Unified Model
Encyclopedia
The Unified Model is a Numerical Weather Prediction
and climate modeling software suite originally developed by the United Kingdom
Met Office
, and now both used and further developed by many weather-forecasting agencies around the world. The Unified Model gets its name because a single model is used across a range of both timescales (nowcasting to centennial) and spatial scales (convective scale to climate system earth modelling). The models are grid-point
based, rather than wave based
, and are run on a variety of supercomputers around the world. The Unified Model atmosphere can be coupled to a number of ocean models. At the Met Office it is used for the main suite of Global Model, North Atlantic and Europe model (NAE) and a high-resolution UK model (UKV), in addition to a variety of Crisis Area Models and other models that can be run on demand. Similar Unified Model suites with global and regional domains are used by many other national or military weather agencies around the world for operational forecasting.
Data for numerical weather prediction is provided by observations from satellites, from the ground (both human and from automatic weather stations), from buoys at sea, radar, radiosonde weather balloons
, wind profiler
s, commercial aircraft and a background field from previous model runs.
The computer model is only adjusted towards the observations using assimilation
, rather than forcing the model to accept an observed value that might make the system unstable (and could be an inaccurate observation).
The Unified Model software suite is written in Fortran
(originally 77 but now predominantly 90) and uses height as the vertical variable.
Because most developments of interest are at near to the ground the vertical layers are closer together near the surface.
suites using the UM.
All of the models use varying resolutions of topography
with greater accuracy at higher resolutions. The limiting factor with all models is that for a weather event to be recorded by the model it must be at least three grid points in size. Thus for the global model at 40 km, a weather system must be at least 120 km to be modelled. This means smaller phenomena such as small depressions, smaller hurricanes and large thunderstorms are too small for the model to catch them. As the resolution increases smaller events can be caught, the 1.5 km model for example, is reputedly capable of modelling individual showers.
of observations.
of observations.
every 3 hours. Example output from the UKV model can be seen here.
for a variety of locations around the UK and other areas of interest to the Met Office.
, the Australian Commonwealth Scientific and Industrial Research Organisation
, the South African Weather Service
, the Norwegian Meteorological Institute
, the New Zealand National Institute of Water and Atmospheric Research
, the [South] Korea Meteorological Administration
and the the Indian Ministry of Earth Sciences
.
, have an operational 40km resolution global forecasting system utilizing the Unified Model. This global system provides boundary conditions for a number of higher resolution regional systems also using the Unified Model.
have an operational 25km resolution global forecasting system utilizing the Unified Model. This global system provides boundary conditions for a 12km resolution regional Unified Model NWP
system covering South-East Asia.
) is a sub-model of the UM that deals with trace gas and aerosol chemistry within the model. This includes calculating the concentrations of climatically relevant gases such as methane
and ozone
, as well as the composition and evolution of aerosols. As with most of the UM, the UKCA was written in a collaboration between the UK Met Office and UK Academia.
Numerical weather prediction
Numerical weather prediction uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of computer simulation in the 1950s that numerical weather predictions produced realistic...
and climate modeling software suite originally developed by the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
Met Office
Met Office
The Met Office , is the United Kingdom's national weather service, and a trading fund of the Department for Business, Innovation and Skills...
, and now both used and further developed by many weather-forecasting agencies around the world. The Unified Model gets its name because a single model is used across a range of both timescales (nowcasting to centennial) and spatial scales (convective scale to climate system earth modelling). The models are grid-point
Finite difference method
In mathematics, finite-difference methods are numerical methods for approximating the solutions to differential equations using finite difference equations to approximate derivatives.- Derivation from Taylor's polynomial :...
based, rather than wave based
Spectral method
Spectral methods are a class of techniques used in applied mathematics and scientific computing to numerically solve certain Dynamical Systems, often involving the use of the Fast Fourier Transform. Where applicable, spectral methods have excellent error properties, with the so called "exponential...
