Submission of the following Expression of Interest by
the Members of the Short-Range Numerical Weather Prediction Programme
In the frame of a Network of Excellence:
Improvement of Weather Forecasting and Risk Assessment
in Europe by Very High Resolution Simulations, Ensemble Forecasting and
Modelling System Developments
Presented by the National Weather Services of the
following Consortia:
ALADIN-LACE Consortium
Austria, Belgium, France, Portugal, Bulgaria, Croatia,
Czech Republic, Hungary, Poland, Romania, Slovakia, Slovenia
COSMO Consortium
Germany, Greece, Italy, Switzerland
HIRLAM Consortium
Denmark, Finland, Iceland, Ireland, The Netherlands,
Norway, Spain, Sweden
and by the
NWS of the United Kingdom of Great Britain
Text prepared by:
Gerard Cats (KNMI, The Netherlands)
Terrence Davies (UKMO, Great Britain)
Jean-François Geleyn (M-F, France)
Nils Gustafsson (SMHI, Sweden)
Jean Quiby (MeteoSwiss, Switzerland)
Need and Relevance
The need for better regional, even local, short-range
(up to 48, better 72 hours) weather predictions is increasing in many circles
of our society, not only in the agricultural, industrial and economic circles
but also in relation with outdoor recreational activities.
But in the first place, risk forecasting has to de
improved, at the foremost place the risk for human life and heavy damages. In
our modern society, also the risk of disruption has to be better assessed:
disruptions in water and power distribution, disruptions in surface and air
transportation. Heavy rain, snowfalls, strong winds and fog are all weather
elements causing disruptions.
The weather elements have to become better forecast
geographically at the regional scale as well as temporally during the day.
The development and implementation of the three
following new techniques will be necessary for a decisive short-range, regional
weather forecasting improvement. They are all three equally important:
- a very
large increase in the resolutions of today's NWP models
- the
use of the ensemble forecasting technique
- the
development of a Community comprehensive modelling system.
The challenges of the very high resolution
From its very beginning and without any interruption,
the NWP technique has witnessed a steady increased in model resolution. It is
realistic to envisage for the next 10 years resolutions of 1km for regional and
local models.
Let us see what the scientific issues and problems are
for
- the data assimilation, i.e. the determination of the
initial conditions
- the numerical aspects, i.e. the techniques used to
solve the basic system of differential equations
- the physical aspects, i.e. the mathematical
representation of the sub-grid atmospheric processes.
Some Scientific Issues on Data Assimilation:
(1) How do we couple the high-resolution model data
assimilation to the data assimilation of the larger scale model providing
lateral boundary conditions? Do we use information from the larger scale model
assimilation as constraints in the high-resolution model data assimilation?
Should we attempt to control also lateral boundary conditions in the
high-resolution model data assimilation?
(2) What is the optimal design of data assimilation
for very high resolution forecasting? 4-dimensional variational techniques have
been very successful for synoptic scale data assimilation, but will this also
be the case for very high-resolution models? If we have to carry out 4D-Var at
the same scale as that of the model, the so-called "regularised"
parameterisation sets will have to evolve while facing new challenges. Indeed
the latter will play a more important role in tangent linear and adjoint
computations since the leading role of dynamical forcing disappears at these
scales. But they may at the same time rely less and less on similarities with
the physics package of the main model, whose internal increased complexity will
make any stable linearisation attempt worthless. Thus we are entitled to ask
ourselves whether the non-linearities of the physical processes will not limit
the usefulness of tangent-linear and adjoint models.
Optional assimilation techniques, for example ensemble
Kalman filters, may be able to handle these non-linearities and should be
investigated.
(3) Due to the large degrees of freedom of
high-resolution models as compared to the number of observations, assimilation
structure function to spread the observed information spatially will certainly
be needed. Flow-dependent structure functions will probably be needed to
separate different mesoscale flow regimes, and a spatial dependency to better
handle, for example, orography effects will
probably also be needed.
(4) The relevant dynamical-physical balances to
constrain the assimilation at the mesoscale need also to be investigated. Moist
processes probably need to be included in these balance conditions. As it is
the case for synoptic scale assimilation, there may be possibilities to apply
statistical balance constraints in the spatial dimensions, but it may also be
possible that we need to be restricted to filtering constraints in the time
dimension. Such filters essentially prohibit unwanted, for example high
frequency, variations.
