Observing System Simulation Experiments for an array of autonomous biogeochemical profiling floats in the Southern Ocean

Abstract

This study uses Observing System Simulation Experiments (OSSEs) to examine the reconstruction of biogeochemical variables in the Southern Ocean from an array of autonomous profiling floats. In these OSSEs, designed to be relevant to the Southern Ocean Carbon and Climate Observation and Modeling (SOCCOM) project, the simulated floats move with oceanic currents and sample dissolved oxygen and inorganic carbon. The annual mean and seasonal cycle of these fields are then reconstructed and compared to the original model fields. The reconstruction skill is quantified with the reconstruction error (RErr), defined as the difference between the reconstructed and actual model fields, weighted by a local measure of the spatiotemporal variability. The square of the RErr is small (<0.5) for 150 floats in most of the domain, which is interpreted to mean that the reconstruction skill is high. An idealized analytical study demonstrates that the RErr depends on the magnitude of the seasonal cycle, spatial gradients, speed of float movement, amplitude of mesoscale variability, and number of floats. These factors explain a large part of the spatial variability in the RErr and can be used to predict the reconstruction skill of the SOCCOM array. Furthermore, our results demonstrate that an array size of 150 floats is a reasonable choice for reconstruction of surface properties and annual‐mean 2000 m inventories, with the exception of the seasonal cycle in parts of the Indo‐Atlantic, and that doubling this number to 300 results in a very modest increase in the reconstruction skill for dissolved oxygen.

Observing Changes in Ocean Carbonate Chemistry: Our Autonomous Future

“…A successful example of such coordination between communities has been demonstrated by the SOCCOM project [148]. During the planning stages of the project, Observing System Simulation Experiments (OSSEs) were used to simulate an array of Southern Ocean biogeochemical profiling floats and to examine the reconstruction skill that could be achieved from the fleet [149,150]. These OSSEs provided critical information about the number of floats required to reproduce observed patterns of oxygen, DIC, and air-sea CO 2 fluxes.…”

Delivering Sustained, Coordinated, and Integrated Observations of the Southern Ocean for Global Impact

“…These tools, known as Observing System Simulation Experiments (OSSEs), are used to estimate the value of ocean observations, with respect to how well they constrain the goals of the observing system. Observing system design evaluation entails subsampling a realistic model solution and determining the ability to then reconstruct this model solution (e.g., Forget et al, 2008;Kurahashi-Nakamura et al, 2014;Kamenkovich et al, 2017). The realistic model solution being sampled is known as the "nature run."…”

Southern Ocean Biogeochemical Float Deployment Strategy, With Example From the Greenwich Meridian Line (GO‐SHIP A12)

“…Thus, the plan for ~200 BGC floats in the Southern Ocean is on track and expected to be successful. We note that this goal is more than sufficient for reconstruction of the annual mean oxygen and DIC, based on Kamenkovich et al (), and so our goal of 200 includes redundancy.…”

“…The minimum spatial sampling density of BGC Argo floats required to resolve key features of the air‐sea carbon exchange in the Southern Ocean has been tested in Observing System Simulation Experiments (OSSEs), suggesting 150–200 floats south of 30°S (Kamenkovich et al, ; Majkut et al, ; Mazloff et al, ). At this sampling density, the BGC floats form an intentionally incoherent array.…”