THERMOSTAD DISTRIBUTION IN THE NORTH PACIFIC SUBTROPICAL GYRE - THE GENERAL MODE WATER AND THE SUBTROPICAL MODE WATER

The upper thermal structure of the midlatitude North Pacific is studie d with the use of all the bathythermograph data compiled in the global ocean temperature and salinity profiles released by the National Ocea nographic Data Center Climatological temperature data are prepared for each 2.5 degrees x 5 degrees (latitude X longitude) rectangle. The up per layer of the subtropical gyre is characterized by two types of the rmostads or mode waters: one in the western basin known as North Pacif ic subtropical mode water (NPSTMW) and the other in the central basin to be named North Pacific central mode water (NPCMW). The NPCMW thermo stad lies centered around 160 degrees W between the Kuroshio Extension and the Kuroshio bifurcation front. Its local core temperature ranges from 10 degrees to 13 degrees C with a somewhat zonally elongated pat tern, in contrast to the more uniform core temperature at 16 degrees-1 7 degrees C of the NPSTMW thermostad lying centered at 150 degrees-160 degrees E south of the Kuroshio Extension. The climatological map of the wintertime mixed layer thickness together with sea surface tempera ture distribution indicates that the NPCMW formation area is likely si tuated south of the Kuroshio bifurcation front and at 175 degrees E-16 0 degrees W extending as far south as about 37 degrees N around 170 de grees W. The climatological geostrophic flow field suggests that the N PCMW thermostad is spread from its formation area by the North Pacific Current flowing primarily eastward with relatively small southward ve locity, which is contrasted with the NPSTMW thermostad spread within t he anticyclonic Kuroshio recirculation region and explains the rather zonally elongated temperature distribution of NPCMW. The NPCMW formati on can be fit into tile recent estimation of the subduction rate of th e main thermocline, coinciding with the region of the moderate subduct ion rate dominated by the lateral induction term.