New Directions for WRF Land Surface Modeling

1. New Directions for WRF Land Surface Modeling Michael Barlage Research Applications Laboratory (RAL) National Center for Atmospheric Research Polar WRF Workshop – 3 November 2011

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) Canopy Water Evaporation Transpiration Turbulent Heat Flux to/from Snowpack/Soil/Plant Canopy Precipitation Condensation on vegetation Deposition/ Sublimation to/from snowpack Direct Soil Evaporation Evaporation from Open Water on bare soil Runoff Snowmelt D Z = 10 cm Soil Heat Flux Soil Moisture Flux D Z = 30 cm D Z = 60 cm Internal Soil Heat Flux Internal Soil Moisture Flux Interflow D Z = 100 cm Gravitational Flow

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) Canopy Water Evaporation Transpiration Turbulent Heat Flux to/from Snowpack/Soil/Plant Canopy Precipitation Condensation on vegetation Deposition/ Sublimation to/from snowpack Direct Soil Evaporation Evaporation from Open Water on bare soil Runoff Snowmelt D Z = 10 cm Soil Heat Flux Soil Moisture Flux D Z = 30 cm D Z = 60 cm Internal Soil Heat Flux Internal Soil Moisture Flux Interflow D Z = 100 cm Gravitational Flow

4. 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 4

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 Courtesy Mike Leuthold, U. Arizona February

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 February

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 February

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 February

10. Simulations compared to SNOTEL observations 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 Modified Noah Noah v3.0 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) 10

11. 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 11

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 Noah Noah-UA SWdn SH SWdn SH + Δcan Δcan= solar radiation intercepted by canopy = f(LAI, canopy reflectance, snow albedo) Δcan (1-α)SWdn (1-α)SWdn- Δcan

14. Noah-MP: Canopy Fluxes 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

15. Simulations compared to SNOTEL observations Noah-MP improves both peak SWE simulation and spring melt timing Modified Noah Noah-MP Noah v3.1+ Noah Noah v3.1 15

16. 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 16

17. 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 17

18. 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

19. Sensible Heat Flux at Niwot Ridge, CO Noah-MPNoah Obs

20. Snow Model Intercomparison • 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)

21. Snow Model Intercomparison LEAF VIC SAST CLM Noah NoahMP

22. Snow Model Intercomparison LEAF VIC SAST CLM Noah NoahMP

23. 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