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To forecast the weather a numerical model of the atmosphere is run several
times a day. Much of the work within the Division has the ultimate aim
of improving the performance of the model. This may be by improving
the representation of physical processes within the model, by improving
the analysis or assimilation schemes or by making better use of the
observations that are received each day. |
| What is numerical modelling |
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Numerical modelling is the process of obtaining an objective forecast
of the future state of the atmosphere by solving a set of equations
that describe the evolution of variables (temperature, wind speed, humidity,
pressure) that define the state of the atmosphere.
The process begins with analysing
the current state of the atmosphere by taking a previous short-range
forecast and using observations to amend this forecast so that the
best guest of the current true state of the atmosphere is obtained.
A computer model is then run to produce a forecast.
All numerical models of the atmosphere are based upon the same set
of governing equations which
are described here in non-mathematical terms. Numerical models differ
in the approximations and assumptions made in the application of these
equations, how they are solved and also in the representation of physical
processes.
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| Components of a numerical model |
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A numerical model of the atmosphere may be very complicated and consist
of several components such as data assimilation, physical parametrizations,
numerical integration schemes and data output schemes.
More about numerical model
components
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| Operational numerical modelling at the Met Office |
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The numerical model in the Met Office is termed the Unified Model
as it is used for both short-term weather forecasts and long climate
simulations run by the Hadley
Centre for Climate Prediction and Research. To produce the weather
forecast, various configurations of the Unified Model are run several
times each day.
More about our operational
models
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| Examples of modelling performance, past, present
and future |
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In August 2002, the Met Office implemented a new operational NWP model.
A fuller description of the work may be found in the June
2002 edition of NWP Gazette and in this factsheet.
Many interesting results have been obtained during a major evaluation
of the new model before implementation and since. The new formulation
also offers an exciting opportunity to begin testing models at very
high resolution, offering a taster of what we might be capable of in
the future.
Read more
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To obtain an overall objective measure of the accuarcy of the numerical
model a quantity known as the NWP index is calculated.
More about the NWP Index
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To run a numerical model for weather forecasting or climate studies
requires a lot of computing power. The Met Office has always used the
latest and most powerful computers available and features highly on
the list of the top 500 supercomputing
sites in the world.
As well as using state-of-the-art supercomputers the Met Office
has always been able to adapt to the changing architecture of supercomputers.
Early computers were scalar processors, then came along vector processors
and now they are massively parallel processors.
More about computers
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The numerical model used at the Met Office is called the Unfied Model
as the same model is used for short-term weather forecasting, long-term
climate simulations and also for ocean modelling. The Unified Model
may be used by research centres and other meteorological institute under
license.
More about the
Unified Model
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