Report on
Second CLOUDMAP2 ROADSHOW Workshop
held on October 7th, 2003 during
the 25th EWGLAM and 10th SRNWP Meetings in Lisbon, Portugal
Authors:
Jean Quiby (MeteoSwiss)
Jean-Marie Bettems (MeteoSwiss)
Hans Roozekrans
(KNMI)
The main objective of the CLOUDMAP2
project is to develop and to introduce new satellite derived cloud products
in the meteorological and climate research communities. The essential success
factor to meet this objective is to directly communicate with the anticipated
end-users. As already proven in the CLOUDMAP1 project the concept of a “roadshow”
along relevant user institutes / communities is a very effective way to promote
the project results and to obtain feedback. This roadshow is organised by
KNMI and embraces a total of five workshops This
second roadshow workshop was an integrated part of the 25th EWGLAM and 10th SRNWP Meetings in Lisbon, Portugal.
The focus of this second roadshow
workshop was to evaluate the potential use of cloud observations in general
and CLOUDMAP2 products in particular in numerical weather prediction (NWP).
The yearly EWGLAM and SRNWP meetings are attended by the NWP community working
in the field of (mostly regional) NWP modeling. This meeting was therefore
an excellent opportunity for this roadshow meeting. Around
80 people attended this workshop (the names are listed in the appendix).
The workshop started at 13.30 AM and ended at 15.30 AM.
The CLOUDMAP2 project team
was represented by:
Hans Roozekrans (KNMI, The Netherlands)
Jean Quiby (MeteoSwiss, Switzerland)
Hans Roozekrans of KNMI started
the workshop with a half-hour presentation of the C2 project and products.
The presentation included an overview of the project partners, a description
of the objectives and the deviations from the C1 project. Also NWP work done
at SMHI and KNMI in the framework of CLOUDMAP2 was presented. The C2 Web
site was named as a valuable
reference for further information (http://www.cloudmap.org).
After this presentation Hans Roozekrans
started the discussion part by presenting the focus of this
workshop, namely the potential use of cloud observations
in NWP:
·
Assimilation
of cloud observations in NWP models
·
Use of cloud observations
for NWP model monitoring
·
Use of cloud observations
for parameterisation work
A total of 8 q
uestions/topics
were prepared to lead the discussion. Questions and a summary of the answers
are reported below. The minutes of the discussion were kindly written by
Jean Quiby and Jean-Marie Bettems of MeteoSwiss.
1. What are the most relevant EO derived observations for NWP?
How important are cloud observations
for NWP?
The
most important satellite data today are the conventional ones or, in other
terms, the ones used operationally. Primarily the temperature and water vapour
profiles derived from the ATOVS sounders of the NOAA satellites. Secondarily
the METEOSAT cloud winds. The future of these data has to be assured.
From
the non-conventional satellite data, the most important for the global models
are or will be the surface winds derived from the QuickSCAT satellites over
seas and oceans.
For the Limited Area Models (LAM) the most relevant EO derived data will be the ZTD (Zenital Total Delays) deduced from the GPS (Global Positioning System) satellites. From these delays, the vertically integrated water vapour can be computed.
Really
important today is only the cloudiness of the geostationary satellites when
it is used to derived winds. At some national weather services (NWS), the
model cloudiness is operationally verified with METEOSAT images.
2. Will
radiance-based data-assimilation be the future trend for all NWP models (global
and regional)?
A
look into the past will strongly influence the answer to be given to this
question.
Let
us consider what happened with the SATEMP data: this product (temperature
profiles) has been largely used at the beginning until the NWP satellite
specialists proved that the direct assimilation of the radiances gives better
results. Thus the answer to this question is “yes” for the global models
as well as for the regional ones. Assimilation of radiances will remain the
most elegant way to use the satellite information.
3. If
so, is there still a role for EO products (retrieved geophysical parameters)
in NWP (e.g. for verification purposes)?
It
is presumably correct to anticipate that these products will have the same
destiny as the SATEM data. In the first years of their existence, they will
be used. Then the NWP groups will prefer to have the primary data (for example
radiances) to develop these products themselves. The trend to use primary
data is already visible for the GPS data: several NWP centres already prefer
to compute the IWV (integrated water vapour) themselves directly from the
ZTD (Zenital Total Delay) instead of receiving from the GPS processing centres
the IWV.
