Dan,<br><br>We had problems with CFL violations on a N Atlantic domain (delta x~15km), apparently due to excessive vertical velocities along the east Greenland coast. Switching to the Adaptive timestep has helped considerably, especially with the the Target CFL set to 1. You may have to experiment with the initial time step and other settings. This is with a PBL scheme.<br>
<br>On a nested 1km grid some, ATM experimental, results suggest  that having 3D diffusion improves the representation of convection and cuts down on spurious , grid point ppn. 2D diffusion and a PBL are used on the coarser parent grid(s). With the adaptive timestep this works fine, though the terrain is rather &#39;smooth&#39; (southern UK). Have n&#39;t tried this yet with steeper, higher terrain.<br>
<br>I would experiment with the spacing of your lowest levels as well. WRF3.1<br><br>Best,<br>David<br><br><br><div class="gmail_quote">On Sat, Sep 11, 2010 at 11:54 PM, Daniel Steinhoff <span dir="ltr">&lt;<a href="mailto:steinhoff.9@buckeyemail.osu.edu" target="_blank">steinhoff.9@buckeyemail.osu.edu</a>&gt;</span> wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
Dear wrf-users,<br>
<br>
I am running simulations over the McMurdo Dry Valleys in Antarctica, a region of complex terrain (mountain peaks approaching 4000 m, deep valleys, coastal).  In order to properly simulate cold pools and other features in the valleys, I&#39;d like to treat diffusion truly horizontally, as Zangl (2002) did in Alpine simulations with MM5.  I&#39;ve seen in the model documentation and tutorial presentation that diff_opt=2 should only be used with grid spacing &lt; 2 km and without PBL parameterization.  Running a 32-8-2 km, 40 vertical levels nested simulation, I&#39;d like to keep the PBL scheme.  Has anyone had success using diff_opt=2 for real data cases with a PBL scheme?<br>


<br>
When I try diff_opt=2, with km_opt=2, 3, or 4, the simulations are more sensitive than otherwise to CFL violations or NaN errors at points on steep slopes (this is after extensive terrain smoothing of a 200 m terrain dataset).  km_opt=2 runs the longest before crashing (about a half hour), whereas the other options crash within minutes.  Interestingly, these CFL violations and NaN errors are more prevalent in the outer grids (for example, either the 32 km or 8 km grids along steep slopes).  Might I be better off running the 32 km and 8 km outer grids with diff_opt=1, and then using ndown for an inner grid of 2 km and using diff_opt=2?  Or is an extremely short timestep required?  I&#39;ve been down to 60 sec on the 32 km grid.  I have similar problems to above with a 27-9-3-1 km nested grid, 51 vertical levels (default spacing) setup also.<br>


<br>
If anyone has any ideas or advice I&#39;d appreciate it.  I am running WRF 3.2.1 on NCAR bluefire.  I&#39;ve pasted the namelist below from the 32-8-2 km simulations.<br>
<br>
Dan<br>
<br>
<br>
&amp;time_control<br>
 run_days                            = 0,<br>
 run_hours                           = 60,<br>
 run_minutes                         = 0,<br>
 run_seconds                         = 0,<br>
 start_year                          = 2006, 2006, 2006,<br>
 start_month                         = 04, 04, 04,<br>
 start_day                           = 15, 15, 15,<br>
 start_hour                          = 12, 12, 12,<br>
 start_minute                        = 00,   00,   00,<br>
 start_second                        = 00,   00,   00,<br>
 end_year                            = 2006, 2006, 2006,<br>
 end_month                           = 04, 04, 04,<br>
 end_day                             = 18, 18, 18,<br>
 end_hour                            = 00, 00, 00,<br>
 end_minute                          = 00,   00,   00,<br>
 end_second                          = 00,   00,   00,<br>
 interval_seconds                    = 21600,<br>
 input_from_file                     = .true.,.true.,.true.,<br>
 history_interval                    = 360,   360,   360,<br>
 frames_per_outfile                  = 1, 1, 1,<br>
 restart                             = .False.,<br>
 restart_interval                    = 720,<br>
 reset_simulation_start              = .false.,<br>
 auxinput4_inname                    = &quot;wrflowinp_d&lt;domain&gt;&quot;,<br>
 auxinput4_interval                  = 360, 360, 360,<br>
 io_form_history                     = 2,<br>
 auxinput4_interval                  = 360, 360, 360,<br>
 io_form_history                     = 2,<br>
 io_form_restart                     = 2,<br>
 io_form_input                       = 2,<br>
 io_form_boundary                    = 2,<br>
 io_form_auxinput4                   = 2,<br>
 nocolons                            = .false.,<br>
 debug_level                         = 0,<br>
 auxhist2_outname                    = &quot;surface_d&lt;domain&gt;_&lt;date&gt;&quot;,<br>
 auxhist2_interval                   = 0, 0, 60,<br>
 io_form_auxhist2                    = 2,<br>
 /<br>
<br>
 &amp;domains<br>
 time_step                           = 120,<br>
 time_step_fract_num                 = 0,<br>
 time_step_fract_den                 = 1,<br>
 max_dom                             = 3,<br>
 e_we                                = 200, 161,  193,<br>
 e_sn                                = 200, 121,  165,<br>
 s_vert                              = 1,   1,     1,<br>
 e_vert                              = 40,  40,  40,<br>
 dx                                  = 32000, 8000,  2000,<br>
 dy                                  = 32000, 8000,  2000,<br>
 grid_id                             = 1,   2,   3,<br>
 parent_id                           = 0,   1,   2,<br>
 i_parent_start                      = 1,  68,  54,<br>
 parent_id                           = 0,   1,   2,<br>
 i_parent_start                      = 1,  68,  54,<br>
 j_parent_start                      = 1, 105,  42,<br>
 parent_grid_ratio                   = 1,   4,   4,<br>
 parent_time_step_ratio              = 1,   4,   4,<br>
 feedback                            = 0,<br>
 smooth_option                       = 0,<br>
 num_metgrid_levels                  = 38,<br>
 num_metgrid_soil_levels             = 4,<br>
 eta_levels                          = 1.00000 , 0.99629 , 0.99258 , 0.98767 , 0.98275 ,<br>
                                       0.97636 , 0.96996 , 0.96184 , 0.95372 , 0.93357 ,<br>
                                       0.90913 , 0.87957 , 0.84531 , 0.80683 , 0.76467 ,<br>
                                       0.71940 , 0.67163 , 0.62198 , 0.57108 , 0.51956 ,<br>
                                       0.46803 , 0.42030 , 0.37613 , 0.33532 , 0.29764 ,<br>
                                       0.26290 , 0.23092 , 0.20152 , 0.17452 , 0.14978 ,<br>
                                       0.12714 , 0.10646 , 0.08761 , 0.07045 , 0.05466 ,<br>
                                       0.03981 , 0.02580 , 0.01677 , 0.00903 , 0.00000 ,<br>
 p_top_requested                     = 5000,<br>
 interp_type                         = 2,<br>
 extrap_type                         = 2,<br>
 t_extrap_type                       = 2,<br>
 use_levels_below_ground             = .true.,<br>
 use_surface                         = .true.,<br>
 lagrange_order                      = 1,<br>
 lowest_lev_from_sfc                 = .false.,<br>
 smooth_cg_topo                      = .false.,<br>
 force_sfc_in_vinterp                = 1,<br>
 smooth_cg_topo                      = .false.,<br>
 force_sfc_in_vinterp                = 1,<br>
 zap_close_levels                    = 0.,<br>
 sfcp_to_sfcp                        = .false.,<br>
 use_adaptive_time_step              = .false.,<br>
 /<br>
<br>
 &amp;dfi_control<br>
 /<br>
<br>
 &amp;physics<br>
 mp_physics                          = 6,     6,     6,<br>
 mp_zero_out                         = 0,<br>
 no_mp_heating                       = 0,<br>
