Wakasa Bay Research Articles

The Structure and Formation Mechanism of Transversal Cloud Bands Associated with the Japan-Sea Polar-Airmass Convergence Zone

During a cold-air outbreak, a broad cloud band is occasionally observed over the Japan-Sea Polar-Airmass Convergence Zone (JPCZ) that forms over the Sea of Japan from the base of the Korean Peninsula to the Japanese Islands. On 14 January 2001, a broad cloud band associated with the JPCZ (JPCZ cloud band) extended in a southeastward direction from the base of the Korean Peninsula to Wakasa Bay, and it stagnated for half a day. The JPCZ cloud band consisted of two cloud regions: one was a long cloud band extending along its southwestern edge (a developed convective cloud band), and the other was the region consisting of cloud bands normal to a wind direction of winter monsoon (transversal cloud bands). The structure and formation mechanism of the transversal cloud bands were examined on the basis of observations (e.g., satellite images, in situ measurement and cloud-pro.ling radar data from an instrumented aircraft and upper-air soundings from observation vessels) and simulation results of a cloud-resolving model with a horizontal resolution of 1 km.The transversal cloud bands had the following characteristic structures; they extended along a northeast-southwest direction, which was parallel to the direction pointed by the vertical shear vector of horizontal wind in the mixed layer, they mainly consisted of convective clouds, which slanted with height toward the down-shear side, and they widened and deepened toward southwest, as the depth of the mixed layer increased. An examination of simulation results presented that the transversal cloud bands were accompanied by roll circulations. The axes of rolls were oriented nearly parallel to the direction of the vertical shear vector in the mixed layer. An analysis of the eddy kinetic energy budget indicated that the roll circulations derived most of its energy from the mean vertical shear and the buoyancy.

Seasonal changes in oocyte size and maturity of the giant jellyfish, Nemopilema nomurai

To determine the reproductive season of the giant jellyfish Nemopilema nomurai, we investigated gonadal maturity in specimens collected from the East China Sea, Korea Strait, Wakasa Bay, and the Shonai Coast of Yamagata Prefecture. After the sex of the samples was determined, the long axis of at least 256 oocytes from each female was measured. In specimens collected from the coast of Japan in 2005 and in 2006, all gonads were sufficiently developed to determine sex. However, 18 of the 20 specimens from the East China Sea collected in July 2005 were immature, and sex could not be determined. The maximum and third quartile of oocyte length had a significant correlation with days elapsed from 30 June, but they were not related to bell diameter. Observations of gonad tissue sections of specimens collected in Wakasa Bay in 2006 confirmed that oocyte length was a good proxy for female maturity. Male maturity could also be determined. In conclusion, the sex of all of the small-sized medusae collected along the coast of Japan was determinable, and their gonads were at various stages of development up to fully mature. Therefore, the occurrence of small-sized jellyfish during the autumn in Wakasa Bay is not caused by recruitment of young population from the nearby coast.

2. 若狭湾周辺海域における急潮

2. 若狭湾周辺海域における急潮

Comparison of bacterial communities in fish farm sediments along an organic enrichment gradient

Aquaculture is of major industrial importance world wide and this has led to concerns over the impact of fish farming on previously pristine marine environments. Fish farm sediments receive a large amount of organic matter due to uneaten food and fecal materials. This organic enrichment of sediment influences the biogeochemical process and benthic microbial communities. This study was performed to investigate the effect of pollution from marine fish farms on the bacterial community structure in the underlying sediments. Sediment samples were collected at four stations along an organic enrichment gradient on the coast of Wakasa Bay in southern Fukui Prefecture, Japan between April 2004 and December 2006. Sagami Bay sediments were also used as a non-fish farming reference site. The bacterial community composition was assessed using PCR amplification, cloning, sequencing, and phylogenetic analysis of 16S rDNA using directly extracted sediment DNA. Most of the clones sequenced fell into six major lineages of the domain Bacteria: γ-, δ-, ε-Proteobacteria, Acidobacteria/ Holophaga, Bacteroidetes, and Planctomycetes. Although there were no significant differences in the bacterial community structures among the sediment samples except for Sagami Bay, a minor change in the composition of 16S rDNA operational taxonomy units (OTUs) between sites was recognized. 16S rDNA sequences related to the γ-Proteobacteria were recovered with relatively higher frequencies from unpolluted sediments than from polluted sediments. In contrast, the most abundant clone sequences from polluted sediment samples were grouped with δ-Proteobacteria. Our data suggests organic enrichment of sediment may influence the composition of bacterial communities; and the δ-Proteobacteria were found and selected for within polluted fish farm sediments.

