Numerical weather prediction: Difference between revisions

Revision as of 16:28, 11 December 2021

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The [[history of numerical weather prediction]] began in the 1920s through the efforts of [[Lewis Fry Richardson]], who used procedures originally developed by [[Vilhelm Bjerknes]]<ref name="Lynch JCP"/> to produce by hand a six-hour forecast for the state of the atmosphere over two points in central Europe, taking at least six weeks to do so.<ref name="Lynch JCP">{{cite journal|last=[[Peter Lynch (meteorologist)|Lynch]]|first=Peter|title=The origins of computer weather prediction and climate modeling|journal=[[Journal of Computational Physics]]|date=March 2008|volume=227|issue=7|pages=3431–44|doi=10.1016/j.jcp.2007.02.034|bibcode=2008JCoPh.227.3431L|url=http://www.rsmas.miami.edu/personal/miskandarani/Courses/MPO662/Lynch,Peter/OriginsCompWF.JCP227.pdf|access-date=2010-12-23|url-status=dead|archive-url=https://web.archive.org/web/20100708191309/http://www.rsmas.miami.edu/personal/miskandarani/Courses/MPO662/Lynch,Peter/OriginsCompWF.JCP227.pdf|archive-date=2010-07-08}}</ref><ref name="Lynch Ch1">{{cite book|last=Lynch|first=Peter|title=The Emergence of Numerical Weather Prediction|url=https://archive.org/details/emergencenumeric00lync|url-access=limited|year=2006|publisher=[[Cambridge University Press]]|isbn=978-0-521-85729-1|pages=[https://archive.org/details/emergencenumeric00lync/page/n11 1]–27|chapter=Weather Prediction by Numerical Process}}</ref> It was not until the advent of the computer and [[computer simulation]]s that computation time was reduced to less than the forecast period itself. The [[ENIAC]] was used to create the first weather forecasts via computer in 1950, based on a highly simplified approximation to the atmospheric governing equations.<ref name="Charney 1950"/><ref>{{cite book|title=Storm Watchers|page=[https://archive.org/details/stormwatcherstur00cox_df1/page/208 208]|year=2002|author=Cox, John D.|publisher=John Wiley & Sons, Inc.|isbn=978-0-471-38108-2|url=https://archive.org/details/stormwatcherstur00cox_df1/page/208}}</ref> In 1954, [[Carl-Gustav Rossby]]'s group at the [[Swedish Meteorological and Hydrological Institute]] used the same model to produce the first operational forecast (i.e., a routine prediction for practical use).<ref name="Harper BAMS">{{cite journal|last=Harper|first=Kristine|author2=Uccellini, Louis W. |author3=Kalnay, Eugenia |author4=Carey, Kenneth |author5= Morone, Lauren |title=2007: 50th Anniversary of Operational Numerical Weather Prediction|journal=[[Bulletin of the American Meteorological Society]]|date=May 2007|volume=88|issue=5|pages=639–650|doi=10.1175/BAMS-88-5-639|bibcode=2007BAMS...88..639H|doi-access=free}}</ref> Operational numerical weather prediction in the United States began in 1955 under the Joint Numerical Weather Prediction Unit (JNWPU), a joint project by the [[U.S. Air Force]], [[U.S. Navy|Navy]] and [[U.S. Weather Bureau|Weather Bureau]].<ref>{{cite web|author=American Institute of Physics|date=2008-03-25|url=http://www.aip.org/history/sloan/gcm/ |title=Atmospheric General Circulation Modeling|access-date=2008-01-13 |archive-url = https://web.archive.org/web/20080325084036/http://www.aip.org/history/sloan/gcm/ |archive-date = 2008-03-25}}</ref> In 1956, [[Norm Phillips|Norman Phillips]] developed a mathematical model which could realistically depict monthly and seasonal patterns in the troposphere; this became the first successful [[climate model]].<ref name="Phillips">{{cite journal|last=Phillips|first=Norman A.|title=The general circulation of the atmosphere: a numerical experiment|journal=Quarterly Journal of the Royal Meteorological Society|date=April 1956|volume=82|issue=352|pages=123–154|doi=10.1002/qj.49708235202|bibcode=1956QJRMS..82..123P}}</ref><ref name="Cox210">{{cite book|title=Storm Watchers|page=[https://archive.org/details/stormwatcherstur00cox_df1/page/210 210]|year=2002|author=Cox, John D.|publisher=John Wiley & Sons, Inc.|isbn=978-0-471-38108-2|url=https://archive.org/details/stormwatcherstur00cox_df1/page/210}}</ref> Following Phillips' work, several groups began working to create [[general circulation model]]s.<ref name="Lynch Ch10">{{cite book|last=Lynch|first=Peter|title=The Emergence of Numerical Weather Prediction|url=https://archive.org/details/emergencenumeric00lync|url-access=limited|year=2006|publisher=[[Cambridge University Press]]|isbn=978-0-521-85729-1|pages=[https://archive.org/details/emergencenumeric00lync/page/n216 206]–208|chapter=The ENIAC Integrations}}</ref> The first general circulation climate model that combined both oceanic and atmospheric processes was developed in the late 1960s at the [[NOAA]] [[Geophysical Fluid Dynamics Laboratory]].<ref>{{cite web|url=http://celebrating200years.noaa.gov/breakthroughs/climate_model/welcome.html|title=The First Climate Model|author=[[National Oceanic and Atmospheric Administration]]|date=2008-05-22|access-date=2011-01-08}}</ref>

