Weather Monitoring 21


The VisualEyes™ system makes use of short-term and long-term numerical forecasts as well as our probabilistic models to provide alerts based on specific requirements. It also allows real-time as well as forecast weather to be viewed.


Detailed forecasts from VisualEyes™ project site-specific alerts for


wind farms shown on a web-based map viewer to allow operators to easily monitor conditions across several sites. These alerts are probabilistic in nature so the operator can determine the appropriate thresholds for their sites for different weather parameters, such as lightning, wind speed, rain, temperature and visibility. These are flagged up clearly on the map when an alert is given.


Medium range weather forecasting


Accuracy continues to improve as better technology becomes available. However, beyond 5 days a probabilistic forecast generally provides a better interpretation of the weather than a deterministic forecast. This is because of increased uncertainty the longer the forecast period is (see graph in Figure 2).


Forecasting the weather


The changes we constantly see in the UK weather make the task of predicting it a challenging one. Ever evolving technology helps the Met Office to gain both a fuller understanding in how the fluid dynamics of the atmosphere work and in processing vast amounts of data used in making today’s weather forecast.


These advances have revolutionised how observations are received from remote locations through to the way weather forecasts are presented on the growing number of media outlets.


Observations are vital to the process of creating forecasts. Data sources are always changing and improving and now include observations of the atmosphere taken from over 36,000 kilometres above the Earth, and of the ocean taken from 2,000 metres below sea level. Sources of observations also include: balloon


profiles, surface data, aircraft observations which provide a range of detail, such as temperature, air pressure, wind speed and direction, humidity and many other properties to provide the starting conditions of our weather forecast model. These vast quantities of observations arrive from sites around the world, measured using World Meteorological Organisation (WMO) standard equipment.


Images of observation equipment


The supply of observational data is absorbed by the increases in supercomputer capacity, which allows vast quantities of data to be assimilated. Around 5 - 10 million pieces of observed information are fed into the Met Office supercomputer each day. It is perhaps thanks mostly to the revolutionary advances made in satellite technology that has had the biggest single impact on how a weather forecast is produced.


All of this information is fed into the supercomputer which uses Numerical Weather Prediction (NWP) models to produce weather forecasts.


A forecast can be deterministic – which is a simple statement about a particular type of weather occurring or not - or probabilistic, which is a statement that asses the risk and is usually expressed in percentage terms as to the likelihood of it happening.


Figure 2: Uncertainty graph Looking to a month ahead, different methods are used to forecast


the weather. One fairly recent development is the use of weather regimes in medium-range weather forecasts.


Decider™ was developed by the Met Office to present medium- range forecasts of 3 to 30 days over Europe. It displays data, temperature, pressure, rainfall, cloud cover, wind speed and wind direction on a map and table format. This makes it easy to view likely upcoming weather and its impacts on the industries such, renewable and energy.


The product summarises a range of forecast outputs and condenses large volumes of information using a synoptic classification known as “weather regimes”.


Each weather regime has a specific set of weather characteristics that accompanies them. Decider™ and its unique objective analysis method acts like a key to enable understanding of local weather patterns embedded within larger scale weather. It has already proved to be highly successful across the energy sector. It is also useful in commodities trading.


Graham Ford, Utilities Business Manager added, “Initially customers were concerned that you needed good meteorological skills to get the best from it. It’s really not that difficult and our scientists have become very adept at explaining it in a simple way that is relevant to the user”.


Forecasts beyond a month take us to climate prediction and the same numerical models used for short range forecasts are used for climate models. Despite the variable nature of weather, evidence shows that the global climate is warming up. Natural variability means that we will always have some cold winters and some hot summers. However, research at the Met Office Hadley Centre shows that for the UK, winters are likely to become milder and wetter. During summer months, temperatures like those seen in 2003 are likely to become a more regular feature of our climate as we head through the 21st century.


Reference Radiosonde for Climate Change Measurement Entered a Prototype Phase


In response to demand from the international scientific community, Vaisala (Finland) is developing a reference radiosonde, an important instrument to measure climate change.


A prototype version of the reference sonde is now available. The instrument is based on Vaisala RS92 radiosonde sensors and DRYCAP@Frostpoint Sensor VRF100, which is capable of measuring extremely low humidity levels.


In its first sounding tests, Vaisala’s reference sonde has received very encouraging results. The measurement accuracy and repeatability of the instrument were at a high level when verified against the results of the cryogenic frostpont hygrometer (CFH), currently considered one of the most accurate measurements for upper atmospheric humidity measurements.


The current reference grade instruments are challenging to operate due to their high price and complexity for routine use. The benefits of Vaisala’s reference sonde compared to the current measurements include ease of use and cost efficiency, thus enabling more frequent climatological soundings.


Vaisala, together with its research partners, is continuing field testing of the reference radio sonde in 2010. In parallel with field testing, the program is also proceeding to develop and test more precise measurements for other atmospheric parameters. Development will continue until the climate science needs, including lower tropospheric requirements, are satisfied for humidity, temperature, pressure and wind soundings.


Reader Reply Card no 56 May/June 2010 IET


AUTHOR DETAILS


John Hammond Met Office Web: www.metoffice.gov.uk


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Reader Reply Card no 57


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