:orphan: Surface Physics =============== | Physics Contents ---------------- `WRF Physics Overview`_ |br| `Cumulus Parameterization`_ |br| Microphysics_ |br| Radiation_ |br| `Planetary Boundary Layer (PBL) Physics`_ |br| `Surface Physics`_ |br| `Using Physics Suites`_ |br| `Physics Options for Specific Applications`_ .. _`WRF Physics Overview`: physics.html .. _`Cumulus Parameterization`: cumulus.html .. _Microphysics: microphysics.html .. _Radiation: radiation.html .. _`Planetary Boundary Layer (PBL) Physics`: pbl.html .. _`Surface Physics`: surface.html .. _`Using Physics Suites`: phys_suites.html .. _`Physics Options for Specific Applications`: specific_applications.html | Surface physics Overview ------------------------ .. image:: images/sfc.png :width: 600px :align: center :height: 450px | .. image:: images/sfc_extension.png :width: 350px :align: center :height: 275px .. image:: images/blank_image.png :width: 800px :height: 25px WRF surface physics consist of surface layer (sfclay) schemes and land surface model (LSM) schemes. Surface layer schemes determine the surface layer components of atmospheric diagnostics, which includes exchange and transfer coefficients. They provide these exchange coefficients for heat and moisture to the land surface model (LSM), which then provides land-surface fluxes of heat and moisture to the planetary boundary layer (PBL). The surface schemes also provide friction stress and water-surface fluxes of heat and moisture to the PBL. LSMs are responsible for soil temperature, moisture, snow prediction and sea-ice temperature. | .. note:: *See the `WRF Tutorial presentation on surface physics`_ for additional details.* .. _`WRF Tutorial presentation on surface physics`: https://www2.mmm.ucar.edu/wrf/users/tutorial/presentation_pdfs/202101/dudhia_physics_surface.pdf | .. _sfc-links: Quicklinks to Surface Sections ------------------------------ Click the following links to go directly to each PBL topic. | :ref:`sfclay` :ref:`sfclay-detail-refs` :ref:`lsm` :ref:`lsm-detail-refs` :ref:`sfc-bldt` :ref:`grid-space` :ref:`turb-diff` :ref:`trop-cyclone` :ref:`sea-ice` :ref:`mosaic` :ref:`sst` :ref:`reg-climate` :ref:`accumulation` :ref:`lake` :ref:`hydro` | .. _sfclay: Surface Layer Schemes --------------------- | .. image:: images/sfc_processes.png :width: 500px :align: center :height: 350px .. image:: images/blank_image.png :width: 800px :height: 25px | The surface layer has a constant flux layer of about 0.1 x PBL height (~100 m). The lowest WRF model level is found within this layer (typically 10-50 m). The WRF surface layer scheme is chosen by the namelist.input parameter "sf_sfclay_physics" in the &physics section. Some key points to note about WRF sfclay schemes is * They use similarity theory to determine exchange coefficients and diagnostics of 2m temperature, 2m qvapor, and 10m winds. * They provide exchange coefficient to land-surface models. * They provide friction velocity to the PBL scheme. * They provide surface fluxes over water points. * Schemes have variations in stability functions and roughness lengths. | Back to :ref:`sfc-links` | .. _sfclay-detail-refs: Surface Layer Scheme Details and References ------------------------------------------- **Revised MM5** |br| *sf_sfclay_physics=1* |br| Removes limits and uses updated stability functions; thermal and moisture roughness lengths (or exchange coefficients for heat and moisture) over the ocean use the COARE 3 formula (`Fairall et al., 2003`_) |br| `Jimenez et al., 2012`_ .. _`Fairall et al., 2003`: https://doi.org/10.1175/1520-0442(2003)016%3C0571:BPOASF%3E2.0.CO;2 .. _`Jimenez et al., 2012`: https://doi.org/10.1175/MWR-D-11-00056.1 | **Eta Similarity** |br| *sf_sfclay_physics=2* |br| Used in Eta model; based on Monin-Obukhov with Zilitinkevich thermal roughness length and standard similarity functions from look-up tables |br| `Monin and Obukhov, 1954`_ |br| `Janjic, 1994`_ |br| `Janjic, 1996`_ |br| `Janjic, 2001`_ .. _`Monin and Obukhov, 1954`: https://moodle2.units.it/pluginfile.php/267453/mod_resource/content/1/ABL_lecture_13.pdf .. _`Janjic, 1994`: https://doi.org/10.1175/1520-0493(1994)122%3C0927:TSMECM%3E2.0.CO;2 .. _`Janjic, 1996`: