| Kaoru Ichikawa | Last modified date：2024.04.25 |
Associate Professor /
Interdisciplinary Graduate School of Engineering Sciences, Department of Earth System Science and Technology, Environmental Metrology /
Division of Earth Environment Dynamics /
Research Institute for Applied Mechanics
Papers
| 1. | K Ichikawa, JQ Zhu, J Noda, R Sakemi, K Yufu and K Matsuura, Ship-borne wave gauge using GNSS interferometric reflectometry, Coastal Engineering Journal, 10.1080/21664250.2024.2342596, 2024.04. |
| 2. | Kaoru Ichikawa , How frequently can we observe winds and waves for safer maritime transport? , La Mer, 10.32211/lamer.61.3-4_345, 61, 3-4, 358-360, 2024.03. |
| 3. | Kaoru Ichikawa, Mean Seasonal Sea Surface Height Variations in and around the Makassar Strait, Remote Sensing, 10.3390/rs15174324, 15, 17, 2023.09, Seasonal variations are significant in currents in the Makassar Strait, 80% of the Indonesian Throughflow (ITF) from the Pacific to the Indian Ocean, and they are in phase with both the monsoon and the sea surface height anomaly (SSHA) difference between two oceans. However, dynamics are not well discussed since gridded SSHA products within the strait are less reliable because of both over-smoothing and contamination in coastal areas. In this study, therefore, 17 years of along-track Jason altimetry data with the ALES retracker are used without grid interpolation to investigate seasonal SSHA variations in and around the Makassar Strait. All SSHA variations are in phase from the southern Celebes Sea to the northern Java Sea through the Makassar Strait, but their amplitude decreases by the distance from the southern shallow area. These amplitude modulations produce the pressure gradient force, which is maximum to the north of 4°S reaching 1.5 × 10^{−6} ms^{−2}, and that would be balanced with the bottom friction of the upper-layer ITF velocity, rather than the wind stress whose magnitude 5 × 10^{−8} ms^{−2} is too small. The SSHA difference between the two oceans is in phase but is isolated from the Makassar Strait by adjacent uncorrelated SSHA variations..  |
| 4. | Xifeng Wang, Kaoru Ichikawa, Coastal Waveform Retracking in the Slick-Rich Sulawesi Sea of Indonesia, Based on Variable Footprint Size with Homogeneous Sea Surface Roughness, Remote Sensing, 10.3390/rs11111274, 11, 11, 1274, 2019.05, [URL], Waveforms of radar altimeters are often corrupted due to heterogeneous sea surface roughness within footprints, such as slicks. In past studies, subwaveform retrackers such as the adaptive leading edge subwaveform retracker (ALES) which use only a section of the waveform have been proposed. However, it is difficult to choose a reasonable estimation window from an individual waveform. In the present study, a post-processed subwaveform retracker is proposed which identifies the waveforms of surrounding along-track points. The size of the estimation window is variable and is determined to keep the sea surface roughness within the corresponding footprint homogeneous. The method was applied to seven years of 20 Hz Jason-2 altimeter data over the slick-rich Sulawesi Sea of Indonesia and compared with ALES and sensor geophysical data record (SGDR) products. The standard deviation of the sea surface dynamic heights was around 0.13 m, even without spatial smoothing or some geophysical corrections. This is only 75% and 25% of the ALES and SGDR results, respectively. Moreover, all retrievals of the range, SWH, and sigma0 include less outliers than the other products. These results indicate that the variable estimation windows determined in the present study can adapt well to the variation of sea surface roughness.. |
| 5. | Kaoru Ichikawa, Takuji Ebinuma, Masanori Konda, Kei Yufu, Low-Cost GNSS-R Altimetry on a UAV for Water-Level Measurements at Arbitrary Times and Locations, Sensors (Basel, Switzerland), 10.3390/s19050998, 19, 5, 2019.02, Together with direct Global Navigation Satellite System (GNSS) signals, the signals reflected at the water surface can be received by an unmanned aerial vehicle (UAV). From the range difference between two GNSS signal paths, the height of the UAV above the water level can be geometrically estimated using the weighted least squares method, called GNSS reflectometry (GNSS-R) altimetry. Experimental low-cost GNSS-R altimetry flights with a UAV were conducted at the coast of Lake Biwa, Japan. Although the height estimated by the GNSS-R altimeter included large short-term noises up to 8 m amplitude, it agreed well with the UAV altitude measured by the post-processed kinematic positioning. By selecting better weight functions in the least square method and using sufficient temporal averaging, the GNSS-R altimetry achieved accuracy in the order of 0.01 m if a sufficient number of GNSS satellites with high elevation angles were available. The dependency of the results on the weight functions is also discussed.. |
| 6. | 「ちきゅう」&DONETのトータル観測ステーション計画(経過報告). |
| 7. | Keisuke Ariyoshi, Shuhei Nishida, Yuya Machida, Takeshi Iinuma, Kan Aoike, Hiroshi Uchida, Akira Nagano, Takuya Hasegawa, Mikiko Fujita, Toru Miyama, Yasumasa Miyazawa, Akira Kuwano-Yoshida, Masahide Wakita, Akiko To, Tatsu Kuwatani, Kaoru Ichikawa, A total station plan combined with "D/V Chikyu" and DONET:Simultaneous observation from seafloor to atmosphere, 2018 OCEANS - MTS/IEEE Kobe Techno-Oceans, OCEANS - Kobe 2018 2018 OCEANS - MTS/IEEE Kobe Techno-Oceans, OCEANS - Kobe 2018, 10.1109/OCEANSKOBE.2018.8559382, 2018.12, DONET (Dense Oceanfloor Network system for Earthquakes and Tsunamis) has been developed and installed around Nankai Trough, which is motivated by the 2004 Sumatra-Andaman Earthquake. DONET contains pressure gauges as well as seismometers, which is expected to detect crustal deformations driven by peeling off subduction plate coupling process. From our simulation results, leveling changes are different sense among at the DONET points even in the same science node. On the other hand, oceanic fluctuations such as melting ice masses through the global warming has so large scale as to cause ocean bottom pressure change coherently for all of DONET points especially in the same node. This difference suggests the possibility of extracting crustal deformations component from ocean bottom pressure data by differential of stacking data. However, this operation cannot be applied to local-scale fluctuations related to ocean mesoscale eddies and current fluctuations, which affect ocean bottom pressure through water density changes in the water column (from the sea surface to the bottom). Recently, Kuroshio current path has been changed drastically, which significantly affect ocean bottom pressures at DONET station points. Therefore, we need integral analysis by combining seismology, ocean physics and tsunami engineering so as to decompose into crustal deformation, oceanic fluctuations and instrumental drift, which will bring about high precision data enough to find geophysical phenomena. Since DONET has been and will be connected to long-term borehole observatories constructed in the Nankai Trough under the Integrated Ocean Drilling Program (IODP) by using the deep-sea drilling vessel Chikyu, we have to discuss the best way to do simultaneous observation from seafloor to atmosphere by taking advantage of this chance.. |
| 8. | Complementary Remote Sensing Observations of the Tsushima Warm Current Patterns, [URL]. |
| 9. | Remote Sensing of the Kuroshio Current System, [URL]. |
| 10. | A Total Station Plan Combined with “D/V Chikyu” and DONET:Simultaneous Observation from Seafloor to Atmosphere. |
| 11. | Kaoru Ichikawa and XiFeng Wang, Coastal retraccking using along-track echograms and its dependency on coastal topography, Earth and Space Science Open Archive, 10.1002/essoar.9ba3ca568e624190.f2914573e2c248dd.1, 2018.04. |
| 12. | Xifeng Wang, Kaoru Ichikawa, Coastal Waveform Retracking for Jason-2 Altimeter Data Based on Along-Track Echograms around the Tsushima Islands in Japan, REMOTE SENSING, 10.3390/rs9070762, 9, 7, 762, 2017.07, Although the Brown mathematical model is the standard model for waveform retracking over open oceans, due to heterogeneous surface reflections within altimeter footprints, coastal waveforms usually deviate from open ocean waveform shapes and thus cannot be directly interpreted by the Brown model. Generally, the two primary sources of heterogeneous surface reflections are land surfaces and bright targets such as calm surface water. The former reduces echo power, while the latter often produces particularly strong echoes. In previous studies, sub-waveform retrackers, which use waveform samples collected from around leading edges in order to avoid trailing edge noise, have been recommended for coastal waveform retracking. In the present study, the peaky-type noise caused by fixed-point bright targets is explicitly detected and masked using the parabolic signature in the sequential along-track waveforms (or, azimuth-range echograms). Moreover, the power deficit of waveform trailing edges caused by weak land reflections is compensated for by estimating the ratio of sea surface area within each annular footprint in order to produce pseudo- homogeneous reflected waveforms suitable for the Brown model. Using this method, altimeter waveforms measured over the Tsushima Islands in Japan by the Ocean Surface Topography Mission (OSTM)/Jason-2 satellite are retracked. Our results show that both the correlation coefficient and root mean square difference between the derived sea surface height anomalies and tide gauge records retain similar values at the open ocean (0.9 and 20 cm) level, even in areas approaching 3 km from coastlines, which is considerably improved from the 10 km correlation coefficient limit of the conventional MLE4 retracker and the 7 km sub-waveform ALES retracker limit. These values, however, depend on the topography of the study areas because the approach distance limit increases (decreases) in areas with complicated (straight) coastlines.. |
| 13. | 同期掃引によるバイスタティクレーダ受信方式. |
| 14. | Satellite Observations : Taiwan Warm Current and Kuroshio Branch Current northeast of Taiwan as seen by along-track altimetry data. |
