ECOSIM Simulation Models
What distinguishes ECOSIM from existing systems is its capability to allow
an integrated quantitative and qualitative analysis of the environment
in urban and industrial areas across different environmental domains
and subdomains. In addition to the state of the
environment in each domain, the interrelations between the domains and
their dynamic behaviour is exploited.
Therefore, the individual domains are linked together on large
scales and the available multimedia data sources and modelling results
are crosscalibrated.
For instance, the system at each local site includes the following
numerical modelling tools, which are connected online to the users
individual monitoring networks:
 meteorological forecasting model;
 air chemistry and dispersion model;
 ground and surface water quality model;
 coastal water pollution model.


Further details of the following models are available:
 MEMO  mesoscale atmospheric model (AUT)
 MODFLOW/MT3D  Groundwater flow and
quality modeling (NTUA)
 DYMOS  air pollution dispersion and air
chemistry model system (GMD)
 POM  Princeton Ocean Model (UA)
In addition to these detailed models for planning purposes, ECOSIM also
includes a number of
forecasting models that
combine fast response with a solid scientific basis.
The generic clientserver architecture makes it very easy to add
any model with a similar structure, i.e., 2 and 3D spatially
distributed dynamic simulation models.

MEMO
Introduction
The nonhydrostatic prognostic mesoscale model MEMO (Kunz and Moussiopoulos,1995)
is a basic constituent of the European Zooming Model (EZM, previously called EUMAC
Zooming Model; Moussiopoulos, 1994 and 1995). The EZM represents one of the most
widely used European air quality model systems for urban scale applications
(about 15 study cases in the last three years).
MEMO solves the conservation
equation for mass, momentum and several scalar quantities in terraininfluenced
coordinates. Nonequidistant grid spacing is allowed in all directions. The numerical
solution is based on second order discretization applied on a staggered grid.
Special care is taken that conservative properties are preserved within the
discrete model equations. The discrete pressure equation is solved with a direct
elliptic solver in conjunction with a generalized conjugate gradient method
(Flassak and Moussiopoulos, 1988).
Advective terms are treated in MEMO with a monotonicity preserving discretization scheme
with only small implicit diffusion. Turbulent diffusion is described with a
two equation turbulence model. Radiative transfer in the atmosphere is
calculated with an efficient scheme based on the emissivity method for longwave
radiation and an implicit multilayer method for shortwave radiation (Moussiopoulos, 1987).
The surface temperature over land is computed from the surface heat budget equation.
The soil temperature is calculated by solving a none dimensional heat
conduction equation for the soil. At lateral boundaries generalized radiation conditions
are implemented. The current standard version of MEMO allows performing nested
grid simulations.


Among other recent applications, MEMO was used in the study launched by the Greek Ministry
of the Environment aiming to assess the environmental impact of constructing the
New Athens Airport (Moussiopoulos et al., 1995). Furthermore, it was one of the
models used in the "Seven cities project" in the context of theAuto/Oil study placed
by the DGXI of the European Union. Previous applications of MEMO are summarized
by Moussiopoulos (1994).
References
 Flassak Th. and Moussiopoulos N. (1988),
Direct solution of the Helmholtz equation using Fourier analysis on the CYBER 205,
Environ. Software 3, 1216.

Kunz R. and Moussiopoulos N. (1995),
Simulation of the wind field in Athens using refined boundary conditions,
Atmospheric Environment 29, 35753591.
 Moussiopoulos N., (1987),
An efficient scheme to calculate radiative transfer in mesoscale models,
Environ. Software 2, 172191.
 Moussiopoulos N., ed. (1994), The EUMAC Zooming Model,
EUROTRAC Special Publication, ISS, Garmish Partenkirchen.
 Moussiopoulos N. (1995), The EUMAC Zooming Model,
a tool for localtoregional air quality studies, Meteorol. Atmos. Phys. 57, 115133.
 Moussiopoulos N., Sahm P., Gikas A., Karagiannidis A.,
Karatzas, K. and Papalexiou S. (1995),
Analysis of air pollutant transport in the Athens basin and in the
Spata area with a threedimensional dispersion model,
in Air Pollution III, Vol 3: Urban Pollution (N. Moussiopoulos, H. Power
and C.A. Brebbia, eds) Computational Mechanics Publications, Southampton, 141152.