https://www2.mmm.ucar.edu/wrf/users/physics/phys_refs/SURFACE_LAYER/eta_part3.pdf .. _`Janjic, 2001`: https://repository.library.noaa.gov/view/noaa/11409 | **QNSE** |br| *sf_sfclay_physics=4* |br| Quasi-Normal Scale Elimination PBL scheme’s surface layer option |br| *No publication available* | **MYNN** |br| *sf_sfclay_physics=5* |br| Nakanishi and Niino PBL’s surface layer scheme |br| *No publication available* | **Pleim-Xiu** |br| *sf_sfclay_physics=7* |br| `Pleim, 2006`_ .. _`Pleim, 2006`: https://doi.org/10.1175/JAM2339.1 | **Total Energy - Mass Flux (TEMF)** |br| *sf_sfclay_physics=10* |br| `Angevine et al., 2010`_ .. _`Angevine et al., 2010`: https://doi.org/10.1175/2010MWR3142.1 | **MM5 Similarity** |br| *sf_sfclay_physics=91* |br| Based on Monin-Obukhov, with Carslon-Boland viscous sub-layer and standard similarity functions from look-up tables thermal and moisture roughness lengths (or exchange coefficients for heat and moisture) over ocean use the COARE 3 formula (`Fairall et al., 2003`_) |br| `Paulson, 1970`_ |br| `Dyer and Hicks, 1970`_ |br| `Webb, 1970`_ |br| `Belijaars, 1994`_ |br| `Zhang and Anthes, 1982`_ .. _`Fairall et al., 2003`: https://doi.org/10.1175/1520-0442(2003)016%3C0571:BPOASF%3E2.0.CO;2 .. _`Paulson, 1970`: https://doi.org/10.1175/1520-0450(1970)009%3C0857:TMROWS%3E2.0.CO;2 .. _`Dyer and Hicks, 1970`: https://doi.org/10.1002/qj.49709641012 .. _`Webb, 1970`: https://doi.org/10.1002/qj.49709640708 .. _`Belijaars, 1994`: https://doi.org/10.1002/qj.49712152203 .. _`Zhang and Anthes, 1982`: https://doi.org/10.1175/1520-0450(1982)021%3C1594:AHRMOT%3E2.0.CO;2 | **Other Options Related to Surface Layer** * **iz0tlnd** : =1 - Chen-Zhang thermal roughness length over land, which depends on vegetation height (works with sf_sfclay_physics = 1, 91, and 5); =0 - original thermal roughness length in each sfclay option |br| `Chen and Zhang, 2009`_ * **shalwater_z0=1** : Shallow-water roughness for offshore roughness adjustment in water depths less tha 100 m. This option works with a specified depth or real bathymetry input, and only with sf_sfclay_physics=1. The bathymetry data is available from WPS/geogrid (kkw - add link). If no bathymetry data is available, set constant depth (in meters; must be positive) using namelist option "shalwater_depth." Any depths outside the range of 10-100 m are rounded to the nearest limit value. |br| `GEBCO Compilation Group, 2021`_ |br| `Jimenez and Dudhia, 2018`_ .. _`GEBCO Compilation Group, 2021`: https://www.bodc.ac.uk/data/published_data_library/catalogue/10.5285/c6612cbe-50b3-0cff-e053-6c86abc09f8f .. _`Jimenez and Dudhia, 2018`: https://doi.org/10.1175/JAMC-D-17-0137.1 .. _`Chen and Zhang, 2009`: https://doi.org/10.1029/2009GL037980 | Back to :ref:`sfc-links` | .. _lsm: Land Surface Model ------------------ | .. image:: images/lsm_processes.png :width: 700px :align: center :height: 500px .. image:: images/blank_image.png :width: 800px :height: 25px | WRF LSM schemes are driven by surface energy and water fluxes. They predict soil temperature and soil moisture in 3 or 4 layers, depending on the scheme, as well as snow water equivalent on the ground. | **Vegetation and Soil** |br| LSMs consider the effects of vegetation and soil components, such as vegetation fraction, vegetation categories (e.g., cropland, forest types, etc.), and soil categories (e.g., sandy, clay, etc.). Below are some key notes. * Processes include evapotranspiration, root zone, and leaf effects. * Vegetation fraction varies seasonally. * Soil categories are considered for drainage and thermal conductivity. | **Snow Cover** |br| LSMs include fractional snow cover and predict snow water equivalent development based on precipitation, sublimation, melting, and run-off. The number of layers is dependent on the scheme. * Single-layer snow (Noah, PX) * Multi-layer snow (RUC, NoahMP, SSiB,CLM4) * 5-layer option has no snow prediction *Note: Frozen soil water is also predicted by the Noah, NoahMP, RUC, and CLM4 schemes.