@AudiovisualMaterial{DinizTodl:2018:CoAdEn,
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.",
affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and NASA",
author = "Diniz, F{\'a}bio Luiz Rodrigues and Todling, R.",
city = "Aveiro, Portugal",
conferencename = "Workshop on Sensitivity Analysis and Data Assimilation in
Meteorology and Oceanography",
date = "01-06 july",
language = "en",
publisher = "Instituto Nacional de Pesquisas Espaciais",
publisheraddress = "S{\~a}o Jos{\'e} dos Campos",
targetfile = "diniz-comparing.pdf",
title = "Comparing the adjoint- and ensemble-based approaches to
observation impact on short-range forecasts",
year = "2018",
urlaccessdate = "11 maio 2024"
}