The United Kingdom’s Met Office is one of the world’s leading providers of environmental and weather-related services. Our solutions and services meet the needs of many communities of interest, from the general public, government and schools, through broadcasters and online media, to civil aviation and almost every other industry sector – in the UK and around the world. It is also home to the Hadley Centre for climate research.
The Public Weather Service (PWS) provides a coherent range of weather information and weather-related warnings that enable the UK public to make informed decisions in their day-to-day activities, to optimise or mitigate against the impact of the weather, and to contribute to the protection of life, property and basic infrastructure.
The PWS also fulfils international commitments on behalf of UK Government, and provides research, and forecast and observational data which are essential inputs to a wide range of Met Office services.
We routinely use satellite data from all over the world as input to our weather prediction models. In our forecast offices, up-to-date satellite imagery provides vital information on the formation and dissipation of active weather systems, improving the scope and accuracy of the products that we can offer to our customers.
Our Space Programme team helps the Met Office ensure that meteorology is properly served by national and international space programmes.. We have a diverse range of experts working in research and development, operations, business and finance who help to shape these programmes to meet our needs and keep them affordable.
Observations and how they are used
Global observations amounting to over 40GB per day are gathered from many different sources including satellites, buoys, ships, aircraft, radiosonde (weather balloons), land stations and more. These observations must be gathered together, standardised, quality checked and quickly “assimilated” into computer models.
Numerical Weather Prediction or NWP is the general term for using a computer to analyse data and predict the weather. The Met Office currently runs an NEC SX-6/SX-8 supercomputer, which provides a total system peak performance of over 3600 GFlops. The programs in the supercomputer form a virtual model of the world’s atmosphere. By applying physical laws to the data, the future state of the atmosphere can be predicted. Researchers continuously monitor the performance of the model in order to learn its strengths and weaknesses and to improve future versions.
When the output of the NWP model reaches the operations centre, the predictions from the various models are interpreted by senior meteorologists who understand both the behaviour of the model and the way that weather systems develop. The predictions are turned into a consistent weather forecast using the model output, current observations, satellite imagery and rainfall radar data. These self-consistent data sets can be used by the Operations Centre to form a coherent and comprehensive narrative or “story”.
The forecaster will use this “story” as their brief, augmented by Observations and NWP Model output, to communicate the forecast and offer advice to customers and to the public.
Over recent years operational meteorology and climate research has continued to grow increasingly dependant on high quality NWP models that in turn rely on steadily improving, sustained sources of data. Satellites have increasingly become the primary source of these data.
Evidence of the positive impact from satellite data on the quality of today’s weather forecasts is clear. Direct economic and social benefits can be associated with this improvement both in terms of the general benefits that accrue from accurate forecasting as well as specific benefits through forecasts tailored to support economic sectors such a civil aviation, shipping, civil security, tourism, and health.
A Met Office study in 2005 compared the accuracy of a forecast 500hPa height field for a 5-day period in July 2001, with and without satellite data included. The study found that forecast accuracy can be improved by up to 10 hours by the addition of satellite data (i.e. the quality of the X + 10 hour forecast is as good with satellite data as the X hour forecast without) in the Northern Hemisphere and up to 48 hours in the Southern Hemisphere (where there are fewer ground based observations).
Satellite data are particularly important over the data sparse, oceanic regions where we have no real ground based alternative to observing.
Error rate of Met Office 24 hour and 72 hour forecasts over the North and Southern Hemisphere
The chart above illustrates a Met Office analysis, showing how the quality of meteorological forecasts has improved over recent years, particularly over the Southern Hemisphere where fewer ground based observations exist. The fact that the quality of forecasts in the Southern Hemisphere is now approximately equal to that in the Northern Hemisphere is testimony to the crucial role that satellite data now play in weather forecasting.
Studies have also demonstrated that satellite data reduce the number of poor quality forecasts, often referred to as forecast ‘busts’. By reducing poor quality forecasts, we can minimize the number of predictions that fail to warn us of high impact events.
European countries have chosen to satisfy their shared requirements for data and products from satellites by establishing EUMETSAT, the “European Centre for the Exploitation of Meteorological Satellites”. This collaborative approach is considered to be the most efficient method of satisfying our national requirements. The Met Office, as a partner in the British National Space Centre, represents the UK in EUMETSAT.
EUMETSAT is an Intergovernmental Organisation established in 1986, which now has 20 member states. It establishes and runs the European contribution to the world’s operational meteorological satellite programme. EUMETSAT has a close working relationship with ESA, which is responsible for the development of the first satellite in each series, from initial definition to pre-launch delivery. EUMETSAT are responsible for satellite launches, developing the remaining satellites in each series, ground segment development and all operational activities. EUMETSAT focus on achieving best value for the money.
