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

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Noah LSM Deficiencies

Flagstaff WRF T2m simulation compared to METAR observations

Febr

uary

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

Febr

uary

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

Febr

uary

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

Febr

uary

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

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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

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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