature difference effective Tsfc for canopy, bare soil, snowpack. 15
Ground Heat Flux canopy (to canopy/soil/snowpack surface) bare soil snowpack soil 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 thickness Tsfc-Tsoil = surface-upper soil layer temp. difference effective Tsfc for canopy, bare soil, snowpack. 16
EMC Land-Hydro Partners/Projects Noah land model development (NCAR, U. Ariz., U. Texas/Austin, U. Wash., WRF land & PBL working groups, others; also freshwater FLake community), NLDAS (Princeton, U. Wash., NASA, OHD, CPC), Remote sensing/land data sets/data assimil. of soil moisture, vegetation, surface temp, snow (JCSDA, NESDIS, NIC, NASA, AFWA), NOAA/CPO (support for NLDAS, GLDAS), WCRP/GEWEX (GLASS/land-hydrology, GABLS/boundary-layer, GHP/hydroclimate projects). 17
North American Land Data Assimilation System: Drought Monitoring & Seasonal Hydro. Prediction Uncoupled modeling: NARR atmos forcing Supports CPC, NIDIS July 30-year climatology www.emc.ncep.noaa.gov/mmb/nldas July 2010 July 1988 (drought year) July 1993 (flood year) NLDAS four-model ensemble soil moisture monthly anomaly 18
Climate Forecast Syst. & 30-yr Reanalysis Global Land Data Assimilation System (GLDAS): Daily update of land states via uncoupled ( open loop ) Noah run in NASA LIS (Land Info. System), driven by CFS assimilation cycle atmos. forcing & blended precip. Reasonable soil moisture climatology, and energy & water budgets closure. Future: 1-km GLDAS under LIS/NEMS (use for NAM, GFS, CFS initial conditions, and NLDAS). May Soil Moisture Climatology from 30-year NCEP Climate Forecast System Reanalysis (CFSR), spun up from Noah land model coupled with CFS. 19
EMC Land Modeling Summary NCEP-NCAR unified Noah land model provides boundary conditions for NCEP operational weather & climate models, i.e. NAM, GFS, CFS. Land model validation using (near-) surface obs, i.e. air temp, RH, wind, soil moisture, surface fluxes, (and upper-air, precipitation scores, etc) suggests model physics upgrades, e.g. Noah-MP upgrades. Extend land modeling for weather and climate to a more fully-coupled Earth System: NLDAS drought monitoring, and seasonal hydrological prediction, other connections between Weather & Climate and Hydrology, Biogeochemical cycles (e.g. 20 carbon), and Air Quality communities & models.
Local Land-Atmosphere Interactions incoming solar above-abl dryness cloud cover precipitation above-abl stability 8 downward longwave 5 7 wind 2 * + canopy conductance 1 4 relative humidity moisture flux entrainment turbulence 3 emitted longwave surface temperature 1 temperature 4 5 sensible heat flux boundarylayer growth 3 7 2 reflected solar albedo 8 soil moisture 6 6 soil heat flux soil temperature +positive feedback for C3 & C4 plants, negative feedback for CAM plants *negative feedback above optimal temperature land-surface processes surface layer & ABL radiation positive feedback negative feedback