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The Unified Model is a numerical weather prediction and
climate modeling Numerical climate models use quantitative methods to simulate the interactions of the important drivers of climate, including atmosphere, oceans, land surface and ice. They are used for a variety of purposes from study of the dynamics of the cl ...
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 profilers, 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 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 Prediction 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.


Global Model

Approximately 16 km resolution with 70 vertical levels.Atmospheric numerical model configurations as of early 2010
Met Office 2010.
Covers the entire globe and 168 hours in the future twice a day, the shortest outlook of the synoptic scale models currently in use (most others run out at least 10 days; furthermore, the Unified Model forecasts are only available out 72 hours for non-paying users). The Global model provides boundary information for the now retired 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 assimilationHybrid variational/ensemble data assimilation
. Met Office 2011.
of observations.


North Atlantic and European model - Retired

The Met Office's North Atlantic and European model (NAE) model had 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 assimilation of observations.


Euro 4km model

70 Vertical levels, 4.4 km horizontal resolution. Run out to 120 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 (this replaced the UK 4 km model in 2011). The forecast is run every 3 hours using boundary conditions from the 25-km global model.The UKV Model
Met Office, January 2012
The resolution is 1.5 km over the UK, and 4 km over surrounding areas.Issues with high-resolution NWP
discussing the UKV model, Met Office 2010.

discussing the UKV model, Met Office 2011.
The UKV model is kept close to observations using 3D-Var data assimilation every 3 hours.


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 waves In meteorology, lee waves are atmospheric stationary waves. The most common form is mountain waves, which are atmospheric internal gravity waves. These were discovered in 1933 by two German glider pilots, Hans Deutschmann and Wolf Hirth, above ...
for a variety of locations around the UK and other areas of interest to the Met Office.


Met Office's Global Wave Model

This models sea waves around the world.


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 Meteorology The Bureau of Meteorology (BOM or BoM) 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 Australian
Commonwealth Scientific and Industrial Research Organisation The Commonwealth Scientific and Industrial Research Organisation (CSIRO) is an Australian Government agency responsible for scientific research. CSIRO works with leading organisations around the world. From its headquarters in Canberra, CSIRO ...
, the South African Weather Service, the Norwegian Meteorological Institute, the New Zealand National Institute of Water and Atmospheric Research, the outh Korea Meteorological Administration and the
National Centre for Medium Range Weather Forecasting National Centre for Medium Range Weather Forecasting (NCMRWF) is a national agency for weather forecasting under the Ministry of Earth Sciences, (transferred from its former parent Ministry of Science and Technology), Government of India. It is a ...
, a subordinate office of the Indian
Ministry of Earth Sciences The Ministry of Earth Sciences was formed on 29 January 2006 from a merger of the India Meteorological Department (IMD), the National Centre for Medium Range Weather Forecasting (NCMRWF), the Indian Institute of Tropical Meteorology (IITM), Pu ...
.


Australian Bureau of Meteorology

The Australian
Bureau of Meteorology The Bureau of Meteorology (BOM or BoM) 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 ...
, have an operational 12 km 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.


outhKorea Meteorological Administration

The outh Korea Meteorological Administration have an operational 10 km resolution global forecasting system utilizing the Unified Model. This global system provides boundary conditions for a 1.5 km resolution local Unified Model NWP system covering the Korean Peninsula Region.


UKCA

United Kingdom Chemistry & Aerosols ( UKCA) 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 An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas. Aerosols can be natural or anthropogenic. Examples of natural aerosols are fog or mist, dust, forest exudates, and geyser steam. Examples of anthropogen ...
. As with most of the UM, the UKCA was written in a collaboration between the
UK Met Office The Meteorological Office, abbreviated as the Met Office, is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy and is led by CEO Penelope ...
and UK Academia.


JULES

Joint UK Land Environment System is a land surface model that has been developed in a collaboration between the Met Office and other research institutes.JULES collaboration
The Met Office 2011. Accessed 10 November 2011
JULES models the exchange of heat and moisture between the Unified Model atmosphere and the land surface and vegetation. JULES can also be used offline to estimate the impacts of different climate models on the land surface and hydrology.


References


External links


Unified Model Collaboration webpage
at the Met Office.
Unified Model Papers

Introduction to the UM by NCAS
{{Atmospheric, Oceanographic and Climate Models Numerical climate and weather models Met Office Scientific simulation software