Concentration / Display / Ensemble Map

Multiple concentration output files from the ensemble or variance dispersion simulation can be processed to produce probability displays. The Ensemble View Map menu calls a special program conprob that reads the concentration files with the ensemble member three-digit suffix (001 to 027) and generates various probability files when the Graphics Only box is NOT checked. When this box is checked, then the existing probability files are used to generate all graphics. The appropriate files are then plotted using concplot according to the menu selection options. Note that the ensemble display menu can be used to convert multiple concentration output files to probability form, regardless of how they were generated. It is not necessary to use the pre-configured ensemble version of the model to create air concentration probability maps. Any number of multiple simulations can be used as long as the file suffixes end with a numeric three-digit sequence. Menu settings for the output file name should reflect the base name without the numeric suffix. An illustration of the Ensemble Display menu is shown below.

The menu includes some of the standard display program (concplot) mapping choices, such as background file, output file name, and zoom factor. One critical difference is that there is an option called Aggregation #. By default this value is set to one, which means that only the ensemble members for one time period are aggregated together to produce the probability display. Hence there would be an independent probability map for each time period. However, multiple time periods may be combined to produce a single probability plot. The entry represents the number of time periods, not the actual time span. For instance, if the model output is set to produce a one-hour average and the model is run for 24 hours, then each ensemble member will have 24 time periods of output. By default the probability output will represent the ensemble member variation for each hour, that is 24 frames of output will be produced. However if the aggregation period is set to 24, then all output times will be combined into one output frame and the ensemble result will represent the hourly variations as well as the member variations.

The menu permits a choice of six different ensemble output display options:

  1. The number of ensemble members at each grid point with concentrations greater than zero shows the spatial distribution of the Number of Ensemble members.
  2. The mean concentration of all ensemble members.
  3. The variance of all ensemble members (the mean square difference between individual members and the mean).
  4. The coefficient of varition of all ensemble members (sqrt(variance)*100/mean).
  5. The probability of concentration produces contours that give the probability of exceeding a fixed concentration value at one of three levels: 1% of the maximum concentration, 10% of the maximum, and the maximum concentration. The maximum is determined to be the first concentration to a power of 10 that is less than the actual maximum value or the value of the maximum set in the data entry box (exponent of 10). The concentration level for the probability display is shown on the graphic with the pollutant identification field set to something like C14, where 14 represents the concentration to the power of 10-14.
  6. The concentration at percentile levels shows the concentration contours of areas where concentrations will be exceeded only at the given probability level. Although several output levels are computed, the probability level choices through the menu are limited to 50, 90, and 95th percentiles.

The conprob extraction program will always produce all the probability variations, one to each output file, for a given aggregation period. If the graphics only checkbox is marked, then the menu skips computing the probability files and uses the existing files in the working directory. The output files may also be plotted individually from the command line using concplot. The conprob output files contain the following information:

The command line options for the probability program conprob [-options] are as follows:



Table of Contents