Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Naoki Hirose Last modified date:2019.06.18

Professor / Center for Oceanic and Atmospheric Research / Research Institute for Applied Mechanics

1. Atsushi Kaneda, Kouta Ayukawa, Naoki Hirose, Tomoharu Senjyu, Yutaka Kumaki, Yosuke Igeta, Ken-ichi Fukudome & Tatsuro Watanabe, Intensification of current in coastal waters around Cape Echizen in summer, Journal of Oceanography, 75, 157-169, 2019.02.
2. Tadanori Yamaguchi, Takako Aketagawa, Katsumi Takayama, Naoki Hirose, Michiya Matsuyama, Migratory routes of different sized swordtip squid (Uroteuthis edulis) caught in the Tsushima Strait, Fisheries Research, 10.1016/j.fishres.2018.08.008, 209, 24-31, 2019.01, Swordtip squid (Uroteuthis edulis) of various sizes are caught on an almost daily basis from early spring to late autumn in the eastern Tsushima Strait and southern Sea of Japan. In this study, we estimated the migratory routes of different sized squid jigged in the Tsushima Strait using statolith analyses, information on seawater temperature distributions and currents, and tracer experiments. Estimates of age and historic water temperatures suggested that both small and large squid hatch in the southern East China Sea and are then transported northeastward with the currents to the northern Kuroshio region. Following this, the small squid are transported north-northwestward to offshore waters, from where many of the squid enter the southern Sea of Japan and some move into coastal waters in the eastern strait, whereas large squid slowly move northward from the northernmost part of the Kuroshio region. Based on these distributions, it is likely that the small squid remain immature due to insufficient water temperatures over shorter durations, whereas the large squid mature in the Kuroshio region. Since migratory routes affect fishing ground formation, this information is important for both efficient fishing operations and stockmanagement of this species..
3. Shin-ichi Ito, Hiroyuki Tsujino, Yasumasa Miyazawa, Naoki Hirose, Kosei Komatsu and Naoki Yoshie, Regional high-resolution ocean models in the western North Pacific and its marginal seas, PICES Scientific Report, 54, 44-55, 2018.10.
4. Sooyeon HAN, Naoki Hirose and Shinichiro Kida, The role of topographically induced form drag on the channel flows through the East/Japan Sea, Journal of Geophysical Research: Oceans, 10.1029/2018JC013903, 123, 9, 6091-6105, 2018.08.
5. Tianran Liu, Bin Wang, Naoki Hirose, Toru Yamashiro, Hiroshi Yamada, High-resolution modeling of the Kuroshio current power south of Japan, Journal of Ocean Engineering and Marine Energy, 10.1007/s40722-017-0103-9, 4, 1, 37-55, 2018.02, [URL].
6. Jung-Eun Sim, Hong-Ryeol Shin, Naoki Hirose, Comparative Analysis of Surface Heat Fluxes in the East Asian Marginal Seas and Its Acquired Combination Data, Journal of the Korean earth science society, 39, 1, 1-22, 2018.02.
7. T. Yamaguchi, T. Aketagawa, M. Miyamoto, Naoki Hirose, M. Matsuyama, The use of statolith analyses and particle-tracking experiments to reveal the migratory route of the swordtip squid (Uroteuthis edulis) caught on the Pacific side of Japan, Fisheries Oceanography, 10.1111/fog.12270, 2018.01, To verify the hypothesis that swordtip squid (Uroteuthis edulis) harvested on the eastern and western sides of Japan originate from a single stock, which is transported from the East China Sea, the hatching ground and migratory route of squid collected from the eastern (Pacific) side of Japan were estimated using micro-increment counts and the Sr:Ca ratios in statoliths as well as backward and forward particle-tracking experiments. The results of both the empirical water temperatures estimated by the Sr:Ca ratios in the statoliths as well as the trajectories and ambient water temperatures of the particles in the experiments supported the hypothesis, suggesting that the sampled individuals experienced cold waters caused by upwelling, originating from the Kuroshio off northern Taiwan. It was found that the environmental settings in the particle-tracking experiments of this study adequately represented the habitats of the squid and that the movement of this species is highly dependent on currents. This information is essential to establishing a stock management system for sustainable fishing..
8. Atsushi Kaneda, Kouta Ayukawa, Naoki Hirose, Tomoharu Senjyu, Yutaka Kumaki, Yosuke Igeta, Ken ichi Fukudome, Tatsuro Watanabe, Intensification of current in coastal waters around Cape Echizen in summer, Journal of Oceanography, 10.1007/s10872-018-0492-y, 1-13, 2018.01, In the coastal areas of Wakasa Bay, the Japan Sea—an observation network for fisheries and a simulation system of coastal currents with a high-resolution numerical model—revealed intensification of current in summer around Cape Echizen. The 2012–2014 current data collected by mooring observations off Takasu, near Cape Echizen, showed that the current’s speed exceeded 40 cm s−1 for more than 5 days around July and August each year. In addition, the 2014 current data collected by a research vessel indicated that the first branch of the Tsushima Warm Current (FBTWC) flowed near the coast when the strong current with an increase of water temperature occurred in the upper layer of coastal waters off Takasu. Similarly, the simulation results revealed that the FBTWC variability caused intensification of the current in coastal waters near Cape Echizen. In addition, they showed that when the strong current was generated in coastal waters off Takasu, cold water accompanied by strong current expanded to coastal seas around Cape Echizen in the subsurface layer. From these results of the observations and the simulation, it was considered that the strong current in the coastal waters off Takasu in summer was attributed to the acceleration of the FBTC, which is accompanied by cold water expansion in the subsurface layer to the vicinity of the coast and contact of the FBTWC along the cold water edge with the coast..
9. Haejin Kim, Katsumi Takayama, Naoki Hirose, Goh Onitsuka, Takafumi Yoshida, Tetsuo Yanagi, Biological modulation in the seasonal variation of dissolved oxygen concentration in the upper Japan Sea, Journal of Oceanography, 10.1007/s10872-018-0497-6, 2018.01, Dissolved oxygen (DO) can be influenced by both physical and biogeochemical conditions of the ocean and is hence an important index for predicting changes in ocean environments. However, the relationship between biogeochemical activities and the DO concentration has not been quantified clearly in the Japan Sea (JS). In this study, we developed a coupled physical-biogeochemical model and clarified the contributions of biological processes to the DO content in the upper JS. We conducted two numerical experiments: with and without the biogeochemical compartments. Taking the biogeochemical factors into account gave better estimations for the spring-to-autumn seasonal migration of the subsurface DO maximum. In the euphotic zone, high photosynthetic production increases the DO concentration from spring to autumn. The strongest positive effect of biological processes on DO concentrations appears in summer at a depth of 30 m and is more than 0.5 ml l−1. As summer progresses to autumn, the vertical pattern of DO concentration in the Tsushima Warm Current (TWC) region shows minima at depths between 50 and 100 m, which is caused by the intrusion of low DO water from the East China Sea. The strongest negative effect on DO concentrations mainly due to the decomposition of detritus occurs in the TWC region below 150 m depth because the water is poorly ventilated by the relatively weak winter convection..
10. Takeshi Matsuno, Naoki Hirose, Jing Zhang, Yang Ki Cho, Dake Chen, Dongliang Yuan, Chin Chang Hung, Sen Jan, Recent progress in Pacific-Asian Marginal Seas (PAMS) studies, Continental Shelf Research, 10.1016/j.csr.2017.07.001, 143, 89-90, 2017.07, [URL].
11. Bin Wang, Naoki Hirose, Dongliang Yuan, Jae Hong Moon, Xishan Pan, Effects of tides on the cross-isobath movement of the low-salinity plume in the western Yellow and East China Seas in winter, Continental Shelf Research, 10.1016/j.csr.2016.06.011, 143, 228-239, 2017.07, Offshore extension of the fresh Subei coast water is identified in winter based on in site salinity observation data in this and previous studies. A high-resolution regional ocean circulation model is used to investigate the cross-isobath movement of low salinity-water over the Yellow and East China Seas, and it has reproduced the salinity distribution observed in the winter of 2014–2015 successfully. The model suggests that the low-salinity water is basically degenerated back to the eastern coast of China in winter because of strong northeasterly wind. However, a part of the low-salinity water extends offshore in the southeast direction across the 20–50 m isobaths over the Yangtze Bank, which cannot be explained by either the northerly winter monsoon or the Changjiang discharge. Numerical experiments suggest that the cross-isobath transport of the soluble substances is highly attributed to the tidal residual current, flowing southeastward across 20–50 m isobaths over the whole Yangtze Bank. The results of controlled experiments also indicate that the bottom shear of the tidal current, rather than the tidal mixing, plays a significant role in the cross-isobath current during winter..