Precipitating Snow Retrievals from Combined Airborne Cloud Radar and Millimeter-Wave Radiometer Observations

Abstract An algorithm for retrieving snow over oceans from combined cloud radar and millimeter-wave radiometer observations is developed. The algorithm involves the use of physical models to simulate cloud radar and millimeter-wave radiometer observations from basic atmospheric variables such as hydrometeor content, temperature, and relative humidity profiles and is based on an optimal estimation technique to retrieve these variables from actual observations. A high-resolution simulation of a lake-effect snowstorm by a cloud-resolving model is used to test the algorithm. That is, synthetic observations are generated from the output of the cloud numerical model, and the retrieval algorithm is applied to the synthetic data. The algorithm performance is assessed by comparing the retrievals with the reference variables used in synthesizing the observations. The synthetic observation experiment indicates good performance of the retrieval algorithm. The algorithm is also applied to real observations from the Wakasa Bay field experiment that took place over the Sea of Japan in January and February 2003. The application of the retrieval algorithm to data from the field experiment yields snow estimates that are consistent with both the cloud radar and radiometer observations.

Retrieval of Atmospheric Integrated Water Vapor and Cloud Liquid Water Content Over the Ocean From Satellite Data Using the 1-D-Var Ice Cloud Microphysics Data Assimilation System (IMDAS)

Reliable prediction of precipitation by numerical weather prediction (NWP) models depends on the appropriate representation of cloud microphysical processes and accurate initial conditions of observations of atmospheric variables. Therefore, to retrieve reasonable cloud distributions, a 1-D variational Ice Cloud Microphysics Data Assimilation System (IMDAS) is developed to improve the predictability of NWP models. The general framework of IMDAS includes the Lin ice cloud microphysics scheme as a model operator, a four-stream fast microwave radiative transfer model in the atmosphere as an observation operator, and a global minimization method that is known as the shuffled complex evolution. IMDAS assimilates the satellite microwave radiometer data set of the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) and retrieves integrated water vapor and integrated cloud liquid water content. This new method successfully introduces heterogeneity into the initial state of the atmosphere, and the modeled microwave brightness temperatures agree well with the observations of the Wakasa Bay Experiment 2003 in Japan. It has significantly improved the performance of the cloud microphysics scheme by the intrusion of heterogeneity into the external global reanalysis data, which resultantly improved atmospheric initial conditions.

Seasonal and interannual variation of subtidal fish assemblages in Wakasa Bay with reference to the warming trend in the Sea of Japan

A bi-monthly underwater visual census was conducted in the subtidal habitat of Nagahama, Wakasa Bay, Sea of Japan, over 5 years from January 2002 to December 2006. A total of 83 fish species and 63,328 individuals were recorded over 120 1-h visual censuses composed of three 2 × 200 m transects. The number of both total individuals (abundance) and species (richness) were strongly correlated with the bottom-water temperature. Species richness was greatest in summer (July–September), with 10–20 species per 400 m2, when the sea-bottom temperature was highest (24–28°C), and lowest in winter (January–March), with 1–8 species per 400 m2, when the temperature was lowest (10–12°C). Five species, i.e., rockfish, Sebastes inermis, wrasse, Pseudolabrus sieboldi, two species of goby, Acentrogobius pflaumii and Tridentiger trigonocephalus, and pygmy filefish, Rudarius ercodes, were frequently observed and present in more than 200 of the total of 360 total transects. While the presence of most fish species was dependent on water temperature, some species were independent of water temperature, including anchovy, Engraulis japonicus, S. inermis, wasp fish, Hypodytes rubripinnis, A. pflaumii and pufferfish, Takifugu poecilonotus. Jack mackerel, Trachurus japonicus, was the most abundant fish, being most typically seen from spring through autumn, with a total of 21,850 individuals observed over the whole census period. Some species showed strong annual fluctuations in abundance. The interannual stability in fish abundance and species richness was probably because the fish assemblage was composed of a sufficiently large number of species, but with the number of each species fluctuating over time. A comparison of the present survey to one in 1970–72 revealed that over the last 30 years southern fish species have significantly increased whereas those indigenous to northern waters have decreased.

