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Information about Numerical Weather Prediction

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An example of 500 mbar geopotential height prediction from a numerical weather prediction model


Numerical weather prediction uses mathematical models of the atmosphere to predict the weather. Manipulating the huge datasets and performing the complex calculations necessary to do this on a resolution fine enough to make the results useful can require some of the most powerful supercomputers in the world.

Physical overview

The atmosphere is a fluid. The basic idea of numerical weather prediction is to sample the state of the fluid at a given time and use the equations of fluid dynamics and thermodynamics to estimate the state of the fluid at some time in the future.

Models

A model, in this context, is a computer program that produces meteorological information for future times at given positions and altitudes. The horizontal domain of a model is either global, covering the entire Earth, or regional , covering only part of the Earth. Regional models also are known as limited-area models.

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A 96-hour forecast of 850 mbar geopotential height and temperature from the Global Forecast System


The forecasts are computed using mathematical equations for the physics and dynamics of the atmosphere. These equations are nonlinear and are impossible to solve exactly. Therefore, numerical methods obtain approximate solutions. Different models use different solution methods. Global models often use spectral methods for the horizontal dimensions and finite difference methods for the vertical dimension, while regional models usually use finite-difference methods in all three dimensions. Regional models also can use finer grids to explicitly resolve smaller-scale meteorological phenomena, since they do not have to solve equations for the whole globe.

Models are initialized using observed data from radiosondes, weather satellites, and other instruments. The irregularly-spaced observations are processed by data assimilation and objective analysis methods, which perform quality control and obtain values at locations usable by the model's mathematical algorithms (usually an evenly-spaced grid). The data are then used in the model as the starting point for a forecast. Commonly, the set of equations used is known as the primitive equations. These equations are initialized from the analysis data and rates of change are determined. The rates of change predict the state of the atmosphere a short time into the future. The equations are then applied to this new atmospheric state to find new rates of change, and these new rates of change predict the atmosphere at a yet further time into the future. This time stepping procedure is continually repeated until the solution reaches the desired forecast time. The length of the time step is related to the distance between the points on the computational grid. Time steps for global climate models may be on the order of tens of minutes, while time steps for regional models may be a few seconds to a few minutes.

Some of the better known numerical models are:

Global models

Regional models

  • WRF The Weather Research and Forecasting Model was developed cooperatively by NCEP and the meteorological research community. WRF has several configurations, including:
* WRF-NMM The WRF Nonhydrostatic Mesoscale Model is the primary short-term weather forecast model for the U.S., replacing the Eta model.
* AR-WRF Advanced Research WRF developed primarily at the U.S. National Center for Atmospheric Research (NCAR) WRF Source Code
  • NAM The term North American Mesoscale model refers to whatever regional model NCEP operates over the North American domain. NCEP began using this designation system in January 2005. Between January 2005 and May 2006 the Eta model (began in Yugoslavia (now Serbia) during the 1970s by Zaviša Janjić and Fedor Mesinger)used this designation. Beginning in May 2006, NCEP began to use the WRF-NMM as the operational NAM.
  • RAMS developed at Colorado State University for numerical simulations of atmospheric meteorology and other environmental phenomena on scales from meters to 100's of kilometers - now supported in the public domain RAMS source code available under the GNU public license
  • MM5 the Fifth Generation Penn State/NCAR Mesoscale Model MM5 Source Code download
  • HIRLAM High Resolution Limited Area Model
  • GEM-LAM Global Environmental Multiscale Limited Area Model, the high resolution (2.5 km) GEM by the Meteorological Service of Canada (MSC)
  • ALADIN The high-resolution limited-area hydrostatic and non-hydrostatic model developed and operated by several European and North African countries under the leadership of Météo-France (ALADIN Community web pages)
  • COSMO The COSMO Model, formerly known as LM, aLMo or LAMI, is a limited-area non hydrostatic model developed within the framework of the Consortium for Small-Scale Modelling (Germany, Switzerland, Italy, Poland and Greece http://cosmo-model.cscs.ch/).