12. Naoki Hirose, Yutaka Kumaki, Atsushi Kaneda, Kouta Ayukawa, Noriyuki Okei, Satoshi Ikeda, Yosuke Igeta, Tatsuro Watanabe, Numerical simulation of the abrupt occurrence of strong current in the southeastern Japan Sea, Continental Shelf Research, 10.1016/j.csr.2016.07.005, 143, 194-205, 2017.07, Coastal set-net fisheries have been frequently damaged by the occurrence of sudden current (known as kyucho) in the Japan Sea. In this study, a high-resolution coastal ocean model is developed to provide a means to predict this stormy current. The 1.5 km-mesh model nested in a regional ocean data assimilation system is driven by mesoscale atmospheric conditions at 1-hour intervals. The modeled results show rapid changes of the coastal current along the San-in Coast, on the eastern side of the Tango Peninsula, and around the Noto Peninsula and Sado Island, mostly associated with strong wind events. These modeled coastal water responses are consistent with in-situ velocity measurements. The simulation also shows that the vortex separated from the Tango Peninsula frequently grows to a bay-scale anticyclonic eddy in Wakasa Bay. Evidently, the coastal branch of the Tsushima Warm Current becomes unstable due to a strong meteorological disturbance resulting in the generation of this harmful eddy..
13. Dongliang Yuan, Yao Li, Bin Wang, Lei He, Naoki Hirose, Coastal circulation in the southwestern Yellow Sea in the summers of 2008 and 2009, Continental Shelf Research, 10.1016/j.csr.2017.01.022, 143, 101-117, 2017.07, The coastal ocean circulation off the Chinese Subei (north Jiangsu Province) coasts in the southwestern Yellow Sea in summer is studied using hydrographic data from four research cruises, moored current meter data in the Lunan (south Shandong Province) trough, and Lagrangian trajectories of satellite-tracked ARGOS surface drifters in the summers of 2008 and 2009. The hydrographic data indicate a fresh water plume extending offshore in the northeastward direction from the Sheyang River mouth and a belt of relatively cold surface temperature from the surrounding areas located offshore of the Subei coasts to the south of the plume in summer. The drifter trajectories show that the Subei coastal current, which is traditionally thought to flow southward year round, flows northward in June through July under the forcing of the southerly monsoon. A northward intrusion along the submarine valley off the Changjiang mouth is indicated by the movement of the drifters, which is persistently strong and independent of the winds. Associated with the northward flow, coastal upwelling is generated offshore of the Subei coast to the south of the Sheyang River plume, below which upwelling is generated but is shut down by the buoyancy of the fresh water at the surface. Coastal upwelling is also observed off the coast of Qingdao city in middle July through early August of 2008, which is forced by the along-shore component of the southerly and southwesterly winds. The Qingdao upwelling in summer is reported for the first time in history..
14. Atsushi Kaneda, Kouta Ayukawa, Naoki Hirose, Jun Tsuzuki, Yutaka Kumaki, Tomoharu Senjyu, Yosuke Igeta, Tatsuro Watanabe, Sudden strong current generated by an eddy in the eastern part of Wakasa Bay, Japan, Journal of Oceanography, 10.1007/s10872-016-0395-8, 73, 2, 181-192, 2017.04, A sudden strong coastal current called a “kyucho” occurred in August 2013 in the eastern coastal waters of Wakasa Bay, Japan. This study examined its characteristics based on both observational data collected by intensive field investigations and the simulation results of a numerical model. The field investigations comprised moored buoy observations near the coast and voyages by a research vessels and fishing boats. The mooring observations indicated that a current speed exceeding 50 cm s−1 occurred abruptly near the eastern coast of the bay, in association with a synchronous change in the current direction. Data collected by acoustic Doppler current profilers (ACDPs) mounted on the vessels showed that a clockwise eddy existed in the bay and that the current on the east side of the eddy generated the kyucho near the coast. Based on the results of the numerical model and the analysis of the ADCP data, it was considered that the clockwise eddy was generated by a strong current at the tip of the Tango Peninsula, in the western part of the bay. As the eddy propagated from west to east across the bay, it induced the kyucho in the coastal waters in the east of the bay..
15. Japanese studies of ocean data assimilation: milestones over the past 20 years and future perspectives.
16. Shin’ichiro Kako, Tomofumi Nakagawa, Katsumi Takayama, Naoki Hirose, Atsuhiko Isobe, Impact of Changjiang River Discharge on Sea Surface Temperature in the East China Sea, Journal of Physical Oceanography, 10.1175/JPO-D-15-0167.1, 46, 6, 1735-1750, 2016.06, [URL].
17. Shiho Kobayashi, Satoshi Nakada, Shuzo Takagi, Naoki Hirose, Parameter optimization of a 3D coastal model using Green’s functions for modelling river plume dynamics, Journal of Advanced Simulation in Science and Engineering, 10.15748/jasse.3.153, 3, 2, 153-164, 2016.04, [URL].
18. Jae Hun Park, Ye Sol Kim, Ho Jin Lee, Hee Yeol Lee, Ho Kyung Ha, Young Gyu Park, Chanhyung Jeon, Naoki Hirose, Internal tide-induced enhancement of cold water intrusion on the continental shelf of the Korea strait, Journal of Coastal Research, 10.2112/SI75-109.1, 1, 75, 542-546, 2016.03, [URL], The Korea Strait bottom cold water (KSBCW), characterized by its temperature < 10°C, is believed to originate from the deep basin of the southwestern East/Japan Sea with a maximum transport in August/September. Although previous studies have suggested possible causes of the enhanced KSBCW intrusion in summer, its mechanism is not yet clear. Here we investigate if tides can affect the strength of KSBCW intrusion using numerical simulations. We utilize a high-resolution regional ocean model with 1/108° grids, covering the Korea Strait and the southwestern East/Japan Sea. Numerical simulations are conducted for several cases, which include semidiurnal tides (M2+S2), diurnal tides (K1+O1), and wind forcings differently to examine their effects on the intrusion. Simulation results reveal that the energetic semidiurnal internal tides, generated around the continental shelf in the northern part of the Korea Strait, can induce the KSBCW intrusion by the internal tidal pumping effect. Two cases including the four major tides reproduce at best a dome-shaped bottom cold water lower than 10°C impinging on the slope southeast coast of Korea, consistent with historical monthly-mean temperature fields. Long-term ferry boat ADCP measurements (> 10 years) across the Korea Strait show that southwestward KSBCW intrusions get stronger 2-3 days after spring tides in summer and fall when the semidiurnal internal tides are strengthened, supporting our simulation results. We therefore propose that the maximum KSBCW intrusion in August/September is caused by the energetic semidiurnal internal tides..
19. Noh Yign, Ok Hyejin, Lee Eunjeong, Toyoda Takahiro, Naoki HIROSE, Parameterization of Langmuir Circulation in the Ocean Mixed Layer Model Using LES and Its Application to the OGCM, JOURNAL OF PHYSICAL OCEANOGRAPHY, 10.1175/JPO-D-14-0137.1, 46, 1, 57-78, 2016.01.
20. Sooyeon Han, Naoki Hirose, Norihisa Usui, Yasumasa Miyazawa, Multi-model ensemble estimation of volume transport through the straits of the East/Japan Sea, Ocean Dynamics, 10.1007/s10236-015-0896-9, 66, 1, 59-76, 2016.01, [URL], The volume transports measured at the Korea/Tsushima, Tsugaru, and Soya/La Perouse Straits remain quantitatively inconsistent. However, data assimilation models at least provide a self-consistent budget despite subtle differences among the models. This study examined the seasonal variation of the volume transport using the multiple linear regression and ridge regression of multi-model ensemble (MME) methods to estimate more accurately transport at these straits by using four different data assimilation models. The MME outperformed all of the single models by reducing uncertainties, especially the multicollinearity problem with the ridge regression. However, the regression constants turned out to be inconsistent with each other if the MME was applied separately for each strait. The MME for a connected system was thus performed to find common constants for these straits. The estimation of this MME was found to be similar to the MME result of sea level difference (SLD). The estimated mean transport (2.43 Sv) was smaller than the measurement data at the Korea/Tsushima Strait, but the calibrated transport of the Tsugaru Strait (1.63 Sv) was larger than the observed data. The MME results of transport and SLD also suggested that the standard deviation (STD) of the Korea/Tsushima Strait is larger than the STD of the observation, whereas the estimated results were almost identical to that observed for the Tsugaru and Soya/La Perouse Straits. The similarity between MME results enhances the reliability of the present MME estimation..
21. Boonsoon KANG, Naoki HIROSE, Kenichi FUKUDOME, Transport variability in the Korea/Tsushima Strait: Characteristics and relationship to synoptic atmospheric forcing, Continental Shelf Research, 10.1016/j.csr.2014.03.010, 81, 15, 55-66, 2014.06, [URL].
22. Satoshi Nakada, Naoki Hirose, Tomoharu Senjyu, Ken ichi Fukudome, Toshihiro Tsuji, Noriyuki Okei, Operational ocean prediction experiments for smart coastal fishing, Progress in Oceanography, 10.1016/j.pocean.2013.10.008, 121, 125-140, 2014.02, [URL], This paper describes a new combination of in situ, high-density observations gathered by fishermen, and a real-time, high-resolution (approx. 1.5. km) prediction model developed toward more efficient fishing. Flow field data can be successfully collected by observations from acoustic Doppler current profilers installed on commercial fishing boats, which uncover sub-mesoscale structures such as small (approx. 10. km) eddies in the eastern boundary current region of the Japan/East Sea. Frequent vertical temperature profiles observed by sensors attached to casting trawl nets indicate fine feature of summertime upwelling area associated with fishing grounds. These observational assets back up routine observations conducted by using stationary buoys, research vessels, commercial passenger lines, and tide gauges. These assets enable evaluation of system predictability and improvement through calibration of physical model parameters in addition to data assimilation using low-resolution remote-sensing satellites. Our prediction system is automated with high-end computers and enables better understanding of sub-mesoscale phenomena for more accurate determination of fishing conditions. High-resolution forecasts of hazardous rapid currents can be delivered via mobile phone to prevent damage to nets..
