Use of adjoint sensitivity to advance process understanding and identify observing needs in the tropical Pacific. US CLIVAR Variations

Adjoint models are an essential tool for performing four-dimensional variational (4DVAR) data assimilation (e.g., Rabier et al. 1993; Stammer et al. 2002; Sugiura et al. 2008; Hoteit et al. 2010). They are also used for inferring space and time-resolved sensitivities in a numerical model of oceanic metrics to perturbations (e.g., Fukumori et al. 2004; Masuda et al. 2010), and evaluation of singular vectors to identify instable modes of the system (e.g., Fujii et al. 2008; Zana et al. 2011). Sensitivity experiments using adjoint models can be used to evaluate and design oceanic observation systems (e.g., Kӧhl and Stammer 2004; Cummings et al. 2014; Loose et al. 2021). This article introduces three studies which evaluate the sensitivity of ocean general circulation models using adjoint models and offers insights into understanding and evaluation of observing needs in the tropical Pacific. Grant no. NA21OAR4310255