 ra_lw_physics                       = 1,     1,     1,<br>
 ra_sw_physics                       = 1,     1,     1,<br>
 radt                                = 30,    10,    10,<br>
 levsiz                              = 59,<br>
 paerlev                             = 29,<br>
 cam_abs_dim1                        = 4,<br>
 cam_abs_dim2                        = 35,<br>
 sf_sfclay_physics                   = 5,     5,     5,<br>
 sf_surface_physics                  = 2,     2,     2,<br>
 sf_urban_physics                    = 0,     0,     0,<br>
 bl_pbl_physics                      = 5,     5,     5,<br>
 bldt                                = 0,     0,     0,<br>
 grav_settling                       = 1,     1,     1,<br>
 bldt                                = 0,     0,     0,<br>
 grav_settling                       = 1,     1,     1,<br>
 cu_physics                          = 3,     0,     0,<br>
 cudt                                = 5,<br>
 cugd_avedx                          = 1,<br>
 isfflx                              = 1,<br>
 ifsnow                              = 0,<br>
 icloud                              = 1,<br>
 swrad_scat                          = 1.,<br>
 surface_input_source                = 1,<br>
 num_soil_layers                     = 4,<br>
 num_land_cat                        = 24,<br>
 num_soil_cat                        = 16,<br>
 usemonalb                           = .false.,<br>
 rdmaxalb                            = .false.,<br>
 rdlai2d                             = .false.,<br>
 sst_update                          = 1,<br>
 seaice_threshold                    = 0.0,<br>
 tmn_update                          = 0,<br>
 bucket_mm                           = -1.,<br>
 maxiens                             = 1,<br>
 maxens                              = 3,<br>
 maxens2                             = 3,<br>
 maxens3                             = 16,<br>
 ensdim                              = 144,<br>
 slope_rad                           = 1,<br>
 topo_shading                        = 1,<br>
 slope_rad                           = 1,<br>
 topo_shading                        = 1,<br>
 shadlen                             = 25000.,<br>
 omlcall                             = 0,<br>
 oml_hml0                            = 50.,<br>
 oml_gamma                           = 0.14,<br>
 isftcflx                            = 0,<br>
 fractional_seaice                   = 1,<br>
 seaice_thickness                    = 1,<br>
 tice2tsk_if2cold                    = .true.<br>
 /<br>
<br>
 &amp;fdda<br>
 grid_fdda                           = 1,     0,     0,<br>
 gfdda_inname                        = &quot;wrffdda_d&lt;domain&gt;&quot;,<br>
 gfdda_interval_m                    = 360,   0,     0,<br>
 gfdda_end_h                         = 60,   0,     0,<br>
 io_form_gfdda                       = 2,<br>
 fgdt                                = 0,<br>
 if_no_pbl_nudging_uv                = 0,     0,     0,<br>
 if_no_pbl_nudging_t                 = 0,     0,     0,<br>
 if_no_pbl_nudging_q                 = 0,     0,     0,<br>
 if_zfac_uv                          = 1,     0,     0,<br>
  k_zfac_uv                          = 13,<br>
 if_zfac_t                           = 1,     0,     0,<br>
  k_zfac_t                           = 13,<br>
 if_zfac_q                           = 1,     0,     0,<br>
  k_zfac_t                           = 13,<br>
 if_zfac_q                           = 1,     0,     0,<br>
  k_zfac_q                           = 40,<br>
 guv                                 = 0.0003,0.0000,0.0000,<br>
 gt                                  = 0.0003,0.0000,0.0000,<br>
 gq                                  = 0.0000,0.0000,0.0000,<br>
 if_ramping                          = 0,<br>
 dtramp_min                          = 60.0,<br>
 grid_sfdda                          = 0,     0,     0,<br>
 rinblw                              = 250.0,<br>
 obs_nudge_opt                       = 0,     0,     0,<br>
 /<br>
