WOA23 Decav Sound Velocity Datasets (Annual, Seasonal and Monthly) 1/4 degree resolution

This dataset contains derived climatological seawater sound-speed fields based on the World Ocean Atlas 2023 (WOA23), NOAA NCEI’s collection of objectively analysed oceanographic climatologies based on World Ocean Database 2023 observations. Its decav reference represents 1955–2022, averaging the seven climatological periods 1955–1964, 1965–1974, 1975–1984, 1985–1994, 1995–2004, 2005–2014 and 2015–2022. This period-based averaging differs from pooling all observations into one mean. Resolution code 04 specifies a 0.25° latitude × 0.25° longitude grid, equivalent to 15 angular minutes. Temporal identifiers distinguish annual climatology ( 00 ); monthly climatologies ( 01 January, 02 February, 03 March, 04 April, 05 May, 06 June, 07 July, 08 August, 09 September, 10 October, 11 November and 12 December); and seasonal climatologies ( 13 January–March, 14 April–June, 15 July–September and 16 October–December). Quarter-degree monthly climatologies are available for the WOA23 seven-period decav average. The seasonal labels use Northern Hemisphere terminology. Annual and seasonal temperature and salinity source fields contain 102 standard depth levels spanning 0–5500 m, whereas monthly fields contain 57 levels spanning 0–1500 m; valid coverage varies with source masking and ocean depth. Sound-speed fields for the WOA23 decav , resolution 04 collection were derived using the Python CalculateSvp class from the objectively analysed temperature ( t_an ) and salinity ( s_an ) fields at the selected source grid cells and standard depths. Two separate estimates are produced: v_an_chen , calculated using the implemented Chen–Millero/UNESCO-type temperature–salinity–pressure polynomial, and v_an_leroy , calculated using the Leroy, Robinson and Goldsmith (2008) temperature–salinity–depth–latitude equation; both yield sound speed in metres per second. For the former, pressure is estimated from depth and latitude using Leroy and Parthiot (1998), with an optional configured regional correction, and converted from MPa to bar before evaluation. The class applies these calculations directly to the climatological inputs without additional spatial or vertical interpolation, extrapolation or missing-value filling. The results are derived climatological sound-speed estimates rather than direct acoustic measurements. The files in this dataset are used with these MB-System tools: mbsvpbest, mbsvproute, mbsvplocation, and mbsvpnearest. They are available here: https://github.com/dwcaress/MB-System References: https://www.ncei.noaa.gov/sites/default/files/2022-06/woa18documentation.pdf https://www.ncei.noaa.gov/access/world-ocean-atlas-2018/ https://www.ncei.noaa.gov/access/world-ocean-atlas-2023/