, and are run on a variety of supercomputers around the world. The Unified Model atmosphere can be coupled to a number of ocean models. At the Met Office it is used for the main suite of Global Model, North Atlantic and Europe model (NAE) and a high-resolution UK model (UKV), in addition to a variety of Crisis Area Models and other models that can be run on demand. Similar Unified Model suites with global and regional domains are used by many other national or military weather agencies around the world for operational forecasting.
Data for numerical weather prediction is provided by observations from satellites, from the ground (both human and from automatic weather stations), from buoys at sea, radar, radiosonde weather balloons
Weather balloon
A weather or sounding balloon is a balloon which carries instruments aloft to send back information on atmospheric pressure, temperature, humidity and wind speed by means of a small, expendable measuring device called a radiosonde...
, wind profiler
Wind profiler
A wind profiler is a type of weather observing equipment that uses radar or sound waves to detect the wind speed and direction at various elevations above the ground. Readings are made at each kilometer above sea level, up to the extent of the troposphere...
s, commercial aircraft and a background field from previous model runs.
The computer model is only adjusted towards the observations using assimilation
Data assimilation
Applications of data assimilation arise in many fields of geosciences, perhaps most importantly in weather forecasting and hydrology. Data assimilation proceeds by analysis cycles...
, rather than forcing the model to accept an observed value that might make the system unstable (and could be an inaccurate observation).
The Unified Model software suite is written in Fortran
Fortran
Fortran is a general-purpose, procedural, imperative programming language that is especially suited to numeric computation and scientific computing...
(originally 77 but now predominantly 90) and uses height as the vertical variable.
Because most developments of interest are at near to the ground the vertical layers are closer together near the surface.
Principal UM suites at the Met Office
The Met Office runs a range of Numerical Weather PredictionNumerical weather prediction
Numerical weather prediction uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of computer simulation in the 1950s that numerical weather predictions produced realistic...
suites using the UM.
All of the models use varying resolutions of topography
Topography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
with greater accuracy at higher resolutions. The limiting factor with all models is that for a weather event to be recorded by the model it must be at least three grid points in size. Thus for the global model at 40 km, a weather system must be at least 120 km to be modelled. This means smaller phenomena such as small depressions, smaller hurricanes and large thunderstorms are too small for the model to catch them. As the resolution increases smaller events can be caught, the 1.5 km model for example, is reputedly capable of modelling individual showers.
Global Model
Approximately 25 km resolution with 70 vertical levels. Covers the entire globe and 144 hours in the future twice a day. The Global model provides boundary information for the North Atlantic European (NAE) model, for which additional shorter runs (48 hours) are produced twice a day. The model is kept close to the real atmosphere using hybrid 4D-Var data assimilationData assimilation
Applications of data assimilation arise in many fields of geosciences, perhaps most importantly in weather forecasting and hydrology. Data assimilation proceeds by analysis cycles...
of observations.
North Atlantic and European model
The Met Office's North Atlantic and European model (NAE) model has 70 levels with a 12 km resolution. It is run out to 48 hours from start. Because the UK is at a northern latitude the computer transposes the model area to an equatorial location so the grid points give an area that is more square. This reduces the load on the model, allowing it to run more quickly. The model is kept close to the real atmosphere using 4D-Var data assimilationData assimilation
Applications of data assimilation arise in many fields of geosciences, perhaps most importantly in weather forecasting and hydrology. Data assimilation proceeds by analysis cycles...
of observations.
UK 4km model
70 Vertical levels, 4 km horizontal resolution. Run out to 36 hours. Now being superseded by the UKV in many applications.UKV model
70 Vertical levels, 1.5 km horizontal resolution. Run out to 36 hours (replacing UK 4km model over the course of 2010-2011). This is run every 6 hours using boundary conditions from the 12-km North Atlantic and European (NAE) model. The resolution is 1.5 km over the UK, and 4 km over surrounding areas. The UKV model is kept close to observations using 3D-Var data assimilationData assimilation
Applications of data assimilation arise in many fields of geosciences, perhaps most importantly in weather forecasting and hydrology. Data assimilation proceeds by analysis cycles...
every 3 hours. Example output from the UKV model can be seen here.
