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Testing and evaluation of the final Noah LSM upgrade in the NCEP NAM (mesoscale Eta) model

Testing and evaluation of the final Noah LSM upgrade in the NCEP NAM (mesoscale Eta) model. Michael Ek, Ken Mitchell, ET AL WRF Land Working Group meeting 13 September 2005. Summer: warm/dry bias during day, typically over areas with larger greenness fractions.

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Testing and evaluation of the final Noah LSM upgrade in the NCEP NAM (mesoscale Eta) model

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  1. Testing and evaluation of the final Noah LSM upgrade in the NCEP NAM (mesoscale Eta) model Michael Ek, Ken Mitchell, ET AL WRF Land Working Group meeting 13 September 2005 Summer: warm/dry bias during day, typically over areas with larger greenness fractions Winter: cold bias during night, typically under calm/clear conditions especially over snowpack, and during day over shallow/melting snowpack

  2. ETA / NOAH LAND-SURFACE MODEL UPGRADES: - assimilation of hourly precipitation -- hourly 4-km radar/gage analysis (Stage IV) • cold season processes(Koren et al 1999) -- patchy snow cover (snow sublimation) -- frozen soil (new state variable) -- snow density (new state variable)- bare soil evaporation refinements -- parameterize upper sfc crust cap on evap - soil heat flux -- new soil thermal conductivity (Peters-Lidard et al 1998) -- under snowpack -- vegetation reduction of thermal cond. (Peters-Lidard et al 1997) - surface characterization-- revised snow albedo algorithm -- dynamic thermal roughness length refinements - vegetation -- deeper rooting depth in forests -- canopy resistance refinements NOAH LSM tested in various land-model intercomparison projects, e.g., GSWP 1 & 2, PILPS 2a, 2c, 2d, 2e, Rhone, DMIP, GLACE.

  3. Summer: warm/dry bias Eastern CONUS, Aug 2004 27C ops Eta model 1-2C warm bias obs 2-m temp 17C

  4. Changes (more) relevant to warm season: -per WRF-Noah land-surface model unification, CMAQ requests, use high-resolution (1-km) vegetation and soils data bases with more classes, vs old 1-degree data sets. -ops EDAS precipitation forcing low bias tended to yield dry soil moisture bias in ops EDAS, so ops canopy conductance had been tuned to higher values to maintain reasonable evaporation rates given low soil moisture bias. -EDASX precipitation increased (Ying Lin's new precip assimilation and related code) with a subsequent soil moisture increase, so vegetation parameters affecting evaporation re-examined.

  5. Changes (more) relevant to warm season: -Lower roughness length for heat ->yields lower skin temperature, and hence lower diagnosed 2-m air temperature ->but no significant change to sensible heat flux due to compensating effects on exchange coefficient and near-surface temperature gradient. ->no significant change to latent heat flux primarily because LE largely affected by canopy conductance, which is much larger than aerodynamic conductance (especially in regions with large greenness fraction)

  6. Testing: -realtime parallel runs: Eta model at 32-km, July and August 2004 (though Noah LSM tested with various changes in parallel since Dec 2003) -retrospective runs: Eta model at 32-km, multiple month-long runs for July and August 2004

  7. USGS 24-class high-resolution (1-km) vegetation data set replaces old SiB 13-class 1-degree data set SiB

  8. New 1-deg TBOT (soil temperature) data base replaces old (global) 2.5-degree data set old 2.5-deg mapped to 12-km grid new 1-deg mapped to 12-km grid Necessary to adjust TBOT for a given terrain elevation (standard lapse rate = 6.5C/km). For model “cold start”, soil temperature states similarly adjusted for different model grid/terrain (ties in with soil moisture re-scaling).

  9. New STATSGO 16-class high-resolution (1-km) soils data base replaces old Zobler 9-class 1-degree data set Zobler

  10. Soil moisture re-scaling -necessary to re-scale soil moisture since Eta with the old soils needed to restart Eta with the new soils. -to preserve surface evaporation (with respect to plant stress) in going from the old (Zobler) to new (STATSGO) soils, convert soil moisture contents in order to maintain relative saturation. BUT... subsequent soil moisture evolution is affected by new soil type and land (veg) class, so soil moisture spin-up is important. sat=0.476 sat=0.404 =0.310 =0.263 soil type A e.g. sand soil type B e.g. clay Relative saturation=0.65

