BEGIN:VCALENDAR VERSION:2.0 PRODID:-//132.216.98.100//NONSGML kigkonsult.se iCalcreator 2.20.4// BEGIN:VEVENT UID:20250428T142611EDT-9019tvucHn@132.216.98.100 DTSTAMP:20250428T182611Z DESCRIPTION: \n\nStudent Seminar Series\n\nDepartment of Atmospheric & Ocea nic Sciences\n\npresents\n\na talk by\n\nAndres Perez Hortal\n PhD student \n\nA heuristic approach for precipitation data assimilation using the inf ormation contained in the ensemble forecast\n\nWe present a simple data as similation (DA) technique named 'Localized Ensemble Mosaic Assimilation' ( LEMA) for the assimilation of radar-derived precipitation observations. Ou r objective is to modify the trajectory of the model toward a new trajecto ry that is closer to observed reality for a long forecast time. The method constructs an analysis mosaic by assigning to each model grid point the i nformation from the ensemble member that is locally closest to the precipi tation observations. The new ensemble forecast is created by relaxing all the background members are relaxed towards the analysis mosaic.\n\nSince L EMA relies only on the information contained in the ensemble forecast\, un der the ideal conditions were the spread of the ensemble forecast captures the actual forecast uncertainties\, LEMA performs as desired. However\, r eal DA experiments using StageIV precipitation observations show that when LEMA uses only the background members to construct the analysis\, the qua lity of the precipitation forecast shows small or no improvements. To over come this limitation\, we expand the spread of the ensemble used to constr uct the analysis mosaic by considering states at different times and state s from forecasts initialized at different times (lagged forecasts). The ex pansion of the ensemble spread provides a better representation of the act ual forecast uncertainties\, resulting in a better performance of LEMA.\n \nFinally\, in LEMA\, all the background ensemble members are relaxed towa rds the single analysis\, reducing the ensemble spread and produces an und erdispersive forecast. This limits the time intervals between successive a pplications of LEMA to ~9h\, at which time the ensemble spread in the fore cast is restored. To shorten the cycling period\, we add to LEMA another h euristic step: nudging the ensemble towards the analysis mosaic while main taining the original background's spread. Using real DA experiments\, we s how that successive DA using LEMA improves the forecast quality\, but it p roduces a slight decrease in the ensemble spread.\n\nWednesday Jan 22/ 2.3 0 PM/ Room 934 Burnside Hall\n\n \n\n \n\n \n DTSTART:20200122T193000Z DTEND:20200122T203000Z LOCATION:Room 934\, Burnside Hall\, CA\, QC\, Montreal\, H3A 0B9\, 805 rue Sherbrooke Ouest SUMMARY:A heuristic approach for precipitation data assimilation using the information contained in the ensemble forecast URL:/meteo/channels/event/heuristic-approach-precipita tion-data-assimilation-using-information-contained-ensemble-forecast-30871 5 END:VEVENT END:VCALENDAR