New Directions for WRF Land Surface Modeling
1Polar WRF Workshop – 3 November 2011
Michael BarlageResearch Applications Laboratory (RAL)
National Center for Atmospheric Research
2
Noah LSM in NCEP Eta, MM5 and WRF Models(Pan and Mahrt 1987, Chen et al. 1996, Chen and Dudhia 2001,
Ek et al., 2003)
Gravitational Flow
Internal SoilMoisture Flux
Internal Soil Heat Flux
Soil Heat Flux
Precipitation
Condensation
onbaresoil
onvegetatio
n
Soil Moisture Flux
Runoff
Transpiration
Interflow
Canopy WaterEvaporation
Direct SoilEvaporatio
n
Turbulent Heat Flux to/fromSnowpack/Soil/Plant Canopy
Evaporationfrom Open Water
Deposition/Sublimation
to/from snowpack
D Z = 10 cm
D Z = 30 cm
D Z = 60 cm
D Z = 100 cm
Snowmelt
3
Noah LSM in NCEP Eta, MM5 and WRF Models(Pan and Mahrt 1987, Chen et al. 1996, Chen and Dudhia 2001,
Ek et al., 2003)
Gravitational Flow
Internal SoilMoisture Flux
Internal Soil Heat Flux
Soil Heat Flux
Precipitation
Condensation
onbaresoil
onvegetatio
n
Soil Moisture Flux
Runoff
Transpiration
Interflow
Canopy WaterEvaporation
Direct SoilEvaporatio
n
Turbulent Heat Flux to/fromSnowpack/Soil/Plant Canopy
Evaporationfrom Open Water
Deposition/Sublimation
to/from snowpack
Snowmelt
D Z = 10 cm
D Z = 30 cm
D Z = 60 cm
D Z = 100 cm
44
Noah LSM Performance
• Noah does some things well– Surface fluxes without snow
present– Summertime simulation in general– Noah is relatively simple, less
parameters
• Noah structure good for satellite-derived surface properties– Albedo, observed from satellite, is
a bulk property (vegetation, snow, soil)
– Vegetation properties like green vegetation fraction are easily used as prescribed vegetation condition
5
Noah LSM Deficiencies
• Related to Snow Physics– Combined snow/vegetation/soil layer– No explicit canopy or liquid water retention– Currently one-layer snow
• Results in:– Under-prediction of snow throughout season– Snow melts too early in spring– Surface skin temperature is limited to (near) freezing with
snow on ground (cannot produce a “warm” canopy)– Limits 2m temperature in cases of warm air advection and
when significant energy absorbed by canopy
6
Noah LSM Deficiencies
Flagstaff WRF T2m simulation compared to METAR observations
Feb
ruar
y
Courtesy Mike Leuthold, U. Arizona
7
Noah LSM Deficiencies
Flagstaff WRF T2m simulation compared to METAR observations
• Cold bias during the day results from capped surface temperature at freezing
• Bias recovers during the night
• When snow is gone, bias is low
Feb
ruar
y
8
Noah LSM Deficiencies
Flagstaff WRF T2m simulation compared to METAR observations
• Cold bias during the day results from capped surface temperature at freezing
• Bias recovers during the night
• When snow is gone, bias is low
Feb
ruar
y
9
Noah LSM Deficiencies
Flagstaff WRF v3.2 T2m simulation compared to METAR observations
• Cold bias during the day results from capped surface temperature at freezing
• Bias recovers during the night
• When snow is gone, bias is low
Feb
ruar
y
10
Simulations compared to SNOTEL observations
Legend legendGS: GOES SW forcingML: model level forcingLV: Livneh albedo TA: terrain adjustmentCH: WRF MYJ stability85: Max albedo = 0.85 ZE: Zo = f(exposed veg)
SWE, snow melt and sublimation between the control simulation and simulation with all changes
Sublimation reduced consistently throughout simulation
Resulting pack increase melts in spring
Noah v3.0
Modified Noah
1111
Simulations compared to Niwot Ridge observations
Diurnal average sensible heat flux for January 2007
Both Noah-MP and Noah-UA do better with fluxes at night
Noah-MP does very well with daytime flux
Noah-UA improves greatly upon both version of current Noah
Keep snow at the expense of energy
12
Addressing with Two Approaches
Noah-UA
• Wang et al. 2010– Canopy shading effect– Reduce exchange