| 15. | Xifeng Wang, Kaoru Ichikawa, Effect of High-Frequency Sea Waves on Wave Period Retrieval from Radar Altimeter and Buoy Data, REMOTE SENSING, 10.3390/rs8090764, 8, 9, 764, 764, 2016.09, [URL], Wave periods estimated from satellite altimetry data behave differently from those calculated from buoy data, especially in low-wind conditions. In this paper, the geometric mean wave period is calculated from buoy data, rather than the commonly used zero-crossing wave period. The geometric mean wave period uses the fourth moment of the wave frequency spectrum and is related to the mean-square slope of the sea surface measured using altimeters. The values of obtained from buoys and altimeters agree well (root mean square difference: 0.2 s) only when the contribution of high-frequency sea waves is estimated by a wavenumber spectral model to complement the buoy data, because a buoy cannot obtain data from waves having wavelengths that are shorter than the characteristic dimension of the buoy.. |
| 16. | Takuji Ebinuma, Kaoru Ichikawa, Takuji Waseda, Yukihito Kitazawa, Hitoshi Tamura, Osamu Isoguchi, Hiroyuki Tomita, GNSS Reflectometry and Multi-Sensor Ocean Wave and Wind Monitoring at Hiratsuka Marine Observation Tower, Proceedings of the International Symposium on GNSS 2015, 584-587, 2016.05. |
| 17. | Hsien-Wen Chen, Cho-Teng Liu, Takeshi Matsuno, Kaoru Ichikawa, Ken-ichi Fukudome, Yih Yang, Dong-Jiing Doong, Wei-Ling Tsai, Temporal variations of volume transport through the Taiwan Strait, as identified by three-year measurements, CONTINENTAL SHELF RESEARCH, 10.1016/j.csr.2015.12.010, 114, 41-53, 2016.02, The water characteristics of the East China Sea depend on influxes from river run-off, the Kuroshio, and the Taiwan Strait. A three-year observation using an acoustic Doppler current profiler (ADCP) operated on a ferry provides the first nearly continuous data set concerning the seasonal flow pattern and the volume transport from the Taiwan Strait to the East China Sea. The observed volume transport shows strong seasonality and linkage to the along-strait wind stress. An empirical regression formula between the volume transport and wind was derived to fill the gaps of observation so as to obtain a continuous data set. Based on this unique data set, the three-year mean of monthly volume transport is north-eastward throughout the year, large (nearly 3 Sv) in summer and low (nearly zero) in winter. The China Coastal Current flows southward in winter, while the northward-flowing Taiwan Strait Current may reverse direction during severe northeasterly winds in the winter or under typhoons. The sea level difference across Taiwan Strait is closely correlated to the transport through the strait, and their relation is found seasonally nearly stable. (C) 2015 Elsevier Ltd. All rights reserved.. |
| 18. | Sergey M. Varlamov, Xinyu Guo, Toru Miyama, Kaoru Ichikawa, Takuji Waseda, Yasumasa Miyazawa, M-2 baroclinic tide variability modulated by the ocean circulation south of Japan, JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, 10.1002/2015JC010739, 120, 5, 3681-3710, 2015.05, We analyze a concurrent simulation result of the ocean circulation and tidal currents using a data-assimilative ocean general circulation model covering the Western North Pacific with horizontal resolution of 1/36 degrees to investigate possible interactions between them. Four sites of active M-2 internal tide variability in open ocean (hot spots), such as Tokara Strait, Izu Ridge, Luzon Strait, and Ogasawara Ridge, are detected from both the satellite observation and the simulation. Energy cycle analysis of the simulated M-2 baroclinic tide indicates two types of the hot spots: dissipation (Tokara Strait and Izu Ridge) and radiation (Luzon Strait and Ogasawara Ridge) dominant sites. Energy conversion from barotropic to baroclinic M-2 tides at the hot spots is modulated considerably by the lower-frequency changes in the density field. Modulation at the two spots (Tokara Strait and Izu Ridge) is affected by the Kuroshio path variation together with the seasonal variation of the shallow thermocline. At the other two sites, influence from changes in the relatively deep stratification through the Kuroshio intrusion into South China Sea (Luzon Strat) and mesoscale eddy activity (Ogasawara Ridge) is dominant in the modulation.. |
| 19. | Satellite altimeters in the early 21st Century. |
| 20. | Decadal Vision in Oceanography (I)-Discussions in the physical oceanography subgroup of the future planning committee, The Oceanographic Society of Japan-. |
| 21. | Decadal Vision in Oceanography (I) : Discussions in the physical oceanography subgroup of the future planning committee, The Oceanographic Society of Japan(Decadal Vision in Oceanography-Special issue of "Oceanography in Japan"-). |
| 22. | Akira Nagano, Kaoru Ichikawa, Hiroshi Ichikawa, Masanori Konda, Kiyoshi Murakami, Volume transports proceeding to the Kuroshio Extension region and recirculating in the Shikoku Basin, JOURNAL OF OCEANOGRAPHY, 10.1007/s10872-013-0173-9, 69, 3, 285-293, 2013.06, [URL], The volume transport of the Kuroshio, the western boundary current of the North Pacific subtropical gyre, varies vigorously due to merging of disturbances propagating from the entire North Pacific. Taking into account the recirculation in the Shikoku Basin by the zonal observation line at 30A degrees N to the west of the Izu-Ogasawara Ridge, we estimated the volume transport in the top 1,000 m layer toward the Kuroshio Extension region. The volume transport of the local recirculation gyre in the Shikoku Basin increases associated with the westward extension of the gyre, particularly in the period of the large meandering path of the Kuroshio south of Japan. Meanwhile, most of the transport variations toward the Kuroshio Extension region correspond to those of the Kuroshio transport on the continental slope south of Japan, which vary independently of those of the recirculation gyre.. |
| 23. | 対馬海峡における長期流況モニタリング. |
| 24. | Akira Nagano, Kaoru Ichikawa, Hiroshi Ichikawa, Yasushi Yoshikawa, Kiyoshi Murakami, Large ageostrophic currents in the abyssal layer southeast of Kyushu, Japan, by direct measurement of LADCP, Journal of Oceanography, doi:10.1007/s10872-013-0170-z, 69, 2, 259-268, 2013.04, With full-depth LADCP velocity data collected in a wide area southeast of Kyushu, Japan, large velocity currents, occasionally exceeding 15 cm s-1, were observed in a thick, 500.1,500 m, near-homogeneous density layer below approximately 3,000 m depth around the steep topographies. The currents were found not to flow along the topographic contours, and to be strongly ageostrophic. The directions of the bottom-layer currents are rather related with phase of the semi-diurnal tides, suggesting deeply intruded internal tides generated at the steep topographies.. |
| 25. | Akira Nagano, Kaoru Ichikawa, Hiroshi Ichikawa, Yasushi Yoshikawa, Kiyoshi Murakami, Large ageostrophic currents in the abyssal layer southeast of Kyushu, Japan, by direct measurement of LADCP, JOURNAL OF OCEANOGRAPHY, 10.1007/s10872-013-0170-z, 69, 2, 259-268, 2013.04, With full-depth LADCP velocity data collected in a wide area southeast of Kyushu, Japan, large velocity currents, occasionally exceeding 15 cm s(-1), were observed in a thick, 500-1,500 m, near-homogeneous density layer below approximately 3,000 m depth around the steep topographies. The currents were found not to flow along the topographic contours, and to be strongly ageostrophic. The directions of the bottom-layer currents are rather related with phase of the semi-diurnal tides, suggesting deeply intruded internal tides generated at the steep topographies.. |
| 26. | Kaoru Ichikawa, Wen Chang Yang, Akihiko Morimoto, Yutaka Yoshikawa, Shigeo Sugitani, Wen-Shan Chiang, Jian-Wu Lai, En Yu Liang, Cho-Teng Liu, Chang-Wei Lee, Kei Yufu, Moeto Kyushima, Satoshi Fujii, Tomoharu Senju, Yoshihiko Ide, Preliminary Results of the Japan-Taiwan Joint Survey on Combining Ocean Radar Data in the Kuroshio Upstream Region, OCEAN SCIENCE JOURNAL, 10.1007/s12601-013-0011-4, 48, 1, 141-148, 2013.03, [URL], Japanese and Taiwanese institutes have collaborated to obtain ocean radar data with significantly increased coverage in the upstream Kuroshio region. An international joint survey was conducted in June 2012, in which intensive in situ observations were performed within the radar coverage. Details of the joint survey are presented in this paper with brief descriptions of preliminary results on the surface and subsurface currents near and within the Kuroshio.. |
| 27. | 永野憲, 市川 香, 市川洋ほか, Subsurface current structures east of Amami-Oshima Island based on LADCP observation, 18, 2, 19-26, 2013.03. |
| 28. | P. Cipollini, J. Benveniste, L. Miller, N. Picot, R. Scharroo, T. Sturb, D. Vandemark, S. Vignudelli, S. Zoffoli, O. Andersen, L. Bao, F. Birol, E. Coelho, X. Deng, W. Emery, L. Fenoglio, J. Fernandes, J. Gomez-Enri, D. Griffin, G. Han, J. Hausman, Kaoru Ichikawa, A. Kostianoy, V. Kourafalou, S. Labroue, R. Ray, M. Saraceno, W. Smith, P. Thibaut, J. Wilkin, S. Yenamandra, Conquering the Coastal Zone: A new frontier for satellite altimetry, "Proceedings of '20 years of Progress in Radar Altimetry', Venice Italy", (ed. L. Ouwehand), 10.5270/esa.sp-710.altimetry2012, ESA SP-710, 2013.02. |
| 29. | Kaoru Ichikawa, Akihiko Morimoto, Kenichi Fukudome, Jong-Hwan Yoon, Yutaka Yoshikawa, Coastal Sea Surface Dynamic Height Monitoring by GPS Mounted on a Ferry Boat, "Proceedings of '20 years of Progress in Radar Altimetry', Venice Italy", (ed. L. Ouwehand), 10.5270/esa.sp-710.altimetry2012, ESA SP-710, 2013.02. |
