The Noah-MP Land Surface Model. Michael Barlage Research Applications Laboratory National Center for Atmospheric Research

Transcription

1 The Noah-MP Land Surface Model Michael Barlage Research Applications Laboratory National Center for Atmospheric Research 1

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

4 Land Surface Models: Summary Land surface models have been used as stand-alone eco-hydrology models or as boundary conditions for atmospheric and hydrology models Land surface models exist within a wide spectrum of complexity Land surface models can be broken down into two parts: Physics: approximating the complex real world by a set of physically-based (hopefully) equations Parameters: adapts the approximated physics to work for heterogeneous surfaces (vegetation/soil/etc.) More complex physics tends to produce more parameters Current generation LSMs aim to improve surface representation especially when significant heterogeneities exist provide land surface process-level information (e.g., multiple surface temperatures) to an expanding user base test multiple process representations in one model 4

5 Model Structural Differences Noah LSM in NCEP NAM/GFS/CFS, NCAR MM5/WRF Models Also operational models in Korea, China, Taiwan Noah-MP LSM in WRF and NCEP CFS and WRF/Hydro T can (x,y,z) Reality Noah Single surface temperature Noah-MP Multiple surface temperatures and distinct canopy T can T leaf T bc (x,y,z) T g (x,y) T snow (x,y,z) Snow (x,y,z) T skin Snow T bc T g T snow (z) Snow 5

6 Noah and Noah-MP LSM Structure Comparison Absorbed SW Sensible Heat O O M M N N Jan 2007 Comparison of observed (O), Noah (N), and Noah-MP (M). Noah has less absorbed solar radiation resulting in colder surface and lower (or negative) sensible heat flux Chen, et al. 2014

7 Noah-MP: a community land model

8 Noah-MP Physical Processes Noah-MP is a land surface model that allows a user to choose multiple options for several physical processes θ atm SH veg θ atm SH bare Canopy radiative transfer with shading geometry Separate vegetation canopy Dynamic vegetation Vegetation canopy resistance Multi-layer snowpack Snowpack liquid water retention Simple groundwater options Snow albedo treatment New frozen soil scheme New snow cover θ leaf θ canopy θ gv Vegetated θ gb Unvegetated

9 Noah-MP: Surface Energy Budget SW dn SW up + LW dn LW up (T sfc ) = SH(T sfc ) + LH(T sfc ) + G(T sfc ) SW dn SW up LW dn LW up SH LH SW dn,lw dn : input shortwave and longwave radiation (external to LSM) SW up : reflected shortwave (albedo) LW up : upward thermal radiation SH : sensible heat flux LH : latent heat flux (soil/canopy evaporation, transpiration) G : heat flux into the soil T canopy T g G

10 Noah-MP Physical Processes Noah-MP is a land surface model that allows a user to choose multiple options for several physical processes snow on canopy Canopy radiative transfer with shading geometry Separate vegetation canopy Dynamic vegetation Vegetation canopy resistance Multi-layer snowpack Snowpack liquid water retention Simple groundwater options Snow albedo treatment New frozen soil scheme New snow cover 4-layer soil 3-layer snow aquifer

11 Noah-MP: Soil Water/Energy Transfer Soil Moisture q æ q ö K = ç D + + t z è z ø z F q - Richards Equation for soil water movement - D, K functions (soil texture, soil moisture) - F q represents sources (rainfall) and sinks (evaporation) Soil/Snow Temperature C T æ T t z è z ( q ) K ( q ) ö = ç t - C, Kt functions (soil texture, soil moisture) - Soil temperature information used to compute ground heat flux ø

12 Noah-MP Physical Processes Noah-MP is a land surface model that allows a user to choose multiple options for several physical processes SW dn Canopy radiative transfer with shading geometry Separate vegetation canopy Dynamic vegetation Vegetation canopy resistance Multi-layer snowpack Snowpack liquid water retention Simple groundwater options Snow albedo treatment New frozen soil scheme New snow cover shaded fraction

13 Noah-MP: more physics, more parameters Noah-MP has a separate canopy and uses a two-stream radiative transfer treatment through the canopy Canopy parameters: Canopy top and bottom Crown radius, vertical and horizontal Vegetation element density, i.e., trees/grass leaves per unit area Leaf and stem area per unit area Leaf orientation Leaf reflectance and transmittance for direct/diffuse and visible/nir radiation Multiple options for spatial distribution Full grid coverage Vegetation cover equals prescribed fractional vegetation Random distribution with slant shading SW dn shaded fraction