* | **Urban Effects** |br| An urban category in LSMs is typically adequate for larger-scale studies. An alternative is to use an urban model with either the Noah or NoahMP LSM scheme. To do this, set sf_urban_physics in namelist.input to one of the following options. * **=1** : Urban Canopy Model (UCM); single layer * **=2** : Building Environment Parameterization (BEP); multi-layer; *only works with YSU, MYJ and BouLac PBL schemes* * **=3** : Building Energy Model (BEM); adds heating and air-conditioning to BEP; *only works with YSU, MYJ and BouLac PBL schemes* .. note:: * NUDAPT detailed map data is available for use in WPS, and includes data for 40+ U.S. cities. * Beginning with V4.3, code is updated to include a capability to use local climate zones, which is incorporated for all three urban applications (`additional details`_) .. _`additional details`: https://ral.ucar.edu/sites/default/files/public/product-tool/urban-canopy-model/WRF_urban_update_Readme_file_WRF4.3.pdf | **LSM Tables** |br| There are LSM tables (text files) available in both the test/em_real and run/ directories within the WRF code structure. These are set categories for the various LSMs, but these properties can be modified in the tables. * **VEGPARM.TBL** : used by Noah and RUC for vegetation categories (albedo, roughness length, emissivity, vegetation properties) * **MPTABLE.TBL** : used by NoahMP * **SOILPARM.TBL** : used by Noah and RUC for soil properties * **LANDUSE.TBL** : used by the 5-layer model * **URBPARM.TBL** : used by urban models | **Initializing LSMs** |br| All LSMs (except for the slab option) require the following additional fields for initialization. * Soil temperature * Soil moisture * Snow liquid equivalent These fields are available in the Grib first-guess files, but do not come from observations. They come from “offline” models driven by observations for rainfall, radiation, surface temperature, humidity, and wind. These are part of operational analysis or reanalysis system. There are consistent model-derived datasets for Noah and RUC LSMs that correspond to the levels in WRF. * Eta/GFS/AGRMET/NNRP for Noah (although some older datasets have limited soil levels available) * RUC for RUC (just North America; limited availability) ECMWF/ERA soil analyses can be used and real.exe interpolates to WRF soil levels, but, resolution of mesoscale land use means there will be inconsistency in elevation, soil type and vegetation. The only adjustment for soil temperature takes place during the real.exe process, and addresses elevation differences between the original elevation and model elevation (SOILHGT used). Inconsistency leads to spin-up, as adjustments occur in soil temperature and moisture at the beginning of the simulation. This spin-up can only be avoided by running an offline model on the same grid (e.g. HRLDAS for Noah), but it may take months to spin up soil moisture. Cycling the land state between forecasts also helps, but may propagate errors (e.g in rainfall effect on soil moisture). | Back to :ref:`sfc-links` | .. _lsm-detail-refs: LSM Scheme Details and References --------------------------------- **5-layer thermal diffusion (SLAB)** |br| *sf_surface_physics = 1* |br| Soil temperature only scheme; uses five layers |br| `Dudhia, 1996`_ .. _`Dudhia, 1996`: https://www.researchgate.net/profile/Jimy-Dudhia/publication/259865197_A_Multi-layer_Soil_Temperature_Model_for_MM5/links/0046352e307710e99c000000/A-Multi-layer-Soil-Temperature-Model-for-MM5.pdf | **Noah** |br| *sf_surface_physics = 2* |br| Unified NCEP/NCAR/AFWA scheme with soil temperature and moisture in four layers; fractional snow cover and frozen soil physics |br| `Tewari et al., 2004`_ * A sub-tiling option can be activated by namelist option **sf_surface_mosaic=1**, and the number of tiles in a grid box is defined by namelist option **mosaic_cat**, with a default value of 3. .. _`Tewari et al., 2004`: https://ams.confex.com/ams/84Annual/techprogram/paper_69061.htm | **RUC** |br| *sf_surface_physics = 3* |br| This model uses a layer approach to the solution of energy and moisture budgets. Atmospheric and soil fluxes are computed in the middle of the first atmospheric layer and the top soil layer, respectively, and these fluxes modify the heat and moisture storage in the layer spanning the ground surface. The RUC LSM uses 9 soil levels with higher resolution near the interface with the atmosphere. .. note:: *If initialized from the model with low resolution near the surface, like the Noah LSM, the top levels could be too moist causing moist/cold biases in the model forecast. Solution: cycle soil moisture and let it spin-up for several days to fit the vertical structure of RUC LSM.