Primary users of EUMETSAT data are the National Meteorological Services, since satellite observations are an essential input to numerical weather prediction systems. The data also assist the human forecaster in the diagnosis of potentially hazardous weather developments. Research Councils, Universities and other government organisations have a direct interest in data from EUMETSAT for their own research and teaching.
Geostationary Satellites
The Meteosat First Generation was initially designed in the early 1970s and launched in 1977; the Meteosat Transition Programme (MTP) was officially started by EUMETSAT in 1995. Currently Meteosat 6 and 7 are operational. Meteosat 7 is at 57.5 å¡, where it provides Indian Ocean coverage. Meteosat 6 is at 67.5 å¡E providing backup to the Indian Ocean service.
In addition to the provision of images of the Earth and its atmosphere every half-hour in three spectral channels (Visible, Infrared and Water Vapour), a range of processed meteorological products are produced. Meteosat also supports the retransmission of data from data collection platforms in remote locations, at sea and on board aircraft, as well as the dissemination of meteorological information in graphical and text formats.
MSG – Meteosat Second Generation
The first in a series of four new geostationary satellites was successfully launched in 2002; the second was launched in 2005. MSG-1 was renamed Meteosat 8 and MSG-2 became Meteosat-9. Meteosat-9 operates as the primary EUMETSAT geostationary satellite at 0 å¡. Meteosat-8 acts as a ‘hot standby’.
The main instrument on the MSG satellites is the Spinning Enhanced Visible and Infrared Imager (SEVIRI). Among the improvements over the first-generation satellites are improved image resolution, more frequent imagery (15 minutes scan rate) and an increased number of spectral channels (12). The UK developed Geostationary Earth Radiation Budget (GERB) instrument aboard all the MSG satellites contributes important data to climate studies. Search and rescue transponders are also flown on the MSG satellites.
The current MSG satellites should deliver observations and services at least until 2018. EUMETSAT and the European Space Agency (ESA) have initiated joint preparatory activities for the definition and planning of the follow-on Meteosat Third Generation (MTG) system. These activities are already well on their way toward ensuring that the MTG satellites and ground systems will be available by 2015 (the date currently assessed by EUMETSAT as the last when MSG will have a fully backed up system in space).
Polar Satellites
In October 2006, EUMETSAT launched MetOp-A, Europe’s first polar-orbiting meteorological satellite. This new satellite series forms the European contribution to a joint European-US polar satellite system called the Initial Joint Polar System (IJPS). Through this international partnership, EUMETSAT has operational responsibility for the morning orbit, while its US counterpart, the National Oceanic and Atmospheric Administration (NOAA) will cover the afternoon orbits.
MetOp-A was officially declared operational in May 2007, after only six months of commissioning. Data from all 11 instruments are now available, offering unprecedented accuracy and resolution of quantities such as temperature and humidity, wind speed, ozone and measurements of trace gases such as carbon dioxide. The data have already improved Met Office model output, most notably for one and two-day forecasts, especially in the tropics and southern hemisphere. Further improvements in the forecasts are expected.
In addition to the benefits MetOp brings to weather forecasting, the instruments on MetOp contribute data to climate studies. Some of these instruments have over 25 years’ heritage, and long-term data sets such as these are extremely useful for climate related monitoring and research..
MetOp was developed in cooperation with ESA, the French space agency CNES, and European industry. The MetOp satellites provide improved data in several areas including temperature and moisture soundings in all weather conditions, imagery of clouds, land and ocean surfaces, air-sea interactions and ozone mapping and monitoring. An important development is that NOAA and EUMETSAT carry identical instruments on both sets of satellites, to help improve global consistency. Thus the NOAA satellites carry certain European developed instruments and vice versa.
The timescales in creating a new programme of satellites are so long that EUMETSAT is already looking forward to requirements for the post-MetOp era. The new generation of satellites should be available for launch beginning in 2019, and should be fully operational by 2020.
The user consultation process has already started and instrument concepts are being analysed. The first step was to assess the requirements in the timeframe beyond 2020 and prioritise them. These requirements are now being considered against the technology available. The Post-EPS Mission Expert Team is performing this task. The next stages are feasibility analysis, spacecraft design and production.
So next time you check the weather forecast for your local area, bear in mind how much goes on behind the scenes, and how observational data is at the core of the process.
Stewart Turner, Space Programme Manager
Met Office FitzRoy Road Exeter EX1 3PB UK
Tel: +44 (0)1392 884260 Fax: +44 (0)870 900 5050
stewart.turner@metoffice.gov.uk | www.metoffice.gov.uk
Further Information
Richard Dumelow (2005). Observing System Experiments using the Met Office three dimensional variational assimilation scheme, Forecasting Research Technical Report No. 461 http://www.metoffice.gov.uk/research/nwp/publications/papers/technical_reports/2005/FRTR461/FRTR461.pdf
Stephen J. English (2006). The value of passive microwave satellite observations to NWP, Forecasting Research Technical Report No. 484