Workshop Agenda

1
Workshop Agenda
Model Overview Model history and features Computational method Trajectories versus concentration Code installation Model operation Example calculations Updating HYSPLIT Meteorological Data Data requirements Forecast data FTP access Analysis data FTP access Display grid domain Vertical profile Contour data Examples 1-5 Particle Trajectory Methods Trajectory computational method Trajectory example calculation trajectory model configuration Trajectory error Multiple trajectories Terrain height Meteorological analysis along a trajectory Vertical motion options Pollutant Plume Simulations Modeling particles or puffs Concentration prediction equations Turbulence equations Dispersion model configuration Defining multiple sources Simulations using emission grids Concentration and particle display options Converting concentration data to text files Example local scale dispersion calculation Special Topics Automated trajectory calculations Trajectory cluster analysis Concentration ensembles Chemistry conversion modules Pollutant deposition Source attribution using back trajectory analysis Source attribution using source-receptor matrices Source attribution functions GIS Shapefile output KML/KMZ output Customizing map labels Scripting for automated operations Extra Topics Modeling PM10 emissions from dust storms Restarting the model from a particle dump file
2
Trajectory Computational Method

• How is a trajectory calculated?
• If we assume that a particle passively follows
  the wind, then its trajectory is just the
  integration of the particle position vector in
  space and time. The final position is computed
  from the average velocity at the initial position
  (P) and first-guess position (P'). 
• P'(t ? t)   P(t) V(P,t) ?t
• P(t?t)    P(t)    0.5 V( P,t)  
   V(P',t?t) ?t
• The integration time step is variable Vmax ?t  
  lt  0.75 meteo. grid spacing

3
Trajectory Computational Method

• The meteorological data remain on the native
  horizontal coordinate system when read by
  HYSPLIT, but are interpolated to an internal
  terrain-following (s) vertical coordinate system
  during computation
• s    ( Ztop Zmsl ) / ( Ztop Zgl )
• Ztop       - top of the trajectory models
  coordinate system Zgl       - height of the
  ground level Zmsl      - height of the
  internal coordinate
• The models internal heights can be chosen at any
  interval, however a quadratic relationship
  between height and model level is specified, such
  that each levels height with respect to the
  models internal index, k, is defined by
•            Zagl ak2 bk c
• The constants are automatically defined such that
  the models internal resolution has the same or
  better vertical resolution than the input
  meteorological data.

4
Trajectory Computational Method

• To illustrate this process, a simple forward
  trajectory was calculated with the NAM 40 km
  meteorological data from (60N, 110W) at 2500
  m-agl for a total of 84 hours using the isobaric
  (constant pressure) vertical motion method, as
  shown below.

The relationship of the trajectory to the
temporal and spatial variations of the 700 hPA
height field (approximate height of trajectory)
is illustrated in the attached animation which
was created using only the standard tools that
come with PC HYSPLIT. 
5
Trajectory Model Configuration
Now that youve had some time to practice running
trajectories, a more thorough description of some
of the GUI inputs will be presented.
Starting Location Setup A starting location(s)
can be entered directly from this menu or a
position may be chosen from a predefined list. 
This list is located in the working directory, is
user editable, and named plants.txt. Heights are
always entered as meters above ground level (agl).
Top of the model (m agl) the height above which
the meteorological data are not processed.  For
calculations within the troposphere, 10 km is a
good value.  Trajectories are terminated when
they reach this height.  Processing fewer levels
reduces computational times.
6
Trajectory Model Configuration
One key feature for any simulation is selecting
the best meteorological data.  In the current
version of HYSPLIT up to 12 meteorological files
may be defined simultaneously. When multiple
files are defined, at each integration step, the
model uses the finest spatial resolution file at
the location and time of the trajectory
end-point. This can be useful if you have
several higher resolution grids nested within
each other. The Add Meteorology Files button is
used to select multiple meteorological data
files. The Clear button will erase all selected
files from the list. In the example below, both
the NAM 12 km and GFS latitude/longitude files
have been selected for the next example.
7
Trajectory Model Configuration
For this example, an isobaric forward trajectory
was started at 1200 UTC on December 19, 2005,
from a height of 2.5 km at 46N, 68W. The total
run time was set to 84 hours and both the NAMF12
and the GFSFLL meteorological data files were
selected (previous slide). Execution of the
CONTROL file for this case results in a
trajectory (right) that goes northeast using the
NAM 12 km forecast file until running off the NAM
domain ( 50N). The model then uses the GFS for
the remainder of the calculation. The
meteorological file identifier is written with
each end-point position in the second column of
the ASCII trajectory tdump output file. The
diagnostic MESSAGE file also provides additional
detail about the calculation.  In this example
the switch from NAM to GFS occurs at 0900 GMT on
December 20, 2005, causing the 0900 and 1200 GMT
data to be reloaded.
8
Trajectory Error

