Transcript
FUTURE
TOUGH
A primary goal in TOUGH was bringing the state of the art in ground-based GPS meteorology to a mature level, rendering it useful to operational meteorology, hence improving European weather forecasts.
Danish Meteorological Institute (coordinator) Swedish Meteorological and Hydrological Institute Met Office, UK Instituto Nacional de Meteorologia de Espania Univ. degli Studi di L’Aquila, CETEMPS, Italy Royal Netherlands Meteorological Institute Finnish Meteorological Institute ACRI-ST, France Chalmers Univ. of Technology, Sweden Norwegian Mapping Authority Agenzia Spaziale Italiana Inst. d’Estudis Espacials de Catalunya, Spain Swiss Federal Office of Topography Res. Inst. of Geodesy, Topo. & Cart., Czech Rep. Technische Universiteit Delft, Netherlands
A meteorological GPS observing system: In the new E-GVAP project (EUMETNET GPS Water Vapour Programme), started April 2005, 11 European national met offices are in collaboration with geodesists transferring the TOUGH and COST716 GPS network into an observing system for NRT GPS ZTD data collection for operational use. More countries will gradually join, and the network will extent and densify. TOUGH recommendations will be used to optimize the system.
Targeting Optimal Use of GPS Humidity Measurements in Meteorology
Use of GPS delays in meteorology: Many European met offices now plan to start utilising NRT GPS ZTD data in their operations. This will be done in various ways: 1) Validation and improvement of weather models via comparison to GPS observations. 2) Data assimilation of the GPS data into numerical weather prediction models, improving the forecasts. 3) As a tool for now-casting (short term forecasting), via maps integrated water vapour made from GPS ZTD observations. Climate monitoring: For climate monitoring the long term stability of measurement series is of vital importance. The results from TOUGH regarding long term biases, co-ordinate system biases, and inter-comparison of different GPS processing methods will help improve stability. GPS slant delays: GPS slant delays represent a next step in ground based GPS meteorology. They provide additional information about the local variability of the atmosphere. In TOUGH, GPS slants were confirmed to be a promising type of new meteorological observations. More slant delays per ground station will become available when the European Galileo satellite system is launched. Optimal use of GPS slant delays in meteorology requires further research. DMI, March 2006
FINAL RESULTS Collaborating organisations COST ACTION 716 University of Purdue, USA GeoForschungsZentrum Potsdam, Germany European Commission, Brussels, Belgium CONTACT POINTS www: tough.dmi.dk email:
[email protected]
TOUGH was a shared-cost project (contract EVG1CT-2002-00080) co-funded by the Research DG of the European Commission within the RTD activities of the Environment and Sustainable Development subprogramme (5’th Framework Programme).
The principle of GPS meteorology
TOUGH RESULTS
About 24 active Global Positioning Satellites (GPS) orbit the Earth. They purpose is to enable fast positioning by use of GPS receivers. However, the atmosphere bends and delays slightly the GPS radio-signals. This effect can be be measured, and the delays are directly related to properties of the atmosphere of importance to weather forecasting. In the case of ground-based receivers these are the pressure at the GPS antenna and the water vapour above. Utilisation of GPS derived atmospheric delays to improve weather forecasting and climate monitoring we call GPS meteorology. How to utilise GPS observations in meteorology in an optimal way is an area of intense scientific research. TOUGH is an inter European project, launched in order to address key issues in ground based GPS meteorology. TOUGH started February 2003 and ran until January 2006.
In TOUGH we have made and tested methods to improve use of ground-based GPS data in numerical weather prediction (NWP) and climate monitoring. Among other things we have: • Improved our ability to determine in near real time (NRT) good estimates of the zenith total delay (ZTD) from GPS observations. During the course of TOUGH the timelag between GPS observation and NRT ZTD estimation has gradually decreased. Zenith delay Likewise the quality of the NRT ZTD estimates Slant delay has gradually improved. Earth Both compared to estimates based on alternative data, and comAtmosphere pared to more precise, post processed GPS delay estimates. The different softwares for estimation of NRT GPS ZTDs were found to produce comparable results. • Studied long term biases and their relation to cut off angle, GPS antenna calibration, environment, and reference frames. • Made recommendations for a future European NRT GPS observing network. • Studied error correlations for GPS ZTDs in space and time, and developed a method for correction.
