Notes on extended–range atmospheric prediction in the Northern Hemisphere winter

We examined the characteristic feature and predictability of low frequency variability (LFV) of the atmosphere in the Northern Hemisphere winter (January and February) by using the empirical orthogonal functions (EOFs) of the geopotential height at 500 hPa. In the discussion, we used the EOFs for geostrophic zonal wind (Uznl) and the height deviation from the zonal mean (Zeddy). The set of EOFs for Uznl and Zeddy was denoted as Uznl-1. Uznl-2, …, Zeddy-1, Zeddy-2…, respectively. We used the data samples of 396 pentads derived from 33 years of NMC, ECMWF and JMA analyses, from January 1963 to 1995. From the calculated scores for Uznl-1, Uznl-2, Zeddy-1, Zeddy-2 and so on we found that Uznl-1 and Zeddy-1 were statistically stable and their scores were more persistent than those of the other EOFs. A close relationship existed between the scores of Uznl-1 and those of Zeddy-1 30-day forecast experiments were carried out with the medium resolution version of JMA global spectral model for 20 cases in January and February for the period of 1984-1992. Results showed that Zeddy-1 was more predicta?ble than the other EOFs for Zeddy Considering these results, we argued that prediction of the Zeddy-1 was to be one of the main target of extended range forecasting     

Transport of Oyashio Water across the Subarctic Front into the Mixed Water Region and Formation of NPIW

Oyashio water flowing into the Mixed Water Region (MWR) and the Kuroshio Extension region that forms North Pacific Intermediate Water (NPIW) has been examined, based on four Conductivity-Temperature-Depth profiler (CTD)/Lowered Acoustic Doppler Current Profiler (L-ADCP) surveys of water masses and ocean currents. There are two processes by which the Oyashio water intrudes across the Subarctic Front (SAF): one is a direct cross-nearshore-SAF transport near Hokkaido along the western boundary, and the other is a cross-offshore-SAF process. Seasonal variations were observed in the former process, and the transport of the Oyashio water across SAF near Hokkaido in the density range of 26.6–27.4σ_θ was 5–10 Sv in spring 1998 and 2001, and 0–4 Sv in autumn 2000, mainly corresponding to the change of the southwestward Oyashio transport. Through the latter process, 5–6 Sv of the Oyashio water was entrained across the offshore SAF from south of Hokkaido to 150° in both spring 2001 and autumn 2000. The total cross-SAF Oyashio water transport contributing to NPIW formation is more than 10 Sv, which is larger than previously reported values. Most of the Oyashio water formed through the former process was transported southeastward through the Kuroshio Extension. It is suggested that the Oyashio intrusion via the latter process feeds NPIW in the northern part of the MWR, mainly along the Subarctic Boundary and SAF. This revised version was published online in July 2006 with corrections to the Cover Date.     

Degradation ofn-paraffin mixture by marine microorganisms in enriched seawater medium

The ability to degraden-paraffin mixture of two bacterial strains,Caulobacter sp. andFlavobacterium sp., isolated from sea water of Tokyo Bay was studied experimentally in the enriched seawater (ESW) medium. These bacteria degraded actively the mixture ofn-tridecane,n-tetradecane,n-pentadecane andn-hexadecane. The maximum rate of degradation was observed after a lag period of 2 to 8 day and these bacteria were found to degrade then-paraffin mixture at rates calculated to be in a range from 3.3×10^?12 to 3.4×10^?11 mg-oil cell^?1 h^?1 at 20°C. The maximum degradation rate,r _m mg-oil l^?1 h^?1, was correlated with the amount of the initial totaln-paraffin,S mg-oil l^?1, as expressed by the following equation: $$rm = (rm)\max \left( {\frac{S}{{S + Km}}} \right)$$ where (r _m )_max denotes the largest value ofr _m whenn-paraffin exists in large excess andK _m is a constant and represents the amount ofn-paraffin at which the degradation rate,r _m , reaches 1/2 of its largest value, (r _m )_max. The values of (r _m )_max andK _m were calculated to be as follows: In the case ofCaulobacter sp. (strain KM-1), (r _m )_max=6.0 mg-oil l^?1 h^?1 andK _m =191 mg-oillesw ^?1; in the case ofFlavobacterium sp., (r _m )_max=5.47 mg-oil l^?1 h^?1 andK _m =152 mg-oillesw ^?1.     