• A common question often arises when running
  trajectories....
• "What is the error associated with a given
  trajectory calculation."
• From the literature, one can estimate the total
  error to be anywhere from 15 to 30 of the travel
  distance. The total error is composed of four
  error components
• physical error due to the inadequacy of the
  datas representation of the atmosphere in space
  and time,
• computational error due to numerical
  inaccuracies,
• measurement errors in creating the models
  meteorological data fields,
• forecast error if using forecast meteorology.
• Physical Error
• The physical component of the error is related to
  how well the numerical fields estimate the true
  flow field. There is no way of knowing this error
  without independent verification data.

9
Trajectory Error

• Computational Error
• The computational component of the error is
  composed of
• the integration error (part of which is due to
  truncation) and,
• the data resolution error, i.e., trying to
  represent a continuous function, the atmospheric
  flow field, with gridded data points of limited
  resolution in space and time.

The integration error component of computational
error can be estimated by computing a backward
trajectory from the forward trajectory endpoint.
The error is then 1/2 the distance of the final
endpoint from the starting point. In this
example, the final endpoint position (67.574N,
26.813W, 2332.7 m AGL) from the previous tdump
endpoints file was used as the starting point (on
the 23th 0000 UTC) for a backward trajectory
calculation.  When running this case, insure that
the endpoints file names are different for both
the forward and backward calculations by setting
the tdump filename to tdumpback, for example.
10
Trajectory Error

• Integration Error
• To show the differences between the forward and
  backward trajectories, display both of them on
  the same plot by entering both file names in the
  Input endpoints box of the Trajectory Display
  GUI using a symbol
• (e.g. ./tdumptdumpback).  Note how the
  backward (blue) trajectory returns very close to
  the initial forward (red) starting location,
  indicating very little integration error. Most
  of the time the integration error is very small
  compared to resolution error. You can also see
  that the model automatically switched back to the
  NAM 12 km grid at 0800 UTC on December 20 by
  viewing the tdumpback endpoints file.

11
Trajectory Error

• Resolution Error
• The resolution error component of computational
  error can be estimated by starting several
  trajectories about the initial point by offset
  ting them in the horizontal and vertical. The
  divergence of these trajectories will give an
  estimate of the uncertainty due to divergence in
  the flow field. An initial offset should be used
  that is comparable to the estimated integration
  error. In this example, there is little
  horizontal error, but vertical offset produces
  spread at later times.
• One component of the resolution error that is
  difficult to estimate relates to the size and
  speed of movement of various flow features
  through the grid. There should be a sufficient
  number of sampling points (in space and time) to
  avoid aliasing errors. Typically, a grid
  resolution of "x" can only represent wavelengths
  of "4x". This error will be a function of the
  meteorological conditions.

12
Trajectory Error
Another method of ascertaining the integration
error is to run trajectories from the same
location using several different sources of
meteorological data. In this example (right),
trajectories have been computed using
meteorological data from NAM(12 km)/GFS (red),
RUC/GFS (blue), and MM545/GFS (green). After the
first 36 hours, differences between trajectories
indicate that the integration error is much
greater than the numerical error. Note that the
green trajectory went up near the end because it
hit Greenland (HYSPLIT is terrain following).
These trajectories are more similar than most
simulations due to the isobaric assumption that
was made for this case.
13
Multiple Trajectories
Multiple Trajectories from same Location
Trajectories can be started at regular time
intervals from the same location by setting the
restart interval to something other than 0 hrs.
Clicking on the Advanced / Configuration Setup /
Trajectory menu tab produces another menu (right)
for entries to the optional trajectory namelist
file SETUP.CFG used by the model for more
options.
Clicking on Multiple trajectories in time Menu
button produces the menu shown to the right. To
demonstrate the restart feature, change the
Restart interval to 3 hrs, click Save, click Save
again, and leave all other trajectory parameters
the same as in the original 700 hPa isobaric
trajectory previously computed at 46N, 68W.
14
Multiple Trajectories
Multiple Trajectories from same Location (cont.)
After clicking on Run Standard Model a message
box (shown at right) will appear to indicate that
a SETUP.CFG configuration file exists and ask if
you want to run with it. In this case since we
made changes to the advanced settings, choose Run
with SETUP.
The resulting trajectory graphic shows new
trajectories every 3 hours, terminating at the
end of the 84 h computational period. 
Trajectories starting after the initial time will
have a shorter duration.  All trajectories can be
set to have the same duration from the Advanced
menu tab.
15
Multiple Trajectories