* The prognostic variable for soil moisture is volumetric soil moisture content, minus the residual soil moisture tied to soil particles, and therefore not participating in moisture transport. The RUC LSM takes into account freezing and thawing processes in the soil. It is able to use explicit mixed-phase precipitation provided by cloud microphysics schemes. It uses a simple treatment of sea ice, which solves heat diffusion in sea ice and allows evolving snow cover on top of sea ice. In the warm season, RUC LSM corrects soil moisture in cropland areas to compensate for irrigation in these regions. Snow accumulated on top of soil can have up to two layers, depending on snow depth (ref S16). When the snow layer is very thin, it is combined with the top soil layer to avoid excessive radiative cooling at night. The grid cell can be partially covered with snow, when snow water equivalent is below a threshold value of 3 cm. When this condition occurs, surface parameters, such as roughness length and albedo, are computed as a weighted average of snow-covered and snow-free areas. The energy budget utilizes an iterative snow melting algorithm. Melted water can partially refreeze and remain within the snow layer, and the rest of it percolates through the snow pack, infiltrates into soil and forms surface runoff. Snow density evolves as a function of snow temperature, snow depth and compaction parameters. Snow albedo is initialized from the maximum snow albedo for the given vegetation type, but it can also be modified, depending on snow temperature and snow fraction. To obtain a better representation of snow accumulated on the ground, the RUC LSM has introduced estimation of frozen precipitation density. The most recent modifications to RUC LSM include refinements to the interception of liquid or frozen precipitation by the canopy, and also the "mosaic" approach for patchy snow with a separate treatment of energy and moisture budgets for snow-covered and snow-free portions of the grid cell, and aggregation of the separate solutions at the end of time step. The datasets needed to initialize RUC LSM include: * High-resolution dataset for soil and land-use types * Climatological albedo for snow-free areas * Spatial distribution of maximum surface albedo in the presence of snow cover * Fraction of vegetation types in the grid cell to take into account sub-grid-scale heterogeneity in computation of surface parameters * Fraction of soil types within the grid cell * Climatological greenness fraction * Climatological leaf area index * Climatological mean temperature at the bottom of soil domain * Real-time sea-ice concentration * Real-time snow cover to correct cycled in RAP and HRRR snow fields Recommended namelist options: |br| sf_surface_physics=3 |br| num_soil_layers=9 |br| usemonalb=.true. *(uses monthly albedo fields from geogrid instead of table values)* |br| rdlai2d=.true. *(uses monthly LAI data from geogrid and is included in the "wrflowinp" file if sst_update=1)* |br| mosaic_lu=1 |br| mosaic_soil=1 .. note:: *See RAP_ and HRRR_ that use RUC LSM as their land component.* `Benjamin et al., 2004`_ |br| `Smirnova et al., 2016`_ .. _`Benjamin et al., 2004`: https://doi.org/10.1175/1520-0493(2004)132%3C0473:MWPWTF%3E2.0.CO;2 .. _`Smirnova et al., 2016`: https://doi.org/10.1175/MWR-D-15-0198.1 .. _RAP: https://rapidrefresh.noaa.gov/RAP .. _HRRR: https://rapidrefresh.noaa.gov/hrrr/HRRR. | **Noah-MP** |br| *sf_surface_physics = 4* |br| Uses multiple options for key land-atmosphere interaction processes. Noah-MP contains a separate vegetation canopy defined by a canopy top and bottom with leaf physical and radiometric properties used in a two-stream canopy radiation transfer scheme that includes shading effects. Noah-MP contains a multi-layer snow pack with liquid water storage and melt/refreeze capability and a snow-interception model describing loading/unloading, melt/refreeze, and sublimation of