Numerical weather prediction: Difference between revisions

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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|archive-date=2002-11-01|archive-url=https://web.archive.org/web/20021101221848/http://www0.ncdc.noaa.gov/oa/climate/conversion/swometardecoder.html|url-status=dead}}</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=2012-0605-2430|archive-url=https://wwwweb.webcitationarchive.org/68eBpzZrK?url=web/20120530232904/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|newspaper=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==