ADMSSTAR – a model of puff dispersion · ADMSSTAR – a model of ... 0 200 400 600 800 1000 1200...
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CERC
ADMSSTAR – a model of
CERCPresentation to
UK Atmospheric Dispersion Modelling
Liaison Committee (ADMLC)
ADMSSTAR – a model ofpuff dispersion
Health Protection Agency
September 2008
David Carruthers and Martin Seaton
Cambridge Environmental Research Consultants
CERCContent
• Applications
• ADMS – plumes and puffs
• Requirements
• Puff dispersion model overview
• Spatially varying meteorology
• Variable terrain and surface roughness
• Observed site meteorological data
• Conclusions
CERCApplications
Currently being implemented in ADMSSTAR 2
• Produced for the Food Standards Agency Interested in accidental and explosive releases
• Includes existing features of ADMSSTAR 1• Includes existing features of ADMSSTAR 1 Radioactive decay
Back calculation from sample strengths
Calculation of MPL contours
CERCADMS - Plumes
• Steady state infinite release
Elevation
• Long term results are the average over a series of independent, infinite, steady state plumes
Plan
CERCADMS - puffs
• Puffs in ADMS 4 also assume steady met conditions but release has finite duration
• Concentration depends on time since release and puff has a defined front and rear
CERCADMS - puffs
1 - - 180
200
400
600
1 - - 300
200
400
600
1 - - 420
200
400
600
0 200 400 600 800 1000 1200 1400
Metres
-600
-400
-200
0
Me
tres
0 200 400 600 800 1000 1200 1400
Metres
-600
-400
-200
0M
etr
es
0 200 400 600 800 1000 1200 1400
Metres
-600
-400
-200
0
Me
tres
180s 300s 420s
Release lasts until 300s
CERCRequirements
• For short releases temporal variation of meteorology can be important
• Ability to handle spatially varying meteorology flow field: Horizontal and vertical wind speed components
boundary layer properties: e.g. boundary layer height, surface heat boundary layer properties: e.g. boundary layer height, surface heat flux
• Generate flow field from terrain data and upwind meteorological conditions
CERCMethod - overview
Multiple puff approach• Overview
A sequence of instantaneous puffs released Each puff advected on a time scale smaller than time scale on which
the meteorology changes Concentration field is the sum of the concentration fields of the
individual puffsindividual puffs
• However Time history of each puff is different, so more complex than steady
state Longer run time
• Advantages Flexible, allows concentration with time with temporally and spatially
varying meteorology Allows incorporation of both small scale and large scale
meteorology
CERCRelease types
• Release can either be continuous or explosive Continuous release has a defined start and end time, a single initial
puff and more are added as the release continues
Explosive release is a single event with 5 initial puffs and no more added over time
fraction of CTH
2 = 0.4
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
3
2
1
2 x = 0.2
x or y
2 z = 0.4
5
4
CERCMethod – details 1
Instantaneous puff
U
Puff properties
• Centre of mass
• Spread parameters
• Amount of material
• Deposition properties
CERCMethod – details 2
• Centre of mass advected based on wind velocity at mean puff height
)()()(
)()()(
ttUtYttY
ttUtXttX
y
x
• Takes into account plume rise and gravitational settling
• Meteorological parameters calculated at mean puff height
)( )()()(
)()()(
spr WWtUttZttZ
ttUtYttY
z
y
CERCMethod – details 3
• Spreading parameters, relative to local streamline, calculated based on change assuming current met conditions persisted since start of release e.g.
