Further evidence for non-reemergence of winter SST anomalies in the North Pacific eastern subtropical mode water area     

Shusaku Sugimoto  Kimio Hanawa 《Journal of Oceanography》2007,63(4):625-635

Following our previous study (Sugimoto and Hanawa, 2005b), we further investigate the reason why reemergence of winter sea surface temperature anomalies does not occur in the North Pacific eastern subtropical mode water (NPESTMW) area, despite its occurrence in the North Pacific subtropical mode water and North Pacific central mode water areas. We use vertical temperature and salinity profiles of the World Ocean Circulation Experiment Hydrographic Program and Argo floats with high vertical and temporal resolution, together with heat flux data through the sea surface. We point out first that one of the causes for non-occurrence of reemergence is that the thickness of NPESTMW is very thin. In addition to this basic cause, two major reasons are found: a vigorous mixing in the lower portion of NPESTMW and less heat input from the atmosphere in the warming season. Since, in the lower portion of NPESTMW and deeper, the stratification is favorable for salt-finger type convection to occur compared with the other mode water areas, vigorous mixing takes place. This is confirmed by both a large Turner Angle there and the existence of staircase structures in vertical temperature and salinity profiles. From the viewpoint of heat input, the NPESTMW area gradually gains heat in the warming season compared with other mode water areas. As a result, NPESTMW cannot be capped so quickly by the shallow summer mixed layer, and water properties of NPESTMW are to be gradually modified, even in the upper portion.  相似文献   

Recorder-Dependent Temperature Error of Expendable Bathythermograph     

Shoichi Kizu  Kimio Hanawa 《Journal of Oceanography》2002,58(3):469-476

The accuracy of temperature measurement by the expendable bathythermograph (XBT) is examined for five types of recorders by comparison with co-located CTD measurements and statistical analysis of temperature profiles including an isothermal layer. A positive temperature error increasing downward is occasionally detected for two types of Japanese recorder which have been commonly used among Japanese oceanographic institutions and marine observatories. This error resembles to that reported by Bailey et al. (1989) and Wright (1991) for a different type of recorders, although its cause is not clearly understood. The irregular occurrence of the error suggests that the problem is not solely due to the recorders but rather by some inconsistency of the whole measuring system including them, an XBT probe and sea water. The error is estimated to increase at a rate of O (0.1°C/100 m), and it could be close to 1°C at the deepest part of the profiles (760 m for Tsurumi T-7). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

A theory of semigeostrophic gravity waves and its application to the intrusion of a density current along a coast     

Atsushi Kubokawa  Kimio Hanawa 《Journal of Oceanography》1984,40(4):247-259

Semigeostrophic gravity waves associated with a coastal boundary current, which has finite and uniform potential vorticity and is bounded away from the coastline by a density front on the ocean surface, are investigated. It is shown that the semigeostrophic coastal current has two waves which are named here the Semigeostrophic Coastal Wave (SCW) and the Semigeostrophic Frontal Wave (SFW). The SCW becomes an elementary Kelvin wave at some limit while the SFW is caused by the existence of the surface density front. The SCW appears mainly as variations in the upper layer depth at the coast and as alongshore velocity at the density front. On the other hand, the SFW appears mainly as variations in the width of the current. When the weak nonlinearity and ageostrophic effect are included, these semigeostrophic gravity waves satisfy the Kortweg- de Vries equation, which suggests that the local changes in the width and/or velocity of the semigeostrophic coastal current propagate as wave-like disturbances.  相似文献   

Experimental study on internal waves in a stratified shear flow     

Tadashi Andow  Kimio Hanawa  Yoshiaki Toba 《Journal of Oceanography》1981,37(4):179-192

