Climate Linked Atlantic Sector Science (CLASS)nmat is a global dataset of monthly mean night marine air temperature (NMAT) that is produced on a 5° latitude by 5° longitude regular grid and covers the period 1880 to 2019.

The temperature values are taken from version 3.0.0 of the International Comprehensive Ocean-Atmosphere Data Set (ICOADS) for the period 1880-2014 and from version 3.0.2 of ICOADS thereafter. The in situ air temperature readings recorded between one hour after sunset and one hour after sunrise have been extracted from ICOADS and the ship data have been adjusted to reduce the effects of varying thermometer heights. The data have been adjusted from their respective recording heights to each of three reference heights: 2m, 10m and 20m. The air temperature readings have been subjected to a quality-control procedure and values that fail these tests have been excluded. Duplicate values have also been excluded. Additional adjustments have been applied to the data during the Second World War to account for non-standard thermometer exposures on some ships.

The adjusted data have been aggregated into monthly mean values in each grid-cell; uncertainty estimates of these gridded values are also provided. The data have not been interpolated across missing grid boxes. In addition to the absolute temperature values, the gridded data also contain anomalies that are expressed with respect to three climatological averages (1961-90, 1971-2000 and 1981-2010).

Averages across three large-scale domains are provided and these have been calculated from the 10m gridded anomaly data fields and these data are provided in comma-separated values (CSV) files. Uncertainty estimates in these averages are also provided.

Dataset description:

Gridded data:

For each of the reference heights (2m, 10m and 20m) there are three files for each of the base periods. These files contain the absolute gridded data at the respective height, the anomaly values and the uncertainty estimates. The uncertainty estimates consist of three components (correlated, uncorrelated sampling) along with the total uncertainty estimates. Uncertainty values from the climatology estimates are also provided. The climatology files contain the smoothed climatology values along with the 200-member ensemble of climatology realizations, which are used to construct the climatology uncertainties. All uncertainties are 1-sigma values.

Time series data:

Monthly and annual anomaly averages across four regions are provided as CSV files: Global, northern/southern hemispheres and the tropics (30S-30N). These files also contain the corresponding uncertainty values.

Format:

The gridded files are available as NetCDF 4 files, and use a factor 6 compression level. The NetCDF files meet CF-compliance version 1.6. The time series data (large-scale averages) computed from the gridded data are available as comma-separated values (CSV).

Please note that the current public release of ICOADS for the period after 2015 (the near-real-time updates) is version 3.0.1. In CLASSnmat we have used version 3.0.2, which is currently a test version and is not yet publicly available.