the canopy-intercepted snow. Multiple options are available for surface water infiltration and runoff, and groundwater transfer and storage including water table depth to an unconfined aquifer. Horizontal and vertical vegetation density can be prescribed or predicted using prognostic photosynthesis and dynamic vegetation models that allocate carbon to vegetation (leaf, stem, wood and root) and soil carbon pools (fast and slow). |br| `Niu et al., 2011`_ |br| `Yang et al., 2011`_ | .. _`Niu et al., 2011`: https://doi.org/10.1029/2010JD015139 .. _`Yang et al., 2011`: https://doi.org/10.1029/2010JD015140 | **Community Land Model Version 4 (CLM4)** *sf_surface_physics = 5* |br| Contains sophisticated treatment of biogeophysics, hydrology, biogeochemistry, and dynamic vegetation. In CLM4, the land surface in each model grid cell is characterized into five primary sub-grid land cover types (glacier, lake, wetland, urban, and vegetated). The vegetated sub-grid consists of up to 4 plant functional types (PFTs) that differ in physiology and structure. The WRF input land cover types are translated into the CLM4 PFTs through a look-up table. The CLM4 vertical structure includes a single-layer vegetation canopy, a five-layer snowpack, and a ten-layer soil column. |br| `Oleson et al., 2010`_ |br| `Lawrence et al., 2011`_ |br| *An earlier version of CLM has been quantitatively evaluated within WRF; referenced here:* |br| `Jin and Wen, 2012`_ |br| `Lu and Kueppers, 2012`_ |br| `Subin et al., 2011`_ | .. _`Oleson et al., 2010`: https://d1wqtxts1xzle7.cloudfront.net/44532695/Technical_Description_of_version_4.0_of_20160408-23450-1lwj9zc-with-cover-page-v2.pdf?Expires=1665619677&Signature=LLxHTun6ZR7rMW87nBTqgEWtA9AstcWdJa~sNhWVF0OPK7uLtgH8effNGt0ZrvdDpp4URljLdF-dW7Bhobr0fp5CB-Loxdh6xlOoDi-ymvmQ3MFVkqOcL~ha6~uzvowZZBtPpa4eUVwaeHHECNwpdovOpHbSQIQWBFYCC5fP3KUEtpirLRZz~vRK29jIVd17Bd8GUSvax8qsXKX-5qck6B4EUCeU7xdiW649EorUVmfrkJHCVk13ICRDTD~mgCpfPFDn6-mgVA7Kv-hYqrODqGDlXFy-ziL4cxfdgbQbB4Vl3W~Hp5tyBH3uNWUJeM4aIggVzvqtCWldrYhovUHfqQ__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA .. _`Lawrence et al., 2011`: https://doi.org/10.1029/2011MS00045 .. _`Jin and Wen, 2012`: https://doi.org/10.1029/2011JD016980 .. _`Lu and Kueppers, 2012`: https://doi.org/10.1029/2011JD016991 .. _`Subin et al., 2011`: https://doi.org/10.1175/2010EI331.1 | **Pleim-Xiu** |br| *sf_surface_physics = 7* |br| Two-layer scheme with vegetation and sub-grid tiling; has been developed and improved over the years to provide realistic ground temperature, soil moisture, and surface sensible and latent heat fluxes in mesoscale meteorological models. The PX LSM is based on the ISBA model (`Noilhan and Planton, 1989`_), and includes a 2-layer force-restore soil temperature and moisture model. The top layer is 1 cm thick, and the lower layer is 99 cm. Grid aggregate vegetation and soil parameters are derived from fractional coverage of land use categories and soil texture types. There are two indirect nudging schemes that correct biases in 2-m air temperature and moisture by dynamic adjustment of soil moisture (`Pleim and Xiu, 2003`_) and deep soil temperature (`Pleim and Gilliam, 2009`_). The PX LSM was primarily developed for retrospective simulation, where surface-based observations are available to inform the indirect soil nudging. While soil nudging can be disabled using the FDDA namelist.input setting **pxlsm_soil_nudge**, little testing has been done in this mode, although some users report reasonable results. `Gilliam and Pleim, 2010`_ discuss implementation in the WRF model and provide typical configurations for retrospective applications. To activate soil nudging the Obsgrid_ objective re-analysis utility must be used to produce a surface nudging file with the naming convention "wrfsfdda_d0*." The PX LSM uses 2-m temperature and mixing ratio re-analyses from this file for deep soil moisture and temperature nudging. To test PX LSM in forecast mode with soil nudging activated, forecasted 2-m temperature and mixing ratio can be used with empty observation files to produce "wrfsfdda_d0*" files, using Obsgrid, but results are tied to the governing forecast model. .. note:: *See a `detailed description of the PX LSM`_, including pros/cons, best practices, and recent improvements.