Global Observing

Many weather systems that affect the UK have their origins far away from our shores. The typical low pressure system that gives us rain and strong winds will have crossed the Atlantic in the previous two or three days from its origin in the eastern Atlantic, or even further afield. Its track is governed by strong winds of the jet stream, at levels where aircraft cruise, which in turn are influenced by the structure of the atmosphere on planetary scales. Forecasts of weather on all time scales, other than the very short term, require observations from most of the globe. Weather is a global phenomenon which requires collaboration between all nations of the world if we are going to make any progress at all.

WMO, or the World Meteorological Organization, is the international body that provides the collaborative framework that is so essential for meteorology. It was founded in 1873 and today comprises of 189 member states and territories which, to all intents and purposes, includes all the countries of the world.

Through WMO, countries agree on how observations should be made and how the global data should be exchanged rapidly so that it reaches each computing centre and forecast office in time to be of use. Countries also agree on filling the gaps in data between one country's observing system and another's. Collaboration in deploying observing systems over the large expanses of the world's oceans is particularly important.

This map of the world shows the location of surface observations available in the Met Office over one 6-hour period and that were received in time for use in its forecast models. Without international collaboration we would be left we would be left with observations over the small area covered by the UK and a few scattered spots over the oceans from the marine systems that are our national responsibility.

It is not just surface observations that are exchanged internationally. Observations using aircraft, balloons, radar and other systems give a picture of the global structure of the atmosphere above the ground. This picture, however, is incomplete because aircraft do not fly everywhere and it is impractical and too costly to deploy balloons and radars from all corners of the world.

Satellites provide the final, and absolutely vital, component of the global observing system. This example shows the coverage of sounding data available at the Met Office over a 6 hour period and received in time for use in its forecast models. Each spot represents a vertical profile of data that provides information on the temperature and humidity structure of the atmosphere. The data are truly three dimensional, or indeed four dimensional if you consider that there is a continuous stream of data available at all times. The cost of developing and operating the satellites used to provide all the data required by our forecast models runs into many billions of pounds, way beyond the resources of any one country. The UK is one of many countries contributing to worldwide network of meteorological satellites that are so important for maintaining the accuracy of our forecasts.

Last updated: 14 October 2015

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