<br>
 &amp;scm<br>
 /<br>
<br>
 &amp;dynamics<br>
 rk_ord                              = 3,<br>
 diff_opt                            = 2,<br>
 km_opt                              = 2,<br>
 diff_6th_opt                        = 1,     1,     1,<br>
 diff_6th_factor                     = 0.06,  0.06,  0.06,<br>
 damp_opt                            = 3,<br>
 zdamp                               = 5000.,  5000.,  5000.,<br>
 dampcoef                            = 0.03,   0.03,   0.03,<br>
 w_damping                           = 0,<br>
 base_temp                           = 268.,<br>
 w_damping                           = 0,<br>
 base_temp                           = 268.,<br>
 base_pres                           = 100000.,<br>
 base_lapse                          = 50.,<br>
 khdif                               = 0,      0,      0,<br>
 kvdif                               = 0,      0,      0,<br>
 smdiv                               = 0.1,    0.1,    0.1,<br>
 emdiv                               = 0.01,   0.01,   0.01,<br>
 epssm                               = 0.1,    0.1,    0.1,<br>
 non_hydrostatic                     = .true., .true., .true.,<br>
 h_mom_adv_order                     = 5,     5,     5,<br>
 v_mom_adv_order                     = 3,     3,     3,<br>
 h_sca_adv_order                     = 5,     5,     5,<br>
 v_sca_adv_order                     = 3,     3,     3,<br>
 time_step_sound                     = 4,     4,     4,<br>
 moist_adv_opt                       = 1,     1,     1,<br>
 scalar_adv_opt                      = 1,     1,     1,<br>
 tke_adv_opt                         = 1,     1,     1,<br>
 gwd_opt                             = 0,<br>
 /<br>
<br>
 &amp;bdy_control<br>
 spec_bdy_width                      = 5,<br>
 spec_zone                           = 1,<br>
 relax_zone                          = 4,<br>
 specified                           = .true., .false.,.false.,<br>
 spec_exp                            = 0.,<br>
 specified                           = .true., .false.,.false.,<br>
 spec_exp                            = 0.,<br>
 periodic_x                          = .false.,.false.,.false.,<br>
 symmetric_xs                        = .false.,.false.,.false.,<br>
 symmetric_xe                        = .false.,.false.,.false.,<br>
 open_xs                             = .false.,.false.,.false.,<br>
 open_xe                             = .false.,.false.,.false.,<br>
 periodic_y                          = .false.,.false.,.false.,<br>
 symmetric_ys                        = .false.,.false.,.false.,<br>
 symmetric_ye                        = .false.,.false.,.false.,<br>
 open_ys                             = .false.,.false.,.false.,<br>
 open_ye                             = .false.,.false.,.false.,<br>
 nested                              = .false.,.true.,.true.,<br>
 /<br>
<br>
 &amp;grib2<br>
 /<br>
<br>
 &amp;tc<br>
 /<br>
<br>
 &amp;fire<br>
 /<br>
<br>
 &amp;namelist_quilt<br>
 nio_tasks_per_group = 0,<br>
 nio_groups = 1,<br>
                                                                                  201,2         99%<br>
 nio_tasks_per_group = 0,<br>
 nio_groups = 1,<br>
 /<br>
<br>
<br>
Daniel Steinhoff<br>
Polar Meteorology Group<br>
Byrd Polar Research Center<br>
The Ohio State University<br>
<a href="mailto:steinhoff.9@buckeyemail.osu.edu" target="_blank">steinhoff.9@buckeyemail.osu.edu</a><br>
<br>
<br>
<br>
<br>
<br>
_______________________________________________<br>
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<a href="mailto:Wrf-users@ucar.edu" target="_blank">Wrf-users@ucar.edu</a><br>
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</blockquote></div><br><br clear="all"><br>-- <br>______________________________________<br>David  Smart<br><br>Research Associate,<br>Mesoscale Modelling Facility,<br>Room G38,<br>AON Benfield Hazards Research Centre,<br>

University College London,<br>____________________________________<br>