The North Pacific Climatology of Winter Mixed Layer and Mode Waters

Abstract

Abstract A climatology of the winter mixed layer in the North Pacific Ocean was constructed using hydrographic data from historical archives and recent observational programs, including the World Ocean Circulation Experiment. The main aim was to provide better knowledge about source areas of upper water masses. The authors have endeavored to preserve water properties near the frontal regions by keeping the smoothing scale as small as possible. The resulting climatology shows considerable differences in the mixed layer depth and its water properties from those derived from the World Ocean Atlas (WOA). Maps of the potential vorticity field of the North Pacific pycnocline are presented using the isopycnally averaged climatology, HydroBase. Three distinct lateral minima of potential vorticity are identified as Subtropical Mode Water (STMW), Central Mode Water (CMW), and Eastern Subtropical Mode Water (ESTMW), in the western, central, and eastern parts of the subtropical gyre, respectively. The HydroBase isopy...