Abundance of picophytoplankton in the halocline of a meromictic lake, Lake Suigetsu, Japan

Numerous (0.5 to 4.8 × 105 cells/ml), small phytoplankton (smaller than 0.5–1 × 1–2 μm in cell size, picophytoplankton) were distributed in the halocline (depth 2–12 m, 4–14 practical salinity units) of the saline meromictic lake, Lake Suigetsu (35°35′ N, 135°52′ E), located in the central part of the coast of Wakasa Bay along the Japan Sea in Fukui Prefecture, Japan. Vertical distribution of phytoplankton revealed that the maximum number of picophytoplankton was always observed near or a little deeper than the oxic-anoxic boundary layer (depth 5–6 m); they were dominant phytoplankton in the water layer deeper than the oxic-anoxic boundary from July to late September 2005. Spectral analysis of autofluorescence emitted from the particle fractions smaller than 5 μm measured with a spectrofluorometer and from individual cells measured with a microscope photodiode array detector revealed that the major component of picophytoplankton was phycoerythrin-rich, unicellular cyanobacteria (picocyanobacteria). Eukaryotic phytoplankton about 2.5 μm in diameter were also found, but the numbers were low. Fluorescence intensity of chlorophyll a at 685 nm (room temperature) emitted from the particle fractions smaller than 5 μm was increased by the addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. These observations indicated that at least some picophytoplankton had a functional photosystem II in the halocline where sulfide, the potential inhibitor of oxygenic photosynthesis, was always present. The large abundance together with their physiological potency suggest that picophytoplankton are one of the important primary producers in the halocline of Lake Suigetsu.

Physical Validation of Microwave Properties of Winter Precipitation Over the Sea of Japan

In order to evaluate variations in the physical properties of winter precipitation over the Sea of Japan, we analyzed the Wakasa Bay Experiment 2003 datasets. The results show that synoptic scale differences in freezing-level height (FLH) were observed between extra-tropical low cases and winter monsoon and upper cold low cases, and that, frozen-particle density and cloud liquid water content (CLWC) observed at the surface showed great variation independent of the precipitation rate, although positive correlation may exist between these two properties. The radiative transfer model (RTM) simulation and the validation using the advanced microwave scanning radiometer on EOS (AMSR-E) and millimeter-wave imaging radiometer brightness temperatures (TBs) indicate that sensitivity to frozen precipitation rate (0-5 mm ldr h <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) was found in 89-GHz polarization-corrected temperature (PCT89), 89-GHz polarization difference (PD89), and 150-GHz TBs and that this sensitivity decreased with FLH due to emission from mixed- and liquid-phase particles. The RTM simulation, however, overestimated the AMSR-E PCT89 depressions for nonzero FLH cases. This indicates that microwave retrieval for winter precipitation requires a priori information about FLH and an efficient mixed-phase-particle model for RTM. The relationship between surface precipitation rate and TBs was also influenced by the observed variation of CLWC. The relationship between PCT89 and PD89 is greatly altered in terms of CLWC. Relationship between AMSR-E PCT89 precipitation sensitivity and CLWC estimated from PCT89 and PD89 was qualitatively consistent with those of the RTM simulations. This suggests that CLWC, another important retrieval parameter, can be estimated from PCT89 and PD89.