)()()()( 2222 tttttt yyyy
• With the plume spread assuming the current met conditions persisted since the start of release
calculated using the standard ADMS plume equations
)(ty
CERCMethod – details 4
• Deposition equations adapted to take into account instantaneous puff approach
• Concentration for individual puff calculated assuming a Gaussian puff (X,Y directions, Z direction like ADMS plume)
• Overall concentration calculated by summing concentrations due to individual puffsdue to individual puffs
• Total accumulated deposition calculated by summing deposition due to each puff at each time step
CERCResults - concentration
Concentration for a single puff after 15 minutes and 30 minutes. The wind direction is 180o for the first 15 minutes and 235o for the second
187000
188000
189000
187000
188000
189000
15 Minutes 30 Minutes
530000 531000 532000 533000 534000 535000 536000 537000 538000 539000 540000
179000
180000
181000
182000
183000
184000
185000
186000
187000
530000 531000 532000 533000 534000 535000 536000 537000 538000 539000 540000
179000
180000
181000
182000
183000
184000
185000
186000
CERCResults – continuous release
188000
189000
Concentration and total accumulated deposition results for a continuous release after two 15 minute met periods with wind directions of 180o and 235o
188000
189000
530000 531000 532000 533000 534000 535000 536000 537000 538000 539000 540000
179000
180000
181000
182000
183000
184000
185000
186000
187000
530000 531000 532000 533000 534000 535000 536000 537000 538000 539000 540000
179000
180000
181000
182000
183000
184000
185000
186000
187000
Concentration Deposition
CERCResults – total deposition
Total accumulated deposition for a 5 minute release over a series of met periods with differing meteorological conditions
CERCSpatially varying meteorology
• Extend this to be able to deal with spatially varying meteorology
1000
2000
3000
4000
res
1000
2000
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4000
res
• Meso scale meteorological data supplied by the Met Office in NetCDF format at 4km or 12km horizontal resolution
-3000 -2000 -1000 0 1000 2000 3000 4000
Metres
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-2000
-1000
0
1000
Met
r
-3000 -2000 -1000 0 1000 2000 3000 4000
Metres
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-2000
-1000
0
1000
Met
r
Hour 1 Hour 2
CERCSpatially varying meteorology 2
• Spatially varying meteorology includes 3D flow fields
3D temperature field
2D rain fall rate, cloud cover, surface roughness and boundary layer height
• This means ADMS met variables need to be calculated across the meteorological grid.
CERCSpatially varying meteorology 3
• ADMS met processor run at each grid point of the input meteorology grid to calculate met properties
• Dispersion calculations carried out in the same way as for spatially homogeneous met data but now met properties are a function of space and time e.g.a function of space and time e.g.
)),(()()( tttUtXttX x X
CERCResults – spatially varying meteorology
Total deposition for two runs with the same set up and for the same time period, the only difference is in the source location
760000
780000
800000
1.151.21.25
820000
840000
0 20000 40000 60000 80000 100000 120000 140000 160000 180000 200000
Metres
600000
620000
640000
660000
680000
700000
720000
740000
Met
res
0.050.10.150.20.250.30.350.40.450.50.550.60.650.70.750.80.850.90.9511.051.11.15
160000 180000 200000 220000 240000 260000 280000 300000 320000 340000
Metres
660000
680000
700000
720000
740000
760000
780000
800000
Met
res
CERCFLOWSTAR
• Use FLOWSTAR (ADMS mean flow and turbulence model) to incorporate effects of Variable terrain height
Variable surface roughness
Both
• This can be incorporated within the spatially varying meteorology framework with an upstream condition for FLOWSTAR determined from the spatially varying meteorology
CERCFLOWSTAR
Horizontal locations of flow field data for variable terrain embedded within the meso scale meteorology data. The extent of the terrain region is given by the green box.
CERCResults - FLOWSTAR
80000
85000
11001140 80000
85000
Without terrain With terrain
Total deposition for two runs with the same set up and for the same time period, except that one run uses variable terrain height
160000 165000 170000 175000 180000 185000 190000
Metres
55000
60000
65000
70000
75000
80000
Me
tre
s
20601001401802202603003403804204605005405806206607007407808208609009409801020106011001140
160000 165000 170000 175000 180000 185000 190000
Metres
55000
60000
65000
70000
75000
80000
Me
tre
s
CERCObserved site met data
• With spatially varying meteorology can include site observed values of Wind speed and direction
Surface temperature
Rain fall rate
• Used to improve calculations near to the source
• Observed site data relaxes over a radius of influence back to the meso scale meteorological data
CERC
Total deposition for two runs with the same set up and for the same time period, except that one run has site observed data changing the wind speed near the source
Results – observed site data
No site data Wind on site 315o
186000
188000
190000
14
TotDepBq/m² Cs-137 - - -
186000
188000
190000
520000 522000 524000 526000 528000 530000 532000 534000 536000 538000 540000
Metres
170000
172000
174000
176000
178000
180000
182000
184000
Met
res
0.05
1
2
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13
520000 522000 524000 526000 528000 530000 532000 534000 536000 538000 540000
Metres
170000
172000
174000
176000
178000
180000
182000
184000
Me
tre
s
CERCConclusions
• Puff dispersion model. Release modelled as a set of instantaneous puffs
Individual puffs properties updated based on local, in time and space, meteorological conditions
• Allows short term releases to be modelled in spatially and temporally varying meteorologytemporally varying meteorology
• Allows complex terrain to be modelled
• Allows observed meteorological data at the source to be incorporated
• Validation and verification of the model
• Further developments …