What about the MODIS derived
products?
From
the MODIS radiances, many products are now operationally derived in the framework
of the CLOUDMAP2 project. Is the NWP community interested in these products?:
=
CTP (Cloud Top Pressure), CTH (Cloud Top Height) and CTT (Cloud Top Temperature):
It is too early today to say whether these parameters will be assimilated
in the future. The only use that can be foreseen in the near future is for
model validation. Example: has the model a tendency to have cirrus cloud
too high or too low?
=
Cloud water: From the NWP point of view, cloud water can only be assimilated
if the other parameters like the vertical wind component or the relative
humidity are correct, otherwise the cloud will
disappear (in case of downward wind in the model) or evaporate (if the relative
humidity is too low).
It
has nevertheless been stressed that we should not wait till we have "perfect"
analyses to introduce these new parameters. Even today new parameters can
still bring some improvement, at least in the first hours of the forecasts.
4. The
current EO observation resolution is 1 km. Is there a potential use for such
detailed data?
Contradictory
opinions have been expressed here.
Arguments
against:
-
Already today we do not use for the global models the ATOVS data with their
full horizontal resolution. Only a subset of the possible
profiles are used. No averaging or super-observations are made today.
-
The amount of data will become gigantic and give a real problem to the National
Weather Services: the overload in communications, processing and archiving
will become disproportionate in the resources necessary for the production
of numerical forecasts.
Arguments
in favour:
-
the horizontal resolution of the NWP models is
steadily increasing. Consequently the spatial density of the observation
must also increase in order to have the small-scale features in the analysis.
When the regional models will have an operational resolution of 1 to 3 km
they will need an EO observation resolution of 1 km.
- Very high resolution maybe useful
for model validation.
5. CLOUDMAP2
aims to provide independent cloud observations. How valuable/important is
this for NWP?
It is definitely important. In order to determine the heights of the winds derived from cloud motion as yielded by the geostationary satellites, information from global models are used. But these models assimilate the same satellites winds. This feedback is a negative feature in this process. A model independent procedure for the determination of the cloud wind heights would be a great advantage. This is theoretically possible with the use of the stereo-matching technique with sensors like MISR or ATSR2.
6. What
is the role for ground based RS cloud data in NWP, e.g. the valuable ARM
sites around Europe?
Very
few comments have been made. It is difficult to answer this question for
the future. For the present time, no ground based RS data are used operationally.
Maybe the NWP community will start to use them for parameterisation development
work and validation purposes.
7. Error
characteristics of observations are important for NWP. Can satellite observations
contribute to derive theses?
Yes. But this property is not
restricted to the satellite observations. Any observing
system can help to derive the error characteristics of another observing
system. The specification of the error characteristics of a new observing
system can be best derived when it is confronted to several other observing
systems.
8. Is
more ocean information required, as land is better covered by synops/surface
observations?
Oceans
are poorly observed. The only observing system able to fill these large data
sparse areas is the space observing system. Both the sounders and the imagers
can contribute, as well as active sensors like the ones mounted on QuickSCAT.
But many satellite observations, like the profiles derived from the sounders,
are best used when they can be “anchored” to a surface pressure or a geopotential
surface height. Thus in situ measurements remain necessary. The great advantage
of the oceans when compared to the land areas is the radiative homogeneity
of the surface.
In relation
to this what will be the value of satellite observations in the context of
a degrading “conventional” observation network?
Or: will the satellite be able
to replace the conventional observations?
The
number of the classical observing stations, surface (SYNOP) and upper-air
(TEMP), has already diminished in Europe and worldwide
and will continue to diminish (cf. the EUCOS plan). Will the satellite be
able to fill the gaps?
To fill the gaps, the NWP community has no choice: the use of the satellite information in the determination of the initial conditions of their models will increase where it is possible. With the rarefaction of the upper air sounding stations, an effort should be made for a stronger use of the AMSU B or AIRS data as a replacement for the loss of the humidity profiles. The use of the SSMI, MODIS or GPS data, which allow a determination of the vertically integrated water vapour, should also be strongly encouraged.
Important
statement: The European short-range NWP Community does not support the thinning
of the conventional observing network, as it will - with the increase of
the model resolution - further aggravate the ratio "number of classical observations/number
of grid points".