Autumn atmospheric preconditioning for interannual variability of wintertime sea-ice in the Okhotsk Sea     

Yoshi N. Sasaki  Yurika Katagiri  Shoshiro Minobe  Ignatius G. Rigor 《Journal of Oceanography》2007,63(2):255-265

Relations in year-to-year variability between wintertime Sea-Ice Concentrations (SICs) in the Okhotsk Sea and atmospheric anomalies consisting of zonal and meridional 1000-hPa wind speeds and 850-hPa air temperatures are studied using a singular value decomposition analysis. It is revealed that the late autumn (October–November) atmospheric conditions strongly influence sea-ice variability from the same season (late autumn) through late winter (February—March), in which sea-ice extent is at its maximum. The autumn atmospheric conditions for the positive sea-ice anomalies exhibit cold air temperature anomalies over the Okhotsk Sea and wind anomalies blowing into the Okhotsk Sea from Siberia. These atmospheric conditions yield anomalous ocean-to-atmosphere heat fluxes and cold sea surface temperature anomalies in the Okhotsk Sea. Hence, these results suggest that the atmospheric conditions affect the sea-ice through heat anomalies stored in sea-ice and oceanic fields. The late autumn atmosphere conditions are related to large 700-hPa geopotential height anomalies over the Bering Sea and northern Eurasia, which are related to a stationary Rossby wave propagation over the North Pacific and that from the North Atlantic to Eurasia, respectively. In addition, the late autumn atmospheric preconditioning also plays an important role in the decreasing trend in the Okhotsk sea-ice extent observed from 1980 to the mid-1990s. Based on the lagged sea-ice response to the late autumn atmosphere, a simple seasonal prediction scheme is proposed for the February–March sea-ice extent using four-month leading atmospheric conditions. This scheme explains 45% of the variance of the Okhotsk sea-ice extent.  相似文献   

Testing of a towed CTD     

Yukio Fujinawa  Yoshinobu Tsuji  Isao Watabe  Ken Sasaki  Masao Nomoto  Toshiaki Hara  Yoshito Tsuji 《Journal of Oceanography》1980,36(5):253-258

The results of laboratory and field experiments on a CTD measuring unit attached to a controllable towed body is described. It was verified that the three-dimensional distribution of salinity and temperature could be observed with sufficient accuracy (to 0.03 in salinity and to 0.01°C in temperature if proper correction is adopted) while cruising at up to 4 knots. A double integrated A/D converter is used to compensate for effects of extraneous environmental changes.  相似文献   

Sedimentary records of multidecadal-scale variability of diatom productivity in the Bungo Channel, Japan, associated with the Pacific Decadal Oscillation     

Michinobu Kuwae  Azumi Yamashita  Yuichi Hayami  Atsushi Kaneda  Takashige Sugimoto  Yoshio Inouchi  Atsuko Amano  Hidetaka Takeoka 《Journal of Oceanography》2006,62(5):657-666

In order to examine the responses of primary productivity in the southern coastal sea of Japan to the Pacific Decadal Oscillation (PDO) in the 20th century, sedimentary records of diatom productivity (diatom valve fluxes) were reconstructed using core samples from the Bungo Channel (BC) in southwest Japan. The record of the Thalassionema spp. flux—the best index of fall primary productivity in the BC—indicated a multidecadal-scale duration with a low flux (1943–1982) and those with a high flux (1913–1943 and 1982–2001); apparent shifts were recognized in 1943 and 1982. The shift in 1982 was also recognized in the flux records of other early summer to fall predominant genera in the BC and, previously, in the biogenic silica records from a broad region of the southeast BC. This indicates that in our records, this shift reflects a general trend in the primary production in the southeast BC. A comparison among the Thalassionema spp. flux records, meteorological data from an observatory adjacent to the core site, and the PDO index showed that the flux records were more similar to the PDO index than the other meteorological records, which suggests that the multidecadal-scale variability of the BC primary productivity may be associated with some marine-derived forcing. The bottom intrusions of nutrient-rich water that upwelled from the shelf slope into the BC, the axis movement or the transport of the Kuroshio Current off the BC, and a basin-scale wind stress in the North Pacific might play an important role in this forcing and mediate between the BC primary productivity and the PDO.  相似文献   

Circulation and Material Transport in Suo-Nada during Spring and Summer     

Rolando S. Balotro  Atsuhiko Isobe  Manabu Shimizu  Atsushi Kaneda  Takatoshi Takeuchi  Hidetaka Takeoka 《Journal of Oceanography》2002,58(6):759-773

An attempt was made to reproduce the circulation pattern in Suo-Nada, Japan during spring and summer season in order to elucidate the water exchange mechanism in the basin. Two hydrographic surveys at the end of each season were conducted covering the entire Suo-Nada area. A three-dimensional hydrodynamic Princeton Ocean Model (POM) was used to compute the current resulting from the observed density and wind field. During spring, a very pronounced counter clockwise gyre is situated near the opening of the basin. This is replaced by a clockwise circulation which seemed to occupy the whole domain during summer. Within each season, however, the vertical distribution of current does not show any remarkable differences, indicating the dominance of horizontal current and a very weak estuarine flow. These observational and numerical results were used to estimate the remnant function and the corresponding average residence time of permanently dissolved matter (PDM) and transformable matter (TM). The results revealed a small difference in the average residence times of materials within each season but a large seasonal variability between spring and summer. Furthermore, calculations based on climatological density fields have indicated a similar trend of variation between the seasonal values of average residence times. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The Optical Characteristics of the Water in the Three Oceans Part—IV     

