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Workshop Agenda

Workshop Agenda. 82. 82. Modeling Particle Motion or Particle Distributions (Puffs).

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Workshop Agenda

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  1. Workshop Agenda 82 82 PC-HYSPLIT WORKSHOP

  2. Modeling Particle Motion or Particle Distributions (Puffs) • To compute air concentrations its necessary to follow all the particles needed to represent the pollutant distribution in space and time. This can be done explicitly by following the trajectory of each particle, where a random component is added to the mean velocity (from the meteorological model), to define the dispersion of the pollutant cloud.  • In the horizontal, the computations can be represented by the following equations: Xfinal(t + Δt) = Xmean(t + Δt) + U'(t + Δt)Δt,where,U'(t + Δt) = R(Δt) U'(t) + U''(1 - R(Δt)2)0.5, (horiz. turbulent velocity) R(Δt) = exp(-Δt/TLu), (auto-correlation coefficient) TLu is the Lagrangian time scale U'' = σuλ,where λ is a random number with mean of 0 and σ of 1.  • The computations can be simplified, if instead of modeling the motion of each particle, we compute the trajectory of the mean particle position and the particle distribution. The standard deviation of the particle distribution can be computed from all the particles,        ______σ2 = (Xi-Xm)2 • or it can be computed without following individual particles by assuming a distribution shape (puff) and relationship to the local turbulence.  Many different formulations can be found in the literature.dσh/dt = √2 σuσu = (Ku / TLu)0.5 • These computations are set in the Advanced / Configuration Setup / Concentration menu, which modifies the SETUP.CFG file. 83

  3. Modeling Particle Motion or Particle Distributions (Puffs) • Below, note the initial differences between the simulation using the 3D particle distribution (left) and the top-hat puff center position method (right). Without the random motion component, the top-hat puff positions follow a straight line during the initial few hours until vertical motions or horizontal divergence begins to act on the particles. In this particular case the primary reason for the sudden expansion of the puff-particles is that they have mixed to higher levels and we are seeing the differential horizontal advection acting upon the particles. 3D Particle Distribution Top-hat Puff Center Positions 84

  4. Modeling Particle Motion or Particle Distributions (Puffs) • The previous example showed a snapshot of the particle or puff center positions after 12 hours.  Air concentrations are computed by summing each particle’s mass as it passes over the concentration grid. • In the particle model mode, the concentration grid is treated as a matrix of cells, each with a volume defined by the grid dimensions.  Therefore the concentration is just the particle mass divided by the cell volume: 3D Particle:      ΔC = q(Δx Δy Δz)-1 Top-Hat:           ΔC = q(Π r2 Δz)-1 Gaussian:        ΔC = q(2Π σh2 Δz)-1 e- 0.5x2/σh2 • In the puff model mode, the concentration grid is considered as a matrix of sampling points, such that the puff only contributes to the concentration if it passes over the sampling point.  In the puff calculation mode it is possible for a puff to pass between points and not be shown on the display: Top-Hat:           ΔC = q(Π r2 Δzp)-1 Gaussian:        ΔC = q(2Π σh2 Δzp)-1 e- 0.5x2/σh2 85

  5. Modeling Particle Motion or Particle Distributions (Puffs) • Shown below are the concentration patterns associated with the particle (left) and puff (right) distributions from the previous example.  Note that the puff distribution is smoother but also initially somewhat broader.  In this particular case, the horizontal puff growth equations give larger values than the particle expansion. The noisy particle distribution indicates that more particles than 5000 used are needed to better represent the horizontal distribution. 3D Particle Distribution Top-hat Puff Center Positions 86

  6. Turbulence Equations The method by which the meteorological data are evaluated to determine the turbulent velocities, used in either the puff or particle computation, is set in the Advanced / Configuration Setup / Concentration menu (below-left). Clicking on the Configure the TURBULENCE method button produces the menu given below-right. 87

  7. Turbulence Equations Turbulence Computation Methods • Standard velocity deformation - The default standard method computes the mixing using a diffusivity approach based upon vertical stability estimates and the horizontal wind field deformation: Kz = k wh z (1 - z/Zi)2 Kh = 2- 0.5(c Δ)2 | ∂u/∂y + ∂v/∂x | • Short-range similarity (fluxes/profile) - In shorter range dispersion simulations (< 100 km) the deformation parameterization used in conjunction with larger scale meteorological fields will not reflect the diurnal variations in horizontal turbulence. In these situations its desirable to use the short-range parameterizations in which the turbulent velocities are computed directly from the stability parameters, heat and momentum fluxes, if available, or derived from the wind and temperature profiles.  The user has the option of forcing the use of the profile to compute stability rather than the fluxes. This may be desirable, especially if the fluxes represent averages rather than instantaneous values. The boundary layer velocity variances are defined as a function of u*, w*, and Zi.  This method does not use the diffusivity and no assumptions are required about turbulent scales. For instance, in the stable/neutral boundary layer: w'2 = 3.0 u*2 (1 – z/zi)3/2 u'2  = 4.0 u*2 (1 – z/zi)3/2 v'2  = 4.5 u*2 (1 – z/zi)3/2 88

