<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Hi Nikhil,<div class=""><br class=""></div><div class="">Forcing WRF with model level data is possible and often done - for example for the ECMWF operational forecasts with 138 hybrid levels nowadays. For ECMWF data, a utility program called calc_ecmwf_p.exe comes with WPS, which takes a text file with coefficients a and b to generate additional intermediate files (prefix PRES). These contain pressure, geopotential height (and relative humidity) for each model level, grid point and time step. The ECMWF model levels are defined as p(k) = a(k) + b(k)*psfc, see the following links:</div><div class=""><br class=""></div><div class=""><a href="http://rda.ucar.edu/datasets/ds627.0/docs/Eta_coordinate" class="">http://rda.ucar.edu/datasets/ds627.0/docs/Eta_coordinate</a></div><div class=""><a href="http://www.ecmwf.int/en/forecasts/documentation-and-support/137-model-levels" class="">http://www.ecmwf.int/en/forecasts/documentation-and-support/137-model-levels</a></div><div class=""><a href="https://www.met.reading.ac.uk/wrf/?page_id=58" class="">https://www.met.reading.ac.uk/wrf/?page_id=58</a></div><div class=""><br class=""></div><div class="">For MERRA, the sigma coordinate is very similar, except that it corresponds to the pressure at the bottom edge of the grid box, whereas you need the pressure at the center (<a href="http://wiki.seas.harvard.edu/geos-chem/index.php/Notes_regarding_GEOS_vertical_grids" class="">http://wiki.seas.harvard.edu/geos-chem/index.php/Notes_regarding_GEOS_vertical_grids</a>, note the typo in the definition of pcenter). You could either re-calculate the indices a and b in order to use calc_ecmwf_p.exe or you could write your own little tool that calculates the missing pressure data and writes it into intermediate format. Template code in Fortran can be found here:</div><div class=""><br class=""></div><div class=""><a href="http://www2.mmm.ucar.edu/wrf/users/docs/user_guide_V3/users_guide_chap3.htm#_Writing_Meteorological_Data" class="">Writing Meteorological Data to the
Intermediate Format</a></div><div class=""><br class=""></div><div class="">Cheers</div><div class=""><br class=""></div><div class="">Dom/</div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On 1/02/2016, at 1:17 PM, Nikhil <<a href="mailto:nikhilgarg.gju@gmail.com" class="">nikhilgarg.gju@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="content-type" content="text/html; charset=utf-8" class=""><div dir="auto" class=""><div class=""><br class=""></div><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class=""><pre class="">In my little experience, I have found that usually data used in WRF from sources for example CFSR, NCEP FNL or ECMWF ERA Interim are interpolated to pressure levels and then ingested in WRF model.</pre><pre class="">I have recently tried to write the WRF input files using the MERRA data, but I have kept the data on the model levels which in case of MERRA are GEOS vertical levels.</pre><pre class="">I was wondering whether real.exe can figure out the vertical distribution
from the GEOS level to the eta level or do I need to provide some
information (example vertical levels) in namelist files for real or metgrid. </pre><pre class="">I have gone through the WRF manual and I could not find any specific
information on the data structure needed by WRF model, apart from a
specific format for intermediate file. For my model, I have used GLDAS
data for soil moisture etc. <font face="monospace, monospace" class="">I have seen some cases on ncl (ncarg) website where they show how the intermediate file are written and I see that usually data in those example scripts is given on pressure levels</font><span style="font-family:arial,sans-serif" class="">.</span></pre><pre class=""><font face="monospace, monospace" class="">I appreciate any help in this matter.</font></pre></div>
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