Seasonal changes in biomass of macrophytes stranded on Yoro Beach along a sargassacean forest in Wakasa Bay, Sea of Japan

Macrophytes stranded on a beach provide food and habitat for many kinds of animals and play important roles in coastal ecosystems. Macrophytes stranded on a sampling beach (56 m long) along a sargassacean forest (400 m long and 88 m wide) were collected every 10 days from late April 2003 to late May 2004. The weight of macrophytes stranded per meter of beach amounted to 1733 g dry wt/m per year. Sargassacean plants were dominant and constituted 72.9% (1263 g dry wt/m per year) of whole stranded macrophytes. Large numbers of macrophytes were stranded just after heavy winter storms and the maximum weight of stranded macrophytes in winter was 407 g dry wt/m. Stranded macrophytes also increased in May to July; the deterioration period of sargassacean species in this region, and the maximum weight in this period was 233 g dry wt/m. The number of sargassacean plants stranded with holdfast increased only in winter. These results suggest that winter storms have an important role in stranding sargassacean plants at Yoro Beach.

Evaluation of radar multiple scattering effects in Cloudsat configuration

Abstract. MonteCarlo simulations have been performed to evaluate the importance of multiple scattering effects in co- and cross-polar radar returns for 94 GHz radars in Cloudsat and airborne configurations. Thousands of vertically structured profiles derived from some different cloud resolving models are used as a test-bed. Mie theory is used to derive the single scattering properties of the atmospheric hydrometeors. Multiple scattering effects in the co-polar channel (reflectivity enhancement) are particularly elusive, especially in airborne configuration. They can be quite consistent in satellite configurations, like CloudSat, especially in regions of high attenuation and in the presence of highly forward scattering layers associated with snow and graupel particles. When the cross polar returns are analysed [but note that CloudSat does not measure any linear depolarization ratio (LDR hereafter)], high LDR values appear both in space and in airborne configurations. The LDR signatures are footprints of multiple scattering effects; although depolarization values as high as −5 dB can be generated including non-spherical particles in single scattering modelling, multiple scattering computations can produce values close to complete depolarization (i.e. LDR=0 dB). Our simulated LDR profiles from an air-borne platform well reproduce, in a simple frame, some experimental observations collected during the Wakasa Bay experiment. Since LDR instrumental uncertainties were not positively accounted for during that experiment, more focused campaigns with air-borne polarimetric radar are recommended. Multiple scattering effects can be important for CloudSat applications like rainfall and snowfall retrievals since single scattering based algorithms will be otherwise burdened by positive biases.

Wakasa Bay: An AMSR Precipitation Validation Campaign

The “ Wakasa Bay Experiment” was conducted in order to refine error models for oceanic precipitation from the Advanced Microwave Sounding Radiometer-Earth Observing System (AMSR-E) measurements and to develop algorithms for snowfall. The NASA P-3 aircraft was equipped with microwave radiometers, covering a frequency range of 10.7–340 GHz, and radars at 13.4, 35.6, and 94 GHz, and was deployed to Yokota Air Base in Japan for flights from 14 January to 3 February 2003. For four flight days (27–30 January) a Gulfstream II aircraft provided by Core Research for Environmental Science and Technology (CREST), carrying an extensive cloud physics payload and a two-frequency (23.8 and 31.4 GHz) microwave radiometer, joined the P-3 for coordinated flights. The Gulfstream II aircraft was part of the “Winter Mesoscale Convective Systems Observations over the Sea of Japan in 2003” (“WMO-03”) field campaign sponsored by Japan Science and Technology Corporation (JST). Extensive data were taken, which addressed all of the experimental objectives. The data obtained with the NASA P-3 are available at the National Snow and Ice Data Center (NSIDC), and they are available free of charge to all interested researchers.

Blood Fluke Infection of Cultured Tiger Puffer &lt;i&gt;Takifugu rubripes&lt;/i&gt; Imported from China to Japan

Monthly samplings of tiger puffer Takifugu rubripes, which had been cultured in China and later introduced to a farm in Kagawa Prefecture, Japan, in May 2005, were conducted over a four-month period commencing in June 2005. Blood flukes were found in the visceral vascular system with the highest number being 162 worms/fish, and their eggs accumulated in the vis-ceral organs. The parasite was classified within the genus Psettarium based on the unique male reproductive system, and tentatively designated as Psettarium sp. TPC (= tiger puffer from China). Molecular analyses, using the ITS2 rDNA gene indicated that the blood flukes of tiger puffer from two other sources (cultured in China and subsequently in the Kyushu area, and cultured in China only) were also Psettarium sp. TPC. This suggests that the infection cycle of Psettarium sp. TPC has been established in China. On the other hand, no evidence was found that its life cycle is complete in Japanese waters. Similar blood flukes were collected in 1993 from post-spawned tiger puffer caught in a set-net in Wakasa Bay, Fukui Prefecture and maintained there for several months. This parasite was differentiated from Psettarium sp. TPC by the presence of 5-6 rows of pre-oral spines and designated as Psettarium sp. TPJ (= tiger puffer from Japan).

