Abstract
Different from the existing global ocean climatological datasets of isothermal layer (ITL) depth (h), a global ocean synoptic dataset of h along with other parameters has been established from temperature profiles of the National Centers for Environmental Information (NCEI) world ocean database 1961–2017. The exponential leap-forward gradient method was used to identify h and thermocline gradient (G) from each temperature profile measured by expendable bathythermograph (XBT) and conductivity, temperature, depth (CTD) instruments. Due to quality and vertical resolution of the profiling data, the numbers of (G, h) pairs are 446,811 out of 964,942 CTD profiles and 755,086 out of 2,303,433 XBT profiles. With the given h, other parameters such as ITL heat content (HITL), sea surface temperature (SST), temperature below ITL (Tm), and quality measures (Q, I) indices are provided. Altogether, the dataset contains 1,201,897 temporally and horizontally varying sets of (G, h, HITL, SST, Tm, Q-index, I-index). Note that we added 200° to the longitude. This synoptic dataset is located on the NCEI website for public use.
Highlights
Background & SummaryExisting global datasets of isothermal layer (ITL) depth (h) are all climatologies on regular grids with 1° horizontal resolution and standard World Ocean Atlas (WOA) vertical depths, either computed from 3D gridded temperature climatology[1,2] or identified from observational temperature profiles and averaged in 1° or 2° cells[3,4]
Since the vertical gradient is strongest in the thermocline and weakest in the ITL (Fig. 1b,c), it is reasonable to assume that the vertical temperature difference inside the ITL is within 10% of Td
All the statistical parameters are comparable between the synoptic and climatological datasets except the mean and standard deviation of G, which were much lower in the climatology datasets such as (0.034 °C/m, 0.022 °C/m) in the WOA13-1°, and (0.034 °C/m, 0.023 °C/m) in the WOA13-0.25°
Summary
Existing global datasets of isothermal layer (ITL) depth (h) are all climatologies on regular grids with 1° horizontal resolution and standard World Ocean Atlas (WOA) vertical depths, either computed from 3D gridded temperature climatology[1,2] or identified from observational temperature profiles and averaged in 1° or 2° cells[3,4]. A recent approach is to use the transition from the near-zero gradient in the ITL to the non-zero gradient in the thermocline to determine h This leads to a maximum curvature method[19,20,21,22]. The dataset contains 1,201,897 sets of (G, h, HITL, SST, Tm, Q-index, I-index), and is located at the NCEI website for public use
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