Extended Abstract

Ongoing developments on Limited Area Ensemble Forecastingand the coordination role of TIGGE LAMTiziana PaccagnellaARPA-SIMC, Hydro-Meteorological and Climate Service of the Emilia-RomagnaRegional Agency for Environmental Protection, Bologna, Italy, tpaccagnella@arpa.emr.itAcknowledgmentsPart of this presentation is based on the TIGGE LAM plan still under writing and I wish to aknowledge theco-authors and particularly Josh Hacker, David Parsons and Richard Swinbank.I really wish to thank all the colleagues who sent me update information about their present activities: JanBarkmeijer, Neil B owler, Jing C hen, Jun Du, Clau de Fisher, Inger L ise Fro gner, Jian dong Gong, Nil sGustavson, Joshua Hacker, Tro nd Iver sen, Ake Joh ansson, Mate Mile, J osè Antonio Garcia Moya, KenMylne, Yong Wang, Xue Ming, Chiara Marsi gli, Andrea Montani, Olivier Nuissier, Nigel Roberts, KazuoSaito, Susanne Theis, Zoltan Toth.I ap ologize but, due t o obvi ous ed iting restrictio ns, I could not give app ropriate vi sibility to th eircontributions in this abstract.IntroductionEnsemble forecasting was initially introduced to improve the predictability of atmospheric motions andprocesses at medium r ange a nd at the sy noptic scale. T hese successful applications, toget her with t henecessity to i mprove t he p redictability of severe /high i mpact weather events, l ed the scientificmeteorological community to develop Ensemble Prediction Systems (EPS) based on Limited Area Models(LAM) to benefit of the higher attainable horizontal resolution.Considering that Global EPS are moving to higher and higher resolution, the main added value fromLAM EPS will be in the representation of phenomena at the convective-permitting/resolving scale. This isan important contribution if considering that high impact/severe events usually are strongly determined orenhanced by a mesoscale or convective scale component. Many open scientific and technical challenges areto be tac kled and sci entific issues cover a wid e s pectrum of problems, most of them common to Glob alEPS: m esoscale predictability, p roper representati on of the different sources of uncertaint y, efficientmethods to generate perturbations, interaction of l ocal perturbations with those transmitted by the drivingglobal systems, calibration of non Gaussian fields, verification of intense and rare events etc.etc.LAM EPS: Scientific issuesThe primary goal of EPS is to represent and quantify the uncertainty associated with numerical weatherprediction. T his uncertainty is due to t he many appr oximations a nd errors affecting t he modelling chai nboth during the assimilation of the meteorological observations and during the model integration. A “good”EPS should pro vide forecast scenari os statistically indistinguishable fro m th e real at mospheric evol ution,quantify the system uncertainty by means of the ensemble spread with the same amplitude of the forecasterror, and should also provide a better deterministic forecast based on the ensemble mean (at least for upperair fields). Going fr om gl obal to L AM EPS, the pr ocess to rep resent for ecast unce rtainty is even moreintricate si nce lar ger s cale perturbations (hereafter referred as larger pe rturbations) interact withperturbations generated to represent smaller scale errors (hereafter referred as local perturbations) typical ofLAM forecasting.A lot of research work has been do ne and is being doing with specific focus on the local perturbationson th e initial cond itions and on t he model trajectories (e .g. Hacker et al 20 10, Wang 2010 (tal k at t hisconference) , Marsigli 2009, Montani et al. 2010, Li et al, 2 008, Jing 2010 (talk at this conference), Wang2010 (tal k at this conference) ). It i s re asonable to expect t hat lo cal pert urbations will be relatively m oreimportant in the s hortest ti me range and at very h igh resol ution (1 -3 k m up to 24 ho urs). It is ag ainreasonable to assume that consistency with bo undary perturbations will sustain better the development oflocal perturbations, but methodologies to assure this consistency is still matter to be investigated. One of themost recent an d advanced work in this direction has been done recently by the Met. Office (Bowl er and-287-