Sulfate-coated dust particles in the free troposphere over Japan

Airborne aerosol collections were performed over Wakasa bay (36°00′N, 135°30′E) in March and Kumano open sea (34°00′N, 136°50′E) and Seto (35°10′N, 137°10′E) in July 2001 at altitudes between 1.0 and 5.8 km. The particles were individually analyzed using transmission electron microscopy (TEM). Relatively large mineral-dust (mostly clay) particles were abundant in the March samples. They also dominated in July in the mid-troposphere higher than 4 km altitude, whereas sea salt and ammonium sulfate were more abundant at lower altitudes. Ca-coated grid samples show many traces of aqueous sulfate droplets. The proportions of former sulfate droplets to the total collected particles apparently increased with increasing relative humidity at the time of sampling. TEM analysis revealed that a significant fraction of these former droplets enclose mineral-dust particles as well as sea salt, soot, and fly ash. Some enclose mixtures of mineral-dust, sea-salt, soot, and fly ash particles. The results provide evidence that mineral dust from the Asian continent could acquire coatings of sulfate while being transported in the free troposphere. The mineral-dust particles probably acquired the sulfate coatings either through heterogeneous uptake of gaseous SO 2 and subsequent oxidation or through coagulation with cloud or fog droplets. The presence of the mixed particles in sulfate droplets also indicates that aggregation of particles of different origins occurred through cloud processing. Such sulfate-coated dust particles would affect cloud formation, precipitation, and chemistry of the free troposphere.

Simultaneous Measurements of Ku- and Ka-Band Sea Surface Cross Sections by an Airborne Radar

The dual-frequency Airborne Precipitation Radar-2 (APR-2) was deployed during the Wakasa Bay Experiment in 2003, for validation of the Advanced Microwave Scanning Radiometer-EOS. Besides providing extensive observations of diverse precipitating systems, this Ku-(13.4 GHz) and Ka-band (35.6 GHz) cross-track scanning radar measured sea surface backscatter simultaneously. While the characteristics of the normalized sea surface cross section sigma0 at Ku-band are well understood and widely published, the existing experimental data concerning sigma0 at Ka-band are scarce and results are inconsistent. In this letter, the Ku/Ka-band sigma0 measurements collected by APR-2, together with the estimated uncertainties, are discussed. In general, the measured sigma0 at Ka-band at around 10deg incidence angle appears to be close to that at Ku-band sigma0, and Ka-band exhibits a nonnegligible difference in wind dependence with respect to Ku-band for moderate to high winds

Changes of the trophic position of the Japanese flounder Paralichthys olivaceus juvenile in a sandy sublittoral area in Wakasa Bay, Sea of Japan, examined by carbon and nitrogen isotope analyses

Changes of the trophic position of the Japanese flounder Paralichthys olivaceus juvenile in a sandy sublittoral area in Wakasa Bay, Sea of Japan, examined by carbon and nitrogen isotope analyses

FIELD OBSERVATION OF MOUNTAIN AND VALLEY WINDS IN THE REINAN AREA OF FUKUI PREFECTURE

The Reinan area is the western part of Fukui Prefecture and bounded on the north by the Wakasa Bay and on the south by the Nosaka mountains. Valleys in the area connect Wakasa Bay and Lake Biwa areas and wind through the valleys plays important roles in heat and pollutants transports between the two area. Field observation was carried out in Sept., 2004 using a Doppler sodar velocitimeter to investigate structures of mountain and valley winds in one of the valleys. The results were examined in relation to macro- and meso- scale wind fields using the AMeDAS data and the objective analysis data by the JMA.