• Extensive impact studies have been made to investigate and optimise the benefit of using ground-based GPS-data in NWP. It is found that forecasts made with NRT GPS data are on average better than without. In particular the GPS data improve forecasts of medium to heavy rain, in some studies also properties such as surface temperature, pressures, and cloudiness. There are also examples of negative impact. − − (EWGLAM stat.lst., ECH anal.) mslp, units in Pa 200 GGG GGN 150 DDG DDN 34882
lution model is green/black 5
100
0 0
6
12 18 24 30 36 42 48 forecast length
0
6
12 18 24 30 36 42 48
length high res. forecast model with GPS.
2mT, units in K
Height at 500hPa, units in m 25
3 GGG GGN DDG 2 DDN
GGG 20 GGN DDG 15 DDN
1
35470
0
4102
Precipitation over 12 hours 10 on 2003-10-03. 5 0 −5Upper
−1 0
6
10mW, units in m/s 2.5 GGG 2 GGN DDG 1.5 DDN
figure is observa-
−10tions. Middle figure is fore12 18 24 30 36 42 48 0 6 12 18 24 30 36 42 48 forecast length cast withforecast GPSlength data. BotHeight at 250hPa, units in m 40tom figure is forecast withGGG GGN GPS data. 30out DDG 34866 20 DDN 4069 10Black-blue-yellow-red
runs from no, over light, to heavy 0 −10rain.
1 0.5
Innovation correlations Model fit (innovations) Model fit (GPS estimates) Model fit (Hirlam forecasts)
with/without GPS, low res. 0 model is red/blue. An improvement in bias is seen for −5
50
Horizontal correlations of the HIRLAM−GPS ZTD innovations
0.9
(EWGLAM stat.lst., ECH anal.) 4091 Height at 850hPa, units in m Statistical verification of 15 GGG GGN surface pressure (July 2003). 10 DDG DDN and bias. RMS High reso-
0
0.8
−0.5
Correlation coefficients
0.7
Spatial error correlation for the GPS -NWP ZTD offsets. Red line is the
0.6 0.5 0.4 0.3
estimated error correlation for the GPS ZTDs.
0.2 0.1 0 −0.1
0
200
400
600
800 1000 Site separation, km
1200
1400
1600
1800
• Developed methods for estimation of GPS slant delays, estimated GPS slants for a network in the Netherlands, determined their error characteristics, and made tools for assimilation of GPS slant delays in NWP models. The tools were proven to work properly in two data assimilation impact studies.
Fig. 6. Horizontal correlations of the ZTD innovations for a one year period (∗). The dash-dotted line represents the contribution of the forecast errors correlations for ZTD, estimated using the NMC method for HIRLAM at a resolution of 22 km. The dashed line shows the best-fit composite model for the innovation correlations. The solid line represents the remaining term, corresponding to the GPS error correlations. Horizontal correlations of the HIRLAM−GPS ZTD innovations
0.9 0.8
GPS receiver sites, January 2005
0.7 Correlation coefficients
GPS receivers
0.6 0.5 0.4 0.3 0.2
Innovation correlations Model fit (innovations) Model fit (GPS estimates) Model fit (Hirlam forecasts)
−20 0
6
12 18 24 30 36 42 48 forecast length
0
6
12 18 24 30 36 42 48 forecast length
• Made recommendations regarding the use of NRT GPS data in operational weather forecasting. TOUGH User Workshop A TOUGH User Workshop was held at the UK Met Office in September 2005, to inform a wider audience about the results obtained in TOUGH. The workshop was attended by specialists in GPS-meteorology and GPS data processing. The presentations from the workshop are available as electronic proceedings at http://tough.dmi.dk.