| 30. | Ichikawa Kaoru, Tatsuya Yamauchi, Yoshikawa Yutaka, Akihiko Morimoto, Shigeo Sugitani, Seasonal variation of the deflection angle of the wind-driven surface flow estimated from altimeters and long-ragne ocean radars, 2011 Ocean Surface Topography Science Team Meeting Abstracts, 149, 2011.10, Ageostrophic velocity component is estimated by subtracting the geostrophic velocity determined from the along-track Jason-1/2 data from the surface velocity observed by long-range ocean radars in the upstream region of the Kuroshio operated by NICT, Japan. Assuming that the ageostrophic component is dominated by the wind-driven surface flow, the speed factor, or the ratio of the speed of the wind-driven flow to the wind speed, and the deflection angle with respect to the wind direction are estimated by the least square method and the QuikSCAT data. Both the speed factor and the deflection angle change seasonally; the former ranges from approximately 1 to 1.5% and tends to be largest in winter, although the changes would be less significant with respect to the accuracy of the velocity data. Meanwhile, the latter varies from 20 to 80 degree clockwise from the wind direction and becomes largest in summer. This tendency is obvious in the offshore region, but insignificant within the Kuroshio. The results would be discussed with possible seasonal variations of the eddy viscosity due to the vertical stratification and wind drag coefficient.. |
| 31. | Akira Nagano, Kaoru Ichikawa, Hiroshio Ichikawa, H Tomita, H Tokinaga, Masanori Konda, Stable volume and heat transports of the North Pacific subtropical gyre revealed by identifying the Kuroshio in synoptic hydrography south of Japan, Journal of Geophysical Research, 10.1029/2009JC005747, 115, C09002, 14pp, 115, C09002, doi:10.1029/2009JC005747, 2010.09. |
| 32. | ICHIKAWA Kaoru, Stable volume and heat transports of the North Pacific subtropical gyre revealed by identifying the Kuroshio in synoptic hydrography south of Japan, A. Nagano, K. Ichikawa, H. Ichikawa, H. Tomita, H. Tokinaga, M. Konda, J. Geophys. Res., 115, C09002, 14pp, Journal of Geophysical Research, 115, C09002, 2010.09. |
| 33. | Akira Nagano, Kaoru Ichikawa, Hiroshi Ichikawa, Hiroyuki Tomita, Hiroki Tokinaga, Masanori Konda, Stable volume and heat transports of the North Pacific subtropical gyre revealed by identifying the Kuroshio in synoptic hydrography south of Japan, JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, 10.1029/2009JC005747, 115, C9, 2010.09, We conducted synoptic hydrographic surveys three times under distinctly different conditions of the Kuroshio in the region off the southern coast of Japan; the large-meander (October 2004) and non-large-meander (September 2005 and September 2006) states. As a result of the water mass analysis, we could separate the volume and heat transports of the North Pacific subtropical gyre from the local recirculation gyre and mesoscale eddies. Despite the different flow conditions of the Kuroshio, the volume transport and the volume transport-averaged temperature of the subtropical gyre fluctuate within the ranges of 23.3-29.0 x 10(6) m(3) s(-1) and 17.3-17.6 degrees C, respectively, which are quite stable with respect to those for the Kuroshio south of Japan estimated in the past studies. Taking into account the decrease in the volume transport-averaged temperature in the North Pacific interior region, the net heat transport of the subtropical gyre across the latitude of 30 degrees N was estimated to be between 0.19 and 0.22 x 10(15) W.. |
| 34. | K. Fukudome, T. Matsuno, C. Liu, K. Ichikawa, Y. Yu, P. Chen, H. Chen, Volume transport flowing into the shelf region of the East China Sea, EOS Trans. AGU, 91, 26, Abstract OS31B-194, West. Pac. Geophys. Meet. Suppl., 2010.06. |
| 35. | K. Ichikawa and T. Endoh, Enhanced transport of the subsurface Kuroshio water toward the continental shelf due to mesoscale variations of the Kuroshio northeast of Taiwan, EOS Trans. AGU, 91, 26, Abstract OS24A-06, West. Pac. Geophys. Meet. Suppl., 2010.06. |
| 36. | Hiroshi Ichikawa, Akira Nagano, Kaoru Ichikawa, Annual Signal Modulation of the Kuroshio Through-flow Volume Transport South of Japan Leading West Pacific Pattern, Proceedings of OceanObs'09: Sustained Ocean Observations and Information for Society (Annex), Venice, Italy, 21-25 September 2009, Hall, J., Harrison, D.E. & Stammer, D., Eds., ESA Publication WPP-306, 2010.04. |
| 37. | Synoptic flow structures in the confluence region of the Kuroshio and the Ryukyu Current. |
| 38. | Akira Nagano, Kaoru Ichikawa, Hiroshi Ichikawa, Masanori Konda, Kiyoshi Murakami, Synoptic flow structures in the confluence region of the Kuroshio and the Ryukyu Current, Journal of Geophysical Research: Oceans, 10.1029/2008JC005213, 114, 6, 2009.06, In the southeastern region of Kyushu, Japan, the Kuroshio from the East China Sea encounters the Ryukyu Current from the east of the Ryukyu Islands. By analyzing . synoptic sections of water properties and geostrophic velocity in August 2004 and October 2005, we distinguished the waters in the Kuroshio southeast of Kyushu to be. separated into an offshore region and a shallow onshore one. The onshore water is derived from the East China Sea, while the offshore water originates from both the east of Amami-Oshima Island and the interior region of the North Pacific. The water mass transport from the east of Amami-Oshima Island may become equivalent to that of the Kuroshio in the East China Sea as in October 2005. The volume transport-averaged temperature of the Kuroshio southeast of Kyushu is significantly lower than that in the East China Sea because of the confluence with the colder Ryukyu Current east of the Amami-Oshima Island. Copyright 2009 by the American Geophysical Union.. |
| 39. | Akira Nagano, Kaoru Ichikawa, Hiroshi Ichikawa, Masanori Konda, Kiyoshi Murakami, Synoptic flow structures in the confluence region of the Kuroshio and the Ryukyu Current, JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, 10.1029/2008JC005213, 114, C6, 2009.06, In the southeastern region of Kyushu, Japan, the Kuroshio from the East China Sea encounters the Ryukyu Current from the east of the Ryukyu Islands. By analyzing synoptic sections of water properties and geostrophic velocity in August 2004 and October 2005, we distinguished the waters in the Kuroshio southeast of Kyushu to be separated into an offshore region and a shallow onshore one. The onshore water is derived from the East China Sea, while the offshore water originates from both the east of Amami-Oshima Island and the interior region of the North Pacific. The water mass transport from the east of Amami-Oshima Island may become equivalent to that of the Kuroshio in the East China Sea as in October 2005. The volume transport-averaged temperature of the Kuroshio southeast of Kyushu is significantly lower than that in the East China Sea because of the confluence with the colder Ryukyu Current east of the Amami-Oshima Island.. |
| 40. | Motohiko Kashima, Shin-Ichi Ito, Kaoru Ichikawa, Shiro Imawaki, Shin-Ichiro Umatani, Hiroshi Uchida, Takashi Setou, Quasiperiodic small meanders of the Kuroshio off Cape Ashizuri and their inter-annual modulation caused by quasiperiodic arrivals of mesoscale eddies, JOURNAL OF OCEANOGRAPHY, 10.1007/s10872-009-0007-y, 65, 1, 73-80, 65(1), 73-80, 2009.02, A quasiperiodic variation of 100-110 days in the Kuroshio path off Cape Ashizuri, resulting from the passage of small meanders, was detected by observation with moored current meters during 1993-1995. TOPEX/POSEIDON altimeter data covering 9 years showed that the quasiperiodic variation period was not persistent and modulated twice, with a 110-day period from mid-1993 to late 1996, a 150-day period from late 1996 to mid-1999, and a 110-day period from mid-1999 to late 2001. The quasiperiodic variations of the Kuroshio path migration were contemporaneous with the quasiperiodic arrivals of mesoscale eddies from the east along 27-32A degrees N over the same 110- and 150-day period quasiperiodic variations. The periodic arrivals of the eddies configure the periodic variations of the Kuroshio path and its inter-annual modulation.. |
| 41. | Motohiko Kashima, Shin Ichi Ito, Kaoru Ichikawa, Shiro Imawaki, Shin Ichiro Umatani, Hiroshi Uchida, Takashi Setou, Quasiperiodic small meanders of the Kuroshio off Cape Ashizuri and their inter-annual modulation caused by quasiperiodic arrivals of mesoscale eddies, Journal of Oceanography, 10.1007/s10872-009-0007-y, 65, 1, 73-80, 2009.01, A quasiperiodic variation of 100-110 days in the Kuroshio path off Cape Ashizuri, resulting from the passage of small meanders, was detected by observation with moored current meters during 1993-1995. TOPEX/POSEIDON altimeter data covering 9 years showed that the quasiperiodic variation period was not persistent and modulated twice, with a ∼110-day period from mid-1993 to late 1996, a ∼150-day period from late 1996 to mid-1999, and a ∼110-day period from mid-1999 to late 2001. The quasiperiodic variations of the Kuroshio path migration were contemporaneous with the quasiperiodic arrivals of mesoscale eddies from the east along 27-32°N over the same ∼110- and ∼150-day period quasiperiodic variations. The periodic arrivals of the eddies configure the periodic variations of the Kuroshio path and its inter-annual modulation.. |
| 42. | Kaoru Ichikawa, Kuroshio variations in the upstream region as seen by HF radar and satellite altimetry data, International Journal of Remote Sensing, 29(21), 6317-6326, doi:10.1080/01431160802175454, 2008.11. |
| 43. | K. Ichikawa, R. Tokeshi, M. Kashima, K. Sato, T. Matsuoka, S. Kojima, S. Fujii, Kuroshio variations in the upstream region as seen by HF radar and satellite altimetry data, International Journal of Remote Sensing, 10.1080/01431160802175454, 29, 21, 6417-6426, 2008.11, Variations of the position and speed of the Kuroshio are studied by a combination of high-resolution high-frequency (HF) ocean radar data and wide-coverage altimetry data. The speed of the Kuroshio and its position are determined along 123.35° E northeast of Taiwan from daily maps of surface geostrophic velocity estimated from HF radar data from August 2001 to February 2005. These two are found to be well correlated for mesoscale variations with periods of a few months, as the Kuroshio tends to be faster (or slower) when its axis moves south (or north). This tendency is significant in summer when the Kuroshio is seasonally intensified and well-defined in the HF radar data. By taking correlation with the sea surface dynamic height anomaly observed by satellite altimeters, these Kuroshio variations in the East China Sea are found to be induced by merging of mesoscale eddies from the east at 21° N and by coincident Kuroshio meanders east of Taiwan.. |
