:orphan: Planetary Boundary Layer (PBL) 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 | Planetary Boundary Layer Overview --------------------------------- .. image:: images/pbl.png :width: 600px :align: center :height: 350px .. image:: images/blank_image.png :width: 800px :height: 25px WRF Planetary Boundary Layer (PBL) schemes' purpose is to distribute surface fluxes with boundary layer eddy fluxes, and allow for PBL growth by entrainment. * There are two different classes of PBL schemes: #. Turbulent kinetic energy prediction (Mellor-Yamada Janjic, MYNN, Bougeault-Lacarrere, TEMF, QNSE, and CAM UW). Some also include non-local mass-flux terms (QNSE-EDMF, MYNN, and TEMF) #. Diagnostic non-local (YSU, GFS, MRF, ACM2) * Above the PBL, all schemes also do vertical diffusion due to turbulence. * PBL schemes can be used for most grid sizes when surface fluxes are present; however, at grid size dx << 1 km, this assumption breaks down. To get around this, you can use 3d diffusion instead of a PBL scheme (coupled to surface physics). This works best when dx and dz are comparable. * The lowest level should be in the surface layer (0.1h). This is important for surface (2m, 10m) diagnostic interpolation. * With ACM2, GFS, and MRF PBL schemes, the lowest full level should be .99 or .995 (not too close to 1). * TKE schemes and YSU can use thinner surface layers. * PBL schemes assume PBL eddies are not resolved. | .. image:: images/pbl_processes.png :width: 500px :align: center :height: 350px .. image:: images/blank_image.png :width: 800px :height: 25px | .. note:: *See the `WRF Tutorial presentation on PBL`_ for additional details.* .. _`WRF Tutorial presentation on PBL`: https://www2.mmm.ucar.edu/wrf/users/tutorial/presentation_pdfs/202101/dudhia_physics_pbl_turbulence.pdf | .. _pbl-links: Quicklinks to PBL Sections -------------------------- Click the following links to go directly to each PBL topic. | :ref:`pbl` :ref:`pbl-detail-refs` :ref:`pbl-add-options` :ref:`bldt` :ref:`grid-spacing` :ref:`diffusion` | .. _pbl: PBL Scheme Options ------------------ | .. csv-table:: :widths: 60, 40, 70, 55, 70, 50 :align: left :header: "Scheme", "Option", "Works With sfclay Option", "Prognostic Variables", "Diagnostic Variables", "Cloud Mixing" "YSU", 1, "1 91", none, exch_h, "QC QI" "MYJ", 2, 2, TKE_PBL, "EL_PBL exch_h", "QC QI" "QNSE-EDMF", 4, TKE_PBL, "EL_PBL exch_h exch_m", "QC QI" "MYNN2", 5, "1 2 5 91", QKE, "Tsq Qsq Cov exch_h exch_m", QC "MYNN3", 6, "1 2 5 91", "QKE Tsq Qsq Cov", "exch_h exch_m", QC "ACM2", 7, "1 7 91", " ", " ", "QC QI" "BouLac", 8, "1 2 91", TKE_PBL, "EL_PBL exch_h exch_m", QC "UW", 9, "1 2 91", TKE_PBL, "exch_h exch_m", QC "TEMF", 10, 10, TE_TEMF, "\*_temf", "QC QI" "Shin-Hong", 11, "1 91", " ", exch_h, "QC QI" "GBM", 12, "1 91", TKE_PBL, "EL_PBL exch_h exch_m", "QC QI" "MRF", 99, "1 91", " ", " ", "QC QI" | Back to :ref:`pbl-links` .. _pbl-detail-refs: PBL Scheme Details and References --------------------------------- **Yonsei University (YSU)** |br| *bl_pbl_physics=1* |br| Non-local-K scheme with explicit entrainment layer and parabolic K profile in unstable mixed layer; includes capability of topdown mixing for turbulence driven by cloud-top radiative cooling, which is separate from bottom-up surface-flux-driven mixing |br| `Hong et al., 2006`_ Additional options specific for use with YSU: * **topo_wind** : =1 - topographic correction for surface winds to represent extra drag from sub-grid topography and enhanced flow at hill tops (`Jimenez and Dudhia, 2012`_); =2 - a simpler terrain variance-related correction * **ysu_topdown_pblmix=1** : option for top-down mixing driven by radiative cooling .. _`Jimenez and Dudhia, 2012`: https://doi.org/10.1175/JAMC-D-11-084.1 .. _`Hong et al., 2006`: https://doi.org/10.1175/MWR3199.1 | **Mellor-Yamada-Janjic (MYJ)** |br| *bl_pbl_physics=2* |br| Eta operational scheme; one-dimensional prognostic turbulent kinetic energy scheme with local