  8. Turbulence Equations Turbulence Computation Methods (Cont.) • Input meteorological model TKE - If the turbulent kinetic energy (TKE) field is available from the meteorological model, then the velocity variances can be computed from its definition and the previous velocity variance equations to yield relationships with TKE: E = 0.5 (u’2 + v’2 + w’2) w’2 = 0.32 E,  u’2 = 0.74 E,  v’2 = 0.85 E u’2  = v’2 = 0.36 w*2 • TKE and mixed layer defined TKE – The TKE can be used with the mixed layer depth as estimated from the TKE profile. • Turbulence velocity variance - Some meteorological data sets may already contain the 3-dimensional component velocity variances.  This would normally be the case for data that have been generated from local measurement programs. The Puff Growth Computation Method section is used to define either the Linear or Square Root with time dispersion equation for the horizontal growth rate of puffs. This option does not affect particle dispersion. The user also has the ability to set ratios of the vertical to the horizontal turbulence for daytime and nighttime in the Turbulence Aniosotropy Factors section (click the Help button for more details). 89

  9. Dispersion Model Configuration • The control file (CONTROL) for dispersion simulations is configured from the Concentration / Concentration Setup menu tab.  The concentration setup layout is identical to the trajectory menu with the exception of an additional button to set the emissions, deposition, and concentration grid (top right). • The Pollutant, Deposition and Grids setup button will bring up a submenu (lower right) with three options (Pollutant, Grids, Deposition). • To make modifications, enter the number of pollutants to define in the Num box and then click on the Specie # or Grid # to access the next menu. • The pollutant emission rate and deposition must be set for each pollutant.  • Several independent concentration grids may be defined for each simulation. However, they may be nested in space or time, if desired.  Concentrations for each pollutant species are output on all grids. 90

  10. Dispersion Model Configuration Definition of Pollutant • An arbitrary 4-character field identifies each pollutant. • The Emission rate is mass units per hour. The actual mass unit is not specified, so for instance, if the units are kg, then concentration output will be in kg/m3.  Any unit is acceptable, however some chemical conversion modules require specific units. • The Hours of emission may be defined in fractional hours. • The pollutant Release start can be set to any time at or after the start of the simulation.  As is true for all time units, zero’s default to the simulation start time in the main menu.  Zero for the month and non-zero values for day and hour cause those values to be treated as relative to the simulation start time. 91

  11. Dispersion Model Configuration Definition of Concentration Grid • Each concentration grid must be defined.  • Zeros for the grid center default to the source location.  • The grid spacing is especially important in concentration computations in determining the cell size (particles) or sampling resolution (puffs).  • When multiple levels are defined, each height represents the top of the cell (particles) or actual height (puffs).  • The averaging time (Avg) starts at the sampling start time for the hours/minutes specified in the output interval.  • Snapshot concentrations (Now) are defined as the average over one time-step at the time interval specified. Max will save the maximum concentration at each grid point over the duration of the output interval. 92

  12. Example Dispersion Calculation Run the dispersion model using these settings: • Source: 28.50N, 80.70W @ 10.0 m • Meteorology: NAM 12 km • Emission: 12 hrs beginning 1200 UTC on 19 Dec 2005 • Output: Snapshot after 12 hrs between the ground and 100 m-agl • Top-hat-horizontal, particle-vertical • 5000 particles • Run Standard Model 93

  13. Example Dispersion Calculation Results: • Change the map background file from arlmap to floridamap in the Concentration Display menu and display the results. • The resulting graphic should be the same as that shown (right). The floridamap file and other high resolution map backgrounds can be downloaded from the NOAA ARL website at: http://www.arl.noaa.gov/ready/hysp_util.html 94

  14. Example Dispersion Calculation • All HYSPLIT simulations generate a text MESSAGE file, which contains diagnostic information about the calculation.  Use the View MESSAGES link from the Advanced menu tab to view the last MESSAGE file. In this case (below), at the end of the simulation, 12.00014 units of mass were still on the domain. The vertical mass distribution showed more than 80% of the mass to be within 1000 m of the ground.  The vertical mass distribution is computed independently of the vertical concentration grid. 95 PC-HYSPLIT WORKSHOP

