Meeting Documents

Estimating the Unobserved: West Antarctic State Estimation Using the Ice-sheet and Sea-level System Model (ISSM), 1992-2023

Abstract

Improving estimates of ice/ocean parameters and states reduces sea level change uncertainty. However, improving estimates in areas such as under the Antarctic Ice Sheet (AIS) is non-trivial, as direct observations are typically not feasible. Data assimilation of time series datasets using models of physical processes can constrain otherwise unobservable states and parameters of the AIS. Capabilities developed within the Ice-sheet and Sea-Level System Model (ISSM) allow for the simultaneous inversion of such unobservables. More specifically, newly improved automatic differentiation/adjoint model capabilities in ISSM allow for the simultaneous inversions of static basal friction and ice rheology, as well as time series estimates of sub-ice shelf melt, grounding line positions, and other parameters. These newly improved estimates are then validated against observations of velocity and thickness changes, and can then be referenced against other estimates within the area of study, which is focused on the Ronne Ice Shelf and surrounding areas in West Antarctica. This study evaluates this methodology over the period 1992-2023. By providing a physically-consistent estimate of unobservable states and parameters to improve estimates for use in the community, enable coupling to other state estimates such as the ECCO ocean circulation model, provide insights into the evolution of the AIS over the past 30 years, and thus constrain sea level change. This work is performed at the California Institute of Technology’s Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration.