Research Applications Laboratory (RAL)
National Center for Atmospheric Research
Polar WRF Workshop – 3 November 2011
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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)
Precipitation
Condensation on vegetation
Transpiration
Canopy Water
Evaporation
Runoff on bare soil
Soil Moisture
Flux
Interflow
Internal Soil
Moisture Flux
Turbulent Heat Flux to/from
Snowpack/Soil/Plant Canopy
Direct Soil
Evaporation
Evaporation from Open Water
Deposition/
Sublimation to/from snowpack
Snowmelt
D Z
= 10 cm
D Z
= 30 cm
D Z
= 60 cm
Gravitational Flow
D Z
= 100 cm
Soil Heat Flux
Internal Soil
Heat Flux
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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)
Precipitation
Condensation on vegetation
Transpiration
Canopy Water
Evaporation
Runoff on bare soil
Soil Moisture
Flux
Interflow
Internal Soil
Moisture Flux
Turbulent Heat Flux to/from
Snowpack/Soil/Plant Canopy
Direct Soil
Evaporation
Evaporation from Open Water
Deposition/
Sublimation to/from snowpack
Snowmelt
D Z
= 10 cm
D Z
= 30 cm
D Z
= 60 cm
Gravitational Flow
D Z
= 100 cm
Soil Heat Flux
Internal Soil
Heat Flux
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• 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
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• 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
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Flagstaff WRF T
2m simulation compared to METAR observations
Courtesy Mike Leuthold, U. Arizona
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Flagstaff WRF T
2m 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
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Flagstaff WRF T
2m 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
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Flagstaff WRF v3.2
T
2m 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
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Simulations compared to SNOTEL observations
Noah v3.0
Modified Noah
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
Legend legend
GS: GOES SW forcing
ML: model level forcing
LV: Livneh albedo
TA: terrain adjustment
CH: WRF MYJ stability
85: Max albedo = 0.85
ZE: Zo = f(exposed veg)
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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
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• 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
• 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 12

SW dn
Noah
SH SW dn
Noah-UA
SH + Δ can
can
Δ can
= solar radiation intercepted by canopy
= f(LAI, canopy reflectance, snow albedo)
(1α)  SW dn
(1α)  SW dn
Δ can
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Canopy Fraction Bare Fraction
• 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
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Simulations compared to SNOTEL observations
Modified Noah
Noah-MP
Noah v3.1+
Noah-MP improves both peak SWE simulation and spring melt timing
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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
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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
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• 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

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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LEAF
VIC
SAST
CLM
Noah
NoahMP

LEAF
VIC
SAST
CLM
Noah
NoahMP

• 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
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