Relationships between release season and feeding performance of hatchery-reared Japanese flounder Paralichthys olivaceus: In situ release experiment in coastal area of Wakasa Bay, Sea of Japan

Two groups of hatchery-reared juveniles of Japanese flounder Paralichthys olivaceus (Temminck and Shlegel) were experimentally released in Wada Beach, Fukui Prefecture, Japan and their feeding state examined in comparison to wild juveniles to investigate the optimal release season and the relationship between food availability and feeding performance of juveniles. We released two groups of 40,000 juveniles of ca. 50 mm size, one group in the early (29 May) and the other in late (2 July) seasons, periods with predicted high and low densities of prey mysids, respectively, although the abundance of mysids fluctuated markedly during the season. Food availability was higher for the early release group than the late release group. Although the main stomach contents of released and wild juveniles were mainly mysids and fish, the feeding state differed between the early and late release groups. The early release group had a stomach content index (SI) similar to that of the wild juveniles, but the SI of the late group was significantly less than that of the early release group and wild juveniles. The percentage of fish with empty stomachs was much higher in the late release group than in the other two groups. In addition, the density decrease rate was significantly more rapid for the late release group than the early release group. Clear correspondence between the food availability and feeding state of the released flounder juveniles indicates that the release of juveniles in an appropriate season when mysids are abundant is crucial for successful stocking.

Vertical distributions of particles and sulfur gases (volatile sulfur compounds and SO 2) over East Asia: Comparison with two aircraft-borne measurements under the Asian continental outflow in spring and winter

We have presented the vertical distributions, between 0.5 and 5.5 km, of particles, volatile sulfur compounds, sulfur dioxide, O 3, and fractions of sulfur over the Japan Sea coast, Wakasa Bay, on 23 April 1996 and 28 December 1995. Comparison of these measurements showed that free tropospheric concentrations of particles and short-lived sulfur gases (CS 2, H 2S, SO 2) on 23 April 1996 were significantly higher than those on 28 December 1995. Clustered isentropic backward trajectory analysis and meteorological data indicated that the difference was associated with air mass transport routes and meteorological conditions. On 23 April 1996, coarse size particles (mineral dust particles) were injected over the arid region associated with dust storms. During transport by westerly winds, these coarse size particles were mixed with short-lived sulfur gases injected by convection over an industrial region. The presence of DMS, confined to the boundary layer, indicated that Asian continental outflow can be modified during long-range transport through mixing with marine air in the boundary layer over the Japan Sea. On the other hand, on 28 December 1995, low concentrations of particles and short-lived sulfur gases, measured at altitudes above 3.0 km, were due to air mass subsidence. It is likely that some photochemical processing was also due to low concentrations of short-lived sulfur gases. Vertical distributions of O 3 concentrations and values of sulfur fraction (SO 4 2−/(SO 4 2−+SO 2)) supported this interpretation. There was no significant difference in concentrations of long-lived COS, except for one sample on 23 April 1996. The low COS concentration coincided with significantly high concentrations of CS 2, suggesting rapid upward transport of COS depleted air masses from the surface.

Reproductive cycle of yellow sea bream Dentex tumifrons in Wakasa Bay, the Sea of Japan off central Honshu

To determine the spawning season and reproductive cycle of the yellow sea bream, Dentex tumifrons, in Wakasa Bay, in the Sea of Japan off central Honshu, seasonal change in the gonadosomatic index (GSI) was examined and histological observations of both ovaries and testes were conducted. The female GSI gradually increased from May, maintained a high level between that vitellogenesis began from May and developed until September. Spent fish began to be observed in October and all the fish collected in December were spent. There was only one peak in the seasonal change in GSI of males and females in Wakasa Bay. Thus, yellow sea bream spawn only in autumn in Wakasa Bay. Differences in the reproductive cycle and number of spawning seasons were found between the two different latitudinal areas, Wakasa Bay and the East China Sea (low latitudinal area) where the spawning seasons were spring and autumn. An increase in water temperature is an important factor to initiate gonadal maturation (recrudescence) and is terminated by the short day-length in Wakasa Bay.