As computers have become more powerful, the size of the initial data sets has increased and [[Atmospheric model#Types|newer atmospheric models]] have been developed to take advantage of the added available computing power. These newer models include more physical processes in the simplifications of the [[Navier–Stokes equations|equations of motion]] in numerical simulations of the atmosphere.<ref name="Harper BAMS"/> In 1966, [[West Germany]] and the United States began producing operational forecasts based on [[primitive equations|primitive-equation models]], followed by the United Kingdom in 1972 and Australia in 1977.<ref name="Lynch JCP"/><ref name="Leslie BOM">{{cite journal|last=Leslie|first=L.M.|author2=Dietachmeyer, G.S. |title=Real-time limited area numerical weather prediction in Australia: a historical perspective|journal=Australian Meteorological Magazine|date=December 1992|volume=41|issue=SP|pages=61–77|url=http://www.bom.gov.au/amoj/docs/1992/leslie2.pdf|access-date=2011-01-03}}</ref> The development of limited area (regional) models facilitated advances in forecasting the tracks of [[tropical cyclone]]s as well as [[air quality]] in the 1970s and 1980s.<ref name="Shuman W&F">{{cite journal|last=Shuman|first=Frederick G.|author-link=Frederick Gale Shuman|title=History of Numerical Weather Prediction at the National Meteorological Center|journal=[[Weather and Forecasting]]|date=September 1989|volume=4|issue=3|pages=286–296|doi=10.1175/1520-0434(1989)004<0286:HONWPA>2.0.CO;2|doi-broken-date=2021-12-22|bibcode=1989WtFor...4..286S|doi-access=free}}</ref><ref>{{cite book|title=Air pollution modeling and its application VIII, Volume 8|author=Steyn, D. G.|publisher=Birkhäuser|year=1991|pages=241–242|isbn=978-0-306-43828-8}}</ref> By the early 1980s models began to include the interactions of soil and vegetation with the atmosphere, which led to more realistic forecasts.<ref>{{cite journal|url=http://www.geog.ucla.edu/~yxue/pdf/1996jgr.pdf |title=Impact of vegetation properties on U. S. summer weather prediction |page=7419 |author1=Xue, Yongkang |author2=Fennessey, Michael J. |journal=[[Journal of Geophysical Research]] |volume=101 |issue=D3 |date=1996-03-20 |access-date=2011-01-06 |doi=10.1029/95JD02169 |bibcode=1996JGR...101.7419X |url-status=dead |archive-url=https://web.archive.org/web/20100710080304/http://www.geog.ucla.edu/~yxue/pdf/1996jgr.pdf |archive-date=2010-07-10 |citeseerx=10.1.1.453.551 }}</ref>