  15. Defining Multiple Sources Now run the dispersion model for 2 sources using these settings: • Source1: 28.50N, 80.70W @ 10.0 m • Source 2: 28.0N, -80.0W @ 10.0 m • Meteorology: NAM 12 km • Emission: 6 hrs beginning 1200 UTC on 19 Dec 2005 • Output: 6 hr average concentration between the ground and 100 m-agl • Top-hat-horizontal, particle-vertical • 5000 particles • Run Standard Model 96

  16. Defining Multiple Sources • A second source added at location 28.0N and 80.0W results in two adjacent, almost identical plumes.  • Note that the emission rate of 1 unit per hour is applied to each source individually. 97 PC-HYSPLIT WORKSHOP

  17. Defining Multiple Sources • The emission rate can be set for each source by including that information after the release height in the Starting Location Setup menu. (A fifth field can be added that sets an initial plume area in square-meters, but is only valid for “puff” simulations.) • In the example shown here (top right), the emission rate of the second source has been increased to 10 units/hr • The concentrations in the second plume (right) have increased by the same amount as the emission increase (10%). • To display the same concentration levels as the last graphic, change the output contour levels in UserSet to 1.0E-09+1.0E-10+1.0E-11+1.0E-12 98 PC-HYSPLIT WORKSHOP

  18. Simulations using Emissions Grids Option 1: Matrix Approach • An emission matrix is defined using three locations; the first two represent the lower left and upper right grid corners, respectively, and the third represents the grid spacing. • Example to run:  Start sources every 0.5 degrees between the grid corners (27.0, -82.0) and (30.0, -79.0). Leave all other parameters the same as the last Florida example, however increase the maximum number of particles to at least 50,000 in the Advanced / Configuration Setup / Concentration menu. • Run the model from the Concentration / Special Simulations / Run Matrix menu option. • Prior to running the model, the CONTROL file is redefined with 49 starting locations (right). 99 PC-HYSPLIT WORKSHOP

  19. Simulations using Emissions Grids • The result (top right) shows 49 plumes over a uniform 0.5 degree grid. • To make the graphic less noisy, from the Concentration Display menu, turn off the source location labeling and remove the black contour lines from the graphic by setting the contour outlines to none • Execute the display to create a considerably simplified graphic (below right). 100 PC-HYSPLIT WORKSHOP

  20. Simulations using Emissions Grids Option 2: Emissions File Approach • Another approach is to define an emissions file, which tabulates hourly emission rates by location.  • An emission.txt file defines the grid to which those emissions data will be accumulated and is located in the working directory.  • A simulation using this approach for the same case (right) is almost identical to the previous matrix run.  • The CONTROL file must define the lower left and upper right corners of the desired emission domain, which may be larger or smaller than the data available.  • Due to the continuous emissions at many locations, these simulations may require the maximum number of particles be increased from the default value as was done for the matrix run. • Information on the format of the emissions file and the emission text file can be found in the HYSPLIT User's Guide under Advanced / Special Topics (S441). 101 PC-HYSPLIT WORKSHOP

  21. Concentration and Particle Display Options Now, we will look at the particle distributions for the Florida case for various source terms. • Setup the following run: • Delete the emission.txt and emission.asc files from the working directory if used previously. • Source1: 28.50N, 80.70W @ 10.0 m • Meteorology: NAM 12 km • Emission: 6 hrs beginning 1200 UTC on 19 Dec 2005 • Output: snapshot at 6 hours between the ground and 100 m-agl • 3D particle horizontal and vertical • 500 particles • Dump the particles after 6 hours (right) • Run Standard Model 102 PC-HYSPLIT WORKSHOP

  22. Concentration and Particle Display Options Results: • Turn back on source labeling and color contour outlines in the Concentration Display menu and execute the display. • The resulting graphic should be the same as that shown (right). • The concentration output clearly shows a noisy pattern indicating too few particles were defined to adequately represent the plume. 103

  23. Concentration and Particle Display Options Setup the following runs: • Rerun the last case, but use 5,000 and 50,000 particles. • Make sure the maximum number of particles is greater than 50,000. • The particles are beginning to better define the plume, but at the expense of longer computational time. 5,000 Particles 50,000 Particles 104

  24. Concentration and Particle Display Options Results: • To speed up the run without loosing the plume structure, change the type of run from a 3D particle to a top-hat-horizontal particle-vertical and reduce the number of particles to 2500 (500 is still not enough to resolve the plume. • The resulting plume (right) covers a similar footprint as the 50,000 3D particle run. 105

  25. Concentration and Particle Display Options Particle Display • In addition to the standard display of particle concentrations, individual particle positions can also be displayed on a map. • The Concentration / Display Options / Particle menu (right) has options to show snapshot particle distributions, assuming that the particle dump option was set in the Advanced / Configuration Setup / Concentration menu before running the particle simulation. • Horizontal, vertical, and cross-sectional views are available. • Other options include color-coding the particles by mass size (Mass Sizing), by height (Color Scale) or output as a shapefile (GIS).