(5) The assimilation related to moist processes will
become crucial, in particular since many observation systems will provide high
resolution information mainly for clouds and precipitation. Furthermore, these
observing systems are associated with complicated error structures, with
weather radar reflectivity as one example. These observation error structures
need to be modelled.
(6) Since many mesoscale and local weather systems are
forced by the lower boundary condition, a proper assimilation of surface
variables is needed for very high-resolution models. The surface variable
assimilation needs to be able to mix remote sensing information (e.g. satellite
images) with observations from the relatively sparsely distributed in-situ
measurements (e.g. surface automatic stations).
Some Scientific Issues on Numerical Aspects:
There are a number of different options. The main
split is between semi-Lagrangian advection with semi-implicit timestepping and
Eulerian advection with either explicit or semi-implicit timestepping.
There are also differences in underlying grids, in
variable staggering and in the choice of the variables themselves. It is
unlikely that we will be able to say which scheme is best unequivocally or even
which combination of components will perform best.
Comparison projects have not been very developed in
the past, with some exceptions (the December 1999 storms). Centres tend to do
their own internal assessment and are usually content to show year-on-year
in-house improvements.
Examples of other open issues:
- What is the lowest resolution (largest gridlength)
we need to produce useful forecasts of severe local weather?
- How fine must be the vertical resolution?
Some Scientific Issues on Physical Aspects:
The so-called «physical» part of the model equations
will undergo an important transformation when going to the scales where
non-hydrostatism is crucial for the dynamics, since one shall have to get rid
simultaneously of two currently widely used key assumptions:
- the forcing of parameterisation calculations will
cease to be treated as horizontally homogeneous, which means that the three
space dimensions will play a role in the computation of turbulent and radiative
fluxes
- there will be less and less need to take into
account details of the flow organisation internal to the mesh-box. Typically,
organised convection and details of the sub-grid scale underlying topography
will cease to generate fluxes of a magnitude comparable to what the explicit
computation will be producing between neighbouring grid points.
This double revolution in the perception that NWP code
designers have of the physics of the atmosphere will also have a strong
influence on the way the parameterisation codes are treated algorithmically:
- old sources of inaccuracies and of latent instabilities
will disappear, while one can safely bet that they shall be replaced by new
ones;
- the organisation of the time step itself (in which
order and with which input are the differing items called) may have to be
reviewed.
The use of the ensemble forecasting technique
Of the three new techniques that will be necessary in
order to meet the meteorological challenges of the future, the ensemble
technique for short-range, meso-scale forecasting is still in its infancy. The
very first European workshop on this topic will take place next autumn in
Spain.
But there is a profound reason why one must use this
technique:
the atmospheric processes or, on the large scale, the
weather systems are only partially deterministic phenomena. The meteorological
processes are chaotic systems, in the sense given to this term in theoretical
physics. But now we apprehend meteorology, particularly with the classical NWP
technique, by a pure deterministic method. This cannot be the best way.
The ensemble forecasting technique is already
successful on the global scale. There is no intrinsic scientific reason why
this method cannot be equally successful for high resolution limited area
models.
The ensemble forecasting technique allows formulating
forecasts in probabilistic terms. That is the basic property on which methods
for risk assessment can be developed.
The development of a common modelling system
The objective of this part of the project is to build
an infrastructure to enable an effective European collaboration for the development
of a very high-resolution numerical weather prediction system.
A high quality development of such a system requires a
concerted effort of research into the physical properties of those systems (see
Point "The challenges of the very high resolution"). The required
intensive interactions between researchers can only be provided for by a state
of the art infrastructure. For effective collaboration across Europe, the
infrastructure should
1.
support facilities for exchange of knowledge between researchers
2.
facilitate exchange of researchers between participants
3.
facilitate exchange of software components
4.
provide access to distributed data bases and other compute facilities.
A variety of developments in the field of information
technology will provide basic components to build the required infrastructure
on. These developments include the results of three current EU projects
= PRISM
(supportive to objective 3 above)
=
DataGRID and EuroGrid (supportive to objectives 3 and 4)
and new web-based technologies (supportive to all
objectives), like emerging standards for remote procedure invocation (e.g.
SOAP, www.w3.org/TR/SOAP; WSDL, www.w3.org/TR/wsdl) and data exchange (XML).
For effective exchange of researchers between
participants (objective 2), novel methods to design and write graphical user
interfaces must be applied.
This enumeration of relevant developments is far from
complete, but it is sufficient to demonstrate that there is a wealth of
developments, which have to be done.
