Report on the WG3 meeting, September 27, 1999, Brussels
By: Sylvia Barlag (KNMI, Chair)
Participants:
Sylvia Barlag (NL), Siebren De Haan (NL), Nils Gustafsson (S), Jennifer Haase (F), Marc Higgins (UK), Hans
Huang (Dk), Christina Köpken (D), Antii Lange (SF), Dave Offiler (UK), Jean Quiby (CH), Henrik Vedel (Dk), Jordi
Villa (Es)
Composition of the Working Group
The chair(wo)man proposed that the following persons are permanent working group members.
Barlag (NL, chair)
Offiler, Higgins (UK)
Gustafsson (S)
Köpken (D)
Vedel (Dk)
Haase (F)
Quiby (CH)
Lange (SF)
Rius (Es)
{Heimo (CH) }
{Pailleux (F) }
In the philosophy of the COST co-operative actions, participation in the working group is open to everyone
wishing to contribute to achieving its goals. For the working group to have profitable interaction the group
consists best of between 5 and 10 persons, having two representatives per country maximum. The people in the
list are all working in the field. During the plenary working sessions, the representatives of the UK, Sweden,
Germany and Denmark presented their work with GPS relevant to meteorology. The representative of Spain,
Rius, is also a participant in WG2 and will especially act as a liaison. It is anticipated that in future the composition
of the group may change, when national meteorological offices start to use the GPS meteorological data.
Goals of Working Group 3
The goals of the WG3 were reminded to participants as the focus for the work to be done:
1) User requirement analysis for all three user communities (NWP, Climate, Climatology)
2) Development of an approach for:
a) NWP assimilation
b) Use in climate research and prediction
c) Use in climate monitoring (climatology)
3) Impact and sensitivity assessment
4) Data specification definition for user communities
Work Plan 1999-2002
In drafting the work plan it was assumed that WG3 will exist until summer 2002. The programme foreseen, firmly
based on national activities, is shown below. Details of activities and their timing are only given for the first phase.
In time the activities of the other phases will become better specified.
1999/9 – 2000/7
Preparation Phase
1999/9 – 2000/1
UR analysis
1999/9 – 2000/1
Recommendations for demo network(s)
1999/9 – 2000/7
Preparation for data assimilation systems
2000/7 – 2001/7
Trials Phase
Assimilation and usage trials
Impact studies
2002/7 – 2002/7
Near-real-time demo Phase
Parallel forecast runs in n.r.t. mode
User Requirements Analysis
WG3 decided to provide a draft analysis of the User Requirements for GPS data, discuss this draft among an
expert group and present the results to WG2 before or at their next meeting, March 4, Matera (I). The
requirements analysis will start from the general User Requirement Statement for Meteorological Data, drafted by
WMO, and proceed to incorporate the capacities of the ideal and the existing GPS network configurations.
Preliminary recommendations for demo networks
The following recommendations were made by WG3 for the network(s) to be useful for meteorology and climate:
1) The data expected from the network should cover (at least) Europe and the Northern Atlantic as much as
possible (island stations!). This could be achieved with the EUREF network, enhanced with national
networks.
2) The WAVEFRONT processing recommendations should be followed.
3) Two data qualities are necessary:
a) As needed for near-real-time data assimilation
b) For climate use (i.e. post-processed)
4) The CLIMAP formats, possibly amended, should be followed for distribution of data.
Preparations for data assimilation systems
In the participating countries preparations have started, or will be started, to assimilate ground based GPS data in
NWP models. In the plenary the preparatory work done by the UK Met Office, by the Deutscher Wetter Dienst, by
the Swedish Institute for Meteorology and Hydrology and by the Danish Met Office was presented. These
activities cover different aspects of the preparatory work. A presentation by an invited expert from the US could
not take place due to non-delivery of the required visa for the speaker (Mr. M. Pondeca). The titles of the
presentations were:




"Derivation of delays from model data with orographic imperfections", by Henrik Vedel (DMI).
"Validation of IWV from DWD numerical forecast models using GPS-IWV, water vapour radiometer, SSM/I
and radiosonde measurements", by Christina Koepken (DWD).
"Simulated Assimilation of GPS TZD at UKMO", by Marc Higgins (UKMO).
" Validation of GPS total delay against HIRLAM, multivariate structure functions for assimilation of GPS total
delay, and preliminary assimilation results", by Nils Gustafsson (SMHI).
In the presentations and the following discussion several problems were addressed.
Corrections for GPS station height or pressure level must be made when preparing the data for assimilation in
NWP models with orographical imperfections. Validation results are very encouraging and show the potential
value of the data. There is a need for good site-dependent bias control and accuracy estimators. Present NWP
models use different data assimilation techniques, most probably leading to different impacts of the data. The
strength of the GPS data should be found in their dense time intervals in comparison to balloon soundings that
are still the most important data source for NWP. Both measurement types are concentrated over land. Several
assimilation techniques still in use can not cope with this high time resolution. For further development of the GPS
data assimilation techniques the main emphasis should be on improving the assimilation techniques per se and
on the derivation of error statistics, as well for the GPS observable as for the model. A specific question that was
raised in this context is whether large spatial error correlations could be circumvented by utilising horizontal
gradients.
Future plans
The working group further discussed the plans for assimilation preparations until summer next year:
 UK (UKMO) will continue their simulations and will be ready for near-real-time assimilation trials by summer
2000. The use of slant delays will also be studied.
 Sweden (SMHI) will continue to work on the present study contract into assimilation of GPS data in the
HIRLAM NWP model. This should deliver result by summer 2000.
 Denmark (DMI) will continue their efforts in the MAGIC project, in the context of the HIRLAM model.
 Germany (DWD) will start assimilation preparations with the German NWP Model from start 2000.

The Netherlands (KNMI) will apply for a study contract for assimilation of GPS data in the HIRLAM model, to
start mid 2000.
 Finland (FMI) will start investigations using their national network data.
 Spain (IEEC) will concentrate on non-real-time studies and applications. For the real-time applications the
Spanish Met Office (INM) will be contacted.
 France (ACRI) will continue to work on the MAGIC project. A future participation of Météo France is
anticipated.
The Swedish, Danish, Netherlands, Finnish and Spanish meteorological institutes work together on the
development of data preparation and assimilation techniques in the context of the HIRLAM project.
Preliminary request for data
With consideration of the work plan the WG3 considered the following data were needed to achieve the goals:
1) 1 month of data in summer 2000
2) 1 month of data in winter 2000/2001
3) continuous data during a TBS period in 2001/2002
For climate use longer data sets with data qualities as mentioned under Networks 3a) should become available
as soon as feasible.
Remarks
The following was stressed by WG3:
 As many error information as available should be distributed, either with the data, or in other forms. These
are e.g. quality data or spatial and timely correlation data.
 Pressure data, when measured at the GPS site, should be made available for climate research and
monitoring purposes.