WRF - Developmental Testbed Center

# halo HALO_NMM_K dyn_nmm8:q2;24:t,u,v,q,w,zThe keyword is halo. The communication is named in the column, sothat it can be referenced in the source code. The entry in the column iscase sensitive (the convention is to start the name with HALO_NMM). The selecteddynamical core is defined in the column. There is no ambiguity, as everycommunication in each Registry file will have the exact same column option.The last set of information is the . The portion in front of the “:” is thestencil size, and the comma-separated list afterwards defines the variables that arecommunicated with that stencil size. Different stencil sizes are available, and are “;”separated in the same column. The stencil sizes 8, 24, 48 all refer to asquare with an odd number of grid cells on a side, with the center grid cell removed (8 =3x3-1, 24 = 5x5-1, 48 = 7x7-1). The special small stencil 4 is just a simple north, south,east, west communication pattern.The convention in the WRF model is to provide a communication immediately after avariable has been updated. The communications are restricted to the mediation layer (anintermediate layer of the software that is placed between the framework level and themodel level. The model level is where developers spend most of their time. Themajority of users will insert communications into the dyn_nmm/solve_m,m.Fsubroutine. The HALO_NMM_K communication defined in the Registry file, in theexample above, is activated by inserting a small section of code that includes anautomatically generated code segment into the solve routine, via standard cpp directives.#ifdef DM_PARALLEL# include "HALO_NMM_K.inc"#endifThe parallel communications are only required when the WRF code is built fordistributed-memory parallel processing, which accounts for the surrounding #ifdef.The period communications are required when periodic lateral boundary conditions areselected (ARW only). The Registry syntax is very similar for period and halocommunications, but the stencil size refers to how many grid cells to communicate, in adirection that is normal to the periodic boundary.# period PERIOD_EM_COUPLE_A dyn_em 2:mub,mu_1,mu_2The xpose (a data transpose) entry is used when decomposed data is to be re-decomposed(ARW only). This is required when doing FFTs in the x-direction for polar filtering, forexample. No stencil size is necessary.WRF-NMM V3: User’s Guide 6-11