coefficient under canopy– Adjust roughness length for
snow and vegetation fraction
– Additional snow cover fractions
• Advantages– Easy to implement– Maintains Noah structure
(added as namelist option)
• Disadvantages– Skin temperature still limited
Noah-MP
• Liang/Niu et al. 2011– Explicit canopy– Multiple snow layers– Snow liquid water retention– Two-stream canopy
radiation– Multiple temperatures
• Advantages– More physical surface
representation– Surface exchange
consistent with LSM• Disadvantages
– Complexity/cost– More parameters
13
Noah-UA: Canopy Shading
SWdn SH SWdn SH + Δcan
(1-α)SWdn (1-α)SWdn- Δcan
Δcan
Noah Noah-UA
Δcan = solar radiation intercepted by canopy
= f(LAI, canopy reflectance, snow
albedo)
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Noah-MP: Canopy Fluxes
• Separate exchange coefficients– Bare ground to atmosphere– Under-canopy ground to canopy– Canopy to atmosphere– Leaf to canopy
• Flux balance– Iterate leaf and canopy temperatures so that heat flux to atmosphere is
balanced with flux from canopy to leaf and canopy to ground
Canopy Fraction Bare Fraction
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Simulations compared to SNOTEL observations
Noah-MP improves both peak SWE simulation and spring melt timing
Noah
Modified Noah
Noah v3.1
Noah v3.1+
Noah-MP
1616
Simulations compared to Niwot Ridge observations
Diurnal average sensible heat flux for January 2007
Both Noah-MP and Noah-UA do better with fluxes at night
Noah-MP does very well with daytime flux
Noah-UA improves greatly upon both version of current Noah
1717
Simulations compared to Niwot Ridge observations
Diurnal average sensible heat flux for January 2007
Both Noah-MP and Noah-UA do better with fluxes at night
Noah-MP does very well with daytime flux
Noah-UA improves greatly upon both version of current Noah
Coupling Noah-MP to WRF
• Noah-MP is coupled to WRF and currently going through testing
• 12 Km horizontal resolution with• NARR data is used as initial condition• WRF Runs starts 1 March 2008, 12Z
– Using WRFV3.3/Noah– Using WRFV3.3/Noah-MP
• Models are integrated for 15 days.• Results are compared
– Noah vs Noah-MP
Sensible Heat Flux at Niwot Ridge, CO
Noah-MP Noah Obs
• Coordinated effort by NCAR to compare surface processes within snow components of land models
• Volunteer participation by several universities• Phase-1a: Control experiment at SNOTEL sites. All forcing comes from WRF
simulation except GOES observed solar radiation• Phase-1b: Same as Phase-1a except daily precipitation from SNOTEL
observations• Phase-1c: Same as Phase-1b except diurnal hourly precipitation
distribution is based on WRF monthly-averaged diurnal distribution• Phase-1d: Same as Phase-1a except that SWE is reset to SNOTEL observed
SWE on the date of maximum• Phase-2a: 2004-2008 simulations for AmeriFlux sites (Niwot Ridge and
GLEES). Forcing comes from NARR except precipitation(NLDAS) and solar radiation
– Phase-2a1: Replacing the 2m Temperature forcing data with the 21m forcing.– Phase-2a2: Ameriflux SW/LW replacing GOES/NARR SW/LW (no obs 2004-2005)– Phase-2a3: 2a1+2a2– Sensitivity with forcing height (ZLVL)
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Snow Model Intercomparison
Snow Model Intercomparison
LEAFVIC
SASTCLM
Noah NoahMP
Snow Model Intercomparison
LEAFVIC
SASTCLM
Noah NoahMP
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Summary
• Other Noah-MP features– Dynamic vegetation– Groundwater treatment– Photosynthesis-based canopy resistance
• A new model (Noah-MP) and new processes within the existing Noah (Noah-UA) are planned to be released in the next WRF release– Both models attempt to address Noah deficiencies in snow
treatment– Noah-MP contains several options for physical
parameterizations within the LSM