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HYSPLIT SREF Dispersion Forecast

EXPERIMENTAL - information may not be current.

Over the past few years, the use of dispersion model ensembles has been an increasingly attractive approach to predict atmospheric transport. The ensembles are generally constructed by combining multiple numerical weather prediction simulations or output from different dispersion models, by introducing variations in a particular model's physics parameterizations, or by different combinations of these variations. In addition, the source term and height distribution can be varied to create dispersion ensembles.

For this application, we create a HYSPLIT ensemble simulation using the 26 meteorological model members from the National Weather Service (NWS) operational Sort Range Ensemble Forecast (SREF). The HYSPLIT model runs are generated by using the Transfer Coefficient Matrix procedure that is updated with the most recent meteorological data at 03, 09, 15 and 21Z.

The figures below show each of the simulation ensemble members as well as a series of statistical measures that describe the ensemble properties such as:

  1. The spatial distribution of the number of members producing concentrations greater than zero.
  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 variation of all ensemble members (the square root of the variance*100 divided by the 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 (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. The probability level choices through the menu are limited to 50, 90, and 95th percentiles.

Refresh/reload your browser for the most recent images. Click on a thumbnail image to expand. The charts are updated four times per day (~00, 06, 12, 18 UTC).

Mean Number of members Variance Coefficient of Variation
Mean Number of members Variance Variance
Probability that concentration exceeds
1% of maximum value 10% of maximum value 100% of maximum value
Probability that concentration exceeds 1% of maximum value Probability that concentration exceeds 10% of maximum value Probability that concentration exceeds 100% of maximum value

Concentration at:
5th percentile 10th percentile 25th percentile 50th percentile
Concentration at 5th percentile Concentration at 10th percentile Concentration at 25th percentile Concentration at 50th percentile
75th percentile 90th percentile 95th percentile
Concentration at 75th percentile Concentration at 90th percentile Concentration at 95th percentile

Individual member plots
nmb_ctl nmb_n1 nmb_n2 nmb_n3
nmb_ctl member nmb_n1 member nmb_n2 member nmb_n3 member
nmb_n4 nmb_n5 nmb_n6
nmb_n4 member nmb_n5 member nmb_n6 member
nmb_p1 nmb_p2 nmb_p3 nmb_p4
nmb_p1 member nmb_p2 member nmb_p3 member nmb_p4 member
nmb_p5 nmb_p6
nmb_p5 member nmb_p6 member
arw_ctl arw_n1 arw_n2 arw_n3
arw_ctl member arw_n1 member arw_n2 member arw_n3 member
arw_n4 arw_n5 arw_n6
arw_n4 member arw_n5 member arw_n6 member
arw_p1 arw_p2 arw_p3 arw_p4
arw_p1 member arw_p2 member arw_p3 member arw_p4 member
arw_p5 arw_p6
arw_p5 member arw_p6 member

This web page is under development and is experimental.
Products may change without notice.
Concentrations are relative to the source of 1 unit.
Contour values may vary from day to day and chart to chart.

Modified: December 4, 2019
US Dept. of Commerce |  NOAA |  NOAA Research |  ARL