• Trajectory Matrix (grid of starting locations)
• The model supports an unlimited number of
  starting locations, however the GUI is limited by
  the users screen size (GUI will extend off the
  bottom with too many selections).
• A matrix of starting locations can be defined by
  selecting three points, representing the lower
  left, upper right, and location increment from
  the Setup Starting Locations menu button (see
  example to the below). 
• Once configured, the Run Matrix option is
  selected through the Special Simulations menu tab
  of the Trajectory menu instead of Run Standard
  Model. 
• This causes the locations defined by the grid (in
  this case 25) to be calculated and written to the
  CONTROL file.

16
Multiple Trajectories
Trajectory Matrix Example

• Rerun the 700 hPa isobaric case again but change
  the Total run time to 24 hours and choose the 3
  source locations from the previous slide.
• From the Advanced/Configuration Setup/Trajectory
  menu choose Define subgrid and MSL/AGL UNITS menu
  and set the height unit Relative to
  mean-sea-level because the terrain height varies
  across the matrix. Save.
• Reset the Restart Interval back to 0. Save.
• Save the advanced settings and run the Matrix
  from the Special Runs menu tab (run with SETUP).
• When finished set the Time Label Interval (hrs)
  to 0 in the Trajectory Display GUI) before
  executing the display (this makes a less
  cluttered display) and the zoom to 80.

The resulting graphic should be similar to the
one shown above a matrix of 24-h duration
isobaric trajectories. Again there is very little
differences noted between the trajectories
indicating small temporal and spatial differences
in the meteorology in this region. Note that we
are using spatial and temporal offsets to
ascertain the trajectory error or in this case
sensitivity to the meteorological data.
17
Terrain Height

• Trajectory starting height defaults to meters AGL
  (above ground level), but can be changed to
  meters MSL (above mean sea level) from the
  Advanced / Configuration Setup menu tab as was
  done in the previous exercise. 
• Regardless of how the input heights are defined,
  internally HYSPLIT treats all heights in a
  terrain following coordinate system based on the
  chosen meteorological data. 
• These heights may be quite different from the
  actual terrain height at a point of interest.
• As an example, examine the various model
  estimated terrain heights (right) for Broomfield
  (KBJC), Colorado, at 39.92N and 105.12W, which
  has a surface height of 1724 m above MSL. 

Model Horizontal Resolution Terrain Height (MSL)
MM5 15 km 2000 m
MM5 45 km 2100 m
NAM 12 km 1970 m
NAM 40 km 1840 m
RUC 20 km 1890 m
GFS 1 deg. 2020 m
18
Terrain Height
The terrain heights for the NAM 12 km (left) and
GFS (right) are shown below (Bloomfield is
indicated by the black star). The terrain in the
vicinity of Bloomfield is much smoother in the
coarser GFS than the NAM and the terrain gradient
is much steeper in the NAM and therefore we would
expect to see differences in the terrains. Also,
when the model terrain is consistently above the
true terrain in all models, one might suspect
that the station is located in a valley, as in
this case. In this situation, all one can do is
assume that true ground-level is at the model's
terrain height and proceed with the realization
that the lower levels of the flow field may at
times be constrained in ways that are not evident
in the coarser gridded meteorological data fields.
NAM
GFS
19
Terrain Height

• In the example to the right, we plotted 3
  separate trajectory results on the same map using
  the NAM 12 km (blue), the MM5 45 km (green), and
  the 1 degree GFS (red) originating from 10 m
  above model ground level (AGL).
• Even though all the trajectories start out at
  the same height AGL, they start at different
  pressure levels due to differences in elevation
  between the data various datasets.

