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How satellites are helping Africa improve weather forecasts

Nowcasting is a system using satellite images to obtain real-time information before bad weather arrives. REUTERS/Mike Hutchings

Weather forecasters can save lives. Based on information from weather prediction models, an advisory warning can be sent a few days before a possible severe weather event such as heavy rainfall or strong winds. Closer to the time, further warnings are issued when forecasters have more certainty.

To do this, weather forecasters rely on nowcasting. This forecasting relies heavily on remote-sensing tools such as satellite or radar systems.

In countries where radar systems are available and well maintained the data gathered form a crucial part of real-time forecasting systems. But in developing countries radar systems are too expensive to obtain and maintain.

Real time warning

In many African countries, basic ground-based observation systems are not adequate to provide a real-time feed of the weather. This lack of data means that the public cannot be warned of severe weather events that could lead to loss of life and property.

But satellite data can provide very useful information in regions where there is no or limited access to expensive observation systems.

Numerical weather prediction data, together with geostationary satellite data, can help nowcasting. This is why the World Meteorological Organisation has thrown its weight behind providing nowcasting in countries where advanced observation data is unavailable. It has launched severe weather forecasting demonstration projects to improve nowcasting in data sparse regions around the world.

Blanket satellite coverage

The Meteosat Second Generation satellite was launched in 2002 by the European Space Agency and the European Organisation for the Exploitation of Meteorological Satellites.

This satellite provides full coverage of the African continent with a time resolution of 15 minutes. The numerous visible, infrared and water vapour channels, as well as colour (red-green-blue) combinations of these channels provide reliable data for nowcasting.

When the satellite was launched, an initiative to get experts in Europe to develop applications for various purposes using the 12 channels provided by the satellite also started. Eight satellite application facilities were established each with an area of focus. These include nowcasting and short range forecasting, climate monitoring, numerical weather prediction, and land surface analysis.

The Nowcasting Satellite Application facility uses data from the geostationary satellite to provide information on clouds related to significant convective systems. By tracking rapidly developing thunderstorms it is possible to identify, monitor and track intense convective system clouds and to detect rapidly developing convective cells.

Warnings saves lives

The rapidly developing thunderstorms software distinguishes different phases of the thunderstorm. It does this by using the different satellite channels to determine cloud depth, vertical extent, cloud top temperature, cooling rate and possible convective activity. Using the images of the past hour, it determines direction and speed of movement. This is then estimated for the next 30 minutes.

With knowledge of the phase of the storm and its intended direction, a forecaster can use the information to issue a weather warning.

A satellite based tool, such as the thunderstorms software, should be used with other data sources such as radar systems and surface observations where possible.

The identification and tracking of thunderstorms is a bigger challenge in data sparse regions than in areas in which expensive and extensive ground and remote observation networks exist. Warning the public about pending severe weather events is the mandate of all operational weather services. They have the power to save lives as well as protect property.

This article is based on an article published in the South African Journal of Science in July 2015.

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