History

British mathematician Lewis Fry Richardson first proposed numerical weather prediction in 1922. Richardson attempted to perform a numerical forecast but it was not successful. The first successful numerical prediction was performed in 1950 by a team composed of the American meteorologist Jule Charney, Norwegian meteorologist Ragnar Fjörtoft and applied mathematician John von Neumann, using the ENIAC digital computer. They used a simplified form of atmospheric dynamics based on the barotropic vorticity equation. This simplification greatly reduced demands on computer time and memory, so that the computations could be performed on the relatively primitive computers available at the time. Later models used more complete equations for atmospheric dynamics and thermodynamics.

Operational numerical weather prediction (i.e., routine predictions for practical use) began in 1955 under a joint project by the U.S. Air Force, Navy, and Weather Bureau.[1]

Ensembles

As proposed by Dr. Edward Lorenz in 1963, it is impossible to definitively predict the state of the atmosphere, owing to the nonlinear nature of fluid dynamics. Furthermore, existing observation networks have limited spatial and temporal resolution, especially over large bodies of water such as the Pacific Ocean, which introduces uncertainty into the true initial state of the atmosphere. To account for this uncertainty, stochastic or "ensemble" forecasting is used, involving multiple forecasts created with different model systems, different physical parameterizations, or varying initial conditions. The ensemble forecast is usually evaluated in terms of the ensemble mean of a forecast variable, and the ensemble spread, which represents the degree of agreement between various forecasts in the ensemble system, known as ensemble members. A common misconception is that low spread amongst ensemble members necessarily implies more confidence in the ensemble mean. Although a spread-skill relationship sometimes exists, the relationship between ensemble spread and skill varies substantially depending on such factors as the forecast model and the region for which the forecast is made.

References

  • Beniston, Martin. From Turbulence to Climate: Numerical Investigations of the Atmosphere with a Hierarchy of Models. Berlin: Springer, 1998.
  • Kalnay, Eugenia. Atmospheric Modeling, Data Assimilation and Predictability. Cambridge University Press, 2003.
  • Thompson, Philip. Numerical Weather Analysis and Prediction. New York: The Macmillan Company, 1961.
  • Pielke, Roger A. Mesoscale Meteorological Modeling. Orlando: Academic Press, Inc., 1984.
  • U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Weather Service. National Weather Service Handbook No. 1 - Facsimile Products. Washington, DC: Department of Commerce, 1979.

See also

External links

mathematical model is an abstract model that uses mathematical language to describe the behaviour of a system. Mathematical models are used particularly in the natural sciences and engineering disciplines (such as physics, biology, and electrical engineering) but also in the social
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weather is the set of all extant phenomena in a given atmosphere at a given time. The term usually refers to the activity of these phenomena over short periods (hours or days), as opposed to the term climate, which refers to the average atmospheric conditions over longer periods of
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For other uses, see Supercomputer (disambiguation).
A supercomputer is a computer that led the world (or was close to doing so) in terms of processing capacity, particularly speed of calculation, at the time of its introduction.
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atmosphere is a layer of gases that may surround a material body of sufficient mass.[1] The gases are attracted by the gravity of the body, and are retained for a longer duration if gravity is high and the atmosphere's temperature is low.
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FLUID (Fast Light User Interface Designer) is a graphical editor that is used to produce FLTK source code. FLUID edits and saves its state in text .fl files, which can be edited in a text editor for finer control over display and behavior.
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Fluid dynamics is the sub-discipline of fluid mechanics dealing with fluids (liquids and gases) in motion. It has several subdisciplines itself, including aerodynamics (the study of gases in motion) and hydrodynamics (the study of liquids in motion).
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Thermodynamics (from the Greek θερμη, therme, meaning "heat" and δυναμις, dynamis, meaning "power") is a branch of physics that studies the effects of changes in temperature, pressure, and volume on
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Meteorology (from Greek: μετέωρον, meteoron, "high in the sky"; and λόγος, logos, "knowledge") is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and
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Spectral methods are a class of techniques used in applied mathematics and scientific computing to numerically solve certain partial differential equations, often involving the use of the Fast Fourier Transform.
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finite-difference equation. Solving this equation gives an approximate solution to the differential equation.