* *Additional References:* `Pleim and Xiu, 1995`_ |br| `Xiu et al., 2001`_ .. _`Noilhan and Planton, 1989`: https://doi.org/10.1175/1520-0493(1989)117%3C0536:ASPOLS%3E2.0.CO;2 .. _`Pleim and Xiu, 2003`: https://doi.org/10.1175/1520-0450(2003)042%3C1811:DOALSM%3E2.0.CO;2 .. _`Pleim and Gilliam, 2009`: https://doi.org/10.1175/2009JAMC2053.1 .. _`Pleim and Xiu, 1995`: https://doi.org/10.1175/1520-0450-34.1.16 .. _`Xiu et al., 2001`: https://doi.org/10.1175/1520-0450(2001)040%3C0192:DOALSM%3E2.0.CO;2 .. _`Gilliam and Pleim, 2010`: https://doi.org/10.1175/2009JAMC2126.1 .. _Obsgrid: https://www2.mmm.ucar.edu/wrf/users/docs/user_guide_v4/v4.2/users_guide_chap7.html .. _`detailed description of the PX LSM`: http://www2.mmm.ucar.edu/wrf/users/docs/PX-ACM.pdf | **Simplified Simple Biosphere (SSiB)** |br| *sf_surface_physics=8* |br| This is the third generation of the Simplified Simple Biosphere Model, and is developed for land/atmosphere interaction studies in the climate model. The aerodynamic resistance values in SSiB are determined in terms of vegetation properties, ground conditions and bulk Richardson number according to the modified Monin–Obukhov similarity theory. SSiB-3 includes three snow layers to realistically simulate snow processes, including destructive metamorphism, densification process due to snow load, and snow melting, which substantially enhances the model’s ability for the cold season study. To use this option, ra_lw_physics and ra_sw_physics should be set to either 1, 3, or 4. The second full model level should be set to no larger than 0.982 so that the height of that level is higher than vegetation height. `Xue et al., 1991`_ |br| `Sun and Xue, 2001`_ .. _`Xue et al., 1991`: https://doi.org/10.1175/1520-0442(1991)004%3C0345:ASBMFG%3E2.0.CO;2 .. _`Sun and Xue, 2001`: https://doi.org/10.1007/BF02919314 | **Other Options Related to LSM** * **ua_phys=.true.** : University of Arizona snow physics for use with Noah LSM |br| `Wang et al., 2010`_ * **sf_surface_mosaic=1** : Sub-tiling option for use with Noah LSM |br| `Li et al., 2013`_ .. _`Wang et al., 2010`: https://doi.org/10.1029/2009JD013761 .. _`Li et al., 2013`: https://doi.org/10.1002/2013JD02065 | Back to :ref:`sfc-links` | .. _sfc-bldt: PBL and Land Surface Time-step (bldt) ------------------------------------- "bldt" is a namelist.input parameter used to determine the minutes between boundary layer and land-surface model calls. The typical value is 0 (every step), and this is reasonable for all schemes, with the exception of the CSM land-surface scheme. CSM LSM is expensive, so it may be better to consider increasing the value of bldt when using it. | Back to :ref:`sfc-links` | .. _grid-space: Model Grid Spacing ------------------ | .. image:: images/pbl_grid_spacing.png :width: 700px :align: center :height: 350px .. image:: images/blank_image.png :width: 800px :height: 25px | WRF PBL schemes are designed for grid resolution >> I in the image above, while LES schemes are designed for grid resolution << I. For coarse grid spacing, all eddies are sub-grid, and 1-D column schemes handle sub-grid vertical fluxes. For fine grid spacing, all major eddies are resolved, and 3-D turbulence schemes handle sub-grid mixing. The remaining grid-spacing is a grey-zone, which is sub-kilometer grids, where PBL and LES assumptions are not perfect. There are scale-aware schemes that can be used for this zone. * Shin-Hong PBL based on YSU, designed for sub-kilometer transition scales (200 m – 1 km); nonlocal mass-flux and Kv term is reduce in strength as the grid size gets smaller and resolved mixing increases * New 3d TKE option (km_opt=5) in V4.2; becomes 3-D LES at fine scales; adds scale-dependent Shin-Hong nonlocal mass flux and implicit vertical diffusion at coarse grid sizes * Other schemes may work in this range but will not have correctly partitioned resolved/sub-grid energy fractions For grid sizes up to about 100m, LES is preferable. | Back to :ref:`sfc-links` | .. _turb-diff: Turbulence and Diffusion ------------------------ The namelist.input parameter "diff_opt" is used to specify the turbulence and mixing