  11. July 2004 obs latent heat flux -offline Noah LSM runs suggested lower canopy conductance -canopy conduct. param’s adjusted (LAI down, Rs-min up for grass/crops, VPD, solar term) in coupled tests

  12. 11-27 July 2004 (17-day) mean of daytime (18z) latent heat flux: 12-km ops ETA (top) vs 32-km control ETAV (bottom) Similar pattern

  13. 11-27 July 2004 (17-day) mean of daytime (18z) latent heat flux: 32-km control ETA (top) vs 32-km parallel ETAL with new Noah LSM (bottom) Generally more latent heat flux in ETAL

  14. Soil moisture spin-up -continuous/cycled ETA parallel tests during July-August 2004 showed that higher latent heat fluxes (vs control ETAV) over eastern CONUS die down after about 1 month of cycling, as land states adjust to the new vegetation and soil parameters. -in August 2004, parallel ETA still had higher latent heat flux than control ETAV, but differences significantly less than July 2004.

  15. Reduced warm bias Eastern CONUS, August 2004 27C 2-m temp 17C

  16. Relative humidity Eastern CONUS, August 2004

  17. Reduced warm bias Western CONUS, August 2004 28C 2-m temp 16C

  18. Relative humidity Western CONUS, August 2004

  19. UPPER AIR: 48-hr forecast, Aug 2004 east, temp east, RH west, temp west, RH

  20. Winter: nighttime cold bias Eastern CONUS, Feb 2004 4C 2-m temp obs 1-2 C nighttime cold bias ops Eta model -4C

  21. Changes (more) relevant to cold season: -For patchy snow cover, changes to parameters: -> snow cover fraction (less snow depth for 100% cover) -> snow albedo (yields higher) -> surface skin temperature (higher via non-snow cover) -> snow sublimation (reduced), in addition to previous patchy skin temp/sensible heat flux, ground heat flux. -Surface emissivity (for snow only): Lup = s T4, s = 1.0, 0.95, 0.90. -PBL: in very stable conditions when PBL depth diagnosed as lowest Eta model level, impose lower limit on eddy diffusivity up to (and one level above) inversion height (positive impact previously demonstrated).

  22. Changes (more) relevant to cold season: -changes to allow for solar zenith angle correction to albedo -- higher at low sun angles in early morning and late afternoon, but not adopted for practical reasons: i.e. avoid further enhancement of early morning cold bias. Testing: -several retrospective 32-km runs: Feb and Mar 2004. -realtime 32-km parallel runs: Noah LSM tested with various changes in parallel until system frozen in Dec04. -real-time 12-km Etax parallel initiated (13 Dec 2004)

  23. Previously, effect of patchy snow cover included in... ...surface skin temp and sensible heat flux (>temp, > flux) ...soil heat flux (>flux from below) Now include patchy snow in latent heat flux calculation

  24. DAILY BASIN-AVERAGE SURFACE MOISTURE FLUX OLD FORMULATION large atmos demand during high-sun season DAILY BASIN-AVERAGE SNOW DEPTH (S.W.E.) current and new formulations diverging NEW FORMULATION NEW FORMULATION March April May June July OBS Offline (uncoupled N-LDAS) results show the effect of the various cold-season changes to the Noah LSM NEW, without patchy snow sublimation March July

  25. 2-m temp s=0.95 Feb 2004 Eastern CONUS Slightly reduced nighttime cold bias 4C obs Etax control -4C

  26. 2-m temp s=0.90 Feb 2004 Eastern CONUS Slightly reduced nighttime cold bias 4C obs Etax control -4C

  27. Now/Future (WRF-era) - Seasonally varying LAI (leaf area index), so more degrees of freedom in seasonal vegetation phenology. - Realtime greenness (nominally weekly). - Further examination of processes and parameters used in determining evapotranspiration (e.g. CO2 via “Noah2”) - Re-examine surface layer formulations. - Emissivity testing/changes (done properly with entire radiation scheme), not only for snow, but for other surface types (e.g. update WRF-Noah-LSM tables).

  28. Now/Future (WRF-era) -Important to consider the interactions/feedbacks between land-surface and PBL, clouds, radiation during model development and testing. -example from observed radiation…

  29. Feb 2004 monthly downward longwave -generally a low bias -significant effect on nighttime surface cooling by low-level clouds -influences changes made in land-surface and PBL formulations e.g. when addressing near-sfc cold biases

  30. PHYSICS “WEB OF PAIN”

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