23. Jae Hong Moon, Naoki Hirose, Seasonal response of the southern East China Sea shelf water to wind-modulated throughflow in the Taiwan Strait, Progress in Oceanography, 10.1016/j.pocean.2013.11.009, 121, 74-82, 2014.02, [URL], Seasonal change of the southern East China Sea (ECS) shelf water and its relation to the throughflow in the Taiwan Strait (TS) was examined based on comparative experiments with inserting passive tracers into a regional ocean model. Through analyzing the model output results, we found that from autumn to winter strong northeasterly wind over the TS significantly weakens the outflow from the TS (i.e., flowing into the ECS) and the Kuroshio water intrudes farther shoreward across the northern shelf of Taiwan in response to the weakened outflow. On the other hand, water flowing into the shelf from the TS extends further offshore from spring to summer when the TS throughflow is enhanced by a wind change from northeasterly to southwesterly and the Kuroshio water retreats seaward off the shelf due to the offshore extension of the shelf water. It suggests that the weakening (strengthening) of the TS throughflow could allow (inhibit) shelf-ward Kuroshio water onto the northeastern shelf of Taiwan, emphasizing that the throughflow modulated by a local wind can be an important factor controlling the seasonal variation of the southern ECS shelf water..
24. Shusaku Sugimoto, Naoki Hirose, Variations in latent heat flux over the eastern Japan sea in december, SOLA Scientific Online Letters on the Atmosphere, 10.2151/sola.2014-001, 10, 1, 1-4, 2014.02, [URL], Variations in latent heat flux (LHF), calculated from daily variables in the OAFlux dataset, were investigated over the Japan Sea for December of 1990-2010 because the December is the month with the largest LHF release. The largest temporal variations in LHF occurred over the eastern Japan Sea (EJS; 137°E-140°E, 38°N-43°N), showing an interannual-scale variation. By performing simple experiments with combinations of raw daily data and daily climatological data, we quantitatively assessed the relative contributions of saturated specific humidity at sea surface temperature (SST), surface air humidity, and surface wind speed in determining the LHF over the EJS. Results showed that SST (saturated specific humidity), which is associated with the Tsushima Warm Current, predominantly determines the LHF; a huge evaporation in the state of the positive SST anomaly. The LHF in the EJS has a strong influence on precipitation over the northern Japanese Islands..
25. Bin Wang, Naoki Hirose, Boonsoon Kang, Katsumi Takayama, Seasonal migration of the Yellow Sea Bottom Cold Water, Journal of Geophysical Research, 10.1002/2014JC009873, 119, 7, 4430-4443, 2014.01, The three-dimensional motion of the Yellow Sea Bottom Cold Water (YSBCW) and the relevant dynamical factors are studied using a regional circulation model and the two-way Lagrangian particle tracking method (PTM). The simulated results are in good agreement with hydrographic observations. The trajectories of the modeled particles show that the subsurface cold heavy water mass from the northern part of the Yellow Sea gradually sinks into deeper layers along the western slope of the Yellow Sea trough with a southward movement from spring to summer. The cold water mass gradually gathers speed from early March to July or August, and eventually reaches its southernmost location in late September or early October. Furthermore, sensitivity experiments demonstrate that tide-induced residual currents under baroclinic conditions are the dominant factor driving deep circulation during summertime in the Yellow Sea. The summer southerly wind and strong surface solar radiation are the secondary factors influencing the southward migration. This study also proposes an improved delimitation for the YSBCW based on temperature statistics in the central basin (deeper than 40 m) between 35°N and 39°N in March with an increase in rate of approximately 0.7°C/month, which is more appropriate than the constants of the 8°C or 10°C isotherms frequently used. Key Points The results show that the Yellow Sea Bottom Cold Water moves southward during summer Tide-induced residual current is dominant on the motion of the YSBCW An improved delimitation for the YSBCW has been proposed.
26. Naoki Hirose, Katsumi Takayama, Jae-Hong Moon, Tatsuro Watanabe, Yoshinori Nishida, Regional data assimilation system extended to the East Asian marginal seas, Umi to Sora (Sea and Sky), 89, 2, 43-51, 2013.12, [URL].
27. Eunjeong Lee, Yign Noh, Naoki Hirose, A new method to produce sea surface temperature using satellite data assimilation into an atmosphere-ocean mixed layer coupled model, Journal of Atmospheric and Oceanic Technology, 10.1175/JTECH-D-12-00238.1, 30, 12, 2926-2943, 2013.12, [URL], A new method of producing sea surface temperature (SST) data for numerical weather prediction is suggested, which is obtained from the assimilation of satellite-derived SST into an atmosphere-ocean mixed layer coupledmodel. TheWeatherResearch and Forecasting (WRF)Model and theNohmixed layer model are used for the atmosphere and ocean mixed layer models, respectively. Data assimilation (DA) is carried out in two steps, based on the estimation from the covariancematchingmethod that the daily mean SST of satellite data is more accurate than themodel data, if the number of data in a grid per day is sufficiently large-that is, the daily mean SST bias correction in the firstDAand the sequential SST anomaly correction in the secondDA. For the second DA, the model restarts from the initial condition corrected by the first DA, and DA is applied every 30min using the nudgingmethod.The dailymean and the diurnal variation of satellite SST are assimilated to the bulk and skin SST, respectively. The modeled results with the new data assimilation scheme are validated by statistical comparison with independent satellite and buoy data such as correlation coefficient, root-meansquare difference, and bias. Furthermore, the sensitivity and seasonal variation of the weighting factor in the secondDAare examined. The newapproach illustrates the possibility of applying the atmosphere-oceanmixed layer coupled model for the production of SST data combined with the assimilation of satellite data..
28. Wang Bin, Hirose Naoki, Jae-Hong Moon, Dongliang Yuan, Difference between the Lagrangian trajectories and Eulerian residual velocity fields in the southwestern Yellow Sea, Ocean Dynamics, 10.1007/s10236-013-0607-3, 63, 5, 565-576, 2013.04, [URL].
29. Seongbong Seo, Young Gyu Park, Jae Hun Park, Ho Jin Lee, Naoki Hirose, The tsushima warm current from a high resolution ocean prediction model, HYCOM, Ocean and Polar Research, 10.4217/OPR.2013.35.2.135, 35, 2, 135-146, 2013.01, [URL], This study investigates the characteristic of the Tsushima Warm Current from an assimilated high resolution global ocean prediction model, 1/12° Global HYbrid Coordiate Ocean Model (HYCOM). The model results were verified through a comparison with current measurements obtained by acoustic Doppler current profiler (ADCP) mounted on the passenger ferryboat between Busan, Korea, and Hakata, Japan. The annual mean transport of the Tsushima Warm Current was 2.56 Sverdrup (Sv) (1 Sv = 106 m3s-1), which is similar to those from previous studies (Takikawa et al. 1999; Teague et al. 2002). The volume transport time series of the Tsushima Warm Current from HYCOM correlates to a high degree with that from the ADCP observation (the correlation coefficient between the two is 0.82). The spatiotemporal structures of the currents as well as temperature and salinity from HYCOM are comparable to the observed ones..
30. Boonsoon KANG, Naoki HIROSE, and Jong-Hwan YOON, Characteristics of high-frequency transport variability in the Korea/Tsushima Strait, Reports of Research Institute for Applied Mechanics, Kyushu University, 143, 49-53, 2012.09.
31. Bin WANG, Naoki HIROSE, Jae-Hong MOON, and Dongliang YUAN, Comparison of tidal and wind contributions to Lagrangian trajectories in the southwestern Yellow Sea, Reports of Research Institute for Applied Mechanics, Kyushu University, 143, 43-48, 2012.09.
32. Jae-Hong Moon, Naoki Hirose, Modeled response of the East China Sea shelf water to wind forcing, Reports of Research Institute for Applied Mechanics, Kyushu University, 143, 7-17, 2012.09.
33. Jae Hong Moon, Naoki Hirose, Ig Chan Pang, Kyung Hoon Hyun, Modeling offshore freshwater dispersal from the changjiang river and controlling factors during summer, Terrestrial, Atmospheric and Oceanic Sciences, 10.3319/TAO.2012.01.10.01(Oc), 23, 3, 247-260, 2012.06, [URL], In this study we examine offshore transport and dispersal pathways of the freshwater discharge from the Changjiang River in the East China Sea (ECS), using a regional ECS model. Comparison between the results for 1996 and 1998 clearly shows that the summer monsoon winds play a significant role in spreading the freshwater discharge offshore and determining the dispersal of freshwater in the ECS. Analysis of 10-year simulation demonstrates that a northeastward freshwater transport to Jeju Island across the northwestern shelf of the ECS dominates during the summer period due to the surface Ekman flow by the southeasterly along-shore wind. Meanwhile, there is virtually no relationship between the amount of the summer discharge and the freshwater pathway toward Jeju Island. Our analysis also suggests that when the summer wind is relatively weak, another freshwater pathway toward the central ECS appears with the ambient along-shelf current between the Taiwan Strait and the Korea Strait..