| 44. | Variations of velocity and transport associated with coastal cyclonic eddies off Shikoku, Japan estimated from moored current meter and IES data, Koji KAKINOKI, Shiro IMAWAKI, Kaoru ICHIKAWA, Shin-ichiro UMATANI and Motohiko KASHIMA, RIAM Reports, 135, 53-59. |
| 45. | Interannual variability of mesoscale eddy activity at the subtropical fronts region and its influence on the generation of Kuroshio large meander, Motohiko KASHIMA, Kaoru ICHIKAWA and Makoto SATAKE, RIAM Reports, 135, 61-67. |
| 46. | Tidal Currents North of the Yaeyama Islands as seen by HF radars Kaoru ICHIKAWA, Ryoko TOKESHI and Shoichiro KOJIMA RIAM Reports, 135, 77-81. |
| 47. | Experimental Estimate of Geostrophic Current from Trajectory Data of Sea-Surface Drifting Buoys Daisuke AMBE and Kaoru ICHIKAWA, RIAM Reports, 135, 83-88.. |
| 48. | Akira Nagano, Hiroshi Ichikawa, Kaoru Ichikawa, Masanori Konda, Bottom currents on the continental slope off Shikoku, OCEANS'08 MTS/IEEE Kobe-Techno-Ocean'08 - Voyage toward the Future, OTO'08 OCEANS'08 MTS/IEEE Kobe-Techno-Ocean'08 - Voyage toward the Future, OTO'08, 10.1109/OCEANSKOBE.2008.4530977, 2008.09, Beneath the Kuroshio south of Shikoku, there exist bottom currents, flowing in the different direction from the Kuroshio. In order to examine their horizontal and vertical characteristics, we analyzed four current data sets obtained by lowered acoustic Doppler current profilers (LADCP) in the region south of Shikoku during 2004-2006. While the surface Kuroshio in the top 700-m layer flows eastward, the bottom currents flow toward the left-hand side of the surface Kuroshio, i.e., to the inshore side. This vertical current structure is found to be maintained even when the Kuroshio moves offshore to the deep-ocean due to the propagation of the small meander of the Kuroshio.. |
| 49. | Koji Kakinoki, Shiro Imawaki, Hiroshi Uchida, Hirohiko Nakamura, Kaoru Ichikawa, Shin-ichiro Umatani, Ayako Nishina, Hiroshi Ichikawa, Mark Wimbush, Variations of Kuroshio geostrophic transport south of Japan estimated from long-term IES observations, JOURNAL OF OCEANOGRAPHY, 10.1007/s10872-008-0030-4, 64, 3, 373-384, 2008.06, Two inverted echo sounders were maintained on coastal and offshore sides of the Kuroshio south of Japan from October 1993 to July 2004. Applying the gravest empirical mode method, we obtained a time series of geostrophic transport. Estimated transports generally agree well with geostrophic transports estimated from hydrography. Their agreement with the hydrographic transports is better than that of transports estimated from satellite altimetry data. The geostrophic transport is expressed as the surface transport per unit depth multiplied by the equivalent depth. The geostrophic transport varies mostly with the surface transport and fractionally with the equivalent depth. Seasonal variation of the geostrophic transport has a minimum in March and a maximum in September, with a range of about one fifth of the total transport.. |
| 50. | Akira Nagano, Hiroshi Ichikawa, Kaoru Ichikawa, Masanori Konda, Bottom currents on the continental slope off Shikoku, OCEANS 2008 - MTS/IEEE KOBE TECHNO-OCEAN, VOLS 1-3, 10.1109/OCEANSKOBE.2008.4530977, 472-475, 2008.04, Beneath the Kuroshio south of Shikoku, there exist bottom currents, flowing in the different direction from the Kuroshio. In order to examine their horizontal and vertical characteristics, we analyzed four current data sets obtained by lowered acoustic Doppler current profilers (LADCP) in the region south of Shikoku during 2004-2006. While the surface Kuroshio in the top 700-m layer flows eastward, the bottom currents flow toward the left-hand side of the surface Kuroshio, Le, to the inshore side. This vertical current structure is found to be maintained even when the Kuroshio moves offshore to the deep-ocean due to the propagation of the small meander of the Kuroshio.. |
| 51. | Taiwan Warm Current and Kuroshio Branch Current northeast of Taiwan as seen by along- track altimetry data, Kaoru Ichikawa and Daisuke Ambe. |
| 52. | Akira Nagano, Hiroshi Ichikawa, Takahiro Miura, Kaoru Ichikawa, Masanori Konda, Yasushi Yoshikawa, Kazuhiro Obama, Kiyoshi Murakami, Reply to comment by Xie-Hua Zhu et al. on “Current system east of the Ryukyu Islands”, Journal of Geophysical Research, 10.1029/2007JC004561, 113, C3, 113, C03021, doi:10.1029/2007JC004561, 2008.03. |
| 53. | Akira Nagano, Hiroshi Ichikawa, Takahiro Miura, Kaoru Ichikawa, Masanori Konda, Yasushi Yoshikawa, Kazuhiro Obama, Kiyoshi Murakami, Reply to comment by Xie-Hua Zhu et al. on "Current system east of the Ryukyu Islands", Journal of Geophysical Research: Oceans, 10.1029/2007JC004561, 113, 3, 2008.03. |
| 54. | K. Kakinoki, S. Imawaki, K. Ichikawa and S. Umatani, Comparison of Sea Surface Dynamic Heights Estimated from Inverted Echo Sounder Data and Satellite Altimeter Data, 九州大学総合理工学報告(Engineering Sciences Reports, Kyushu University), 29(1), 13-17, 2007.11. |
| 55. | Ryoko Tokeshi, Kaoru Ichikawa, Satoshi Fujii, Kenji Sato, Shoichiro Kojima, Estimating the geostrophic velocity obtained by HF radar observations in the upstream area of the Kuroshio, JOURNAL OF OCEANOGRAPHY, 10.1007/s10872-007-0062-1, 63, 4, 711-720, 2007.08, A method to extract geostrophic current in the daily mean HF radar data in the Kuroshio upstream region is established by comparison with geostrophic velocity determined from the along-track altimetry data. The estimated Ekman current in the HF velocity is 1.2% (1.5%) and 48 degrees (38 degrees)-clockwise rotated with respect to the daily mean wind in (outside) the Kuroshio. Furthermore, additional temporal smoothing is found necessary to remove residual ageostrophic currents such as the inertial oscillation. After removal of the ageostrophic components, the HF geostrophic velocity agrees well with that from the altimetry data with rms difference 0.14 (0.12) m/s in (outside) the Kuroshio.. |
| 56. | Tokeshi, R., K. Ichikawa, S. Fujii, K. Sato and S. Kojima, Estimating the geostrophic velocity obtained by HF radar observations in the upstream area of the Kuroshio, Journal of Oceanography, Vol 63(4), 711-720, 2007.06. |
| 57. | A. Nagano, H. Ichikawa, T. Miura, K. Ichikawa, M. Konda, Y. Yoshikawa, K. Obama, K. Murakami, Current system east of the Ryukyu Islands, JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, 10.1029/2006JC003917, 112, C6, 2007.06, [1] The Ryukyu Current System (RCS) is a northeastward current southeast of the Ryukyu Islands. The variation of current structure in the RCS region was investigated on the basis of the absolute geostrophic velocity estimated by inverse calculation using hydrographic data. Three realizations of the RCS are examined from cruises in May, September, and October 2002. It was found that the current structure in the RCS region is divided into upper and lower layers by an isopycnal surface of 26 sigma(theta). The currents in both layers proceed northeastward along the eastern slope, east of the Ryukyu Islands. The current in the upper layer merges with the inflow from the interior region, resulting in larger northeastward volume transport southeast of Amami-Oshima Island than southeast of Okinawa Island. The volume transport from the east reaches more than 40% of that southeast of Amami-Oshima Island. On the other hand, the current in the lower layer is not affected by inflow from the east. It is also found that the upper RCS gains heat mainly through the advection of warm water from the east, resulting in an increase in the downstream temperature by about 0.5 degrees C on average.. |
| 58. | A. Nagano, H. Ichikawa, T. Miura, K. Ichikawa, M. Konda, Y. Yoshikawa, K. Obama, K. Murakami, Current system east of the Ryukyu Islands, Journal of Geophysical Research: Oceans, 10.1029/2006JC003917, 112, 6, 2007.06, The Ryukyu Current System (RCS) is a northeastward current southeast of the Ryukyu Islands. The variation of current structure in the RCS region was investigated on the basis of the absolute geostrophic velocity estimated by inverse calculation using hydrographic data. Three realizations of the RCS are examined from cruises in May, September, and October 2002. It was found that the current structure in the RCS region is divided into upper and lower layers by an isopycnal surface of 26 σθ. The currents in both layers proceed northeastward along the eastern slope, east of the Ryukyu Islands. The current in the upper layer merges with the inflow from the interior region, resulting in larger northeastward volume transport southeast of Amami-Oshima Island than southeast of Okinawa Island. The volume transport from the east reaches more than 40% of that southeast of Amami-Oshima Island. On the other hand, the current in the lower layer is not affected by inflow from the east. It is also found that the upper RCS gains heat mainly through the advection of warm water from the east, resulting in an increase in the downstream temperature by about 0.5°C on average. Copyright 2007 by the American Geophysical Union.. |
| 59. | Kaoru Ichikawa, Flow of abyssal water into Wake Island Passage: Properties and transports from hydrographic surveys, Journal of Geophysical Research, Vol. 112, C04008, doi:10.1029/2006JC004000, 2007.04. |
