@InProceedings{DinizTodl:2018:CoAdEn,
               author = "Diniz, F{\'a}bio Luiz Rodrigues and Todling, R.",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and NASA",
                title = "Comparing the adjoint- and ensemble-based approaches to 
                         observation impact on short-range forecasts",
                 year = "2018",
         organization = "Workshop on Sensitivity Analysis and Data Assimilation in 
                         Meteorology and Oceanography",
             abstract = "GMAO is one of the few Centers around the world that has been 
                         evaluating observation impact on the twenty-four hour forecasts 
                         using an adjoint-based approach for many years. This is 
                         implemented within its near-real time GEOS data assimilation 
                         system (DAS) which involves the adjoint of the GEOS general 
                         circulation model (GCM), responsible for calculating forecast 
                         sensitivities, and the adjoint of the Grid-point Statistical 
                         Interpolation (GSI) analysis, responsible for calculating analysis 
                         sensitivities. The GMAO implementation of the adjoint-based 
                         observation impact dates back to the times when GEOS DAS was still 
                         running 3dVar. More recently, the GEOS assimilation approach has 
                         evolved, first into ensemble hybrid 3dVar, and as of January 2017 
                         into hybrid 4dEnVar. These ensemble hybrid systems rely on a 
                         reduced-resolution ensemble running in parallel with the 
                         high-resolution hybrid analysis, and combine an ensemble of GEOS 
                         GCM integrations with the Ensemble Square-Root Filter (EnSRF) 
                         analysis. The adjoint-based observation impact tool is 
                         automatically available in systems implementing traditional or 
                         hybrid, 3D or 4D, variational methods. Many hybrid data 
                         assimilation systems currently used at NWP centers do not have an 
                         adjoint of the underlying GCM, thus lacking the ability to 
                         evaluate observation impact through traditional adjoint-based 
                         methods. In such systems, an argument can be made for deriving 
                         observation impacts on forecasts using an ensemble-based approach 
                         instead. Unfortunately, typical hybrid systems use ensembles that 
                         operate at different resolution than the deterministic forecasting 
                         model which result in degraded forecast quality when compared to 
                         the central high-resolution forecasts. Worse still is the fact 
                         that in many hybrid systems, the ensemble analysis handles the 
                         observing system in substantially different ways than the way the 
                         hybrid, deterministic, analysis does. This particular issue is 
                         enough to argue that an ensemble-based approach to observation 
                         impact is bound to provide an incorrect assessments of the 
                         observations used in the hybrid systems. This presentation 
                         compares these approaches to observation impact using GEOS DAS.",
  conference-location = "Aveiro, Portugal",
      conference-year = "01-06 july",
             language = "en",
        urlaccessdate = "27 abr. 2024"
}