  26. Concentration and Particle Display Options Particle Display • Rerun the 50,000 3D particle simulation to produce a PARDUMP particle dump file. • Then choose the particle vertical cross-section with the color Scale option checked. • As seen in the graphic (right), the center line of the cross-section is drawn automatically based upon the particle distribution. • The particles toward the west are at a higher level than those to the east.

  27. Concentration and Particle Display Options Pointer Select Concentration Display • Another display option is to view the concentration values directly on the grid without any interpolation through the Concentration / Display Options / Pointer Select tab. • This option will draw the entire concentration domain as defined in the concentration grid setup menu. The grid span may need to be reduced to zoom in on the area of interest. • Click on the initial map domain image with the right mouse button to display the concentrations (right). In this case the full 30 x 30 degree concentration grid defined previously covers an area much larger than the plume.

  28. Converting Concentration Data to Text Files • The concentration output file is in a binary format, however there are several options available through the Concentration / Utility Programs menu that can be used to convert the concentration data to other formats. • First, prepare a multi-time period output file by setting up a simulation as in the previous example, but with the following changes: Top-hat-horizontal particle-vertical, No particle dump interval (0), 12 hour simulation, 12 hour continuous release, 500 particles, and 1 hour average concentrations. • Check the Fix-Exp box in the Display menu to keep the contours constant and you may need to change the name of the output file from partplot to concplot. • After displaying the Postscript output, create an animated gif image by using the Concentration / Utility Programs / Convert Postscript menu by checking the animate box in the Postscript Conversion menu. • The continuous emission plume moves southwest and then more to the south near the end of the simulation.

  29. Converting Concentration Data to Text Files Time Series Data Extraction • Next, select the Concentration / Utility Programs / Grid to Station menu (right). • Select a point downwind in the plume (27.7N, 81.0W), • Give it a unique Integer ID (2781), • Set the Concentration Multiplier to 1.0, • and choose a Log Ordinate scale. • Click Extract Data and an ASCII con2stn.txt file will be created with the concentration values interpolated to that location.  (An input file with the station locations must be created for multiple locations). • Selecting the Display Time Series Yes button results in the creation of a time series plot (right). In this case the peak concentration occurred at 1600 UTC on 19 December 2005.

  30. Converting Concentration Data to Text Files • The Concentration / Utility Programs / Convert to ASCII menu will convert every non-zero grid point value to its ASCII equivalent, writing the output to one file per time period unless you specify Single File. • Files are labeled according to the name of the binary file, Julian day, and hour of the sampling period. • See the contents of this file for the output from the first time period. • This file can useful when importing the data into other mapping applications.

  31. Example Local Scale Dispersion Calculation • HYSPLIT can be configured for applications such as emergency response, when the scale of the simulation is on the order of 10-30 km. • For this example, set up the run as shown below for Washington, D.C. 38.880N 77.027W @10m and 100m, 1200 UTC 19 December 2005, NAM 12 km forecast data, 1-hr emission and simulation, 1-hr average concentration after 1 hr, Lat/lon Grid Resolution of 0.001 degrees, and Grid Span of 1.0 degrees lat/lon. Using the Advanced / Configuration Setup / Concentration menu, set: 3-D particle horizontal and vertical method, 1000 particles, 10000 maximum number of particles, and Short-range similarity (fluxes) method for the turbulence computation. Run Standard Model

  32. Example Local Scale Dispersion Calculation • After running the model, set the Concentration Display menu to the following (right) • Output File: concplot • Number of rings to 4 every 10 km • Map background to countymap • Zoom to 100% • Dyn-Exp contours • Turn on the contour outlines  • Turn on the Google Earth option

  33. Example Local Scale Dispersion Calculation • The resulting plume (below left) produces a very narrow plume moving southeast into Maryland over the 1 hour period. • As will be discussed later, the Google Earth file (HYSPLITconc.kmz) was created and allows the emergency manager to overlay the plume with other geographic features (below right). This file can be provided directly to the emergency manager.

  34. Example Local Scale Dispersion Calculation • Now assume the release was very small and only lasted 15 minutes. Use the Concentration setup / Pollutant, Deposition and Grids setup menu (right) to define a 15 minute (0.25h) release of one unit of mass. Note that since the release rate required is per hour, you will need to multiply the mass by 4 in this case. • Also, change the averaging period to 10 minutes over the 1 hour simulation, which can be defined in the Concentration Grid Setup menu. • Run the model and create an animated GIF (right). To keep the contours from changing as the concentrations decrease, you may want to fix the contours by checking Fix-Exp box in the Concentration Display menu.

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