| 60. | Hiroshi Uchida, Hirofumi Yamamoto, Kaoru Ichikawa, Ikuo Kaneko, Masao Fukasawa, Takeshi Kawano, Yuichiro Kumamoto, Flow of abyssal water into Wake Island Passage: Properties and transports from hydrographic surveys, JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, 10.1029/2006JC004000, 112, C4, C04008, 2007.04, [1] Water mass characteristics and volume transports of abyssal water flowing northward into Wake Island Passage in the North Pacific Ocean were examined by carrying out high-quality hydrographic surveys in May 2003, October 2004, and December 2005 along with mooring observations from May 2003 to December 2005. Close linear relationships between potential temperature (theta) and salinity, dissolved oxygen, and silicate were seen below theta approximate to 1.1 degrees C (approximate to 4000 m). The relationships above theta approximate to 1.1 degrees C were scattered and were separated into relatively salty, oxygen-rich, silicate-poor water to the south, and water with the opposite properties to the north. The results suggested that there was a boundary between water masses at theta approximate to 1.1 degrees C in the deep passage. In addition to the three hydrographic sections, two hydrographic sections previously surveyed in the deep passage in 1975 and 1999 were reexamined for transport estimates. Geostrophic calculations relative to the theta = 1.1 degrees C surface indicated northward transports of the abyssal water from 0.5 to 2.2 Sv (1 Sv = 10(6) m(3) s(-1)) below this surface. When 1-year mean estimated velocities at theta = 1.1 degrees C surface were used for reference, mean transport from the five estimates increased from 1.4 to about 4 Sv. The temperature of abyssal water colder than 1.1 degrees C was found to have increased by an average of 0.012 degrees C between 1975 and 2005. This warming is greater than double the standard deviation from the temporal mean temperature profile obtained from mooring observations.. |
| 61. | Hiroshi Uchida, Hirofumi Yamamoto, Kaoru Ichikawa, Ikuo Kaneko, Masao Fukasawa, Takeshi Kawano, Yuichiro Kumamoto, Flow of abyssal water into Wake Island Passage: Properties and transports from hydrographic surveys, Journal of Geophysical Research: Oceans, 10.1029/2006JC004000, 112, 4, 2007.04, Water mass characteristics and volume transports of abyssal water flowing northward into Wake Island Passage in the North Pacific Ocean were examined by carrying out high-quality hydrographic surveys in May 2003, October 2004, and December 2005 along with mooring observations from May 2003 to December 2005. Close linear relationships between potential temperature (θ) and salinity, dissolved oxygen, and silicate were seen below θ ≈ 1.1°C (≈4000 m). The relationships above θ 1.1°C were scattered and were separated into relatively salty, oxygen-rich, silicate-poor water to the south, and water with the opposite properties to the north. The results suggested that there was a boundary between water masses at θ ≈ 1.1°C in the deep passage. In addition to the three hydrographic: sections, two hydrographic sections previously surveyed in the deep passage in 1975 and 1999 were reexamined for transport estimates. Geostrophic calculations relative to the θ = 1.1°C surface indicated northward transports of the abyssal water from 0.5 to 2.2 Sv (1 SV = 106 m3 s-1) below this surface. When 1-year mean estimated velocities at θ = 1.1°C surface were used for reference, mean transport from the five estimates increased from 1.4 to about 4 Sv. The temperature of abyssal water colder than 1.1°C was found to have increased by an average of 0.012°C between 1975 and 2005. This warming is greater than double the standard deviation from the temporal mean temperature profile obtained from mooring observations. Copyright 2007 by the American Geophysical Union.. |
| 62. | Hiroshi Uchida, Hirofumi Yamamoto, Kaoru Ichikawa, Ikuo Kaneko, Masao Fukasawa, Takeshi Kawano, Yuichiro Kumamoto, Flow of abyssal water into Wake Island Passage: Properties and transports from hydrographic surveys, JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, 10.1029/2006JC004000, 112, C4, 2007.04, [1] Water mass characteristics and volume transports of abyssal water flowing northward into Wake Island Passage in the North Pacific Ocean were examined by carrying out high-quality hydrographic surveys in May 2003, October 2004, and December 2005 along with mooring observations from May 2003 to December 2005. Close linear relationships between potential temperature (theta) and salinity, dissolved oxygen, and silicate were seen below theta approximate to 1.1 degrees C (approximate to 4000 m). The relationships above theta approximate to 1.1 degrees C were scattered and were separated into relatively salty, oxygen-rich, silicate-poor water to the south, and water with the opposite properties to the north. The results suggested that there was a boundary between water masses at theta approximate to 1.1 degrees C in the deep passage. In addition to the three hydrographic sections, two hydrographic sections previously surveyed in the deep passage in 1975 and 1999 were reexamined for transport estimates. Geostrophic calculations relative to the theta = 1.1 degrees C surface indicated northward transports of the abyssal water from 0.5 to 2.2 Sv (1 Sv = 10(6) m(3) s(-1)) below this surface. When 1-year mean estimated velocities at theta = 1.1 degrees C surface were used for reference, mean transport from the five estimates increased from 1.4 to about 4 Sv. The temperature of abyssal water colder than 1.1 degrees C was found to have increased by an average of 0.012 degrees C between 1975 and 2005. This warming is greater than double the standard deviation from the temporal mean temperature profile obtained from mooring observations.. |
| 63. | K. Ichikawa and R. Tokeshi, Interactions with eddies in the upstream of the Kuroshio as seen by the HF radar and altimetry data, Proceedings of ISRS 2006 PORSEC, ISSN 1226-9743, 969-972, 2006.11. |
| 64. | Tokeshi, R., K. Ichikawa, S. Fujii, K. Sato and S. Kojima, Estimating the geostrophic velocity component in the sea surface velocity observed by the HF radar in the upstream of the Kuroshio, Proceedings of ISRS 2006 PORSEC, ISSN 1226-9743, 672-675., 2006.11. |
| 65. | M Konda, H Ichikawa, IS Han, XH Zhu, K Ichikawa, Variability of current structure due to meso-scale eddies on the bottom slope southeast of Okinawa Island, JOURNAL OF OCEANOGRAPHY, 10.1007/s10872-006-0024-z, 61, 6, 1089-1099, 61(6), 1089-1099, 2005.12, The relationship between the vertical profile of current on the bottom slope southeast of Okinawa Island and the offshore meso-scale eddy propagated from the east was examined by combined use of the data obtained by a moored upward-looking ADCP (Acoustic Doppler Current Profiler), PIES (Inverted Echo Sounder with Pressure gauge), hydrographic surveys and satellite altimetry during a period from November 2000 to August 2001. The variability of current component parallel to the isobath in the layer over 600 m is found to be markedly different from that in the layer below 600 m. The current variability in the upper and the lower layer can be well explained by the first and second modes of the EOF (Empirical Orthogonal Function) decomposition. The PIES and the sea surface height anomaly data suggest that the first mode represents the surface-trapped current associated with the approach of the offshore meso-scale eddy from the east, whereas the second mode has a bottom-intensified structure. The second mode velocity tends to delay to the first mode. The hydrographic data derived from CTD (Conductivity-Temperature-Depth meter) and PIES data along the line across the isobath suggest that the second mode component is generated by the interaction between the meso-scale eddy and the bottom topography.. |
| 66. | Daisuke Ambe, Shiro Imawaki, Kaoru Ichikawa, Hiroshi Uchida, Detecting the Kuroshio axes south of Japan by using altimeter and drifter data, 2005 IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2005 25th Anniversary IGARSS 2005 IEEE International Geoscience and Remote Sensing Symposium, 10.1109/IGARSS.2005.1525967, 5424-5427, 2005.12, The Kuroshio axes south of Japan was detected by [1] every 10 days from October 1992 to December 2000 from the sea-surface velocity field obtained by combining satellite altimeter and sea-surface drifter data. The axes was obtained by tracking the maximum current speed position of respective points in the Kuroshio. That axes clearly expresses the effect of the bottom topography; three modes were observed when the Kuroshio ran over the Izu Ridge. The axis was very stable to the south of Tosa-bae,' off the Kii Channel.. |
| 67. | Zhongzhe Zhang, Kaoru Ichikawa, Effects of the Kuroshio on coastal sea level south of Japan, 2005 IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2005 25th Anniversary IGARSS 2005 IEEE International Geoscience and Remote Sensing Symposium, 10.1109/IGARSS.2005.1525968, 5428-5431, ISBN 0-7803-9051-2, 2005.12, Correlation between the Kuroshio and coastal sea level south of Japan is examined during a non-large meander period using the altimetry and tide gauge data after removing the steric height component. The sea level varies uniformly in a region bounded by the coast and the mean Kuroshio axis, which stretches for several hundreds kilometers along the coast. These variations are related with the Kuroshio velocity, as coastal sea level decreases (or increases) when the Kuroshio is faster (or slower).. |
| 68. | Kaoru Ichikawa, Surface velocity monitoring by satellite altimetry and repeated ADCP observations, 2005 IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2005 25th Anniversary IGARSS 2005 IEEE International Geoscience and Remote Sensing Symposium, 10.1109/IGARSS.2005.1525966, 5420-5423, ISBN 0-7803-9051-2, 2005.12, A method has been developed to monitor the surface velocity by combining satellite altimetry data and repeated acoustic Doppler current profiler (ADCP) observations. First, geostrophic velocity calculated from the altimetry data is compared with the ADCP observations, resulting in their good agreement after adjusting their spatial scales. Then, a set of observations of the temporal mean velocity is obtained by subtracting the altimetry velocity anomaly from the ADCP observations. Regularly sampled time series of surface velocity can be determined by adding the averaged mean velocity and the altimetry anomaly components, which describes variations of the Kuroshio and the Subtropical Countercurrent well.. |
| 69. | ZZ Zhang, K Ichikawa, Influence of the Kuroshio fluctuations on sea level variations along the south coast of Japan, JOURNAL OF OCEANOGRAPHY, 10.1007/s10872-006-0014-1, 61, 5, 979-985, 61, 979-985, 2005.10, [URL], The correlation between the Kuroshio and coastal sea level south of Japan has been examined using the altimetry and tide gauge data during the period 1992-2000. The sea level varies uniformly in a region bounded by the coast and the mean Kuroshio axis, which stretches for several hundred kilometers along the coast. These variations are related with the Kuroshio velocity, as coastal sea level decreases (or increases) when the Kuroshio is faster (or slower). To the east of the Kii Peninsula, where sea level variations are different from these to the west, movement of the Kuroshio axis additionally affects coastal sea level variations.. |