MODFLOW/MT3D
The models MODFLOW and MT3D are being applied to the
Ano Liosia Landfill in the Athens case study.
MODFLOW is a threedimensional finitedifference groundwater
flow model. It has a modular structure that allows it to be easily
modified to adapt the code for a particular application.
MODFLOW simulates steady and nonsteady flow in an irregularly shaped flow
system in which aquifer layers can be confined, unconfined, or a combination
of confined and unconfined. Flow from external stresses, such as flow to wells,
areal recharge, evapotranspiration, flow to drains, and flow through river
beds, can be simulated. Hydraulic conductivities or transmissivities for
any layer may differ spatially and be anisotropic (restricted to
having the principal direction aligned
with the grid axes and the anisotropy ratio between horizontal coordinate
directions is fixed in any one layer), and the storage coefficient may
be heterogeneous.
The model requires input of the ratio of vertical hydraulic conductivity to
distance between vertically adjacent block centres.
Specified head and specified flux boundaries can
be simulated as can a head dependent flux across the model's outer boundary
that allows water to be supplied to a boundary block in the modelled area
at a rate proportional to the current head difference between a
"source" of water outside the modelled area and the boundary block.
MODFLOW is currently the most used numerical model in the
U.S. Geological Survey for groundwater flow problems.
 
MT3D is a model for simulation of advection, dispersion and chemical
reactions of contaminants in groundwater flow systems in either two or three
dimensions. The model uses a mixed EulerianLagrangian approach to the
solution of the advectivedispersivereactive equation, based on
combination of the method of characteristics and the modified method
of characteristics. This approach combines
the strength of the method of characteristics for eliminating numerical
dispersion and the computational efficiency of the modified method of
characteristics.
The MT3D transport model was developed for use with any blockcentered finite
difference flow model such as MODFLOW and is based on the assumption that
changes in concentration field will not affect the flow field significantly.
The MT3D transport model can be used to simulate changes in concentration of
singlespecies miscible contaminants in groundwater considering advection,
dispersion and some simple chemical reactions, with various types of boundary
conditions and external sources or sinks. The chemical reactions included in
the model are equilibriumcontrolled linear or nonlinear sorption and
firstorder irreversible decay or biodegradation. Currently, MT3D accommodates the
following spatial discretization capabilities and transport boundary conditions:
 confined, unconfined or variably confined/unconfined aquifer layers;
 inclined model layers and variable cell thickness within the same layer;
 specified concentration or mass flux boundaries; and
 the solute transport effects of external sources and sinks
such as wells, drains, rivers, areal recharge and evapotranspiration.

DYMOS  air pollution dispersion and air chemistry
model system
At GMD FIRST the DYMOS
system (Sydow, 1994) has been developed, a parallelly implemented air pollution
simulation system for mesoscale applications.
DYMOS consists of three meteorology/transport models and one air chemistry model for
the calculation of photochemical oxidants like ozone.
The meteorology/transport models include REWIMET  a hydrostatic mesoscale Eulerian
model with a low vertical resolution, GESIMA  a nonhydrostatic mesoscale Eulerian
model with a high vertical resolution, and one Lagrangian model.
The air chemistry model is CBMVI dealing with 34 species in 82 reaction equations
for simulating the photochemical processes in the lower atmosphere.
Air pollution simulations require extremely large amounts of computing time.
In order to make the results of case studies available to users within an
acceptable period of time or to enable a smog prediction to be made at all
(computing time less than simulation period), the DYMOS system was parallelized
(Schmidt and Haenisch, 1994). A messagepassing version was developed from the sequential
program and implemented on various parallel computers.
By means of the DYMOS system, contracted by the environmental department of
the state government of Berlin and the ministry for environment of the state
Brandenburg summer smog analyses were carried out concerning the duration of
a measuring campaign in July 1994 (Mieth, Unger and Sydow, 1994).