CAM
The Crisis Area Model is a 12 km model that can be run for any area of the world should the need arise. This can include military use (the MMU use this on deployed operations) or environmental catastrophes.Mountain Wave Models
This high resolution model provides information on mountain wavesLee waves
In meteorology, lee waves are atmospheric standing waves. The most common form is mountain waves, which are atmospheric internal gravity waves...
for a variety of locations around the UK and other areas of interest to the Met Office.
UM suites outside the Met Office
Unified Model suites which are similar to those from the Met Office are run by the Australian Bureau of MeteorologyBureau of Meteorology
The Bureau of Meteorology is an Executive Agency of the Australian Government responsible for providing weather services to Australia and surrounding areas. It was established in 1906 under the Meteorology Act, and brought together the state meteorological services that existed before then...
, the Australian Commonwealth Scientific and Industrial Research Organisation
Commonwealth Scientific and Industrial Research Organisation
The Commonwealth Scientific and Industrial Research Organisation is the national government body for scientific research in Australia...
, the South African Weather Service
South African Weather Service
The South African Weather Service is the meteorological service under the South African government's Department of Environmental Affairs and Tourism. SAWS is a member of the World Meteorological Organization. The agency is similar to the United States' National Weather Service.Under the South...
, the Norwegian Meteorological Institute
Norwegian Meteorological Institute
Norwegian Meteorological Institute is the Norwegian national institute for weather forecasts.The three main offices are located in Oslo, Bergen and Tromsø. The Institute has around 500 employees and keeps around 650 paid observers of various kinds around the country...
, the New Zealand National Institute of Water and Atmospheric Research
National Institute of Water and Atmospheric Research
The National Institute of Water and Atmospheric Research or NIWA , is a Crown Research Institute of New Zealand. Established in 1992, NIWA conducts commercial and non-commercial research across a broad range of disciplines in the environmental sciences...
, the [South] Korea Meteorological Administration
Korea Meteorological Administration
The Korea Meteorological Administration is the National Meteorological service for Korea. The service started in 1904 joining the WMO in 1956. Numerical Weather Prediction is performed using the Unified Model software suite.-External links:* * *...
and the the Indian Ministry of Earth Sciences
Ministry of Earth Sciences (India)
The Ministry of Earth Sciences formed in 2006 from a merger of the India Meteorological Department , the National Centre for Medium Range Weather Forecasting , the Indian Institute of Tropical Meteorology , Pune , and Earth Risk Evaluation Centre , and the Ministry of Ocean Development. It is one...
.
Austrialian Bureau of Meteorology
The Australian Bureau of MeteorologyBureau of Meteorology
The Bureau of Meteorology is an Executive Agency of the Australian Government responsible for providing weather services to Australia and surrounding areas. It was established in 1906 under the Meteorology Act, and brought together the state meteorological services that existed before then...
, have an operational 40km resolution global forecasting system utilizing the Unified Model. This global system provides boundary conditions for a number of higher resolution regional systems also using the Unified Model.
[South] Korea Meteorological Administration
The [South] Korea Meteorological AdministrationKorea Meteorological Administration
The Korea Meteorological Administration is the National Meteorological service for Korea. The service started in 1904 joining the WMO in 1956. Numerical Weather Prediction is performed using the Unified Model software suite.-External links:* * *...
have an operational 25km resolution global forecasting system utilizing the Unified Model. This global system provides boundary conditions for a 12km resolution regional Unified Model NWP
NWP
*Numerical Weather Prediction*National Writing Project*National Woman's Party*Northwestern Pacific Railroad*New World Pasta*Northwest Passage, polar waterways along the northern coast of Canada...
system covering South-East Asia.
UKCA
United Kingdom Chemistry & Aerosols (UKCAUKCA
The United Kingdom Chemistry and Aerosols is a community Chemistry-Aerosol-Climate model which are research runs of the Met Office's operational Unified Model...
) is a sub-model of the UM that deals with trace gas and aerosol chemistry within the model. This includes calculating the concentrations of climatically relevant gases such as methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
and ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
, as well as the composition and evolution of aerosols. As with most of the UM, the UKCA was written in a collaboration between the UK Met Office and UK Academia.