14 More modelistic view of Noah-MP Direct (visible,nir) θ z Diffuse (visible,nir) Reflectance and transmittance of individual leaf elements defined by vegetation type ρ L (VIS/NIR) LAI SAI τ L (VIS/NIR)

15 What interesting things can we do? Over a Noah- MP grid, individual tree elements can be randomly distributed and have overlapping shadows SE Minnesota in Google Maps

16 What does that mean visually? SW dn SW dn Option 1 Option 2 shaded fraction shaded fraction

17 Noah-MP LSM Options Using prescribed vegetation fraction varying from 5% to 100% as radiation fraction Increasing vegetation fraction increases snow, decreases albedo SW dn Option 1 shaded fraction

18 Noah-MP LSM Options Using randomly distributed shadows as radiation-active fraction using sun angle Complex interaction between vegetated and shadowed fraction and canopy/snow radiation absorption SW dn Option 2 shaded fraction

19 Key Input to the Noah-MP LSM Land-cover/vegetation classification Many sources, generally satellite-based and general Soil texture class Also general with large consolidations Many secondary parameters that can be specified as function of the above

20 Datasets: NLCD Land Cover

21 Parameters: Land Cover MPTABLE.TBL contains a look-up table for vegetation classes Limitations: All pixels with the same vegetation have the same parameters Modifying parameters affects all vegetation of the same type

22 MODIS 1km Leaf Area Index Climatology Vegetation varying in time and space Comparison of MODIS LAI to default table-based LAI 22

23 Datasets: Soil Texture

24 Parameters: Soil Texture SOILPARM.TBL contains a look-up table for soil texture classes Limitations: All pixels with the same soil type have the same parameters Modifying parameters affects all soil of the same type

25 Datasets: 3D Soil Properties

26 Conclusions Land surface models are evolving to address structural deficiencies and to expand user bases Evolving land surface model structure is leading to new challenges, e.g., parameters, parameters! Knowledge of both model structure and parameter assumptions is useful to properly use an LSM Continued progress is being made on extensions to Noah-MP: crop and dynamic vegetation modules, urban coupling, parameter estimation 26

27 Days in Feb Challenges for Noah LSM Structure FEB1 FEB13 FEB20 FEB27 Forecast Hour (Initialized at 12Z daily) Flagstaff WRF/Noah v3.2 T 2m simulation (red) compared to METAR observations(black) Cold bias during the day results from capped surface temperature at freezing Bias recovers during the night When snow is gone, bias is low KFLG Forecast Bias (ºC) 27

28 Noah-MP: a community land model Noah-MP is an extended version of the Noah LSM with enhanced Multi-Physics options to address critical shortcomings in Noah 1. Leaf area index (prescribed; predicted) 2. Turbulent transfer (Noah; NCAR LSM) 3. Soil moisture stress factor for transpiration (Noah; SSiB; CLM) 4. Canopy stomatal resistance (Jarvis; Ball-Berry) 5. Snow surface albedo (BATS; CLASS) 6. Frozen soil permeability (Noah; Niu and Yang, 2006) 7. Supercooled liquid water (Noah; Niu and Yang, 2006) 8. Radiation transfer: Modified two-stream: Gap = f(3d structure; solar zenith angle;...) 1-GVF Two-stream applied to the entire grid cell: Gap = 0 Two-stream applied to fractional vegetated area: Gap = 1-GVF 9. Partitioning of precipitation to snowfall and rainfall (CLM; Noah) 10. Runoff and groundwater: TOPMODEL with groundwater TOPMODEL with an equilibrium water table (Chen&Kumar,2001) Original Noah scheme BATS surface runoff and free drainage More to be added Total of ~50,000 permutations can be used as multi-physics ensemble members

29 Sides of the Box A land atmosphere model (e.g., WRF) is like a box Energy, mass, and water flow through the sides of the box Must provide this flow to the model running inside the box A land surface model (LSM) sits at the bottom of the box

30 Noah-MP Calling Structure Example Process Options Noah-MP Canopy resistence - Jarvis - Ball-Berry ENERGY WATER CARBON Radiative Transfer - Two-stream - Geometric shade Runoff Options - Free Drainage - 2D Aquifer Vegetation Growth - Prescribed phen. - Dynamic Veg.