34. MOON JAEHONG, Hirose Naoki, MORIMOTO Akihiko, Green's function approach for calibrating tides in a circulation model for the East Asian marginal seas, Journal of Oceanography, 10.1007/s10872-011-0097-1, 68, 2, 345-354, 2012.04, [URL], A simple effective method of inverse estimation provided by model Green's functions is examined to calibrate tides in a regional circulation model for the East Asian marginal seas. The Green's function optimization derived by perturbing the model parameters significantly improves the estimate relative to observation as compared with baseline integration. Among the optimized model parameters, the largest effects on cost function reduction come first from the harmonic constant of M 2 along the open boundaries with the optimized values of 89.7 ± 0.8% for amplitude, and second from the bottom friction with the optimized value of (3.06 ± 0.08) × 10 -3..
35. Masaru Yamamoto, T. Ohigashi, K. Tsuboki, Naoki Hirose, Cloud-resolving simulation of heavy snowfalls in Japan for late December 2005
Application of ocean data assimilation to a snow disaster, Natural Hazards and Earth System Sciences, 10.5194/nhess-11-2555-2011, 11, 9, 2555-2565, 2011.10, [URL], We applied eddy-resolving ocean data assimilation to a cloud-resolving atmospheric simulation of a snow disaster and investigated the effects of mesoscale eddies on a heavy snowfall event in late December 2005. Ocean circulation model (OCM) data assimilation reproduces mesoscale sea surface temperature (SST) structures, which are smoothed out by optimum interpolation. This difference between OCM-assimilation and optimum-interpolation SSTs affects the atmospheric boundary layers over oceanic mesoscale eddies. The atmospheric response to the SST difference is complex at the cold tongue in the central Sea of Japan. Although the horizontal wind and turbulent mixing are quickly and locally affected by the low SST, the atmospheric temperature and water amounts are greatly affected by the upstream high SST via the northwesterly advection. In the heavy snowfall areas, the OCM assimilation greatly affects 10-day accumulated precipitation, though it does not largely influence 10-day mean vertical structures of wind, temperature and water vapor. Thus, we should recognize the significance of oceanic mesoscale eddies for heavy snowfall..
36. M. Yamamoto, Y. Maeda, and N. Hirose, Meteorological influences of eddy-resolving ocean assimilation around the cold tongue to the north of the Japanese Islands during winter 2004/2005, Asia-Pacific Journal of Atmospheric Sciences, 10.1007/s13143-011-0019-6, 47, 4, 319-327, 2011.08, [URL].
37. Hirose, N., Inverse estimation of empirical parameters used in a regional ocean circulation model, Journal of Oceanography, 10.1007/s10872-011-0041-4, 67, 3, 323-336, 2011.06.
38. Ami Ueda, Masaru Yamamoto, Naoki Hirose, Meteorological influences of SST anomaly over the East Asian marginal sea on subpolar and polar regions
A case of an extratropical cyclone on 5-8 November 2006, Polar Science, 10.1016/j.polar.2010.11.002, 5, 1, 1-10, 2011.04, [URL], The eddy-resolving Japan Sea (East Sea) data assimilation affects the mid-level troposphere via vertical wind in the early stage of an explosively developing extratropical cyclone on 5-8 November 2006, and its influence further propagates toward the subpolar and polar regions. Two types of atmospheric responses (convective and gravity-wave patterns) to a sea surface temperature (SST) difference resulting from the ocean data assimilation are found in the early stage of the cyclone development over the western and central Japan Sea. A gravity-wave (convective) pattern appears when the near-surface atmosphere is stable (unstable). The atmospheric signals induced by the SST anomaly resulting from assimilation of the ocean circulation model are subject to advection and can deform with time owing to nonlinearity and instability. The differences in atmospheric and surface temperatures are widely and rapidly spread over the polar region by strong synoptic-scale cyclonic advection. On the other hand, the SST effects on vertical flow and precipitation are limited to narrow areas around the northern Japan Sea and the Pacific cold front in the fully developed stage. Such a developing cyclone is potentially important as a transporter of the meteorological influence over the Japan Sea toward the polar region..
39. Masaru Yamamoto, Naoki Hirose, Possible modification of atmospheric circulation over the northwestern Pacific induced by a small semi-enclosed ocean, Geophysical Research Letters, 10.1029/2010GL046214, 38, 3, 2011.02, [URL], The surface conditions of a small semi-enclosed ocean (the Japan Sea), largely controlled by the volume transport of the warm current, influence the monthly mean atmospheric circulation over the northwestern Pacific via active cyclogenesis. The new dynamical processes induced by the Japan Sea are proposed in this letter. When the surface temperature in the Japan Sea is lowered in a regional atmospheric model, the monthly mean potential vorticity is increased over the Japanese Islands, and the monthly mean Okhotsk Low is intensified at the 500-hPa level. In the case of an amplified Okhotsk Low, the mean cyclonic flow transports a cold air over the Japan Sea toward the Pacific and transports relatively warm air over the Bering Sea toward Siberia. Such westerly/easterly air mass advections over the northwestern Pacific area could produce the Japan-Siberia temperature anomaly in the lower-level troposphere via enhancement of the Okhotsk Low, which contributes to the weakness of the synoptic-scale north-south temperature gradient at 120°-180°E. This newly-found westerly cold/easterly warm ocean air-mass advection enhanced by the amplified quasi-stationary eddy that acts to reduce the temperature gradient is distinct from poleward heat transport by well-known transient baroclinic waves or annual mean Ferrel circulation..
40. Kawamura, H., T. Ito, T. Kobayashi, S. Otosaka, N. Hirose, and O. Togawa, Simulation of concentrations of anthropogenic radionuclides in the Japan Sea, Proceedings of Joint International Conference on Supercomputing in Nuclear Applications and Monte Carlo 2010 (SNA + MC 2010), 2010.10.
41. Satoshi Nakada, You Ichiro Sasajima, Naoki Hirose, Yutaka Yoshikawa, Jong Hwan Yoon, A study of the dynamic factors of the summer-time upwelling in the Tsushima Warm Current region, Deep-Sea Research Part II: Topical Studies in Oceanography, 10.1016/j.dsr2.2010.04.006, 57, 19-20, 1799-1808, 2010.10, [URL], The dynamic factors governing the summer-time upwelling along the Japanese shelf area and its structures are examined using an eddy-resolving ocean general circulation model. A sensitivity experiment suggests that the dominant factor is the topographic irregularities that enhance the upwelling along the shelf slope but the influences of the seasonal variation of the Tsushima Warm Current (TWC) inflow and wind stress are insignificant. The dynamic analysis shows that the upwelling is a part of the secondary, overturning circulation that appears along the shelf from April to October. The dynamic structure shows the dominant term balance in essence, i.e. a triad of the term of pressure gradient, Coriolis force, and horizontal advection. The local pattern of the upwelling is closely correlated to the horizontal variations of the shelf slope and the horizontal advection term. The horizontal variation in the shelf topography is a key factor to determine the local pattern of the summer-time upwelling..
42. Hideyuki Kawamura, Toshimichi Ito, Takuya Kobayashi, Shigeyoshi Otosaka, Naoki Hirose, Orihiko Togawa, Numerical experiment for strontium-90 and cesium-137 in the Japan Sea, Journal of Oceanography, 10.1007/s10872-010-0053-5, 66, 5, 649-662, 2010.09, [URL], A numerical experiment is carried out to reproduce distribution of concentration of 90Sr and 137Cs, estimate their total amount and verify their source in the Japan Sea. Model results are in good agreement with observational findings in the Japan Sea expeditions between 1997 and 2002 by the Japan Atomic Energy Agency. Vertical profiles of the concentration of 90Sr and 137Cs show exponential decreases with depth from the sea surface to the sea bottom. From the model and observational results, it is suggested that the concentration of 90Sr and 137Cs in the surface layer is approximately in the range of 1.0-1.5 Bq/m3 and 2.0-2.5 Bq/m3, respectively. On the other hand, it is found that the concentration in the intermediate and deep layer is higher than that observed in the northwestern Pacific Ocean, suggesting active winter convection in the Japan Sea. The total amount of 90Sr and 137Cs in the seawater is evaluated to be 1.34 × 1015 Bq and 2.02 × 1015 Bq, respectively, in the numerical experiment, which demonstrates an estimation by observational data obtained in the Japan Sea expeditions. The total amount of 90Sr and 137Cs changed during the second half of 20th century corresponding to deposition at the sea surface with the maximums of 4.86 × 1015 Bq for 90Sr and 7.33 × 1015 Bq for 137Cs, respectively, in the mid-1960s. The numerical experiment suggests that the main source of 90Sr and 137Cs has been global fallout, although there have been some potential sources in the Japan Sea..
43. Ueno, G., T. Higuchi, T. Kagimoto, and N. Hirose, Maximum likelihood estimation of error covariance in ensemble-based filters and its application to a coupled atmosphere-ocean model, Q. J. R. Meteorol. Soc., 10.1002/qj.654, 136, 650, 1316-1343, 2010.07.