| 70. | T Takikawa, H Ichikawa, K Ichikawa, S Kawae, Extraordinary subsurface mesoscale eddy detected in the southeast of Okinawa in February 2002, GEOPHYSICAL RESEARCH LETTERS, 10.1029/2005GL023842, 32, 17, 32, L17602, doi:10.1029/2005GL023842, 2005.09, [URL], In February 2002, a subsurface mesoscale eddy with extraordinary features was detected at a depth of about 300 dbar in the southeast of Okinawa ( a part of the Ryukyu Islands). The water mass occupying this subsurface eddy is characterized as the North Pacific Subtropical Mode Water (NPSTMW) with salinity maximum and thick thermostad; its temperature, salinity and potential density at the core of the eddy are 18.4 degrees C, 34.81 and 25.06 sigma(theta), respectively. Thickness and width of the eddy are about 300 m and 100 km, respectively. Mixing between the eddy and the surrounding water mass is also found. Such eddy with the NPSTMW has never been detected during ten years.. |
| 71. | K. Ichikawa, N. Gohda, M. Arai and A. Kaneko, Variations of the Subtropical Counter-Current as seen by repeated ADCP and satellite altimetry data, Proceedings of The Indonesia Ocean Forum 2005 and the 13th PAMS/JECSS Workshop, 161-164, 2005.07. |
| 72. | XH Zhu, H Ichikawa, K Ichikawa, K Takeuchi, Volume transport variability southeast of Okinawa Island estimated from satellite altimeter data, JOURNAL OF OCEANOGRAPHY, 10.1007/s10872-005-0004-8, 60, 6, 953-962, 60, 953-962, 2004.12, [URL], A nine-year-long record of the northeastward volume transport (NVT) in the region southeast of Okinawa Island from 1992 to 2001 was estimated by an empirical relation between the volume transport obtained from the ocean mooring data and the sea surface height anomaly difference across the observation line during 270 days from November 2000. The NVT had large variations ranging from -10.5 Sv (1 Sv = 10(6) m(3)s(-1)) to 30.0 Sv around its mean of 4.5 Sv with a standard deviation of 5.5 Sv. This large variation was accompanied by mesoscale eddies from the east, having a pronounced period from 106 to 160 days. After removal of the eddy, NVT was found to fluctuate from 2 Sv to 12 Sv with a quasi-biennial period.. |
| 73. | Aliasing in repeat observations with inacculate sampling intervals, Kaoru Ichikawa, Oceanography in Japan. |
| 74. | Monitoring of the surface currents by repeated ADCP observations and satellite altimeters, K. Ichikawa, N. Gohda, M. Arai and A. Kaneko, Kaiyo Monthly. |
| 75. | Estimation of the Kuroshio axis south of Japan by combining satellite altimetry data and drifting buoy trajectories, D. Ambe, S. Imawaki, H. Uchida, and K. Ichikawa. |
| 76. | Review: Kuroshio Variation Prediction Experiments, S. Imawaki and K. Ichikawa, Kaiyo Monthly. |
| 77. | D Ambe, S Imawaki, H Uchida, K Ichikawa, Estimating the Kuroshio axis south of Japan using combination of satellite altimetry and drifting buoys, JOURNAL OF OCEANOGRAPHY, 10.1023/B:JOCE.0000038343.31468.fe, 10.1023/b:joce.0000038343.31468.fe, 60, 2, 375-382, Vol. 60, 375-382, 2004.04, [URL], By tracking the locally strongest part of the sea-surface velocity field, which was obtained by integrating data of satellite altimeters and surface drifting buoys, we extracted the Kuroshio axis south of Japan every 10 days from October 1992 to December 2000. The obtained axes clearly express the effect of the bottom topography; three modes were observed when the Kuroshio ran over the Izu Ridge. The axis was very stable to the south of 'Tosa-bae,' off the Kii Channel. Mean current speed at the Kuroshio axis gradually increased from 0.65 m/s south of Kyushu to 1.45 m/s off Enshu-nada.. |
| 78. | K Ichikawa, N Gohda, M Arai, A Kaneko, Monitoring surface velocity from repeated ADCP observations and satellite altimetry, JOURNAL OF OCEANOGRAPHY, 10.1023/B:JOCE.0000038342.87237.e3, 60, 2, 365-374, Vol. 60, 365-374, 2004.04, [URL], A method has been developed to monitor the surface velocity field by combining repeated acoustic Doppler current profiler (ADCP) observations and satellite altimetry data. The geostrophic velocity anomaly is calculated from the sea surface height anomaly field estimated from the altimetry data by an optimal interpolation. It has been confirmed that this accurately observes the smoothed velocity anomaly field when the interpolation scales are set according to the spatio-temporal sampling pattern of the altimeter used. The velocity anomaly obtained from the altimetry data is subtracted from the repeated ADCP observations to estimate temporal mean velocity along the ship tracks. Regularly sampled, nine-year time series of surface velocity can then be obtained by adding the computed mean velocity and the altimetry anomaly components. This clearly illustrates surface velocity fluctuations such as the movement of the Kuroshio axis due to its meandering and an increase of the interannual variability of the Subtropical Countercurrent toward its downstream region.. |
| 79. | D Ambe, S Imawaki, H Uchida, K Ichikawa, Estimating the Kuroshio axis south of Japan using combination of satellite altimetry and drifting buoys, JOURNAL OF OCEANOGRAPHY, 10.1023/B:JOCE.0000038343.31468.fe, 60, 2, 375-382, 2004.04, By tracking the locally strongest part of the sea-surface velocity field, which was obtained by integrating data of satellite altimeters and surface drifting buoys, we extracted the Kuroshio axis south of Japan every 10 days from October 1992 to December 2000. The obtained axes clearly express the effect of the bottom topography; three modes were observed when the Kuroshio ran over the Izu Ridge. The axis was very stable to the south of 'Tosa-bae,' off the Kii Channel. Mean current speed at the Kuroshio axis gradually increased from 0.65 m/s south of Kyushu to 1.45 m/s off Enshu-nada.. |
| 80. | Zhongzhe Zhang and Kaoru Ichikawa, Effect of the Kuroshio on coastal sea level south of Kyushu, Proceedings of 12th PAMS/JECSS Workshop, 4-10-1〜4, 2003.11. |
| 81. | Kaoru Ichikawa and Yuichi Sumikawa, Amplitude modulation of a-few-month Kuroshio variations southwest of Kyushu, Proceedings of 12th PAMS/JECSS Workshop, 4-3-1〜4, 2003.11. |
| 82. | S. Imawaki, H. Uchida, K. Ichikawa, D. Ambe, Estimating the high-resolution mean sea-surface velocity field by combined use of altimeter and drifter data for geoid model improvement, Space Science Reviews, 10.1023/A:1026106904472, 108, 1-2, 195-204, Vol.108, 195-204, 2003., 2003.11, [URL]. |
| 83. | Han, I.-S., X.-H. Zhu, J.-H. Park, H. Ichikawa, A. Kaneko, K. Ichikawa and M. Konda, Estimated Northeastward Mean Current Around the East of Okinawa Islands, Proceedings (CD-ROM) of Techno-Ocean 2002, Electric File: /PDF/TL-2-6.pdf, 2002.11. |
| 84. | Kaoru Ichikawa and Atsushi Kaneda, Spatial Representability of Coastal Sea Level Variations Near the Kuroshio, Pan Ocean Remote Sensing Conference (PORSEC) 2002 Proceedings, Vol.1, 7-10, 2002.09. |
| 85. | Kaoru Ichikawa and Keiko Suito, Capability of the Complex EOF analysis -- with demonstrations to the NCEP data, 九州大学総合理工学報告, 24(1), 23-28, 2002.06. |
| 86. | Sea-surface variations as seen by satellite altimetry, K. Ichikawa, Oceanography in Japan. |
| 87. | Masahisa Kubota, Kaoru Ichikawa, Naoto Iwasaka, Shoichi Kizu, Masanori Konda, Kunio Kutsuwada, Introduction of Japanese Ocean Flux data sets with Use of Remote sensing Observations (J-OFURO), Journal of Oceanography, 10.1023/A:1015845321836, 58, 213-225, 2002.03. |
| 88. | Variation of the Kuroshio in the Tokara Strait induced by meso-scale eddies. |
| 89. | Alexander Ostrovskii, Arata Kaneko, Alice Stuart-Menteth, Kensuke Takeuchi, Toshio Yamagata, Jae Hun Park, Xiao Hua Zhu, Noriaki Gohda, Hiroshi Ichikawa, Kaoru Ichikawa, Atsuhiko Isobe, Masanori Konda, Shin Ichiro Umatani, Kuroshio Observation Program Towards Real-Time Monitoring the Japanese Coastal Waters, Ocean and Polar Research, 23, 2, 141-160, 2001.06, The challenge of predicting the Japanese coastal ocean motivated Frontier Observational Research System for Global Change (FORSGC) and the Japan Marine Science and Technology Center (JAMSTEC) to start a multiyear observational programme in the upstream Kuroshio in November 2000. This field effort, the Kuroshio Observation Program (KOP), should enable us to determine the barotropic and baroclinic components of the western boundary current system, thus, to better understand interactions of the currents with mesoscale eddies, the Kuroshio instabilities, and path bimodality. We, then, will be able to improve modeling predictability of the mesoscale, seasonal, and inter-annual processes in the midstream Kuroshio near the Japanese main islands by using this knowledge. The KOP is focused on an enhanced regional coverage of the sea surface height variability and the baroclinic structure of the mainstream Kuroshio in the East China Sea, the Ryukyu Current east of the Ryukyu's, and the Kuroshio recirculation. An attractive approach of the KOP is a development of a new data acquisition system via acoustic telemetry of the observational data. The monitoring system will provide observations for assimilation into extensive numerical models of the ocean circulation, targeting the real-time monitoring of the Japanese coastal waters.. |