Commissioned by Greenpeace the influence of emissions caused by traffic in Munich on
the ozone concentration in the Munich area was analysed for a typical midsummer day in
1994 (Smid, 1996).
In the ECOSIM project the DYMOS models REWIMET, GESIMA and CBMIV will be used
for simulating the air pollution dispersion and air chemistry at the
three validation sites. The necessary wind field input will be supplied by the MEMO model.
References
 P. Mieth, S. Unger and A. Sydow, "Scenario Analysis of a Summer Smog
Episode in Berlin", Proc. Second International Conference on Air Pollution,
September 27  29, 1994, Barcelona, Spain.
 M. Schmidt, R. Haenisch,
"Implementation of an air pollution transport model on parallel hardware",
Proc. International Conference on Massively Parallel Processing,
June 21  23, 1994, Delft, The Netherlands.

K. Smid, "Cities cause ozone smog in rural areas", GMDSpiegel, Special:
Simulation Models, Sankt Augustin, 1996.

A. Sydow, "Parallel simulation of air pollution", In: K. Brunnstein and E.
Raubold (eds.), 13th World Computer Congress 94,
Volume 2, Elsevier Science B.V., NorthHolland, 1994, pp. 605612.

POM  Princeton Ocean Model
The Princeton Ocean Model (POM) is an ocean circulation numerical model designed
by A.Blumberg and G.Mellor (1987) for both coastal and open ocean studies.
It is a public domain model that is being used by a large number of research
and academic institutes all over the world.
By June 1996 the POM users group had about 200 members. Due to its ability
to simulate both shallow water and deep ocean dynamics, it has been used for
a variety of applications ranging from small scale coastal management problems
to general circulation studies of the Atlantic Ocean.
POM is a threedimensional, primitive equation numerical model.
The prognostic variables are the three components of the
velocity UVW the temperature T and the salinity S fields.
The equation of state is used for the computation of potential density.
Two more prognostic equations are used to calculate turbulent kinetic energy and
turbulent macroscale. These equations are part of the Mellor  Yamada 2.5
turbulence closure scheme used for the calculation of vertical diffusivity.
Horizontal diffusivities are calculated according to the Smagorinsky formula.
A set of vertical integrated equations of continuity and motion are also solved
to provide free surface variations.


These equations usually called external mode, are solved with a small time
step that
obeys the CFL law; for computer time economy, the 3D equations are solved with a
different (larger) time step using the socalled time splitting technique.
In the vertical, the model uses the sigma coordinate system which is the most
appropriate for areas with significant topographic variability.
The horizontal grid uses curvilinear orthogonal coordinates which are very useful
in applications with complex coastline.
The horizontal finite difference scheme is staggered, the socalled Arakawa Cgrid.
Finally, the model can handle open boundaries through appropriate user
defined boundary conditions. One of the most successful applications of POM
is the East Coast Ocean Forecast System (ECOFS) that has been producing
daily 24hour forecasts on an operational basis for almost three years at
NOAA's National Center for Environmental Prediction.
POM has been extensively used the last few years in a large number
of EU funded (DGXII  MAST) research projects in European Seas
(eg. MAST0039C(A), MAS2CT930055, MAS2CT940107). One of these projects,
the MEDMEX (Mediterranean Model Evaluation Experiment) is comparing the
most well know ocean circulation models, among them POM,
using the Mediterranean sea as a test basin.
For more information, visit the POM home page at
http://www.aos.princeton.edu/htdocs.pom/