Kanau Matsuike  Tsutomu Morinaga  Tadayoshi Sasaki 《Journal of Oceanography》1970,26(1):52-60

An attempt to the approximate figures of seasonal distribution of solar energy reached to and penetrated in the water of the oceans, as a preliminary step to the estimation of primary production in the oceans from the optical point, was performed in the Indian Ocean, North Pacific Ocean and Antarctic Ocean on the same lines in the part III. In consequence, the total amount of solar energy for the year in each depth showed marked differences in each zone of the oceans as illustrated in Fig. 5. By way of example, it could be said that underwater solar energy already came to 33.4 Kg·cal/cm²·year in 10 m deep in the equator of Indian Ocean and was 54% of that, in the Kuroshio region of the North Pacific Ocean, 44% in the Sub-Antarctic zone, 13% in the Antarctic zone and 6% in the Antarctic Convergence zone, respectively. Besides, on the assumption that a lower limit of the photic zone is marked by the depth here underwater surface solar energy is reduced to 1% or 5g·cal/cm²·day, the ratio of the total photic zone for the year in unit area of sea surface was approximately 100∶80∶60∶25 or 100∶75∶50∶20 in the equator of the Indian Ocean, Kuroshio region, Sub-Antarctic zone, and Antarctic and Antarctic Convergence zones, respectively.  相似文献   

Tidal currents influenced by topographic eddies in Uchiumi Bay     

Hidetaka Takeoka  Hajime Murao 《Journal of Oceanography》1993,49(5):491-501

In the current record taken in Uchuimi Bay during summer in 1990, we find anomalous features that the tidal currents during spring and neap tides are quite different in both speed and direction, and the transition between them takes place suddenly. Relation between the variation of tidal current and the observed internal tide is examined, but they are poorly correlated. By examining the direction and phase of the current, it is inferred that these anomalous features are caused by the influence of topographic eddies formed perioidically in Uchiumi Bay.  相似文献   

Water exchange in a time-varying transport field     

Hidetaka Takeoka 《Journal of Oceanography》1987,43(1):21-27

The average residence time and the remnant function which are quantitative expressions of water exchange in coastal waters are investigated in a timevarying transport field by using a simple model. It is shown that the influence of temporal variation on the average residence time and concentration is small, when the ratio of the period of variation to the average residence time in the average state is small, and the influence is large when the ratio is large. The results are applied to the Seto Inland Sea, Lake Hamana, and Osaka Bay.  相似文献   

Progress in Seto Inland Sea Research     

Hidetaka Takeoka 《Journal of Oceanography》2002,58(1):93-107

The Seto Inland Sea is a representative coastal sea in Japan with a complicated geometry and thus a variety of marine environments. This sea is, at the same time, one of the most industrialized areas in Japan, and its marine environment has been significantly affected by the anthropogenic impacts over the last four decades. The wide range of marine environments in this sea and the serious environmental issues resulting from these impacts have attracted the attention of Japanese coastal oceanographers. It is believed that the nature and scope of these studies might be an example of the progress of Japanese coastal oceanography. The historical changes in the Seto Inland Sea environment in the last four decades are briefly summarized, and the progress in the studies of the Seto Inland Sea is reviewed with reference to historical changes. Some recent research topics and activities are also mentioned. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Roles of horizontal processes in the formation of density stratification in Hiuchi-Nada     

Hidetaka Takeoka  Yasuhiko Ohno  Norifumi Inahata 《Journal of Oceanography》1991,47(2):33-44

Roles of horizontal processes in the formation of the density stratification in Hiuchi-Nada are investigated by means of a two-dimensional numerical model. In Hiuchi-Nada, vertically mixed and stratified regions are formed due to the regional difference of the tidal currents, and a tidal front is formed between the two regions. The horizontal mixing across the tidal front suppresses the development of the stratification, which is developed too much in the absence of the horizontal mixing. The moderate, realistic stratification cannot be realized in the model without the horizontal mixing. Density currents are formed due to the density distribution associated with the mixed and stratified states. These currents contribute to the horizontal mixing through the shear effect. Horizontal heat transfer from the outside water generates the vertical circulation and causes the stratification. This effect dominantly appears at the early and late stages of the stratified season. The stratification is initiated before the beginning of the surface heating and persists beyond the end, due to the horizontal heat transfer.  相似文献   

The Kyucho in the Bungo Channel,Japan —Periodic intrusion of oceanic warm water     

Hidetaka Takeoka  Hideki Akiyama  Takahiro Kikuchi 《Journal of Oceanography》1993,49(4):369-382

Kyucho is a sudden and swift current which is usually accompanied by rise of water temperature. Several features of the Kyucho in the Bungo Channel, Japan, are presented through field observations. The Kyucho in the Bungo Channel is an intrusion of warm water from the Pacific Ocean into the eastern half of the Bungo Channel, being driven gravitationally and advancing along the eastern coast of the channel. The Kyucho occurs usually in summer and seldom occurs in winter. It occurs at neap tides showing the prominent spring-neap periodicity. The modulation of the vertical mixing intensity associated with the variations of tidal current, wind and surface heating etc. is supposed to be a main cause of springneap and seasonal periodicities.  相似文献