Growth characteristics ofChattonella antiqua

Nutrient requirements of a red tide flagellate,Chattonella antiqua, were investigated in a laboratory culture experiment. Growth ofC. antiqua was supported by nitrate and ammonium, and by urea to a limited extent, but not by glycine, alanine and glutamate. Orthophosphate served as a good phosphorus source but glycerophosphate did not. Fe³⁺ (1µM) fully promoted the flagellate's growth in the presence of 80µM of EDTA. The addition of Mn²⁺ (0–20µM), Zn²⁺ (0–10µM) and Co²⁺ (0–0.4µM) did not show any effect. Among three vitamins tested, only B₁₂ (6 ng 1^?1) served as a growth factor. Glucose, acetate and glycolate did not improve growth in the light nor did they support growth in darkness. The minimum cell quotas for nitrogen, phosphorus, iron and B₁₂ were estimated to be 11 pmoles ce^?1, 1.0, ～0.09 and 1.1 fg cell^?1, respectively.     

Warm water intrusion from the Kuroshio into the coastal areas south of Japan

Sea surface temperature (SST) has been measured in the south of Japan using a thermometer set up in the ferry boat to investigate the characteristics of the warm water intrudes into the coastal areas from the Kuroshio. Time series analysis was applied to the SST data with satellite images and hydrographic observation data from April 1987 to September 1989. The results indicate that the warm Kuroshio water intruded into the coastal areas on the Enshu-nada and the Kumano-nada Seas intermittently with periods of about 50 and 20 days associated with the fluctuation of the Kuroshio path and the Kuroshio frontal disturbance respectively. The intrusion with a 50-day period was dominant when the Kuroshio took a stationary small meander path (B- and C-types). The warm water spread to the west at 20 cm s^–1, and was estimated to have a depth of 150 m at least and supply enough heat to make up the loss due to the evaporation in the coastal area. During the straight path of the Kuroshio, it was detected that the warm water intruded into coastal areas only with a 20-day period. The warm water that intrudes with a period of 20 days spreads to the west at 25 cm s^–1 in a small scale.     

Estimates of Energy Dissipation Rates in the Three-Dimensional Deep Ocean Internal Wave Field

Using the “Eikonal Approach” (Henyey et al., 1986), we estimate energy dissipation rates in the three-dimensional Garrett-Munk internal wave field. The total energy dissipation rate within the undisturbed GM internal wave field is found to be 4.34 × 10⁻⁹ W kg⁻¹. This corresponds to a diapycnal diffusivity of about 0.3 × 10⁻⁴ m²s⁻¹, which is less than the value 10⁻⁴ m²s⁻¹ required to sustain the global ocean overturning circulation. Only when the high vertical wavenumber, near-inertial current shear is enhanced can diapycnal diffusivity reach ∼10⁻⁴ m²s⁻¹. It follows that the energy supplied at low vertical wavenumbers and low frequencies is efficiently transferred to high vertical wavenumbers and near-inertial frequencies in the mixing hotspots in the real ocean.     