option. When diffusion is used with a PBL scheme, vertical diffusion is deactivated, so diff_opt only affects horizontal diffusion. * **diff_opt=0** : no turbulence or explicit spatial numerical filters * **diff_opt=1** : (default); evaluates the 2nd-order diffusion term on coordinate surfaces; limited to constant vertical diffusion coefficient (kvdif); should not be used with calculated diffusion coefficient options (km_opt=2,3); can be used with PBL schemes that include vertical diffusion internally; horizontal diffusion acts along model levels; simple numerical method with only neighboring points on the same model level * **diff_opt=2** : evaluates mixing terms in physical space (stress form - x,y,z); strictly horizontal and better for complex terrain - avoids diffusion up and down slopes included in "diff_opt=1;" horizontal diffusion acts on strictly horizontal gradients; numerical method includes vertical correction term, using more grid points; for stability, diffusion strength is reduced in steep coordinate slopes (dz ~ dx) | **Recommended Diffusion Options** |br| #. Real-data case with PBL option on * diff_opt=2 * km_opt=4 * Less diffusive in complex terrain (while diff_opt=1 diffuses along slopes) * These options compliment vertical diffusion done by the PBL scheme #. High-resolution real-data cases (~100m grid) * No PBL scheme * diff_opt=2 * km_opt=2 or 3 (TKE or Smagorinsky scheme) #. Idealized cloud-resolving (dx= 1-3 km) modeling (smooth or no topography, no surface heat fluxes) * diff_opt=2 * km_opt=2 or 3 #. Complex topography with no PBL scheme * diff_opt=2 is more accurate for sloped coordinate surfaces, and prevents diffusion up/down valley sides, but can still potentially be unstable with complex terrain * WRF is incapable of handling slopes > 45 degrees - can use "epssm," which is a damping term that can be increased to help with steep slopes (e.g., 0.5-1.0) | Back to :ref:`sfc-links` | .. _trop-cyclone: Tropical Cyclone Options ------------------------ The following options, specific to tropical cyclone options, can be added to the &physics section of namelist.input. **Ocean Mixed Layer Model** |br| *sf_ocean_physics=1* |br| Ocean Mixed Layer Model; 1-d slab ocean mixed layer (specified initial depth); includes wind-driven ocean mixing for SST cooling feedback |br| `Pollard et al., 1973`_ .. _`Pollard et al., 1973`: https://doi.org/10.1080/03091927208236105 | **3d PWP Ocean** |br| *sf_ocean_physics=2* |br| 3-d multi-layer (~100) ocean, salinity effects; fixed depth |br| `Price, 1981`_ |br| `Price et al., 1994`_ |br| `Lee and Chen, 2012`_ .. _`Price, 1981`: https://doi.org/10.1175/1520-0485(1981)011%3C0153:UORTAH%3E2.0.CO;2 .. _`Price et al., 1994`: https://doi.org/10.1175/1520-0485(1994)024%3C0233:FSRTAM%3E2.0.CO;2 .. _`Lee and Chen, 2012`: doi:10.1175/JAS-D-12-046.1 | **Alternative surface-layer option for high-wind ocean** |br| *surface (isftcflx=1,2)* |br| Modifies Charnock relation to give less surface friction at high winds (lower Cd); modifies surface enthalpy (Ck, heat/moisture) either with constant z0q (isftcflx=1) or Garratt formulation (isftcflx=2); *must be used with sf_sfclay_physics=1* | Back to :ref:`sfc-links` | .. _sea-ice: Fractional Sea Ice ------------------ The fractional sea ice option (**fractional_seaice=1**) includes input sea-ice fraction data that partitions land and water fluxes within a grid box, treating sea-ice as a fractional field. The option requires fractional sea-ice as input data; data sources may include those from GFS or the `National Snow and Ice Data Center`_; use **XICE** for the Vtable entry instead of SEAICE; this option works with sf_sfclay_physics = 1, 2, 5, and 7, and sf_surface_physics = 2, 3, and 7. .. _`National Snow and Ice Data Center`: https://nsidc.org/ | Back to :ref:`sfc-links` | .. _mosaic: Sub-grid Mosaic --------------- Without using an additional sub-grid mosaic option, the default behavior is to use a single dominant vegetation and soil type per grid cell. However, the following schemes have additional options available. * Noah: use **sf_surface_mosaic=1** to allow multiple categories within a grid cell * RUC: use **mosaic_lu=1** and **mosaic_soil=1** to allow