44. Goh Onitsuka, Kazutaka Miyahara, Naoki Hirose, Shuyo Watanabe, Hitoshi Semura, Reiko Hori, Tetsuya Nishikawa, Kuniaki Miyaji, Mineo Yamaguchi, Large-scale transport of Cochlodinium polykrikoides blooms by the Tsushima Warm Current in the southwest Sea of Japan, Harmful Algae, 10.1016/j.hal.2010.01.006, 9, 4, 390-397, 2010.05, [URL], Since 2002, blooms of the harmful dinoflagellate Cochlodinium polykrikoides Margalef have occurred in the eastern San-in area, the Japanese coastal area fronting the southwest Sea of Japan. To investigate the occurrence mechanisms of the blooms, numerical experiments were conducted using a Lagrangian particle-tracking model, under different hydrographic conditions in 2002-2008. The results of Lagrangian simulations revealed that the source region of the blooms was located in the southeast Korean coastal area, >500 km away from the eastern San-in area. They were transported by the Tsushima Warm Current over about two weeks to one month. The blooms in the eastern San-in area were thought to occur only when a series of sequential conditions were met, which included preceding outbreaks in Korean waters, southwesterly winds in the Tsushima Strait, and the nearshore position of the Tsushima Warm Current off the San-in coast, veering eastward from the Korean peninsula..
45. Jae Hong Moon, Naoki Hirose, Jong Hwan Yoon, Ig Chan Pang, Offshore detachment process of the low-salinity water around Changjiang Bank in the East China Sea, Journal of Physical Oceanography, 10.1175/2010JPO4167.1, 40, 5, 1035-1053, 2010.05, [URL], A patchlike structure of low-salinity water detached from the Chanjiang "Diluted Water" (CDW) is frequently observed in the East China Sea (ECS). In this study, the offshore detachment process of CDW into the ECS is examined using a three-dimensional numerical model. The model results show that low-salinity water is detached from the CDW plume by the intense tide-induced vertical mixing during the spring tide period when the tidal current becomes stronger. During the spring tide, thickness of the bottom mixed layer in the sloping bottom around Changjiang Bank reaches the mean water depth, implying that the stratification is completely destroyed in the entire water column. As a result, the offshore detachment of CDW occurs in the sloping side of the bank where the tidal energy dissipation is strong enough to overcome the buoyancy effect during this period. On the other hand, the surface stratification is retrieved during the neap tide period, because the tidal current becomes substantially weaker than that in the spring tide. Wind forcing over the ECS as well as tidal mixing is a critical factor for the detachment process because the surface wind primarily induces a northeastward CDW transport across the shelf region where tide-induced vertical mixing is strong. Moreover, the wind-enhanced cross-isobath transport of CDW causes a larger offshore low-salinity patch, indicating that the freshwater volume of the low-salinity patch closely depends on the wind magnitude..
46. Masaru Yamamoto, Naoki Hirose, Atmospheric simulations using OGCM-assimilation SST
Influence of the wintertime Japan sea on monthly precipitation, Terrestrial, Atmospheric and Oceanic Sciences, 10.3319/TAO.2009.03.18.03(IWNOP), 21, 1, 113-122, 2010.02, [URL], Temperature data for the Japan Sea obtained from ocean data assimilation modeling is applied to atmospheric simulations of monthly precipitation for January 2005. Because the volume of flow of the Tsushima Warm Current was large during the winter season, the sea surface temperature (SST) and coastal precipitation were higher in comparison with those in 2003. In order to evaluate influence of SST on monthly precipitation, we use surface temperatures of the Japan Sea in 2003 and 2005 for comparative simulations of precipitation for January 2005. The precipitation in experiment C (using cool SST data in 2003) is smaller than that in experiment W (using warm SST data in 2005) in a large part of the sea area, since the small evaporation results from the low SST over the upstream area of northwesterly winter monsoon. In the domain of 33.67 - 45.82°N and 125.89 - 142.9°E, the averaged evaporation and precipitation in experiment C are 10% and 13% smaller than those in experiment W, respectively. About half of the difference between the precipitations observed for January 2003 and 2005 in a heavy snow area is equal to the difference between the two simulations. Our results show that the mesoscale SST difference between 2003 and 2005 is related to the local difference of monthly precipitation..
47. Onitsuka, G., N. Hirose, K. Miyahara, T. Ota, J. Hatayama, Y. Mitsunaga, and T. Goto, Numerical simulation of the migration and distribution of diamond squid (Thysanoteuthis rhombus) in the southwest Sea of Japan, Fisheries Oceanography, 10.1111/j.1365-2419.2009.00528.x, 19, 1, 63-75, 2010.01, [URL].
48. Hideyuki Kawamura, Toshimichi Ito, Naoki Hirose, Tetsutaro Takikawa, Jong Hwan Yoon, Modeling of the branches of the Tsushima Qarm Current in the eastern Japan Sea, Journal of Oceanography, 10.1007/s10872-009-0039-3, 65, 4, 439-454, 2009.12, [URL], The branches of the Tsushima Warm Current (TWC) are realistically reproduced using a three-dimensional ocean general circulation model (OGCM). Simulated structures of the First Branch and the Second Branch of the TWC (FBTWC and SBTWC) in the eastern Japan Sea are mainly addressed in this study, being compared with measurement in the period September-October 2000. This is the first numerical experiment so far in which the OGCM is laterally exerted by real volume transports measured by acoustic Doppler current profiler (ADCP) through the Tsushima Straits and the Tsugaru Strait. In addition, sea level variation measured by tide-stations along the Japanese coast as well as satellite altimeters is assimilated into the OGCM through a sequential data assimilation method. It is demonstrated that the assimilation of sea level variation at the coastal tide-stations is useful in reproducing oceanic conditions in the nearshore region. We also examine the seasonal variation of the branches of the TWC in the eastern Japan Sea in 2000. It is suggested as a consequence that the FBTWC is continuous along northwestern Honshu Island in summertime, while it degenerates along the coast between the Sado Strait and the Oga Peninsula in other seasons. On the other hand, a mainstream of the SBTWC exists with meanders and eddies in the offshore region deeper than 1000 m to the north of the Sado Island throughout the year..
49. Prediction of Kyucho by a circulation model of the Japan Sea.
50. Masaru Yamamoto, Naoki Hirose, Regional atmospheric simulation of monthly precipitation using high-resolution SST obtained from an ocean assimilation model
Application to the wintertime Japan sea, Monthly Weather Review, 10.1175/2009MWR2488.1, 137, 7, 2164-2174, 2009.10, [URL], The present study examines the influence of an assimilation SST product on simulated monthly precipitation. The high-resolution SST structures located close to the oceanic front and coastal areas are important in regional atmospheric simulations over semienclosed marginal seas such as the Japan Sea. Two simulations are conducted using assimilation and interpolation SST products (experiments R and N, respectively), for January 2005. The surface heat fluxes and PBL height in experiment R are lower than those in experiment N in coastal areas and the cold tongue. A decrease of 4 K in SST leads to decreases of 120 W m-2 in surface sensible and latent fluxes and 300 m in PBL height. The precipitation in experiment R is less than that in experiment N for the sea area except at 38°N, 137°E. The cold tongue in the central Japan Sea acts to reduce moisture supply via the latent heat flux, resulting in low precipitation in coastal areas. The fact that the difference between observed and modeled precipitation in experiment R is 21% less than that in experiment N demonstrates that the assimilation of SST data leads to improved regional atmospheric simulations of monthly precipitation..
51. Validation of the number of branches in the Tsushima Warm Current based on assimilated estimates, [URL].
52. Satoshi Nakada, Naoki Hirose, Seasonal upwelling underneath the Tsushima Warm Current along the Japanese shelf slope, Journal of Marine Systems, 10.1016/j.jmarsys.2009.02.015, 78, 2, 206-213, 2009.09, [URL], Seasonal upwelling variations are examined in the eastward coastal boundary branches of the Tsushima Warm Current (TWC). The climatological pattern and the fundamental hydrographic structure of the seasonal appearance of cold water are revealed by analyzing the temperature profile data around the Japanese shelf area. Seasonal maps of temperature at the intermediate layer around 200 m depth show the rise of the main pycnocline along the Japanese coast due to seasonal subsurface cooling from May to September. The cold water areas appear around the strong curvature in the continental shelf break. These areas are confined to the south of the TWC thermal front, i.e., to the coastal boundary region. The seasonal appearance of the localized cooling areas implies that the seasonal upwelling is induced by horizontal variations in shelf topography and the intensifying TWC from May to September..
53. Jae Hong Moon, Naoki Hirose, Jong Hwan Yoon, Comparison of wind and tidal contributions to seasonal circulation of the Yellow Sea, Journal of Geophysical Research, 10.1029/2009JC005314., 114, 8, 2009.08, [URL], [1] Seasonal circulation of the Yellow Sea (YS) in response to wind and tidal forces is examined using a three-dimensional numerical model. Wind forcing affects the wintertime circulation of the YS; on the other hand, the summer southerly monsoon is weak and therefore has little impact on the circulation, on the basis of comparative experiments with and without wind conditions. Results indicate that the Yellow Sea Warm Current (YSWC) along the YS trough exists regardless of wind forcing. However, strong winter northerly winds intensify the southward coastal flows along both coasts of the YS, and therefore, the northward intrusion of the YSWC becomes stronger. These flows in the YS are substantially weakened when wind forcing is not applied to the model. In addition to wind-driven circulation, tide-induced circulation is also dominant in the YS, particularly in summer. In winter, the tidal effect weakens the upwind and downwind flows in response to the strong northerly winds, while in summer, tidal forcing induces a strong southward residual flow along the western slope and a cyclonic gyre with a bottom cold water dome at the central region of the YS. The southward residual current possibly explains the southward movement of the Yellow Sea Bottom Cold Water as observed in summer. Comparison to the effects of parameterized tidal mixing suggests that residual flow driven by explicit tidal forcing plays an important role in the summertime circulation of the YS..