Winter Oceanographic Conditions in the Southwestern Part of the Okhotsk Sea and Their Relation to Sea Ice

In the southwestern part of the Okhotsk Sea, oceanographic and sea-ice observations on board the icebreaker Soya were carried out in February 1997. A mixed layer of uniform temperature nearly at the freezing point extending down to a depth of about 300 m was observed. This is much deeper than has previously been reported. It is suggested that this deep mixed layer originated from the north (off East Sakhalin), being advected along the shelf slope via the East Sakhalin Current, accompanied with the thick first-year ice (average thickness 0.6 m). This vertically uniform winter water, through mixing with the surrounding water, makes the surface water more saline (losing a characteristic of East Sakhalin Current Water) and the water in the 100–300 m depth zone less saline, colder, and richer in oxygen (a characteristic of the intermediate Okhotsk Sea water). The oceanographic structure and a heat budget analysis suggest that new ice zone, which often appears at ice edges, can be formed through preconditioning of thick ice advection and subsequent cooling by the latent heat release due to its melting. This revised version was published online in August 2006 with corrections to the Cover Date.     

Possible source of the antarctic bottom water in the Prydz Bay Region

It has been inferred that the Prydz Bay region is one of the source regions of Antarctic Bottom Water (AABW) based on rather indirect evidence. In order to examine this inference, we investigate the hydrographic condition of the bay based mainly on XCTD data obtained during the Japanese Whale Research Program in the Antarctic (JARPA). The JARPA hydrographic data reveal Circumpolar Deep Water (CDW), which is a salty, warm water mass approaching the shelf break, and capture Modified CDW (MCDW) intruding into the shelf water. AABW production requires mixing of CDW and cold shelf water saltier than 34.6 psu, which is a saltier type of Low Salinity Shelf Water (LSSW). Saltier LSSW is observed near the bottom over the shelf, being mixed with MCDW. We further identify saltier LSSW near the shelf break. This saltier LSSW appears close enough to unmodified CDW to be mixed with it over the continental slope, indicating a possible source of AABW in Prydz Bay.     

Inter-manufacturer Difference and Temperature Dependency of the Fall-Rate of T-5 Expendable Bathythermograph

The fall-rate of the T-5 expendable bathythermograph (XBT) produced by Tsurumi Seiki (TSK) Co., Ltd and that by Sippican Inc., are intercompared by a series of contemporaneous and colocated measurements with conductivity-temperature-depth (CTD) profilers. It is confirmed that the fall-rates of the two manufacturers' T-5 differ by about 5 percent, despite the fact that they had been believed to be identical for many years. The cause of the difference is discussed on the basis of a detailed cross-examination of the two T-5 models. It is found for the first time that the two models are different in several respects. The manufacturer's fall-rate equation is only applicable to the Sippican T-5, for which Boyd and Linzell's (1993) equation seems to be slightly more accurate. Kizu et al.'s (2005) equation gives a clearly less biased depth than the manufacturers' equation for the TSK T-5. It is also found that the fall-rates of both T-5 models are dependent on water temperature, perhaps because of viscosity. The temperature-dependency of the fall-rate of the TSK T-5 is larger than that of the Sippican T-5.     

Tritium in the northwestern North Pacific

Vertical profiles of tritium in seawater were determined for samples collected during the period from 1988 to 1990 at fourteen stations in the northwestern North Pacific (the Oyashio region) including the Okhotsk Sea and the Bering Sea. The profiles usually had a maximum in the surface layer and decreased gradually with depth down to 1,000 m. The water column inventory of tritium averaged 63% of the total atmospheric input in this region.The horizontal distribution of tritium showed a maximum in the region facing the Okhotsk Sea near 45°N for every isopycnal surface of ₀ ranging from 26.60 to 27.40. The ages of the intermediate water were calculated for the respective isopycnal surfaces in the maximum region. This calculation assumed that the intermediate water was formed by the isopycnal mixing of two water masses—the Okhotsk Sea and the Bering Sea Component Waters, which had been produced in wintertime by the diapycnal mixing of the surface and the deep waters in the respective marginal seas. The results show that the intermediate water in this region was formed in the late 1980's for the water which has ₀ of 26.60 to 26.80 and about 1970 for the water which has ₀ of 27.00 to 27.40. Although we have estimated the mean ages of the intermediate water, the horizontal profile of dissolved oxygen suggests that the Okhotsk Sea Component Water is younger than the mean age.