This paper describes experiments on interfacial phenomena in a stratified shear flow having a sharp velocity shear at a density interface. The interface was visualized in vertical cross-section using dye, and the flow pattern was traced using aluminum powder. Two kinds of internal waves with different phase velocities and wave profiles were observed. They are here named p(positive)-waves and n(negative)-waves, respectively. By means of a two-dimensional visualization technique, the following facts have been confirmed regarding these waves. (1) The two kinds of waves propagate in the opposite direction relative to a system moving with the mean velocity at the interface, and their dispersion relations approximately agree with the two solutions of interfacial waves in a two-layer system of a linear basic shear flow. (2) The p-wave has sharp crests and flat troughs, and the n-wave has the reverse of this. This difference in wave profile is due to the finite amplitude effect. (3) Phase velocity of each wave lies within the range of the mean velocity profile, so that a critical layer exists and each wave has a “cat's eye” flow pattern in the vicinity of the critical layer, when observed in a system moving with the phase velocity. Consequently, these two waves are symmetrical with respect to the interface. The mechanisms of generation of these waves, and the entrainment process are discussed. It is inferred that when the “cat's eye” flow pattern is distorted and a stagnation point approaches the interface, entrainment in the form of a stretched wisp from the lower to the upper layer occurs for the p-wave, and from the upper to the lower layer for the n-wave.  相似文献   

Subsurface Water Masses in the Central North Pacific Transition Region: The Repeat Section along the 18° Meridian     

Toshio Suga  Kazunori Motoki  Kimio Hanawa 《Journal of Oceanography》2003,59(4):435-444

A repeat hydrographic section has been maintained over two decades along the 180° meridian across the subarctic-subtropical transition region. The section is naturally divided into at least three distinct zones. In the Subarctic Zone north of 46°N, the permanent halocline dominates the density stratification, supporting a subsurface temperature minimum (STM). The Subarctic Frontal Zone (SFZ) between 42°–46°N is the region where the subarctic halocline outcrops. To the south is the Subtropical Zone, where the permanent thermocline dominates the density stratification, containing a pycnostad of North Pacific Central Mode Water (CMW). The STM water colder than 4°C in the Subarctic Zone is originated in the winter mixed layer of the Bering Sea. The temporal variation of its core temperature lags 12–16 months behind the variations of both the winter sea surface temperature (SST) and the summer STM temperature in the Bering Sea, suggesting that the thermal anomalies imposed on the STM water by wintertime air-sea interaction in the Bering Sea spread over the western subarctic gyre, reaching the 180° meridian within a year or so. The CMW in this section originates in the winter mixed layer near the northern edge of the Subtropical Zone between 160°E and 180°. The CMW properties changed abruptly from 1988 to 1989; its temperature and salinity increased and its potential density decreased. It is argued that these changes were caused by the climate regime shift in 1988/1989 characterized by weakening of the Aleutian Low and the westerlies and increase in the SST in the subarctic-subtropical transition region. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Analysis of year-to-year variation of water temperature along the coast of the Japan sea     

Tomowo Watanabe  Kimio Hanawa  Yoshiaki Toba 《Progress in Oceanography》1986,17(3-4)

Mean monthly records of coastal sea surface temperature data (CSST) obtained from stations along the Japanese coasts of the Japan Sea and from those in the related seas for the period 1941–1984 were analyzed by using various methods of time series analysis, for the purpose of clarifying the nature of the year-to-year variations of the state of the Japan Sea. The year-to-year variations in the Japan Sea were found to be closely related to those in the East China Sea and in the western North Pacific. Specific results are as follows. (1) A sudden cooling in the early 1960's occurred in the southern stations of the Japan Sea and continued to the end of the analyzed data. (2) Variations, with about a 6-year periodicity, were observed at most stations, and were especially dominant in the southern stations of the Japan Sea (3) These variations could be traced back to the Kuroshio region of the East China Sea. (4) Variations, with about a 10-year periodicity, were also observed in the northern stations of the Japan Sea.  相似文献   

North Pacific Subtropical Mode Waters Observed in Long XBT Cross Sections along 32.5°N Line     