| 90. | Kaoru Ichikawa, Variation of the Kuroshio in the Tokara Strait induced by Meso-Scale Eddies, Journal of Oceanography, 10.1023/A:1011174720390, 57, 1, 55-68, 2001.06, Temporal variations of the Kuroshio volume transport in the Tokara Strait and at the ASUKA line are decomposed by phase-propagating Complex EOF modes of high-resolution sea surface dynamic topography (SSDT) field during the first tandem period of TOPEX/POSEIDON and ERS-1 (from October 1992 to December 1993). Both variations are dominated by a mode with nearly semi-annual cycle, which indicates a series of interactions between the Kuroshio and meso-scale eddies. Namely, northern part of a westward-propagating meso-scale eddy at 23°N is captured into the southern side of the Kuroshio at the south of Okinawa, then it moves downstream along the Kuroshio path passing the Tokara Strait, and reaches to the ASUKA line where it merges with another eddy propagating from the east at 30°N. The variation at the ASUKA line is, however, less dominated by this mode; instead, it includes the SSDT variations in the south of Shikoku and the east of Kyushu which would be directly affected by eddies from the east without passing the Tokara Strait. On the other hand, the same analysis for movements of the Kuroshio axis in the Strait indicates that they are governed by short-term variations locally confined to the Kuroshio in the East China Sea without being induced by meso-scale eddies. This results, however, seem to depend strongly on a time scale of interest. It is suggested that the long-term movements of the Kuroshio axis in the Strait would demonstrate coincidence with SSDT variation in the south of Japan.. |
| 91. | Shiro Imawaki, Shigeru Aoki, Yoichi Fukuda, Kaoru Ichikawa, Shin-ichi Ito, H. Kawamura, M. Kubota, T. Kuragano, K. Matsumoto, T. Nagai, A. Sengoku, H. YOritaka, Mass, heat, and salt transports in the western North Pacific, 8, 62-64, 2001.04. |
| 92. | Kaoru Ichikawa, Correlated variations of the Kuroshio in the East China Sea and in the Tokara Strait, Preprint Full Paper for 11th PAMS/JECSS Symposium, 175-178, 2001.04. |
| 93. | A. Kaneko, A. Ostrovskii, A. Stuart-Mentecth, K. Takeuchi, T. Yamagata, J.-H. Park, X.-H. Zhu, N. Gohda, H. Ichikawa, K. Ichikawa, A. Isobe, M. Konda, and S. Umatani, Acoustic monitoring of the Kuroshio Current system, Journal of Marine Acoustic Society of Japan, 28(4), 236-255, 2001.01. |
| 94. | A. Ostrovskii, A. Kaneko, A. Stuart-Menteth, K. Takeuchi, T. Yamagata, J.-H. Park, X. H. Zhu, N. Gohda, H. Ichikawa, K. Ichikawa, A. Isobe, M. Konda and S. Umatani, Kuroshio Observation Program: Towards Real-Time Monitoring the Japanese Coastal Waters, Ocean and Polar Research, 23(2), 141-160, 2001.01. |
| 95. | Kaoru Ichikawa, Variation of the Kuroshio in the Tokara Strait induced by meso-scale eddies, Journal of Oceanography, 57(1), 55-68, 2001.01, [URL]. |
| 96. | Kaoru Ichikawa, Coastal impacts of offshore meso-scale eddies through the Kuroshio variation, Mer, 38, 4, 219-226, 2000.12, In order to assess the influence of offshore meso-scale eddies in coastal areas facing to the Kuroshio, temperature data in the Bungo Channel and altimetry sea surface height (SSH) data are analyzed. It is east of Okinawa, far away from the Bungo Channel, where the SSH variation is most strongly correlated with the coastal temperature changes with periods of several weeks to months. Complex empirical orthogonal function analysis of the SSH variation indicated strong coherency with the coastal temperature for a train of meso-scale eddies propagating northeastward from east of Okinawa to south of Shikoku, suggesting that variations of the Kuroshio in front of the Bungo Channel induce the coastal temperature changes. However, in areas other than east of Okinawa and south of Shikoku, larger SSH variations which would not correlate well with the coastal temperature variations are detected showing that cross correlation with the coastal temperature is not significant in these regions.. |
| 97. | Velocity variations in the western North Pacific, N. Gohda, K. Ichikawa, M. Arai, H. Zheng and Y. Zhu, Kaiyo Monthly. |
| 98. | IY Yasuda, S Ito, Y Shimizu, K Ichikawa, K Ueda, T Honma, M Uchiyama, K Watanabe, N Sunou, K Tanaka, K Koizumi, Cold-core anticyclonic eddies south of the Bussol' Strait in the northwestern subarctic Pacific, JOURNAL OF PHYSICAL OCEANOGRAPHY, 10.1175/1520-0485(2000)0302.0.CO;2, 30, 6, 1137-1157, Vol. 30, 1137-1157, 2000.06, [URL], Summer hydrographic surveys from 1993 to 1997 in the area south of the Kuril Islands in the northwestern subarctic Pacific showed the existence of anticyclonic eddies south of the Bussol' Strait at almost the same location but with variable sizes and intensities depending on the year. Every eddy had a cold, low salinity and low potential vorticity core, suggesting a strong influence from the Okhotsk Sea water. Two formation processes and annual variations were found with satellite data analyses. One is the case where eddies are locally formed south of the Bussol' Strait and intensified from summer to fall with the supply of Okhotsk Sea water as observed in 1993. In the other case, Kuroshio warm-core rings that had translated northeastward are arrested near the Bussol' Strait and amplified with the supply of Okhotsk Sea water as seen from summer to autumn in 1995. In winter, eddies tend to move northeastward with decay. The 1992 eddy moved northeastward then northward in winter and was eventually absorbed into the East Kamchatka Current. Mechanisms of the northeastward movements and the formations of the Bussol' eddies were discussed. A pseudo-P effect due to deep northeastward currents along the Kuril-Kamchatka Trench could be responsible for the northeastward movement. Since the volume transport of the coastal Oyashio water along the southern Kuril Islands is constrained by the potential vorticity difference between the Okhotsk Sea and the western subarctic gyre (WSAG), eddies could be generated and intensified when a outflow rate from the Okhotsk Sea exceeds the critical transport. The observed annual variations of the eddy evolution might be explained by the critical transport variation associated with an annual change of the WSAG.. |
| 99. | IY Yasuda, S Ito, Y Shimizu, K Ichikawa, K Ueda, T Honma, M Uchiyama, K Watanabe, N Sunou, K Tanaka, K Koizumi, Cold-core anticyclonic eddies south of the Bussol' Strait in the northwestern subarctic Pacific, JOURNAL OF PHYSICAL OCEANOGRAPHY, 10.1175/1520-0485(2000)0302.0.CO;2, 30, 6, 1137-1157, 2000.06, Summer hydrographic surveys from 1993 to 1997 in the area south of the Kuril Islands in the northwestern subarctic Pacific showed the existence of anticyclonic eddies south of the Bussol' Strait at almost the same location but with variable sizes and intensities depending on the year. Every eddy had a cold, low salinity and low potential vorticity core, suggesting a strong influence from the Okhotsk Sea water. Two formation processes and annual variations were found with satellite data analyses. One is the case where eddies are locally formed south of the Bussol' Strait and intensified from summer to fall with the supply of Okhotsk Sea water as observed in 1993. In the other case, Kuroshio warm-core rings that had translated northeastward are arrested near the Bussol' Strait and amplified with the supply of Okhotsk Sea water as seen from summer to autumn in 1995. In winter, eddies tend to move northeastward with decay. The 1992 eddy moved northeastward then northward in winter and was eventually absorbed into the East Kamchatka Current. Mechanisms of the northeastward movements and the formations of the Bussol' eddies were discussed. A pseudo-P effect due to deep northeastward currents along the Kuril-Kamchatka Trench could be responsible for the northeastward movement. Since the volume transport of the coastal Oyashio water along the southern Kuril Islands is constrained by the potential vorticity difference between the Okhotsk Sea and the western subarctic gyre (WSAG), eddies could be generated and intensified when a outflow rate from the Okhotsk Sea exceeds the critical transport. The observed annual variations of the eddy evolution might be explained by the critical transport variation associated with an annual change of the WSAG.. |
| 100. | K. Ichikawa and A. Kaneda, Coastal impacts of offshore meso-scale eddies through the Kuroshio variation, La Mer, 38(4), 219-226, 2000.01. |
| 101. | Evaluation of advection heat flux at the sea surface, K. Ichikawa and S. Imawaki, Kiyo Monthly. |
| 102. | Movement of warm-core rings off Tohoku as seen by satellite altimetry, K. Ichikawa, Kaiyo Monthly. |
| 103. | Tetsuo Yanagi, Akihiko Morimoto, Kaoru Ichikawa, Co-tidal and co-range charts for the East China Sea and the Yellow Sea derived from satellite altimetric data, Journal of Oceanography, 53, 3, 303-309, 1997.06, Co-tidal and co-range charts of eight major constituent tides in the East China Sea and the Yellow Sea are drawn from the results of the harmonic analysis of TOPEX/POSEIDON altimetric data. Those of M2, S2, K1 and O1 constituents agree well with the traditional ones estimated from tide gauge data at coastal stations. Those Of N2 and K2 are similar to those of M2 constituent and those of P1 are similar to K1 constituent, respectively. The amplitude of Sa constituent is large and its phase leads in the shallow part of the East China Sea and the Yellow Sea. The altimetric data from TOPEX/POSEIDON manifest very useful not only in the open ocean dynamics study but also in the coastal ocean dynamics study including tidal phenomena.. |
| 104. | T Yanagi, A Morimoto, K Ichikawa, Seasonal variation in surface circulation of the East China Sea and the Yellow Sea derived from satellite altimetric data, CONTINENTAL SHELF RESEARCH, 10.1016/S0278-4343(96)00054-4, 17, 6, 655-664, 1997.05, Seasonal variation in the surface circulation of the East China Sea and the Yellow Sea is investigated using altimetric data of TOPEX/POSEIDON and numerical model output. In the Yellow Sea an anticlockwise circulation develops during summer and a clockwise one during winter. In the East China Sea an anticlockwise circulation occurs during winter. Such results coincide well with those obtained by the numerical experiment and drifter buoys experiment. (C) 1997 Elsevier Science Ltd.. |
