introduction to atmospheric dispersion...
TRANSCRIPT
Introduction to atmospheric dispersion modelling
M.Sofiev
Content
• Main parts of the atmosphere
• Basic terms
atmospheric tracer
temporal and spatial scales
life time in the atmosphere
life cycle of atmospheric tracers
• Dispersion equation
• Langrangian and Eulerian dispersion models
• Parts of a dispersion model
• Model Quality Assurance
• Summary
Major layers of the atmosphere
• Troposphere (tropos=mixing): interaction with surface
• Stratosphere: ozone-uv heating
• Mesosphere: mixing again
• Thermosphere: O2, N2 – solar radiation heating
• Ionosphere: ions
• Exosphere: fast molecules escape to the open space
0
20
40
80
100
60
Altitude
, km
103
102
10
10-2
10-3
1
Pre
ssure
, hP
a
10-1
t r o p o p a u s e
s t r a t o p a u s e
m e s o p a u s e
troposphere
strato
sph
ere
mesosp
here
thermosphere
0 20 40-60 -40 -20-80
Temperature, C
Basic terms
• Atmospheric tracer: a compound, which is transported with atmospheric flows but does not affect them (sufficiently low concentration)
some impact exists always: feedback to meteorological processes
• Tracer lifetime: a time period needed for 2-fold (or e-fold) reduction of amount of the tracer in the atmosphere
condition- and process-dependent: e.g. lifetime with regard to advection
general meaning: lifetime is related to relaxation times for any process involving this tracer (not 1:1 though)
• Spatial and temporal scales
related to lifetime
temporal scales are translated into spatial ones via wind speed
processes and their imporatnce are related to scales 1sec
100sec
1hr
1yr
10yr
1 day
Tim
e s
cale
100km 1000km 10,000km100m 1km 10km1m
Spatial scale
10m
100yr CFCs
CH4
CH3Br
CH3CCl3
CO
Aerosols
SO2
Trop O3
NOx
DMS
C3H6
N2O
H2O2
C5H8
CH3O2
HO2
NO3
OH
Boundary layermixing time
Inter-hemispheric
mixing time
Hemispheric
mixing time
- - mesoscale
regional
scale
global
scale
micro
scale
local
scale
Pollution cycle in the troposphere
Chemical & physical reactionsTransportEmission
Diffusion in deep layersDiffusion in deep layers
LOADLOAD
Content
• Main parts of the atmosphere
• Basic terms
atmospheric tracer
temporal and spatial scales
life time in the atmosphere
life cycle of atmospheric tracers
• Dispersion equation
• Langrangian and Eulerian dispersion models
• Parts of a dispersion model
• Model Quality Assurance
• Summary
Dispersion equation
• Mass conservation
transport
sources
sinks
• Scale separation
mean flow
turbulence
• Closure problem
K-theory turbulent diffusion coefficient
(x0,y0,z0)
x
z
y
u(x0-x/2) u(x0+x/2)
w(z0-z/2)
w(z0+z/2)
v(y0+y/2)
v(y0-y/2)
3
1
( )i
i i
cu c E R
t x
( / )( ) ( )
i ii
i i i
C CLC U C K R C E
t x x x
From concentration to load
p is a weight (sensitivity) function of the load:
– Population exposure
– Ecosystem damage
– Observational site
)(),( cityxxtxp ( , ) ( ) 1( )
ecosystemp x t p t A
0
( , ) load functional
T
M dt C p dx C p
( , ) ( ) 1( , , )site beg end
p x t t t t x x
Alternative way to get the load function
* * * *
* *
( , ) ( , ) ( , ) ( , )
adjoint dispersion equation
M C E C LC LC C p C
LC p
* ( ) ( )i ii
i i i
L U K R Ct x x x
, * 0
*( ) 0
x
C C
C t T
Consider some function C* satisfying
L* C* = p, where L* is adjoint to L.