54. Naoki Hirose, Kazuya Nishimura, Masaru Yamamoto, Observational evidence of a warm ocean current preceding a winter teleconnection pattern in the northwestern Pacific, Geophysical Research Letters, 10.1029/2009GL037448, 36, 9, 2009.05, [URL], The role of the extratropical ocean in climate remains unclear due to the complexities in air-sea interaction processes. We have found robust evidence for the Tsushima Warm Current (TWC) preceding the western Pacific (WP) teleconnection pattern by conducting an analysis over the past 30 years. The WP index in winter sharply succeeds the volume transport of the TWC in autumn, but rather smoothly connects with the El Niño indices, indicating a considerable role of the ocean current in the climate system. Correlation patterns of seasonal precipitation over the Japanese Islands are also consistent with this relationship. The significant lead-lag correlations with the coherent structures of surface temperature indicate ocean-to-atmosphere feedback in which the interannual variation of the wind-driven current, represented by the TWC transport, influences the regional climate conditions associated with the WP pattern in winter..
55. Kosuke Mori, Takeshi Matsuno, Tomoharu Senjyu, Naoki Hirose, In Seong Han, Short-term temperature and salinity variations in the Tsushima Strait in 2004
Behavior of the surface low-salinity water in the strait, Journal of Oceanography, 10.1007/s10872-009-0028-6, 65, 3, 301-310, 2009.05, [URL], Temporal variations in temperature and salinity observed in 2004 were investigated on a short time scale in the Tsushima Strait. The data were obtained by long-term in situ measurements at Mitsushima and Futaoi Island using an instrument equipped with a piston-type wiper to avoid biofouling. In addition, the temperature and salinity values of the surface layer obtained by a commercial ferryboat between Hakata and Busan were used to investigate their spatiotemporal variations. Temperature and salinity variations with a time scale of several days had a negative correlation in the summer. This evidence suggests that a warm and less saline water mass, which is considered to be mainly the Changjiang Diluted Water (CDW), flowed intermittently through the Tsushima Strait in summer. In late July 2004, a large low-salinity water mass was detected in the Tsushima Strait. At that time, the freshwater transport through the Tsushima Strait transiently reached about 12 × 104 m3s-1, which is estimated from observed acoustic Doppler current profiler (ADCP) data along a ferryboat line and inferred salinity profiles. This estimated value is more than double the maximum of the climatological monthly mean of the Changjiang discharge. Furthermore, salinity and surface current data obtained by high frequency ocean radar (HF radar) indicate that water properties at Mitsushima may occasionally represent part of the water flowing through the western channel via a countercurrent, although Mitsushima is geographically located in the eastern channel..
56. Nakamura, K., N. Hirose, B.H. Choi and T. Higuchi, Particle filtering in data assimilation and its application to boundary condition of tsunami simulation model, Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications, 353-366, 2009.02, [URL].
57. Jae Hong Moon, Naoki Hirose, Jong Hwan Yoon, Ig Chan Pang, Effect of the along-strait wind on the volume transport through the Tsushima/Korea Strait in September, Journal of Oceanography, 10.1007/s10872-009-0002-3, 65, 1, 17-29, 2009.01, [URL], Recent investigation suggests that volume transport through the Tsushima/ Korea Strait often has double peaks during the summer to autumn period with decreasing transport in September. The satellite-observed wind changes from weak northwestward (across-strait) in summer to strong southwestward (along-strait) in early autumn (September) in the strait. Such a strong along-strait wind is related to tropical cyclones, which frequently pass through the East China Sea in September. The effect of the along-strait wind component on the transport variation is examined using a three-dimensional numerical model. The simulated volume transport through the Tsushima/Korea Strait shows realistic seasonal and intra-seasonal variations. According to sensitivity experiments on local winds, the transport variations in September are mainly generated by strong along-strait (southwestward) wind rather than weak across-strait wind. The strait transport responds to the along-strait wind (southeastward), which produces a sea level increase along the Korean coast, resulting in the geostrophic balance across the strait. The transport minimum through the Tsushima/Korea Strait in September can be determined by the combination of the across-strait geostrophic and along-strait ageostrophic balances..
58. Naoki Hirose, Sergey Varlamov, Prediction of Kyucho by a circulation model of the Sea of Japan, Nippon Suisan Gakkaishi, 10.2331/suisan.75.891, 75, 5, 891-892, 2009.01, [URL].
59. Yoshida, S. and N. Hirose, Non-isostatic sea-level variability simulated using a global barotropic ocean model, Pacific Oceanography, 4, 27-35, 2008.06.
60. Masaru Yamamoto, Naoki Hirose, Influence of assimilated SST on regional atmospheric simulation
A case of a cold-air outbreak over the Japan Sea, Atmospheric Science Letters, 10.1002/asl.164, 9, 1, 13-17, 2008.01, Sea surface temperature (SST) assimilated using an ocean circulation model is used for the atmospheric simulation of a cold-air outbreak over the Japan Sea. The upward surface-turbulent heat fluxes are significantly influenced by the high-resolution SST structure resulting from mesoscale oceanic eddies. A strong deceleration of the outbreak due to local convective activity arises in a coastal area when using the assimilated SST data, in good agreement with observations; however, this feature is not observed when using the interpolated SST. In general, the use of assimilated temperature does improve regional atmospheric simulations..
61. You Ichiro Sasajima, Satoshi Nakada, Naoki Hirose, Jong Hwan Yoon, Structure of the subsurface counter current beneath the Tsushima warm current simulated by an ocean general circulation model, Journal of Oceanography, 10.1007/s10872-007-0077-7, 63, 6, 913-926, 2007.12, [URL], The subsurface counter current beneath the Tsushima Warm Current is simulated using a three-dimensional circulation model. The model well reproduces the counter current beneath the Tsushima Warm Current on the shelf break. The counter current appears as nearshore parts of the subsurface clockwise circulations from spring to early winter. The clockwise circulations are separated by developed shelves such as the Oki Spur and the Noto Peninsula, thus the counter current is not a continuous flow along the Japanese coast in this model. The vertical structure of the counter current can be explained by a density structure with the thermal wind relationship. The permanent and seasonal pycnoclines form mutually opposite horizontal density gradients near the Japanese coast in summer. Such a density structure results in a speed maximum of the counter current away from the bottom. It is remarkable that the second baroclinic mode is dominant in nearshore parts of the subsurface clockwise circulations in summer, which are attributed to the density structure. Similar density structures are also found in some coastal regions of the world oceans where subsurface counter currents are expected..
62. Naoki Hirose, Hideyuki Kawamura, Ho Jin Lee, Jong Hwan Yoon, Sequential forecasting of the surface and subsurface conditions in the Japan Sea, Journal of Oceanography, 10.1007/s10872-007-0042-5, 63, 3, 467-481, 2007.06, [URL], This study estimates a realistic change of the Japan Sea by assimilating satellite measurements into an eddy-resolving circulation model. Suboptimal but feasible assimilation schemes of approximate filtering and nudging play essential roles in the system. The sequential update of error covariance significantly outperforms the asymptotic covariance in the sequential assimilation due to the irregular sampling patterns from multiple altimeter satellites. The best estimates show an average rms difference of only 1.2°C from the radiometer data, and also explain about half of the sea level variance measured by the altimeter observation. The subsurface conditions associated with the mesoscale variabilities are also improved, especially in the Tsushima Warm Current region. It is demonstrated that the forecast limit strongly depends on variable, depth, and location..
63. Miyahara, K., N. Hirose, G. Onitsuka, andS. Gorie, Catch distribution of diamond squid (Thysanoteuthis rhombus) off Hyogo Prefecture in the western Sea of Japan and its relationship with seawater temperature, Bulletin of the Japanese Society of Fisheries Oceanography, 71, 2, 106-111, 2007.05.
64. Masaru Yamamoto, Naoki Hirose, Impact of SST reanalyzed using OGCM on weather simulation
A case of a developing cyclone in the Japan Sea area, Geophysical Research Letters, 10.1029/2006GL028386, 34, 5, 2007.03, [URL], It is difficult to estimate high-resolution sea surface temperature (SST) distributions in coastal areas under cloudy and rainy weather conditions. This study makes use of dynamical estimates of SST produced by combining satellite measurements into an eddy-resolving ocean general circulation model (OGCM). The reanalyzed SST provides an improved surface boundary condition for mesoscale atmospheric simulations. We examined a developing cyclone passing over the Japan Sea in comparative experiments undertaken using reanalyzed and satellite-measured SSTs. Mesoscale features of the SSTs resulting from ocean dynamics influence the development of the cyclone. In particular, the surface turbulent heat flux, precipitable water, and cloud water are sensitive to the difference between the two sets of SSTs. In these experiments, the simulation results obtained using the reanalyzed SST data are more similar to observed data than the results obtained using satellite-measured SST..