multiple categories within a grid cell * Pleim-Xu: additionally averages properties of sub-grid categories | Back to :ref:`sfc-links` | .. _sst: Sea-surface Update ------------------ To use the sea-surface update option, set **sst_update=1** in the &physics section of namelist.input. This option reads a lower boundary file periodically to update the sea-surface temperature (as opposed to being fixed with time, which is default) * Should be used for long-period simulations (a week or more) * A file called **wrflowinp_d0n** will be created by real * Sea-ice can be updated, as well * Vegetation fraction update is included; allows seasonal change in albedo, emissivity, and roughness length if using the Noah LSM * **usemonalb=.true.** to use monthly albedo input | Back to :ref:`sfc-links` | .. _reg-climate: Regional Climate Options ------------------------ * **tmn_update=1** : Updates deep-soil temperature for multi-year future-climate runs * **sst_skin=1** : Adds a diurnal cycle to sea-surface temperature * **output_diagnostics=1** : Ability to output max/min/mean/std of surface fields in a specified period (e.g. daily) * **bucket_mm** and **bucket_J** : Provides a more accurate way to accumulate water and energy for long-run budgets (see the next section) | Back to :ref:`sfc-links` | .. _accumulation: Accumulation Budgets -------------------- * Some outputs fields are accumulated from the start of the simulation * These include rainfall totals (mm or kg/m2) RAINC, RAINNC, and radiation totals (J/m2), ACLWUPT, ACSWDNB, etc. * Averages over any period can use just the output at the end minus output at the beginning, divided by the interval * For regional climate simulations (months), 32-bit accuracy makes adding small time-step values to accumulated totals inaccurate since only about 7 significant figures are stored. * Use **bucket_mm** and **bucket_J** to carry the total in integer and remainder parts, e.g. * Total rain = RAINC + I_RAINC*bucket_mm * Default bucket value is typical monthly accumulation * bucket_mm=100 mm and bucket_J=109 Joules | Back to :ref:`sfc-links` | .. _lake: Lake Model ---------- The CLM 4.5 lake model (**sf_lake_physics=1**) was obtained from the ommunity Land Model version 4.5 (CLM4) with some modifications. It is a one-dimensional mass and energy balance scheme with 20-25 model layers, including up to 5 snow layers on the lake ice, 10 water layers, and 10 soil layers on the lake bottom. The lake scheme is used with actual lake points and lake depth derived from the WPS, and can also be used with user-defined lake points and lake depth in WRF (**lake_min_elev** and **lakedepth_default**). The lake scheme is independent of a land surface scheme and therefore can be used with any land surface scheme embedded in WRF. |br| `Gu et al., 2013`_ |br| `Subin et al., 2012`_ There are also global bathymetry data available for most large lakes. This can be obtained from the `WPS Geographical Static Data Downloads`_ web page, and can be used during the WPS/geogrid process. .. _`Gu et al., 2013`: https://link.springer.com/article/10.1007/s10584-013-0978-y .. _`Subin et al., 2012`: https://doi.org/10.1029/2011MS000072 .. _`WPS Geographical Static Data Downloads`: https://www2.mmm.ucar.edu/wrf/users/download/get_sources_wps_geog.html | Back to :ref:`sfc-links` | .. _hydro: WRF-Hydro --------- This capability couples the WRF model with hydrology processes (such as routing and channeling). It requires a separate compile by setting the environment variable WRF_HYDRO. In a c-shell environment, issue |br| ``setenv WRF_HYDRO 1`` |br| or in a bash environment, issue |br| ``export WRF_HYDRO=1`` |br| before configure and compile. Once WRF is compiled, copy files from the hydro/Run/ directory to your working directory (e.g. test/em_real/). This option requires a specail initialization for hydrological datasets. Please refer to the `RAL WRF-Hydro Modeling System`_ web page for detailed information. .. _`RAL WRF-Hydro Modeling System`: http://www.ral.ucar.edu/projects/wrf_hydro | Back to :ref:`sfc-links` | .. image:: images/blank_image.png :width: 800px :height: 25px Next section: `Using Physics Suites`_ | | | | .. _`Using Physics Suites`: phys_suites.html