Kimio Hanawa  Hiroyuki Yoritaka 《Journal of Oceanography》2001,57(6):679-692

The S/V Shoyo, of the Hydrographic Department, Japan Coast Guard, has conducted high-density expendable bathythermograph (XBT) measurements along the 32.5°N line in the North Pacific every year from 1990 to 1993 as a part of the Japanese-World Ocean Circulation Experiment (WOCE). These XBT data are analyzed here, focusing on year-to-year variations of the inventory and core layer temperature (CLT) of the North Pacific subtropical mode water (NPSTMW). Large year-to-year changes are found in the NPSTMW CLTs estimated in longitudes between 140°E and 160°E. CLT values were found of 17.4°C in 1990, 17.1°C in 1991, 17.3°C in 1992 and 17.6°C in 1993. Inspection of the wintertime westerlies over the formation area and sea surface temperature distribution revealed that this change in CLT can be qualitatively attributed to the strength of atmospheric cooling in the formation area in the previous winter. Although a large year-to-year variation of NPSTMW inventory was also found, it is hard to state any relationship between CLT and atmospheric forcing. There is a possibility that different observational seasons may affect the inventory. It has also been found that the thermocline depth in 1991 was shallower in the sea area east of 180° than in 1992 and 1993. Associated with this change, the North Pacific central mode water (NPCMW), characterized by thermostad with temperatures ranging from 14°C to 11°C, appears in the sea area east of 180° in the 1992 and 1993 cross sections. The 1993 cross section, which ranged from the Japanese coast to the west coast of North America, possessed another thermostad in the surface layer, with a temperature of about 17°C in the eastern part of the cross section, off California. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

A New Fall-Rate Equation for T-5 Expendable Bathythermograph (XBT) by TSK     

Kizu  Shoichi  Yoritaka  Hiroyuki  Hanawa  Kimio 《Journal of Oceanography》2005,61(1):115-121

The accuracy of the manufacturer’s fall-rate equation for the T-5 Model of expendable bathythermograph (XBT) has been investigated based on about 300 collocated pairs of XBT-CTD (Conductivity-Temperature-Depth profiler) measurements in various climatological regions. We found that the equation systematically overestimates depth by about 5% for the T-5 produced by Tsurumi Seiki, Co. Ltd. (TSK), but almost no bias is associated with the T-5 produced by Sippican, Inc., in USA. The cause of this difference is not clear, because the two manufacturers’ T-5 probes are reported to have identical shape and weight in water. We propose a new fall-rate equation for the TSK T-5: z(t) = 6.54071t - 0.0018691t ², where z(t) is depth in meters at time, t, in seconds.  相似文献   

Outbreak of warm water from the Kuroshio South of Japan     

Y. Toba  H. Kawamura  K. Hanawa  H. Otobe  K. Taira 《Journal of Oceanography》1991,47(6):297-303

During the concentrated observation (April–May 1988) conducted as a part of the Ocean Mixed Layer Experiment (OMLET) in the sea area south of Japan, a conspicuous outbreak of warm water occurred from the large-meander region of the Kuroshio toward the southwest in the direction of the former Ocean Weather Station “T”. A series of NOAA-AVHRR infrared images clearly showed the process of this event. A surface buoy-mooring system deployed in this experiment recorded the arrival of this outbreak of water, in terms of the rise of sea-surface temperature (SST) of 1.5°C and the flow of warm water of 1.5kt toward the northwest at “T”. We studied this phenomenon by combining time series of infrared SST images with the oceanographic data obtained by two research vessels. The warm water was about 100 m deep in the section at 137°E along the edge of the Off-Shikoku Warm Water. It was estimated that about twenty outbreaks of this kind in a year can compensate a large heat loss to the atmosphere above this ocean region.  相似文献   

Detection of systematic errors in XBT data and their correction     

Kimio Hanawa  Hiroyuki Yoritaka 《Journal of Oceanography》1987,43(1):68-76

Comparison experiment between XBT of T-7 probe and CTD was conducted at 15 stations in the sea area centered on 29°N, 135°E in December 1985. There were systematic errors in XBT temperature profiles in comparison with CTD temperature profiles. The main cause of errors was attributed to an error in the free-fall speed of the XBT probes which was provided by the XBT maker. A previous equation for depth correction proposed by Heinmilleret al. (1983) could not give effective correction for our data. A new equation between the probe depth and the elapsed time from landing of the probe on the water was obtained by the method of adjusting temperature gradients of XBT profiles to those of CTD profiles. This equation agreed with the theoretical result given by Seaver and Kuleshov (1982) much better than that of Heinmilleret al. (1983). Systematic errors due to a scatter of values of the reference resistance and variation of B-constant of thermistors used in XBT also seemed to exist. After an adjustment using the temperature difference between XBT and CTD in the mixed layer with depths of about 100 m, the standard deviation of temperature difference between XBT and CTD from the surface to the depth of 750 m was 0.14°C.  相似文献