The output of forecast models based on [[atmospheric dynamics]] is unable to resolve some details of the weather near the Earth's surface. As such, a statistical relationship between the output of a numerical weather model and the ensuing conditions at the ground was developed in the 1970s and 1980s, known as [[model output statistics]] (MOS).<ref name="MOS"/><ref>{{cite book|title=Air Weather Service Model Output Statistics Systems|author1=Best, D. L. |author2=Pryor, S. P. |year=1983|pages=1–90|publisher=Air Force Global Weather Central}}</ref> Starting in the 1990s, model ensemble forecasts have been used to help define the forecast uncertainty and to extend the window in which numerical weather forecasting is viable farther into the future than otherwise possible.<ref name="Toth"/><ref name="ECens"/><ref name="RMS"/>

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The [[atmosphere]] is a [[fluid]]. As such, the 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. The process of entering observation data into the model to generate [[initial value problem|initial conditions]] is called ''initialization''. On land, terrain maps available at resolutions down to {{convert|1|km|mi|1|sp=us}} globally are used to help model atmospheric circulations within regions of rugged topography, in order to better depict features such as downslope winds, [[Lee wave|mountain wave]]s and related cloudiness that affects incoming solar radiation.<ref>{{cite book|url=https://books.google.com/books?id=lMXSpRwKNO8C&pg=PA56|title=Parameterization schemes: keys to understanding numerical weather prediction models|author=Stensrud, David J.|page=56|year=2007|publisher=Cambridge University Press|isbn=978-0-521-86540-1}}</ref> The main inputs from country-based weather services are observations from devices (called [[radiosonde]]s) in weather balloons that measure various atmospheric parameters and transmits them to a fixed receiver, as well as from [[weather satellite]]s. The [[World Meteorological Organization]] acts to standardize the instrumentation, observing practices and timing of these observations worldwide. Stations either report hourly in [[METAR]] reports,<ref>{{cite web|title=Key to METAR Surface Weather Observations|url=http://www.ncdc.noaa.gov/oa/climate/conversion/swometardecoder.html|publisher=[[National Oceanic and Atmospheric Administration]]|access-date=2011-02-11|author=[[National Climatic Data Center]]|date=2008-08-20}}</ref> or every six hours in [[SYNOP]] reports.<ref>{{cite web|title=SYNOP Data Format (FM-12): Surface Synoptic Observations|publisher=[[UNISYS]]|archive-url=https://web.archive.org/web/20071230100059/http://weather.unisys.com/wxp/Appendices/Formats/SYNOP.html|archive-date=2007-12-30|date=2008-05-25|url=http://weather.unisys.com/wxp/Appendices/Formats/SYNOP.html}}</ref> These observations are irregularly spaced, so they 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.<ref name="Krishnamurti Annu Rev FM">{{cite journal|last=Krishnamurti|first=T. N.|title=Numerical Weather Prediction|journal=[[Annual Reviews (publisher)|Annual Review of Fluid Mechanics]]|date=January 1995|volume=27|issue=1|pages=195–225|doi=10.1146/annurev.fl.27.010195.001211|bibcode=1995AnRFM..27..195K}}</ref> The data are then used in the model as the starting point for a forecast.<ref>{{cite web|title=The WRF Variational Data Assimilation System (WRF-Var)|publisher=[[University Corporation for Atmospheric Research]]|archive-url=https://web.archive.org/web/20070814044336/http://www.mmm.ucar.edu/wrf/WG4/wrfvar/wrfvar-tutorial.htm|archive-date=2007-08-14|date=2007-08-14|url=http://www.mmm.ucar.edu/wrf/WG4/wrfvar/wrfvar-tutorial.htm}}</ref>