65. Numerical simulation of Kyucho along the eastern coast of the Noto Peninsula in 2004.
66. Genta Ueno, Tomoyuki Higuchi, Takashi Kagimoto, Naoki Hirose, Application of the ensemble Kalman filter and smoother to a coupled atmosphere-ocean model, Scientific Online Letters on the Atmosphere, 10.2151/sola.2007-002, 3, 5-8, 2007.01, [URL], We report an application of the ensemble Kalman filter (EnKF) and smoother (EnKS) to an intermediate coupled atmosphere-ocean model of Zebiak and Cane, into which the sea surface height (SSH) anomaly observations by TOPEX/POSEIDON (T/P) altimetry are assimilated. Smoothed estimates of the 54,403 dimensional state are obtained from 1,981 observational points with 2,048 ensemble members. While assimilated data are SSH anomalies alone, the estimated sea surface temperature (SST) anomalies reproduce primary temporal characteristics of the actual SST. The smoothed estimate of the zonal wind anomalies is also consistent with the observation except for the westerly anomalies in the western Pacific..
67. Data assimilation model for Japan Sea circulation, [URL].
68. Daisuke Inazu, Naoki Hirose, Shoichi Kizu, Kimio Hanawa, Zonally asymmetric response of the Japan Sea to synoptic pressure forcing, Journal of Oceanography, 10.1007/s10872-006-0108-9, 62, 6, 909-916, 2006.12, [URL], We investigated the sea level response of the Japan Sea to changes in atmospheric pressure using barotropic shallow water models driven by idealized synoptic pressure forcing. The regional response lags behind the synoptic pressure forcing because the adjustment is slowly established by water exchange through narrow, shallow straits. The sea level response of the realistic Japan Sea to the idealized forcing varies with geographical location and shows zonally asymmetric variations in amplitude and phase. The simulated response is in good agreement with the observed response of sea level recorded at Japanese coastal tide gauges. The results of a simple one-dimensional model indicate that the zonally asymmetric pattern, with an eastward-propagating pressure system, is essentially caused by bottom friction in shallow straits. This asymmetry arises if the typical wavelength of the synoptic pressure system is slightly larger than the spatial scale of the Japan Sea..
69. Ueno, G., T. Higuchi, T. Kagimoto, and N. Hirose, Prediction of ocean state by data assimilation with the ensemble Kalman filter, Proceedings of Joint 3rd International Conference on Soft Computing and Intelligent Systems and 7th International Symposium on advanced Intelligent Systems (SCIS & ISIS 2006), 1884-1889, 2006.09.
70. G. Ueno, T. Higuchi, T. Kagimoto, Naoki Hirose, Application of the ensemble Kalman filter to atmosphere-ocean coupled model, NSSPW - Nonlinear Statistical Signal Processing Workshop 2006, 10.1109/NSSPW.2006.4378835, 2006.06, [URL], We report the first application of the ensemble Kalman filter (EnKF) to an intermediate coupled atmosphere-ocean model by [1], into which the sea surface height (SSH) anomaly observations by TOPEX/POSEIDON (T/P) altimetry are assimilated. Smoothed estimates of the 54,403 dimensional state are obtained from 1981 observational points with 2048 ensemble members. While data assimilated are SSH anomalies alone, an ensemble experiment of 2002/03 El Niño event based on the EnKF can predict consistent Niño 3 sea surface temperature (SST) anomalies about 5 months in advance..
71. Kazuyuki Nakamura, Tomoyuki Higuchi, Naoki Hirose, Sequential data assimilation:Information fusion of a numerical simulation and large scale observation data, Journal of Universal Computer Science, 12, 6, 608-626, 2006.06, [URL], Data assimilation is a method of combining an imperfect simulation model and a number of incomplete observation data. Sequential data assimilation is a data assimilation in which simulation variables are corrected at every time step of observation. The ensemble Kalman filter is developed for a sequential data assimilation and frequently used in geophysics. On the other hand, the particle filter developed and used in statistics is similar in view of ensemble-based method, but it has different properties. In this paper, these two ensemble based filters are compared and characterized through matrix representation. An application of sequential data assimilation to tsunami simulation model with a numerical experiment is also shown. The particle filter is employed for this application. An erroneous bottom topography is corrected in the numerical experiment, which demonstrates that the particle filter is useful tool as the sequential data assimilation method..
72. Naoki Hirose, Ken ichi Fukudome, Monitoring the Tsushima warm current improves seasonal prediction of the regional snowfall, Scientific Online Letters on the Atmosphere, 10.2151/sola.2006-016, 2, 61-63, 2006.01, [URL], Seasonal predictions of rain or snowfall are usually too uncertain at regional scales. We suggest utilizing subsurface ocean measurements to improve long-term weather forecasts. The example we give is that regional snowfall in Japan can be predicted by a simple regression from an acoustic Doppler current profiler attached to a regular ferryboat to observe the transport of the Tsushima Warm Current. The lag correlation is shown to exceed 0.75 attributed to the simple underling marine meteorology and regional oceanography. The relationship certainly improves seasonal precipitation estimates led by the winter monsoon absorbing the latent heat from the Japan Sea. We predict there will be less snowfall this winter of 2005/2006 than in 2004/2005 despite the heavy snowfall event in the last December..
73. H. Kawamura, T. Kobayashi, Naoki Hirose, T. Ito, O. Togawa, Oil spill simulation in the Japan Sea, 6th International Conference on Environmental Problems in Coastal Regions including Oil and Chemical Spill Studies, COASTAL ENVIRONMENT 2006, CENV06 Environmental Problems in Coastal Regions VI Including Oil and Chemical Spill Studies, 10.2495/CENV060261, 88, 273-278, 2006.01, [URL], An assessment system of the marine environment in the Japan Sea is being developed at the Japan Atomic Energy Agency. This study aims to confirm the validity of the assessment system by reproducing the oil spill at the incident of Russian tanker Nakhodka in January 1997. As a main subject, one of the data assimilation techniques, an approximate Kalman filter, was applied to the assessment system by combining an ocean general circulation model with sea level measurements of satellite data. Using calculated ocean currents, simulations of the behaviour of spilled oil were performed with a particle random-walk model. A number of experiments with different parameters and situations showed that the assimilated daily ocean currents with wind drift were for the simulation for movement of spilled oil..
74. Hirose, N., I. Fukumori, C.-H. Kim, and J.-H. Yoon, Numerical simulation and satellite altimeter data assimilation of the Japan Sea circulation, Deep Sea Research II, 10.1016/j.dsr2.2004.09.034, 52, 11-13, 1443-1463, 52, 1443-1463, 2005.08.
75. Hirose, N, Least-squares estimation of bottom topography using horizontal velocity measurements in the Tsushima/Korea Straits, Journal of Oceanography, 10.1007/s10872-005-0085-4, 61, 4, 789-794, 2005.08, [URL].
76. Manda, A., N. Hirose, and T. Yanagi, Feasible method for the assimilation of the satellite-derived SST with an ocean circulation model, J. Atmos. Ocean. Tech., 10.1175/JTECH1744.1, 22, 6, 746-756, 22 (6), 746-756, 2005.06, [URL].
77. Rui M. Ponte, Naoki Hirose, Propagating bottom pressure signals around Antarctica at 1-2-day periods and implications for ocean modes, Journal of Physical Oceanography, 10.1175/1520-0485(2004)034<0284:PBPSAA>2.0.CO;2, 34, 1, 284-292, 2004.01, [URL], Previous studies of barotropic ocean dynamics have shown that several global normal modes are possible at periods between 1 and 2 days. The role of these modes in diurnal tidal dynamics is well documented, but finding evidence for their direct excitation by atmospheric forcing has remained elusive. Analyses of a barotropic ocean model and a limited number of bottom pressure records in the Southern Ocean described here provide evidence for large-scale, coherent signals propagating westward around Antarctica at 1-2-day periods. Phases are roughly consistent with the fundamental Kelvin wave structure underlying a number of normal modes with significant expressions in the Southern Ocean. Model and data results suggest the weak excitation of several of these normal modes by atmospheric pressure fluctuations. Strong dissipation also contributes to their weak amplitudes and makes it difficult to detect a truly global signal in the data..
78. Assimilation of intermediate float data into a barotropic shallow water model using an approximate Kalman filter.
79. Comparison of data assimilation methods in a wind driven ocean circulation field.
80. Numerical experiments of the mechanism of the southwestward countercurrent east of the Tsushima Islands.
81. Manda, A., N. Hirose, and T. Yanagi, Application of a Nonlinear and Non-Gaussian Sequential Estimation Method for an Ocean Mixed Layer Model, Eng. Sci. Rep., Kyushu Univ, 25, 285-289, 2003.09.
82. Reanalysis of the Japan Sea circulation using approximate smoother.
83. Tetsuo Yanagi, Goh Onitsuka, Naoki Hirose, John Hwan Yoon, A numerical simulation on the Mesoscale dynamics of the spring bloom in the sea of Japan, Journal of Oceanography, 10.1023/A:1021691221793, 57, 6, 617-630, 2001.12, [URL], The northward migration of spring bloom was observed in the Sea of Japan from April to May 1997 by the Ocean Color and Temperature Scanner (OCTS) on board the Advanced Earth Observing Satellite (ADEOS). This phenomenon is well simulated with a numerical ecosystem model coupled with a hydrodynamic model. The hydrodynamic model is the Geophysical Fluid Dynamics Laboratory (GFDL) Modular Ocean Model (MOM). The ecosystem model consists of five components: dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), phytoplankton, zooplankton and detritus. Results of the numerical ecosystem model suggest that the mesoscale development of the spring bloom in the Sea of Japan is related to that of sea water temperature, and that the bloom is limited by the depletion of DIN..