| 105. | Kaoru Ichikawa, Shiro Imawaki, Estimating the sea surface dynamic topography from Geosat altimetry data, Journal of Oceanography, 10.1007/BF02236532, 52, 1, 43-68, 1996.02, Optimal interpolation method is applied to Geosat altimetry data both to remove orbit error and to separate temporal mean sea surface dynamic topography (SSDT) from temporal fluctuations around the mean. Loss of long-wavelength oceanic signals at orbit error reduction procedure is smaller in this method thao that in conventional collinear methods, but the areal average height over the study domain is still removed as the orbit error. The fluctuation SSDT is quantitatively esaluated by sea level data from tide gauge stations at Japanese islands. The correlation coefficient of the two sea-level variations is 0.83 when the loss of the areal average is compensated by the seasonal variation of the areal average height determined from the climatological monthly-mean SSDT. In addition, the improvement of the geoid model by combined use of Seasat altimetry data and hydrographic data is validated through the estimated temporal mean SSDT. In a local area where hydrographic data contemporary with the Seasat mission exist, the geoid model has been significantls improved so that the absolute SSDT can be determined from combination of the altimetrs data and geoid model; the absolute SSDT describes the onset event of a quasi-stationary large meander of the Kuroshio south of Japan very wed. Outside this local area, however, errors of several tens of centimeters still remain in the improved geoid model.. |
| 106. | Kaoru Ichikawa, Shiro Imawaki, Haruo Ishii, Comparison of surface velocities determined from altimeter and drifting buoy data, Journal of Oceanography, 10.1007/BF02235462, 51, 6, 729-740, 1995.11, Surface velocities determined from trajectory of a drifting buoy from March through November 1987 are compared with surface geostrophic velocities determined from sea surface dynamic topography (SSDT) obtained from altimetry data with the aid of long-term hydrographic observation data. In general, these velocities show similar temporal variations in both zonal and meridional components, except in a period when obvious error is found in the altimetric SSDT field. When the buoy was trapped by several mid-ocean meso-scale eddies, the comparison is especially good. Systematic discrepancy is found, however, when the buoy was in the Kuroshio region, because of using both temporally and spatially smoothed mean SSDT estimated from hydrographic data instead, surface geostrophic velocities determined from the altimetric SSDT referred to the improved geoid model result in better comparison. © 1995 Journal of the Oceanographic Society of Japan.. |
| 107. | Comparison of surface velocities determined from altimeter and drifting buoy data. |
| 108. | S. Aoki, S. Imawaki, K. Ichikawa, Baroclinic disturbances propagating westward in the Kuroshio extension region as seen by a satellite altimeter and radiometers, Journal of Geophysical Research, 10.1029/94JC02255, 100, C1, 839-855, 1995.01, The Geosat radar altimeter data during the first year of its exact repeat mission are analyzed to investigate the behavior of individual anomalies of sea surface dynamic topography (SSDT) and their statistical properties in the Kuroshio Extension region. The SSDT anomalies are compared with mesoscale anomalies of sea surface temperature (SST) derived from satellite radiometer data. Remarkable baroclinic anomalies are detected in the time series of both SSDT and SST, and their westward propagation is clearly traced. -from Authors. |
| 109. | S AOKI, S IMAWAKI, K ICHIKAWA, BAROCLINIC DISTURBANCES PROPAGATING WESTWARD IN THE KUROSHIO EXTENSION REGION AS SEEN BY A SATELLITE ALTIMETER AND RADIOMETERS, JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, 10.1029/94JC02255, 10.1029/94jc02255, 100, C1, 839-855, 1995.01, The Geosat radar altimeter data during the first year of its exact repeat mission are analyzed to investigate the behavior of individual anomalies of sea surface dynamic topography (SSDT) and their statistical properties in the Kuroshio Extension region. The SSDT anomalies are compared with mesoscale anomalies of sea surface temperature (SST) derived from satellite radiometer data. Remarkable baroclinic anomalies are detected in the time series of both SSDT and SST, and their westward propagation is clearly traced. The pinching-off of a Kuroshio Extension meander at 147 degrees E is clearly seen as the coalescence of two cyclonic anomalies which had moved fairly constantly westward without changing their relative positions, Westward propagation is statistically dominant in the SSDT and SST anomaly held, Approximate agreement between SSDT and SST anomalies suggests the baroclinic nature of the anomalies. The westward phase speed of SSDT anomalies is faster than the theoretical phase speed of the baroclinic first-mode long Rossby wave in the upstream region of the Kuroshio Extension. In the downstream region it is consistent with the theoretical value but is somewhat faster around 35 degrees N. In the area between 170 degrees E and 180 degrees, SSDT anomalies have a structure like plane waves with major axis oriented NW-SE in the northern part and NE-SW in the southern part. The distribution of the Reynolds stress suggests the tendency of acceleration of the mean current by those anomalies. This strong acceleration tendency at 170 degrees E-180 degrees may be related to bathymetry.. |
| 110. | K ICHIKAWA, S IMAWAKI, LIFE-HISTORY OF A CYCLONIC RING DETACHED FROM THE KUROSHIO EXTENSION AS SEEN BY THE GEOSAT ALTIMETER, JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, 10.1029/94JC01139, 10.1029/94jc01139, 99, C8, 15953-15966, 1994.08, The sea surface dynamic topography (SSDT; sea surface height relative to the geoid) is approximately estimated by combining the temporal fluctuation of SSDT determined from altimetry data with the climatological mean SSDT calculated from hydrographic data. This approximated SSDT, or composite SSDT, is obtained in the area southeast of Japan for the first year (1986-1987) of the Geosat Exact Repeat Mission. Variations in the Kuroshio Current System are well described by the composite SSDT. In particular, a complete life history of a cyclonic ring is observed for the first time in this region, namely, westward propagation of a southward meander of the Kuroshio Extension, its pinching-off to form a cyclonic ring, the ring's westward movement, its coalescence with the Kuroshio, and its eastward advection. All available hydrographic data and cloud-free satellite infrared images support the existence of this series of phenomena.. |
| 111. | K. Ichikawa, S. Imawaki, Life history of a cyclonic ring detached from the Kuroshio Extension as seen by the Geosat altimeter, Journal of Geophysical Research, 99, C8, 15,953-15,966, 1994.01, The sea surface dynamic topography (SSDT) sea surface height relative to the geoid) is approximately estimated by combining the temporal fluctuation of SSDT determined from altimetry data with the climatological mean SSDT calculated from hydrographic data. This approximated SSDT, or composite SSDT, is obtained in the area southeast of Japan for the first year (1986-1987) of the Geosat Exact Repeat Mission. Variations in the Kuroshio Current System are well described by the composite SSDT. In particular, a complete life history of a cyclonic ring is observed for the first time in this region, namely, westward propagation of a southward meander of the Kuroshio Extension, its pinching-off to form a cyclonic ring, the ring's westward movement, its coalescence with the Kuroshio, and its eastward advection. All available hydrographic data and cloud-free satellite infrared images support the existence of this series of phenomena. -Authors. |
| 112. | Kaoru Ichikawa, Shiro Imawaki, Fluctuation of the sea surface dynamic topography southeast of Japan as estimated from Seasat altimetry data, Journal of Oceanography, 10.1007/BF02239003, 48, 2, 155-177, 1992.06, The sea surface dynamic topography (the sea surface height relative to the geoid hereafter abbreviated SSDT) can be divided into the temporal mean SSDT and the fluctuation SSDT around the mean. We use the optimal interpolation method to reduce the satellite radial orbit error and estimate the fluctuation SSDT southeast of Japan from Seasat altimetry data during the 17-day near-repeat mission. The fluctuation SSDT is further combined with the mean geopotential anomalies estimated from hydrographic data during the Seasat mission in order to give the approximated total SSDT, called here the composite SSDT (the approximated mean plus fluctuation SSDT's). The fluctuation SSDT is in accord with the low-frequency sea-level fluctuation recorded at tide gauge stations in the Japanese islands. The composite SSDT describes thoroughly variations of the location of the Kuroshio axis south of Japan determined on the basis of the GEK (Geomagnetic Electro-Kinematograph) surface velocities and the horizontal temperature distribution. The composite SSDT also agrees with oceanic variations east of Japan found in the temperature distribution at the depth of 200 m. These results confirm that the SSDT derived from altimetry data can provide fairly precise synoptic views of low-frequency oceanic phenomena. © 1992 Journal of the Oceanographic Society of Japan.. |
| 113. | Fluctuation of the sea surface dynamic topography southeast of Japan as estimated from Seasat altimetry data. |
| 114. | Shiro Imawaki, Kaoru Ichikawa, Hajime Nishigaki, Mapping the mean sea surface elevation field from satellite altimetry data using optimal interpolation, Marine Geodesy, 10.1080/01490419209388039, 15, 1, 31-46, 1992.01, Optimal interpolation technique is applied to satellite altimetry data in order to recover a sea surface elevation signal from the data, which includes a large satellite radial orbit error, also to make a map of temporal mean sea surface dynamic topography (SSDT, the mean surface height relative to the geoid). The method is applied to Seasat data for a study area southeast of Japan, for which a fairly precise gravimetric geoid is available. Estimated mean elevation field relative to the best available geoid qualitatively shows existence of the Kuroshio in a limited local area close to Honshu, Japan. But for the whole of the area studied, the elevation field is much more rugged than expected mean SSDT and appears to include a relatively large geoid error; namely, the mapped mean sea surface elevation field cannot describe the mean SSDT field. Instead, correction of the provided geoid is evaluated by this altimetrically estimated elevation field together with the mean SSDT estimated from hydrographic data.. |
Unauthorized reprint of the contents of this database is prohibited.