Visual wind wave data from VOS: a substantial component of wind wave observing system Sergey K. Gulev and Vika Grigorieva (P.P. Shirshov Institute of Oceanology, RAS, email@example.com) Visual wave observations (assimilated in ICOADS) are available effectively from the mid 19th century and represent the longest records of wind wave information worldwide taken with a unique observational practice. Visual wave data are characterized by quite strong systematic and random errors. Maximum random observational errors in wins sea height amount to 1 meter with maximum random observational errors in swell height being up to 1.6 meters. Significant uncertainties (both random and systematic) in wind wave periods estimates of up to 2-3 seconds may result from the deviation of the actual observational practices from the guidelines. VOS-based climatological estimates of wave characteristics also suffer from spatially and temporally inhomogeneous sampling with the largest sampling errors (up to 1.5-2 meters in wave height) identified in the poorly observed regions of the Southern Ocean and subpolar Northern Hemisphere. We will present 60-yr climatology of wind waves based on visual observations. It includes estimates of heights and periods of wind sea and swell as well as derived SWH and dominant period along with error estimates. Climatology allows for the analysis of linear trends and patterns of interannual variability in wind wave characteristics worldwide. Analysis of the earlier 20th century records of visual wave data for selected ship routes demonstrated centennial increase of SWH (of 8-10 cm/decade) in the North Pacific, with no significant centennial trends in the Atlantic. Visual VOS data also allow for estimates of extreme wind waves for the last several decades, if only in well sampled North Atlantic and North Pacific mid latitudes. Further prospects for the improvement of the accuracy of visual wind wave data will be discussed. These include installation onboard of selected VOS rolling sensors and recording of ship radar scans for providing alternative data for the validation of visual wave estimates.
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