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Q1. When I try to run the function, I get the following error message (or something similar): Error opening script file: plotskew(temp,dewp,wspd,wdir) ANSWER: You need to have a copy of the function in the script you are executing. That is, it is not sufficient to have the plotskew.gs function in the same directory-- a copy of the script must be in the driver script you are executing (the driver script containing the plotskew command). In other words, this will NOT work: ----- Beginning of driver script ---- "open test.ctl" "set t 1" "set x 1" "set y 1" "set z 1 16" rc=plotskew(t,d,spd,dir) ----- End of driver script----- But, this WILL work: ----- Beginning of driver script ---- "open test.ctl" "set t 1" "set x 1" "set y 1" "set z 1 16" rc=plotskew(t,d,spd,dir) function plotskew(sndtemp,snddewp,sndspd,snddir) "clear" ************************************************ * GrADS Script to Plot a SkewT/LogP Diagram . . . (rest of plotskew script) ----- End of driver script-----
Q2. The SkewT/LogP diagram plots fine, and the wind barbs show up ok, but the temperature and dewpoint traces are not on the diagram. ANSWER: Make sure your temperature and dewpoint data are in Celsius.
Q3. When I run the script, only the SkewT/LogP diagram appears. Or, the temperature and dewpoint plots appear garbled or erratic, and clearly not representative of the data I'm trying to plot. ANSWER: Several things could be wrong. First, make sure that you have set the environment to one point in (X,Y,T), and that you have specified the vertical range of the environment-- all before executing the plotskew function. Here are two examples: "set t 5" "set x 3" "set y 4" "set z 1 16" OR "set t 5" "set lon -75.5" "set lat 45.2" "set lev 1050 100" Second, make sure your datafile is written correctly. Third, make sure you are passing the correct argument names (and in the correct order) to the plotskew script.
Q4. I'm trying to run the function on a set of station data, but get numerous errors. ANSWER: To the best of my knowledge, the function will not work in any way with station data. You might want to try rewriting the station data to gridded data format, or use the GrADS functions that convert station data to gridded data. Then retry the function.
Q5. I have data for temperature and dewpoint, but not for wind direction or speed. This causes the script to crash when I run it. ANSWER: Use '-1' for any variable you are not passing. For example, if you have only temperature data in variable 'temp', the call to plotskew should look like: rc=plotskew(temp,-1,-1,-1) You do not need to turn off the options for variables you are not using. When you pass the -1, the corresponding options are automatically turned off. (If no wind data is passed, no hodograph or wind profile is plotted, regardless of the option setting in the script).
Q6. Can I overlay soundings from multiple times/locations? ANSWER: Yes. The default mode is to clear the screen at the beginning of each execution of plotskew. To overlay multiple soundings, you first must set the "ClrScrn" option to 0 at the beginning of the script. Then, all successive calls to plotskew will be superimposed upon the first. Do not forget to respecify the environment dimensions before each call to plotskew. For example, "set t 1" "set x 1" "set y 1" "set lev 1050 100" rc=plotskew(temp,dewp,-1,-1) "set t 4" "set x 1" "set y 1" "set lev 1050 100" rc=plotskew(temp,dewp,-1,-1) Superimposes temperature and dewpoint plots from soundings at two different times, but the same location. If multiple copies of the plotskew script are created, each overlay can be assigned different colors to make the various soundings more visible. While this is not the most efficient method for overlay, it certainly is the simplest and involves no modification of the code, only options. When performing overlays, you may want to turn off or relocate some options to prevent clutter when text,etc is overwritten (such as Wind barbs, and indices).
Q7. The script runs too slowly. How can I speed it up? ANSWER: The SkewT script makes extensive use of the basic drawing primatives in GrADS. Further, a lot of the math calculations required for skewT/logP plots have to be performed within the script since they are not intrinsic functions (yet!) to GrADS. As a result, the script may run more slowly than some users would like. Generally, if all options are turned on, the script will only run tolerably fast enough on a machine with a 1GHz processor or faster. This can be accelerated by doing one or all of the following: 1. Turn off moist adiabat plotting. These lines are drawn by iteration and take the longest to calculate. Done by setting DrawThtw = 0. Average speed increase: 20%. 2. Turn off one or both of the parcel tracers. Done by setting DrawPrcl = 0 and/or DrawPMax = 0. Average speed increase: 5%. 3. Turn off stability index calculations. Done by setting DrawIndx = 0. Average speed increase: 25%.
Q8. Can I use the script if I have data "holes"--pressure levels at which either temperature, dewpoint, or wind data is missing? Versions of the plotskew script dated on or after August 26, 1999 DO allow the use of datasets with holes in them. Versions of the script prior to this date will crash when trying to use datasets with holes, however.
Last Updated: 21 March 2017.
Mail questions to:
Bob Hart ( firstname.lastname@example.org)