A variety of methods are used to gather observational data for use in numerical models. Sites launch radiosondes in weather balloons which rise through the [[troposphere]] and well into the [[stratosphere]].<ref>{{cite web|last=Gaffen|first=Dian J.|title=Radiosonde Observations and Their Use in SPARC-Related Investigations|archive-url=https://web.archive.org/web/20070607142822/http://www.aero.jussieu.fr/~sparc/News12/Radiosondes.html|archive-date=2007-06-07|date=2007-06-07|url=http://www.aero.jussieu.fr/~sparc/News12/Radiosondes.html}}</ref> Information from weather satellites is used where traditional data sources are not available. Commerce provides [[pilot report]]s along aircraft routes<ref>{{cite journal|last=Ballish|first=Bradley A.|author2=V. Krishna Kumar |title=Systematic Differences in Aircraft and Radiosonde Temperatures|journal=[[Bulletin of the American Meteorological Society]]|date=November 2008|volume=89|issue=11|pages=1689–1708|doi=10.1175/2008BAMS2332.1|bibcode=2008BAMS...89.1689B|access-date=2011-02-16|url=http://amdar.noaa.gov/docs/bams_ballish_kumar.pdf}}</ref> and ship reports along shipping routes.<ref>{{cite web|author=National Data Buoy Center|url=http://www.vos.noaa.gov/vos_scheme.shtml|title=The WMO Voluntary Observing Ships (VOS) Scheme|access-date=2011-02-15|date=2009-01-28|publisher=[[National Oceanic and Atmospheric Administration]]}}</ref> Research projects use [[weather reconnaissance|reconnaissance aircraft]] to fly in and around weather systems of interest, such as [[tropical cyclone]]s.<ref name="Hurricane Hunters">{{cite web|year=2011|author=403rd Wing|url=http://www.hurricanehunters.com|title=The Hurricane Hunters|publisher=[[Hurricane Hunters|53rd Weather Reconnaissance Squadron]]|access-date=2006-03-30|archive-date=2012-06-24|archive-url=https://www.webcitation.org/68eBpzZrK?url=http://www.hurricanehunters.com/|url-status=dead}}</ref><ref name="SunHerald">{{cite news|author=Lee, Christopher|title=Drone, Sensors May Open Path Into Eye of Storm|url=https://www.washingtonpost.com/wp-dyn/content/article/2007/10/07/AR2007100700971_pf.html|journalnewspaper=The Washington Post|access-date=2008-02-22|date=2007-10-08}}</ref> Reconnaissance aircraft are also flown over the open oceans during the cold season into systems which cause significant uncertainty in forecast guidance, or are expected to be of high impact from three to seven days into the future over the downstream continent.<ref>{{cite web|url=http://www.noaanews.noaa.gov/stories2010/20100112_plane.html|title=NOAA Dispatches High-Tech Research Plane to Improve Winter Storm Forecasts|date=2010-11-12|access-date=2010-12-22|author=[[National Oceanic and Atmospheric Administration]]}}</ref> Sea ice began to be initialized in forecast models in 1971.<ref>{{cite book|url=https://books.google.com/books?id=lMXSpRwKNO8C&pg=PA137|author=Stensrud, David J.|page=137|title=Parameterization schemes: keys to understanding numerical weather prediction models|publisher=[[Cambridge University Press]]|year=2007|isbn=978-0-521-86540-1}}</ref> Efforts to involve [[sea surface temperature]] in model initialization began in 1972 due to its role in modulating weather in higher latitudes of the Pacific.<ref>{{cite book|url=https://books.google.com/books?id=SV04AAAAIAAJ&pg=PA38|pages=49–50|title=The Global Climate|author=Houghton, John Theodore|publisher=Cambridge University Press archive|year=1985|isbn=978-0-521-31256-1}}</ref>

==Computation==