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Southern Ocean air–sea fluxes are a critical component of the climate system but are historically undersampled due to the remoteness of the region. While much focus has been placed on interannual flux variability, it has become increasingly clear that high-frequency fluctuations, driven by processes like storms and (sub-)mesoscale eddies, play a nonnegligible role in longer-term changes. Therefore, collecting high-resolution in situ flux observations is crucial to better understand the dynamics operating at these scales, as well as their larger-scale impacts. Technological advancements, including the development of new uncrewed surface vehicles, provide the opportunity to increase sampling at small scales. However, determining where and when to deploy such vehicles is not trivial. This study, conceived by the Air–Sea Fluxes working group of the Southern Ocean Observing System, aims to characterize the statistics of high-frequency air–sea flux variability. Using statistical analyses of atmospheric reanalysis data, numerical model output, and mooring observations, we show that there are regional and seasonal variations in the magnitude and sign of storm- and eddy-driven air–sea flux anomalies, which can help guide the planning of field campaigns and deployment of uncrewed surface vehicles in the Southern Ocean. 

Ocean surface radiation measurement best practices have been developed as a first step to support the interoperability of radiation measurements across multiple ocean platforms and between land and ocean networks. This document describes the consensus by a working group of radiation measurement experts from land, ocean, and aircraft communities. The scope was limited to broadband shortwave (solar) and longwave (terrestrial infrared) surface irradiance measurements for quantification of the surface radiation budget. Best practices for spectral measurements for biological purposes like photosynthetically active radiation and ocean color are only mentioned briefly to motivate future interactions between the physical surface flux and biological radiation measurement communities. Topics discussed in these best practices include instrument selection, handling of sensors and installation, data quality monitoring, data processing, and calibration. It is recognized that platform and resource limitations may prohibit incorporating all best practices into all measurements and that spatial coverage is also an important motivator for expanding current networks. Thus, one of the key recommendations is to perform interoperability experiments that can help quantify the uncertainty of different practices and lay the groundwork for a multi-tiered global network with a mix of high-accuracy reference stations and lower-cost platforms and practices that can fill in spatial gaps. 

Abstract Proposals from multiple nations to deploy air–sea flux moorings in the Southern Ocean have raised the question of how to optimize the placement of these moorings in order to maximize their utility, both as contributors to the network of observations assimilated in numerical weather prediction and also as a means to study a broad range of processes driving air–sea fluxes. This study, developed as a contribution to the Southern Ocean Observing System (SOOS), proposes criteria that can be used to determine mooring siting to obtain best estimates of net air–sea heat flux ( Q net ). Flux moorings are envisioned as one component of a multiplatform observing system, providing valuable in situ point time series measurements to be used alongside satellite data and observations from autonomous platforms and ships. Assimilating models (e.g., numerical weather prediction and reanalysis products) then offer the ability to synthesize the observing system and map properties between observations. This paper develops a framework for designing mooring array configurations to maximize the independence and utility of observations. As a test case, within the meridional band from 35° to 65°S we select eight mooring sites optimized to explain the largest fraction of the total variance (and thus to ensure the least variance of residual components) in the area south of 20°S. Results yield different optimal mooring sites for low-frequency interannual heat fluxes compared with higher-frequency subseasonal fluxes. With eight moorings, we could explain a maximum of 24.6% of high-frequency Q net variability or 44.7% of low-frequency Q net variability.