vertical mixing |br| `Janjic, 1994`_ |br| `Mesinger, 1993`_ .. _`Janjic, 1994`: https://doi.org/10.1175/1520-0493(1994)122%3C0927:TSMECM%3E2.0.CO;2 .. _`Mesinger, 1993`: https://www2.mmm.ucar.edu/wrf/users/physics/phys_refs/PBL/MYJ_part2.pdf | **Quasi-Normal Scale Elimination (QNSE-EDMF)** |br| *bl_pbl_physics=4* |br| A TKE-prediction option that uses a new theory for stably-stratified regions; daytime part uses eddy diffusivity mass-flux method with shallow convection (mfshconv = 1); includes shallow convection using a mass-flux approach through the whole cloud-topped boundary layer |br| `Sukoriansky et al., 2005`_ .. _`Sukoriansky et al., 2005`: https://doi.org/10.1007/s10546-004-6848-4 | **Mellor-Yamada Nakanishi and Niino Level 2.5 (MYNN2)** |br| *bl_pbl_physics=5* |br| Predicts sub-grid TKE terms; includes shallow convection using a mass-flux approach through the whole cloud-topped boundary layer; includes a capability of top-down mixing for turbulence driven by cloud-top radiative cooling, which is separate from bottom-up surface-flux-driven mixing |br| `Nakanishi and Niino, 2006`_ |br| `Nakanishi and Niino, 2009`_ |br| `Olson et al., 2019`_ .. _`Nakanishi and Niino, 2006`: https://doi.org/10.1007/s10546-005-9030-8 .. _`Nakanishi and Niino, 2009`: https://doi.org/10.2151/jmsj.87.895 .. _`Olson et al., 2019`: https://doi.org/10.25923/n9wm-be49 Additional options specific for use with MYNN: * **icloud_bl=1** : option to couple subgrid-scale clouds from MYNN to radiation * **bl_mynn_cloudpdf** : =1 - `Kuwano et al., 2010`_ ; =2 - `Chaboureau and Bechtold, 2002`_ (with mods, default) * **bl_mynn_cloudmix=1** : mixing cloud water and ice (qnc and qni are mixed when scalar_pblmix=1) * **bl_mynn_edmf=1** : activate mass-flux in MYNN * **bl_mynn_mixlength** : =1 is from RAP/HRRR; =2 is from blending .. _`Kuwano et al., 2010`: https://doi.org/10.1002/qj.660 .. _`Chaboureau and Bechtold, 2002`: https://doi.org/10.1175/1520-0469(2002)059%3C2362:ASCPDF%3E2.0.CO;2 | **Mellor-Yamada Nakanishi and Niino Level 3 (MYNN3)** |br| *bl_pbl_physics=6* |br| Predicts TKE and other second-moment terms |br| `Nakanishi and Niino, 2006`_ |br| `Nakanishi and Niino, 2009`_ |br| `Olson et al., 2019`_ .. _`Nakanishi and Niino, 2006`: https://doi.org/10.1007/s10546-005-9030-8 .. _`Nakanishi and Niino, 2009`: https://doi.org/10.2151/jmsj.87.895 .. _`Olson et al., 2019`: https://doi.org/10.25923/n9wm-be49 | **ACM2** |br| *bl_pbl_physics=7* |br| Asymmetric Convective Model with non-local upward mixing and local downward mixing |br| `Pleim, 2007`_ .. _`Pleim, 2007`: https://doi.org/10.1175/JAM2539.1 | **BouLac** |br| *bl_pbl_physics=8* |br| Bougeault-Lacarrère PBL; a TKE-prediction option; designed for use with BEP urban model |br| `Bougeault, 1989`_ .. _`Bougeault, 1989`: https://doi.org/10.1175/1520-0493(1989)117%3C1872:POOITI%3E2.0.CO;2 | **UW** |br| *bl_pbl_physics=9* |br| TKE scheme from CESM climate model; includes shallow convection using a mass-flux approach from the cloud base; includes capability of topdown mixing for turbulence driven by cloud-top radiative cooling, which is separate from bottom-up surface-flux-driven mixing |br| `Bretherton and Park, 2009`_ .. _`Bretherton and Park, 2009`: https://doi.org/10.1175/2008JCLI2556.1 | **Total Energy - Mass Flux (TEMF)** |br| *bl_pbl_physics=10* |br| Sub-grid total energy prognostic variable, plus mass-flux type shallow convection; includes shallow convection using a mass-flux approach through the whole cloud-topped boundary layer |br| `Angevine et al., 2010`_ .. _`Angevine et al., 2010`: https://doi.org/10.1175/2010MWR3142.1 | **Shin-Hong** |br| *bl_pbl_physics=11* |br| Includes scale dependency for vertical transport in convective PBL; vertical mixing in the stable PBL and free atmosphere follows YSU; this scheme also has diagnosed TKE and mixing length output |br| `Shin and Hong, 2015`_ .. _`Shin and Hong, 2015`: https://doi.org/10.1175/MWR-D-14-00116.1 | **Grenier-Bretherton-McCaa (GBM)** |br| *bl_pbl_physics=12* |br| A TKE scheme; tested in cloud-topped PBL cases; includes shallow convection using a mass-flux approach from the cloud base |br| `Grenier and Bretherton, 2001`_ .. _`Grenier and Bretherton, 2001`: https://doi.org/10.1175/1520-0493(2001)129%3C0357:AMPPFL%3E2.0.CO;2 | **TKE (E)-TKE dissipation rate (epsilon) (EEPS)** |br| *bl_pbl_physics=16* |br| This scheme predicts TKE, as well as TKE dissipation rate; it also advects both TKE and the dissipation rate; **Only works with sf_sfclay_physics options 1, 91, and 5** |br| *No publication available* | **MRF** |br| *bl_pbl_physics=99* |br| Older version of YSU (option 1) with implicit treatment of entrainment layer as part of non-local-K mixed layer |br| `Hong and Pan, 1996`_ .. _`Hong and Pan, 1996`: https://doi.org/10.1175/1520-0493(1996)124%3C2322:NBLVDI%3E2.0.CO;2 | Back to :ref:`pbl-links` | .. _pbl-add-options: Additional PBL Options ---------------------- **LES PBL** |br| Settings for a large-eddy-simulation (LES) boundary layer: bl_pbl_physic = 0 |br| isfflx = 1 |br| sf_sfclay_physics = *any option, except 0* |br| sf_surface_physics = *any option, except 0* |br| diff_opt = 2 |br| km_opt = 2 or 3 This uses diffusion for vertical mixing. Alternative idealized ways of running the LES PBL are chosen with "isfflx = 0 or 2". It is best to use dx~dz, especially in the boundary layer, and avoid stretching to very large dz/dx aspect ratios at upper levels. This also tends to work better with continuous stretching to the top, rather than with fixed upper-level dz when dz >> dx. | **SMS-3DTKE** |br| This is a 3D TKE subgrid mixing scheme that is self-adaptive to the grid size between the large-eddy simulation (LES) and mesoscale limits (new since V4.2). It can be activated by setting bl_pbl_physic = 0 |br| km_opt = 5 |br| diff_opt = 2 |br| sf_sfclay_physics = 1, 5, or 91 | **Gravity Wave Drag** |br| *gwd_opt* |br| Can be used for all grid sizes with appropriate input fields from geogrid to represent sub-grid orographic gravity-wave vertical momentum transport * **=1** : (default); gravity wave drag and blocking; recommended for all grid sizes; includes the subgrid topography effects gravity wave drag and low-level flow blocking; input wind is rotated to the earth coordinate, and output is adjusted back to the projection domain - this enables the scheme to be used for all map projections supported by WRF; to apply this option, appropriate input fields from geogrid must be used; see the (kkw - link) Selecting Static Data for the Gravity Wave Drag Scheme in Chapter 3 of this guide for details * **=3** : gravity wave drag, blocking, small-scale gravity drag and turbulent orographic form drag; similar to option 1, with an additional two subgrid-scale sources of orographic drag: one is small-scale GWD (`Tsiringakis et al., 2017`), which represents gravity wave propagation and breaking in and above stable boundary layers; the other is the turbulent orographic form drag of `Beljaars et al., 2004`_. Both are applicable down to a grid size of 1 km. Large-scale GWD and low-level flow blocking from gwd_opt=1 are properly adjusted for the horizontal grid resolution. More diagnostic fields from the scheme can be output by setting namelist option "gwd_diags=1." New GWD input fields are required from WPS. .. _`Tsiringakis et al., 2017`: https://doi.org/10.1002/qj.3021 .. _`Beljaars et al., 2004`: https://doi.org/10.1256/qj.03.73 | **Fog** |br| *grav_settling=2* |br| Gravitational settling of fog/cloud droplets | Back to :ref:`pbl-links` | .. _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:`pbl-links` | .. _grid-spacing: 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:`pbl-links` | .. _diffusion: 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:`pbl-links` | .. image:: images/blank_image.png :width: 800px :height: 25px Next section: `Surface Physics`_ | | | | .. _`Surface Physics`: surface.html