WRF - Developmental Testbed Center

&mod_levspress_pa = 201300 , 200100 , 100000 ,95000 , 90000 ,85000 , 80000 ,75000 , 70000 ,65000 , 60000 ,55000 , 50000 ,45000 , 40000 ,35000 , 30000 ,25000 , 20000 ,15000 , 10000 ,5000 , 1000/Within the &mod_levs namelist record, the variable press_pa is used to specify a list oflevels to keep; the specified levels should match values of xlvl in the intermediateformat files (see the discussion of the WPS intermediate format for more information onthe fields of the intermediate files). The mod_levs program takes two command-linearguments as its input. The first argument is the name of the intermediate file to operateon, and the second argument is the name of the output file to be written.Removing all but a specified subset of levels from meteorological data sets is particularlyuseful, for example, when one data set is to be used for the model initial conditions and asecond data set is to be used for the lateral boundary conditions. This can be done byproviding the initial conditions data set at the first time period to be interpolated bymetgrid, and the boundary conditions data set for all other times. If the both data setshave the same number of vertical levels, then no work needs to be done; however, whenthese two data sets have a different number of levels, it will be necessary, at a minimum,to remove (m – n) levels, where m > n and m and n are the number of levels in each of thetwo data sets, from the data set with m levels. The necessity of having the same numberof vertical levels in all files is due to a limitation in real, which requires a constantnumber of vertical levels to interpolate from.The mod_levs utility is something of a temporary solution to the problem ofaccommodating two or more data sets with differing numbers of vertical levels. Should auser choose to use mod_levs, it should be noted that, although the vertical locations of thelevels need not match between data sets, all data sets should have a surface level of data,and, when running real_nmm.exe and wrf.exe, the value of p_top must be chosen to bebelow the lowest top among the data sets.C. calc_ecmwf_p.exeIn the course of vertically interpolating meteorological fields, the real program requires3-d pressure and geopotential height fields on the same levels as the other atmosphericfields. The calc_ecmwf_p.exe utility may be used to create such these fields for use withECMWF sigma-level data sets. Given a surface pressure field (or log of surface pressurefield) and a list of coefficients A and B, calc_ecmwf_p.exe computes the pressure at anECMWF sigma level k at grid point (i,j) as P ijk = A k + B k *Psfc ij . The list of coefficientsused in the pressure computation can be copied from a table appropriate to the number ofsigma levels in the data set fromWRF-NMM V3: User’s Guide 3-22