20
Meteorological Analysis Along a Trajectory

• HYSPLIT can provide details on some of the
  meteorological parameters along the trajectory if
  the appropriate boxes are selected by the user in
  the Advanced/Configuration Setup/Trajectory menu.
  
• This information can be useful in diagnosing why
  a trajectory took the path it did, to show the
  underlying terrain height, to show the mixed
  layer depth along the trajectory, or to show if
  any precipitation was being produced along the
  trajectory path by the meteorological model.
• Currently only ambient and potential temperature,
  precipitation, mixing depth, relative humidity,
  solar radiation, and terrain height are available
  to output or display.
• One or more meteorological fields may be selected
  and all will be written to the trajectory
  endpoints file in the columns to the right,
  however only the rightmost (or last selected)
  variable will be plotted at the bottom of the
  trajectory map if the plotting option is enabled.

21
Meteorological Analysis Along a Trajectory
Trajectory Example

• Configure the model for a trajectory originating
  at Broomfield, Colorado, (39.92N and 105.12W)
  using the NAM 12 km data.
• Set the starting height to 1500 m,
• the vertical motion data field to 0 (Data),
• and the total run time to 84 hours.
• In the advanced trajectory menu click on Add
  METEOROLOGY output along trajectory
• Choose Terrain Height (right) and Save.
• Save the configuration and choose Run with SETUP.
  A flag is set in the SETUP.CFG when
  meteorological variables are selected.
• In order to plot the terrain height along the
  trajectory in the vertical cross-section plot,
  choose Meters-agl as the vertical coordinate in
  the Trajectory Display menu.

22
Meteorological Analysis Along a Trajectory

• For the most part, the resulting trajectory
  (right) follows the terrain as the terrain
  descends from Colorado into Texas.
• If you choose Pressure as the Vertical
  Coordinate, the trajectory may look like it is
  descending in height, but in reality it is
  following the descending terrain, so care must be
  exercised when interpreting the up or down
  movement of trajectories with respect to height
  above model ground level and pressure vertical
  height coordinates.
• The terrain heights can be viewed as the
  right-most column of the trajectory endpoints
  file (tdump)

23
Meteorological Analysis Along a Trajectory

• Rerun the last case, but instead of Terrain
  Height, select Mixing Depth.
• In order to display a meteorological variable
  other than Terrain Height, select Meteo-varb as
  the vertical coordinate in the Trajectory Display
  menu (upper-right).
• This plot shows that the mixed layer depth along
  the trajectory varied from 250 m on the first day
  (HYSPLIT sets the lower depth to a minimum of 250
  m) to 659 m during the afternoon of the 21st.

24
Vertical Motion Options

• There are six vertical motion options in
  PC-HYSPLIT.
• The suggested default (0data) uses the vertical
  velocity field included with most meteorological
  data.
• Other options may be required for special
  situations such as following the transport of a
  balloon on a constant density surface, comparing
  isobaric flow fields between data sets, or
  situations when the meteorological datas
  vertical velocity field may be too noisy compared
  with the time step at which the data are
  available (high spatial resolution simulations).
• In the sigma option the trajectory remains on its
  original terrain following sigma surface.
• In the isobaric, isentropic, and constant density
  (isopycnic) options, the vertical velocities are
  computed from the equation,
• W (- ?q/?t u ?q/?x v ?q/?y) / (?q/?z)
• where W is the velocity required for the
  trajectory to remain on the q surface (pressure,
  potential temperature, density).   Note that the
  equation results in only an approximation of the
  motion and a trajectory may drift from the
  desired surface.
• In the divergence option, the vertical velocities
  are computed from the vertically-integrated
  horizontal divergence in the meteorological data.

25
Vertical Motion Options

• Shown below (left) is the same trajectory of the
  previous example using the NAM 12 km vertical
  velocity fields.  To the right is the same
  trajectory computed using the divergence option.
  This graphic shows the choice of vertical motion
  can greatly impact the transport direction as the
  divergence method introduced more vertical motion
  and hence the particle entered different
  transport winds.