84. Naoki Hirose, Ichiro Fukumori, Victor Zlotnicki, Rui M. Ponte, Modeling the high-frequency barotropic response of the ocean to atmospheric disturbances
Sensitivity to forcing, topography, and friction, Journal of Geophysical Research, 106, C12, 30987-30995, 2001.12, This study examines high-frequency sea level variations forced by changes in surface atmospheric pressure and wind and their sensitivity to different forcing mechanisms, bottom topography resolution, and amount of friction in a barotropic ocean model. Optimal model performance, defined in terms of the explained variance in satellite altimeter and bottom pressure data, is found when using relatively strong friction, equivalent to a damping timescale of only a few days over the deep ocean, and topography with minimal smoothing. Spatial variations of the optimal friction parameter seem to reflect the roughness of bottom topography. The model demonstrates skill in simulating the wind-driven response as well as the nonequilibrium response to atmospheric pressure variations..
85. Naoki Hirose, Ichiro Fukumori, Rui M. Ponte, A non-isostatic global sea level response to barometric pressure near 5 days, Geophysical Research Letters, 10.1029/2001GL012907, 28, 12, 2441-2444, 2001.06, [URL], Changes in surface atmospheric pressure usually induce an isostatic response in the ocean characterized by an adjustment in sea level at the rate of approximately -1cm/hPa. Nonisostatic signals are, however, observed at many tropical tide gauges at periods near 5 days. Our analysis of satellite observations reveals the global nature of these signals, involving nonisostatic sea level fluctuations with nearly uniform phase within separate basins and an out-of-phase oscillation between the Atlantic and Pacific Oceans. Comparisons with a barotropic model further link the observed signals to forcing by a large scale pressure wave in the atmosphere and show that constrictions between basins prevent an isostatic response from being established. The apparent forced, nonresonant nature of the nonisostatic response contrasts with the predominantly resonant ocean dynamics at higher frequencies and may be relevant to explain the behavior of the long period tides..
86. Sergey M. Varlamov, Jong Hwan Yoon, Naoki Hirose, Hideyuki Kawamura, Ken Shiohara, Simulation of the oil spill processes in the Sea of Japan with regional ocean circulation model, Journal of Marine Science and Technology, 4, 3, 94-107, 2000.12, [URL], A simulation of the movement of spilled oil after the incident of the Russian tanker Nakhodka in the Sea of Japan, in January 1997, was performed by a particle tracking model incorporating advection by currents, random diffusion, the buoyancy effect, the parameterization of oil evaporation, biodegradation, and beaching. The currents advecting spilled oil were defined by surface wind drift superposed on the three-dimensional ocean currents obtained by the Geophysical Fluid Dynamics Laboratory modular ocean model (GFDL MOM), which was forced by the climatological monthly mean meteorological data, or by the European Center for Medium Range Weather Forecasts (ECMWF) daily meteorological data, and assimilated sea surface topography detected by satellite altimeter. A number of experiments with different parameters and situations showed that the wide geographical spread of oil observed is not explained by wind drift alone, and that including the simulated climatological currents gives better results. The combination of surface wind drift and daily ocean currents shows the best agreement between the model and observations except in some coastal areas. The daily meteorological effect on the ocean circulation model results in a stronger variability of currents that closely simulates some features of the nonlinear large-scale horizontal turbulent diffusion of oil. The effect of different parameterizations for the size distribution of model oil particles is discussed..
87. Yoon, J.-H. and N. Hirose, Assimilation of satellite altimeter data with circulation models of the Japan Sea., Proceeding of International workshop on remote sensing of marine environment in the northwest Pacific region, 2000.10.
88. Hirose, N., I. Fukumori, C.-H. Kim, and J. H. Yoon, Hindcast and forecast experiments for the Japan/East Sea circulation., Symposium 'En route to GODAE,' Biarritz, France, CD-ROM., 2000.07.
89. Naoki Hirose, Alexander G. Ostrovskii, Quasi-biennial variability in the Japan Sea, Journal of Geophysical Research, 105, C6, 14011-14027, 2000.06, [URL], The TOPEX/Poseidon (T/P) altimetry reveals quasi-biennial (QB) variability in the southern Japan Sea. Sea surface height anomalies of a biennial nature are most energetic in the Yamato Basin, the southeastern most part of the Japan Sea, where they can be as large as 20 cm and extend for 100-200 km. On the basis of the in situ measurements of Maizuru Marine Observatory, the 2-3 year variations are associated with thermohaline anomalies in the upper 300 m layer. The local QB oscillation is studied with a reduced gravity model of the Japan Sea. The model is forced by European Centre for Medium-Range Weather Forecasting daily wind and seasonal inflows/outflows through the three major straits of the sea. The model sensitivity experiments suggest that the QB variability can be associated with the sea's response to wind forcing of particular years, more specifically, 1992 and 1996, and to some extent, 1994. An approximate Kalman filter is employed for assimilation of the T/P altimeter data into the reduced gravity model. It filters out observational noise and intraseasonal sea level variability and allows the model to dynamically interpolate T/P observations. The results of the assimilation indicate that the QB anomalies are strongest at 37.5° N, 134.5° E and propagate west-northwest with a speed of ∼0.01 m s-1, contributing to variations of the Tsushima Warm Current..
90. Naoki Hirose, Ichiro Fukumori, Jong Hwan Yoon, Assimilation of TOPEX/POSEIDON altimeter data with a reduced gravity model of the Japan Sea, Journal of Oceanography, 10.1023/A:1007707405711, 55, 1, 53-64, 1999.02, [URL], Sea level data measured by TOPEX/POSEIDON over the Japan Sea from 1993 to 1994 is analyzed by assimilation using an approximate Kalman filter with a 1.5 layer (reduced-gravity) shallow water model. The study aims to extract signals associated with the first baroclinic mode and to determine the extent of its significance. The assimilation dramatically improves the model south of the Polar Front where as much as 20 cm2 of the observed sea level variance can be accounted for. In comparison, little variability in the northern cold water region is found consistent with the model dynamics, possibly due to significant differences in stratification..
91. Naoki Hirose, Hyun Chul Lee, Jong Hwan Yoon, Surface heat flux in the East China Sea and the Yellow Sea, Journal of Physical Oceanography, 10.1175/1520-0485(1999)029<0401:SHFITE>2.0.CO;2, 29, 3, 401-417, 1999.01, [URL], Climatological monthly mean variations of the surface heat fluxes over the East China Sea and the Yellow Sea are calculated by both a data analysis and a numerical simulation. The result of the data analysis based on the empirical/bulk method agrees well with the directly observed solar radiation and several previous studies of the surface heat fluxes. An adjustment in the formation of the Haney-type heat flux is presented by comparing to the result of the bulk method. The numerical simulation of these seas using an ocean general circulation model demonstrates the success of the improved Haney-type condition over the original one in simulating sea surface temperature. The surface heat flux simulated in the Yellow Sea is more reasonable than by the data analysis considering the total heat budget of this sea..
92. Reanalysis of the Japan Sea circulation using approximate smoother.
93. Takata, T., S. M. Varlamov, N. Hirose, and J.-H. Yoon,, Interannual variation of the surface heat flux in the Japan Sea, Proceeding of the CREAMS'97 International Symposium, 1997.01.
94. Kai, M., N. Hirose, and J.-H. Yoon, The barotropic response to the wind in the Japan Sea during 1978-1992, Proceeding of the CREAMS'97 International Symposium, 1997.01.
95. Hirose, N., I. Fukumori, and J.-H. Yoon, Assimilation of sea surface topography with a reduced gravity model of the Japan Sea, Proceeding of the CREAMS'97 International Symposium, 1997.01.
96. Hirose, N., C.-H. Kim, and J.-H. Yoon, Heat budget in the Japan Sea, Journal of Oceanography, 52, 553-574, 1996.10, [URL].
97. Hirose, N., and J.-H. Yoon, The barotropic response to the wind in the Japan Sea, Proceedings of Fourth CREAMS Workshop, 1996.02.
98. Naoki Hirose, Cheol Ho Kim, Jong Hwan Yoon, Heat budget in the Japan sea, Journal of Oceanography, 10.1007/BF02238321, 52, 5, 553-574, 1996.01, [URL], The long-term mean (31-year mean) surface heat fluxes over the Japan Sea are estimated by the bulk method using the most of the available vessel data with the resolution of 1° × 1°. The long-term annual mean net heat flux is about -53 W m-2 (negative sign means upward heat flux) with the annual range from 133 W m-2 in May to -296 W m-2 in December. The small gain of heat in the area near Vladivostok seems to indicate the existence of cold water flowing from the north. In that area in winter, the mean loss of heat attains about 200 W m-2, and the Bowen's ratio is over the unity. The largest insolation occurs in May in the Japan Sea, and the upward latent heat flux becomes the largest in November in this area. The heat flux of Haney type is also calculated, and the result shows that the constant Q1 has the remarkable seasonal and spatial variation, while the coefficient Q2 has relatively small variation throughout all seasons. Under the assumption of constant volume transport of 1.35 × 106 m3s-1 through the Tsugaru Strait, the long-term averages of the volume transport through the Tsushima and Soya Straits are estimated to be about 2.20 and 0.85 × 106 m3s-1 from the result of the mean surface heat flax, respectively..