This archive contains answers to questions sent to Unidata support through mid-2025. Note that the archive is no longer being updated. We provide the archive for reference; many of the answers presented here remain technically correct, even if somewhat outdated. For the most up-to-date information on the use of NSF Unidata software and data services, please consult the Software Documentation first.
>From: John Merrill <address@hidden> >Organization: UCAR/Unidata >Keywords: 200307101905.h6AJ59Ld017477 >Hello, > I see PLCL defined as a diagnostic parameter in Appendix A, and would >like to map or plot this over an area using >gridded fields, again Nogaps analysis/forecast or Reanalysis fields. >Using gdmap with gfunc=plcl and glevel=1000, >for example, I get "Input grid plcl... not found." I've not tried >entering the formula after gfunc=, but am beginning to think >that's how these specialized parameters are used - is that so? I've >never used gddiag, and don't have the impression that >forcing the calculation of a field using this program is what's needed here. > Secondly, and related only in that this will be used with gridded >analysis fields, how does one use the LOWS (or >HIGH) parameter to scan, e.g., PMSL, in my case with gvcord=none; >glevel=0? Perhaps LOWS(pmsl,5), indicating >the field of interest and a 5 grid point "squradius", but does the >program then march through the grid and report extrema >which are "further apart" then this distance? And what does it yield or >report - the value, the grid location or both? >I'm tracking the progression of disturbances over time in a large area, >and wonder if I use of this parameter will simplify >my work. Is this used with gdmap, with gdlist, or in some other way? >I've used carefully-selected limits in HILO in >GDPLOT2, but could easily wade through a list of _all_ relative lows for >each synoptic time, using a script to loop through >the times. Thanks. John > John, Appendix A are parameters, not grid diagnostic functions which are in Appendix B1 and B2. However, I do have a function available which you can use as GVCORD = PRES GLEVEL = 1000 GFUNC = PLCL (PRES, TMPC, DWPC) another way to use typical surface grids (from the NCEP models) GVCORD = NONE GLEVEL = 0 GFUNC = PLCL ( PRES, tmpc@2%HGHT, dwpc@2%HGHT) The PLCL function is one I created on the way making a general CAPE function. As for highs and Lows, you can plot these values on a map using gdplot2 like: GDPFUN = high(emsl,5) TYPE = p The type P will plot the data value, or you can use markers etc. The high and lows function will return -9999 for all grid points except the relative maxima. Steve Chiswell