A characterization of the North Atlantic STMW layer climatology using World Ocean Atlas 1994 data

Abstract

The North Atlantic Subtropical Mode Water (STMW) layer was identified based on its temperature, large thickness, and small temperature gradient. Comparisons between this method and identifying the STMW layer using a density-based (i.e., potential vorticity) criteria indicate that this method successfully identifies the STMW layer as the remnant of the previous winter's convective mixing. By using this temperature-based characterization of the STMW layer, this method was able to develop a climatology using the large number of expendable bathythermographs (XBTs) deployed between 1968 and 1988, and contained in the World Ocean Atlas 1994 historical hydrographic database. From this climatology, the STMW layer that is the remnant of the previous winter's convective activity is typically found between 175 and 450 m, has an average temperature near 18°C, and has a mean temperature gradient of 0.5°C (100 m)-1. Comparisons of the STMW temperature, thickness, and temperature gradient characteristics in this climatology agree with other observations of the North Atlantic STMW layer.