Investigation of a calibration change in the ocean surface wind measurements from the TAO buoy array

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Abstract During routine analyses of the calibration stability of ocean surface wind retrievals from satellites, we identified a significant bias between satellite measurements and wind observations from the TAO buoy array, starting in mid-2020 until present. After extensive investigation, we determined that the bias did not arise from anomalies in the satellites’ calibration or coding errors, as it appeared regardless of which satellite these buoys were compared to. A sudden increase of about 10% (0.5–0.8 m/s) in wind speed observations was first identified in over 40 TAO buoys that were serviced between March and September 2020. Our concerns were shared with scientists at the National Data Buoy Center (NDBC), who confirmed our estimates. The exact source of this sudden change is still under investigation, but it appears to be related to changes in the calibration of buoy anemometers installed during recent service trips. By 2024, all currently-operating TAO buoys under NDBC management have been serviced since 2020, and they all manifest a sudden wind speed increase post-service in the public-facing buoy data. This change is a source of concern because the stability of the integrated satellite-buoy system is vital for international ocean observation programs. The aim of this paper is to inform the research community about this spurious wind signal in the TAO array, discuss the impact it could have on the research community, and prevent it from being misinterpreted as climate variability, impacting the calibration of other observing systems, or affecting derived data products such as ocean surface fluxes.