{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,28]],"date-time":"2025-10-28T14:48:51Z","timestamp":1761662931671,"version":"3.41.2"},"reference-count":18,"publisher":"American Geophysical Union (AGU)","issue":"D23","license":[{"start":{"date-parts":[[2010,12,3]],"date-time":"2010-12-03T00:00:00Z","timestamp":1291334400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["J. Geophys. Res."],"published-print":{"date-parts":[[2010,12,16]]},"abstract":"<jats:p>In variational data assimilation systems, background error covariances are often estimated from a temporal and spatial average. For a limited area model such as the Aire Limited Adaptation Dynamique Developpment International (ALADIN)\/France, the spatial average is calculated over the regional computation domain, which covers western Europe. The purpose of this study is to revise the temporal stationarity assumption by diagnosing time variations of such regionally averaged covariances. This is done through examination of covariance changes as a function of season (winter versus summer), day (in connection with the synoptic situation), and hour (related to the diurnal cycle), with the ALADIN\/France regional ensemble Three\u2010Dimensional Variational analysis (3D\u2010Var) system. In summer, compared to winter, average error variances are larger, and spatial correlation functions are sharper horizontally but broader vertically. Daily changes in covariances are particularly strong during the winter period, with larger variances and smaller\u2010scale error structures when an unstable low\u2010pressure system is present in the regional domain. Diurnal variations are also significant in the boundary layer in particular, and, as expected, they tend to be more pronounced in summer. Moreover, the comparison between estimates provided by two independent ensembles indicates that these covariance time variations are estimated in a robust way from a six\u2010member ensemble. All these results support the idea of representing these time variations by using a real\u2010time ensemble assimilation system.<\/jats:p>","DOI":"10.1029\/2010jd014095","type":"journal-article","created":{"date-parts":[[2010,12,2]],"date-time":"2010-12-02T21:00:49Z","timestamp":1291323649000},"source":"Crossref","is-referenced-by-count":13,"title":["A diagnostic study of time variations of regionally averaged background error covariances"],"prefix":"10.1029","volume":"115","author":[{"given":"Maria","family":"Monteiro","sequence":"first","affiliation":[{"name":"CPPN Instituto de Meteorologia I.P.  Lisbon Portugal"}]},{"given":"Lo\u00efk","family":"Berre","sequence":"additional","affiliation":[{"name":"CNRM\/GMAP, M\u00e9t\u00e9o\u2010France  Toulouse France"}]}],"member":"13","published-online":{"date-parts":[[2010,12,3]]},"reference":[{"key":"e_1_2_8_2_1","doi-asserted-by":"publisher","DOI":"10.1175\/MWR3189.1"},{"key":"e_1_2_8_3_1","doi-asserted-by":"publisher","DOI":"10.1175\/1520-0493(2000)128<0644:EOSAMF>2.0.CO;2"},{"key":"e_1_2_8_4_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1600-0870.2006.00165.x"},{"key":"e_1_2_8_5_1","unstructured":"Berre L. O.Pannekoucke G.Desroziers S. E.\u015etef\u0103nescu B.Chapnik andL.Raynaud(2007) A variational assimilation ensemble and the spatial filtering of its error covariances: Increase of sample size by local spatial averaging paper presented atECMWF Workshop on Flow\u2010Dependent Aspects of Data Assimilation 11\u201313 June Eur. Cent. for Medium\u2010Range Weather Forecasts Reading U.K."},{"key":"e_1_2_8_6_1","unstructured":"Berre L. G.Desroziers L.Raynaud R.Montroty andF.Gibier(2009) Consistent operational ensemble variational assimilation paper 196 presented atFifth WMO International Symposium on Data Assimilation 5\u20139 October 2009 WMO Melbourne Australia."},{"volume-title":"Atmospheric Data Analysis","year":"1991","author":"Daley R.","key":"e_1_2_8_7_1"},{"key":"e_1_2_8_8_1","doi-asserted-by":"publisher","DOI":"10.1175\/MWR2929.1"},{"key":"e_1_2_8_9_1","doi-asserted-by":"crossref","first-page":"195","DOI":"10.3402\/tellusa.v51i2.12316","article-title":"A reformulation of the background error covariance in the ECMWF global data assimilation system","volume":"51","author":"Derber J.","year":"1999","journal-title":"Tellus Ser. 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O.Vignes N.Gustafsson T.Landelius andS.Thorsteinsson(2007) Background errors in HIRLAM variational data assimilation presented atECMWF Workshop on Flow\u2010Dependent Aspects of Data Assimilation 11\u201313 June Eur. 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