Erland Kallen Straits Times 8 Jun 19;
The science of meteorology has made tremendous progress over the last 20 years. Today, the quality of a five-day weather forecast (a weather prediction five days ahead) is about the same as a three-day forecast was 20 years ago. If we assign the value 100 to a perfect forecast, the five-day forecasts today would get about 93 marks. This is particularly true for the mid-latitudes, both in the northern and southern hemispheres.
Over the tropics, forecasts have also improved, but there are still some outstanding issues, such as the prediction of localised thundery showers. For large-scale features such as tropical cyclone tracks and monsoons, the forecasts have become much better - five-day forecasts today are as good as two-day forecasts were 20 years ago.
But regional areas of rain showers and thunderstorms are hard to predict, even a day or two ahead. Thunder showers have a much shorter lifespan than large-scale monsoon winds or tropical cyclones.
But we are now seeing research progress that will improve tropical forecasts. This stems from advances in weather prediction science. Weather scientists rely on observations of temperature, winds, pressure and moisture as well as physics. Using the laws of physics together with supercomputers, scientists are able to set up computer models that calculate the evolution of the weather well ahead of the actual weather events occurring.
The challenge is to use all of the information in the observations as well as possible, and to make the prediction computations as accurate as possible.
PIONEERING RESEARCH
At the Centre for Climate Research Singapore (CCRS), the research branch of the Meteorological Service Singapore (MSS), researchers are developing a new regional weather forecasting model that will provide a platform for enhanced prediction accuracy over Singapore.
The centre was founded in 2013 and comprises more than 30 researchers looking into advancing scientific understanding and prediction of the country's weather and climate.
It is the first in the world to use high-resolution computer models to simulate weather and climate over Singapore and the wider South-east Asia region.
Together with observations and global prediction data from the European Weather Centre, the centre expects to improve the accuracy of one-to two-day weather forecasts over Singapore. The higher resolution and improved accuracy of the regional model will provide more detailed forecasts than before.
No other weather service in the tropics has been combining efforts from all over the world in a programme of this kind. The model predictions developed at CCRS will be delivered to the operational meteorologists at MSS for their use in weather forecast and warning services to users and stakeholders, including the public.
Providing accurate weather forecasts is vitally important to society.
Across the globe, it has been estimated that society benefits economically - more than 10 times the cost of investments made in computers, satellites and weather science - as a result of the prediction improvements made over the past decades.
Observational information comes from a large number of sources, from local weather stations to satellites orbiting up to 36,000km from the earth's surface. The centre also uses weather balloons and measurements from commercial aircraft, which provide temperature, wind and humidity data.
Most of the land-based weather observations and the aircraft data come from the Northern Hemisphere and much of it is outside the tropics.
Satellites, on the other hand, cover all areas of the earth and continuously provide a huge amount of observation data. More than 40 million observations are provided every day by the global weather observing system. All satellites fly well above the atmosphere and therefore satellites use remote sensing techniques such as cameras, infrared sensors and microwave instruments to measure electromagnetic radiation that can be translated into temperature and humidity information.
AEOLUS SATELLITE
Wind information is a crucial part of the observations needed to initialise forecasts, particularly in the tropics. But wind data from satellites had until recently mainly been determined from cloud movements, and this has many limitations.
That changed in August last year, when the European Space Agency launched a pioneering satellite called Aeolus (the keeper of winds in Greek mythology).
It measures atmospheric winds from space using a Doppler lidar. Here, a very powerful laser fires light pulses slantwise down towards the atmosphere and sensitive instruments measure the Doppler shift of the reflected light pulses. This gives a much more accurate measurement of atmospheric winds.
Aeolus is the first Doppler wind lidar in space and it has taken more than 20 years to develop.
The quality of the data received so far is very promising, and the data is expected to improve the accuracy and availability of atmospheric wind data significantly, especially over the tropics.
Providing accurate weather forecasts is vitally important to society.
Across the globe, it has been estimated that society benefits economically - more than 10 times the cost of investments made in computers, satellites and weather science - as a result of the prediction improvements made over the past decades.
One example is superstorm Sandy in 2012. The European Weather Centre predicted this storm more than a week ahead of it hitting the east coast of the United States. This gave sufficient time for big cities such as New York to prepare itself for a major storm by moving trains to safe places and alerting the general public, for example.
Future developments will lead to even better forecasts, and tropical cities like Singapore are likely to benefit most from improvements anticipated over the next five years.
• Professor Erland Kallen is director of the Centre for Climate Research Singapore, the research branch of the Meteorological Service Singapore. He was director of research at the European Centre for Medium-Range Weather Forecasts from 2009 to 2017.