This infrastructure will be built with components
developed in earlier projects, both in Europe and in other parts of the world;
where components or the "glue" between components are missing they
will be developed.
The infrastructure should be flexible enough not to inhibit
the deployment of any meteorological component, to allow competitive
developments. It should also be flexible enough for implementation in all
participating institutes. This implies that it should not compromise their
operational procedures, or, preferably, even be able to support those
procedures. It also implies that the new infrastructure should not be based on
expensive proprietary software.
The primary aim of the system to be developed is to
facilitate European cooperation on research on very high resolution NWP. There
is a genuine research effort contained in this part of the project, as it aims
at developing novel methods to support cooperation in research.
A second research effort in this part of the project
is to design the target infrastructure in such a way that it supports a wide
range of implementations of NWP systems, both for research and operations.
Excellence
Today's Numerical Weather Prediction (NWP) models have
reached a degree of complexity that makes it difficult for a country, even for
a large country, to develop and test with its own resources all the modules of
a leading edge numerical model for the simulation of the atmospheric processes,
inclusive the difficult determination of adequate initial conditions from the
observations. As a consequence, groups of NWS have formed to share the work of
the development and subsequent improvement of a NWP model.
We have today in Europe four groups, called Consortia,
each one centred on a model.
These Consortia are: ALADIN, COSMO, HIRLAM and the
UKMO. The list of the participants in each Consortium is given at the beginning
of this document.
The work done inside each Consortium can be qualified
of very good; this is proved by the fact that our 4 meso-scale Limited Area
Models (LAM)
- the ALADIN model of the ALADIN Consortium
- the Local Model of the COMO Consortium
- the HIRLAM model of the HIRLAM Consortium
- the LAM UM of the UKMO
are top models, leading models when compared to
similar models in other parts of the world.
This shows that there is a profound know-how and
remarkable skills in our Consortia supported by top European scientists filling
all the present needs for methodological and theoretical expertise.
The exchange of information and some common actions
between the Consortia are co-ordinating in the EUMETNET Short-Range NWP
Programme (http://srnwp.cscs.ch).
This Programme is responsible for series of workshops
on the most actual and/or most difficult topics related to the short-range NWP
on the meso-scale (srnwp.cscs.ch -> LC Workshops for all the past and future workshops).
Two of the 4 Consortia organise each year a Seminar of
several days for young scientists, many of them PhD students. These Seminars
are very successful (For more information, see srnwp.cscs.ch -> Education).
It is very important to consider that the scientific
developments in the Consortia is not only due to the NWS involved, by is also
due to the contributions of a significant number of Universities: many European
NWS work together with one or more universities of their country.
Some examples:
- the German Weather Service with the University of
Bonn (Department of Meteorology)
- the Swedish Meteorological and Hydrological
Institute with Stockholm University (Department of Meteorology)
- Meteo-France with the Paul-Sabatier University of
Toulouse
- MeteoSwiss with the Swiss Federal Institute of
Technology (Institute for Atmosphere and Climate)
- the UKMO with Reading University (Institute of
Meteorology)
- DNMI with the Oslo University.
The National Weather Services grouped in their 4
Consortia together with the Universities they are working with form the
strongest network in atmospheric sciences in Europe, a true Network of
Excellence.
And that Network has two great assets: it already
exists and works well; it has the critical mass required for a project of that
size.
But this Network - surely one of the strongest in the
world in its field - has not presently the personal capacities and the
financial strengths for an integrated, full-scale development of these 3 new
technologies (very-high resolution, ensemble forecasting and comprehensive
modelling system).
A strong external financial support is needed.
Such a support could allow a decisive step forward in
weather forecasting, inclusive risk assessment that would respond to the
legitimate expectations of the future.
Priority Thematic Area, Partnerships, Management of
the Project
This Expression of Interest fits exactly in Thematic
Area 1.1.6.3, sub-area "Operational forecasting and modelling" as
well as, in the sub-area "Complementary research", with the topic
"Development of advanced methods for risk assessment".
Next to the reinforcement of the collaboration between
the NWS forming the four Consortia for NWP in Europe, it is also a strong
intention of this Project not only to reinforce the collaboration between the
NWS and the Universities they are already working with, but also to enlarge the
collaboration of the NWS to other Universities in order to draw the maximum of
the European research potential in meteorology.
We think that a project of this magnitude should be
professionally managed. But the work of the Project Manager must be supervised
by a Scientific Committee made of the most prominent scientists active in the
Project, half coming from the NWS, half from the Universities.
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