The error between the approximate solution and the true solution is determined by the error that is made by going from a differential operator to a difference
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A radiosonde (Sonde is French for probe) is a unit for use in weather balloons that measures various atmospheric parameters and transmits them to a fixed receiver.
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A weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth. These meteorological satellites, however, see more than clouds and cloud systems.
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The primitive equations are a version of the Navier-Stokes equations that describe hydrodynamical flow on the sphere under the assumptions that vertical motion is much smaller than horizontal motion (hydrostasis) and that the fluid layer depth is small compared to the radius of the
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Climate models use quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice. They are used for a variety of purposes from study of the dynamics of the weather and climate system to projections of future climate.
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Global Forecast System (GFS) is global numerical weather prediction model run by NOAA. This model is run four times a day and produces forecasts up 16 days in advance, but with decreasing spatial and temporal resolution over time (it is widely accepted that beyond 7 days the
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National Oceanic and Atmospheric Administration (NOAA) is a scientific agency of the United States Department of Commerce focused on the conditions of the oceans and the atmosphere.
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United States Navy (USN) is the branch of the United States armed forces responsible for conducting naval operations. The U.S. Navy currently has over 340,000 personnel on active duty and nearly 128,000 in the Navy Reserve.
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The Global Environmental Multiscale Model (GEM) is an integrated forecasting and data assimilation system developed in the Recherche en Prévision Numérique (RPN), Meteorological Research Branch (MRB), and the Canadian Meteorological Center (CMC).
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The Meteorological Service of Canada (MSC) is a division of Environment Canada, which primarily provides public meteorological information and weather forecasts and warnings of severe weather and other environmental hazards.
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The European Centre for Medium-Range Weather Forecasts (ECMWF) is an international organisation based at Reading, England that was founded in 1975.

Objectives

The objectives of the ECMWF are:

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Motto
"Dieu et mon droit" [2]   (French)
"God and my right"
Anthem
"God Save the Queen" [3]
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Met Office (originally an abbreviation for Meteorological Office, but now the official name in itself), which has its headquarters at Exeter in Devon, is the United Kingdom's national weather service.
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The Deutsche(r) Wetterdienst (Translated from German as German Meteorological Service), residing in Offenbach, Germany (near to Frankfurt, Germany), is a scientific agency that monitors weather and meteorological conditions over Germany and offers weather services for the
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METEO-FRANCE is the French national meteorological service.

The organisation was established by decree in June 1993 and is a department of the Ministry of Transportation. It is headquartered in Paris but many domestic operations have been decentralised to Toulouse.
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The Reading Intermediate General Circulation Model (IGCM), is a simplified or "intermediate" Global climate model, which is developed by members of the Department of Meteorology at the University of Reading, and by members of the Stratospheric Dynamics and Chemistry Group of
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University of Reading is a university in the English town of Reading, Berkshire. Established in 1892, receiving its Royal Charter in 1926, the University has a long tradition of research, education and training at a local, national and international level.
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The Weather Research and Forecasting (WRF) model is a computer program with a dual use for forecasting and research. It is the latest numerical program model to be adopted by the National Weather Service as well as the U.S. military and private meteorological services.
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Yugoslavia (Jugoslavija in the Latin alphabet, Југославија in Cyrillic; English: South Slavia, or literary The Land of South Slavs
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Anthem
Bože pravde
God of Justice


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HIRLAM, the High Resolution Limited Area Model, is a Numerical Weather Prediction (NWP) forecast system developed by the international HIRLAM programme.

HIRLAM programme is a cooperation between following European meteorological institutes:

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