Then
Dual features of dispersion problem
(1/ )( ) ; ; ( , )
i ii
i i i
L U K R LC E M p Ct x x x
* * * *( ) ; ; ( , )i ii
i i i
L U K R LC p M E Ct x x x
Forward problem:
Inverse (adjoint) problem
Content
• Main parts of the atmosphere
• Basic terms
atmospheric tracer
temporal and spatial scales
life time in the atmosphere
life cycle of atmospheric tracers
• Dispersion equation
• Langrangian and Eulerian dispersion models
• Parts of a dispersion model
• Model Quality Assurance
• Summary
Classifications of models
Model principles
– Eulerian
– Lagrangian
– Gaussian
– statistical Monte-Carlo
Scales
– global
– continental
– regional
– local/urban
Classifications of models.2
Chemicals
– acid
– ozone
– greenhouse gas
– inert aerosol/dust
– radio-activity
– toxic
– persistent pollutants
Model media
– atmospheric
– multi-media
– integrated models
Classifications of models.3
Input data
– climatological
– real-time data
Time dimension: direction, horizon
– re-analysis
– now-casting
– forecasting
Problem to solve
– forward
– inverse
Content
• Main parts of the atmosphere
• Basic terms
atmospheric tracer
temporal and spatial scales
life time in the atmosphere
life cycle of atmospheric tracers
• Dispersion equation
• Langrangian and Eulerian dispersion models
• Parts of a dispersion model
• Model Quality Assurance
• Summary
SILAM v.5: outlook
• Modules
8 chemical and physical transformation modules (6 open for operational use),
6 source terms (all open),
2 aerosol dynamics (one open)
3D- and 4D- Var
• Domains: from global to beta-meso scale (~1km resolution)
• Meteo input:
ECMWF
HIRLAM, AROME, HIRHAM, ECHAM, and any other who can write GRIB-1 or GRIB-2
WRF
SOx
Acid-basic
CB4
Pollen
General PM
Radioactive
Passive
self-decay Long-lived
multi-media
Transformations
Area
Point
Nuclear bomb
Source types
Map of
species masses
Em
iss
ion
Tra
nsfo
rma
tio
n
Dynamics
Advection
diffusion
Aerosol
dynamics
Bio-VOC
Pollen
Sea salt
Simple
Basic
Transformation
Dry
Wet
Deposition
Initialization,
3D-Var
Simulation control
forward adjoint 4D-Var
AROME
NWP model HIRLAM-MBE NWP model
Physiography,
forest mapping
Aerobiological
observations
FMI regional AQ assessment and forecasting
platform
Satellite
observations
Phenological
observations SILAM
CTM model
EVALUATION:
NRT model-measurement
comparison
Aerobiological
observations
Meteorological
data: ECMWF
Online AQ
monitoring
Phenological
models
Fire Assimilation
System
HIRLAM-RCR
NWP model
AQ
products
CLRTAP/EMEP
emission data
http://silam.fmi.fi
Satellite
observations
Global boundary cond.
+ own simulations
WRF
TVM
SILAM scales
• Global
• Continental
• Regional
• Meso-scale
SO2 3.5.2003
Content
• Main parts of the atmosphere
• Basic terms
atmospheric tracer
temporal and spatial scales
life time in the atmosphere
life cycle of atmospheric tracers
• Dispersion equation
• Langrangian and Eulerian dispersion models
• Parts of a dispersion model
• Model Quality Assurance
• Summary
Model vs reality
I.Repin. Zaporozhje Cossacks are writing a letter to Turkish sultan
• Model is never a copy of reality
It represents only those features, which are deemed to be important for a
specific application
• The extent of their similarity is to be established in each specific case
W.Kandinski. Cossacks
Model Quality Assurance (QA)
• Tests of individual modules (development stage)
• Sensitivity runs
• Model-measurement comparison
• Model-model comparison
Model-measurement comparison
• The only connection between model and reality
• Data sets from different origin
point observations vs grid-mean model results
representativeness error
instrumental errors
• Observations are expensive => sparse
• Limited number of observed variables
• Specific statistical methods are required to obtain non-trivial conclusions
Model inter-comparison
• Useful if lacking measurements
• Similar features of data
• Large data sets => high accuracy
• Wide variety of analytical methods
• Ensemble model
• Possibly, no connection to reality
Summary
• Distribution of an atmospheric pollutant is described via dispersion equation, which is a representation of the mass conservation law
• Duality of dispersion problem allows for usage of forward and adjoint dispersion equations
identical final results – the load
choice depends on specific task
• Model quality assurance implies several actions and covers ALL stages of the model development