查看更多>>摘要：Abstract The Kuroshio south of Japan exhibits bimodal variations between large meander (LM) and non-LM paths. The Kuroshio LM drastically changes the distribution of currents and water temperature in the surface and subsurface layers, affecting atmospheric conditions, marine ecosystems, and fisheries resources. The most recent Kuroshio LM event occurred in August 2017 and is still continuing as of March 2025 (LM2017). Through studies of the long-lived LM2017, many new insights into the Kuroshio LM and its impact have been gained in recent years. This study aims to organize and share our current understanding of the Kuroshio LM and its impacts by reviewing past and present studies. Future directions for research on the Kuroshio LM and its impacts are also presented. This review advances the literature by covering not only the oceanic dynamics of the Kuroshio LM, but also its impacts on ocean conditions, atmospheric phenomena, lower ecosystems, and fisheries resources, thereby presenting the first attempt at such a comprehensive review of the Kuroshio LM.
查看更多>>摘要：Abstract Radiocesium released from the Fukushima Dai-ichi Nuclear Power Plant (FNPP1) in 2011 resulted in radioactive contamination in the North Pacific Ocean. A portion of the FNPP1-derived radiocesium settled in the North Pacific had been transported by the mode waters, the subtropical mode water (STMW) and central mode water (CMW). We measured radiocesium concentration in the western subtropical area from 2015 to 2021 and revealed the temporal changes in the FNPP1-derived radiocesium by 2021. The FNPP1-derived radiocesium circulated along the anti-cyclonic circulation of STMW within the western subtropical area in the time-scale of 3‒6 years. During the circulation, the inventory of the FNPP1-derived radiocesium in the western subtropical area decreased with the time constant of 4‒8 years, which agrees with the renewal time of STMW. The inventory was estimated to be 4.6 ± 1.8 PBq in 2017‒2018 and 3.3 ± 1.1 PBq in 2019‒2021. We also observed the FNPP1-derived radiocesium in the western tropical area for the first time in 2020. It is suggested that the FNPP1-derived radiocesium in the western tropical area had not been transported southward from the western subtropical area but eastward from the subarctic/subtropical boundary area in the eastern North Pacific. In that case, the approximate 1.3 PBq of the inventory loss in the western region was probably transported to the eastern region within the western subtropical area between 2017‒2018 and 2019‒2021. The FNPP1-derived radiocesium will be usable for studies on the thermocline circulations in the North Pacific Ocean in the future.
查看更多>>摘要：Abstract The ocean off the Sanriku coast, Japan, where the Kuroshio Extension (KE) meets the Oyashio, has unique dynamics and hosts rich marine resources. Since April 2023, the KE, typically flowing eastward around 36°N, exhibited an extreme northward meander, reaching 40°N by the winter of 2024. An anticyclonic eddy pinched off from the KE’s northern edge in late May 2024. The Japan Meteorological Agency conducted hydrographic surveys that cross this eddy and the KE along about 145°E in late May 2024. The hydrographic data revealed that thick warm-salty subtropical water replaced the cold-fresh subarctic water off the Sanriku coast, with temperatures 10 °C warmer at depths of 50–400 dbar compared to past decades. The Subtropical Mode Water, characterized by vertical uniformity, existed north of 40°N, more than 500 km further north of its conventional distribution area. From April 2023 to August 2024, satellite data indicated record-high sea surface temperature off the Sanriku coast (+ 4.9 °C), with intense marine heatwave conditions almost every day. In the winter of 2024, over the very warm ocean off the Sanriku coast, 300 W m–2 more heat than usual in the form of turbulent heat flux was released from the ocean to the atmosphere, and air temperature and humidity increased up to around 800 hPa level, from atmospheric reanalysis data. In addition to monitoring these unprecedented ocean conditions off the Sanriku coast, it is important to assess their impact on the marine environment, fisheries, and, ultimately, the local economy.
查看更多>>摘要：Abstract The polar night jet (PNJ), characterized by strong zonal-mean zonal winds at 60–80° N and 50 hPa, shows interannual variability that is distinctively observed in late November. The autumnal acceleration tendency of the PNJ exhibits the alternative of monotonous acceleration and temporary deacceleration marked by a “short break” and consequently represents bimodal fluctuations. Statistical analyses using reanalysis and objective analysis datasets in this study reveal that the reduction of Arctic sea ice concentration (SIC) predominantly contributes to the PNJ short break, rather than other potential factors such as the quasi-biennial oscillation (QBO) and the El Niño-Southern Oscillation (ENSO) variability. The PNJ short break is usually accompanied by the upward propagation of Rossby waves from the troposphere to the stratosphere over Siberia. When the Arctic SIC is lower than climatology, particularly in the Barents–Kara Sea, the increased heat flux at the sea surface causes deceleration events inherent to late November. In contrast, the intensity of the submonthly-scale PNJ deceleration and acceleration is affected little by the phase of the QBO, while the phase of the QBO is thought to contribute to the seasonal means of the PNJ. While ENSO variability can also give favorable conditions for the deceleration of the zonal-mean westerly winds, the upward wave propagation is observed mainly over the North Atlantic and Europe rather than over Siberia.
查看更多>>摘要：Abstract It has been recently found that North Pacific Subtropical Mode Water impacts the overlying thermal structure by uplifting the isotherms when it thickens. How the thickness variation of North Atlantic Subtropical Mode Water, also known as Eighteen Degree Water (EDW), affects the overlying thermal and biogeochemical structure through such uplifting effect has been investigated using Argo float data and shipboard observation data at Bermuda Atlantic Time-series Study site. When EDW was thicker, the overlying isotherms were uplifted, leading to a decrease in temperature centered at 50–100 dbar in the warm season; in addition, the oxycline existing around 100 dbar and the nitracline at 100–150 dbar also tended to be uplifted, leading to an increase of apparent oxygen utilization and nitrate concentrations in the lower euphotic layer; furthermore, there is a tendency that chlorophyll-a maximum around 100 dbar shallowed, and primary production integrated in the euphotic layer increased during the spring bloom season. Thus, although the core of thicker EDW tends to have less nitrate as shown by previous studies, thicker EDW tends to increase biological production in the euphotic layer through the enhanced uplifting effect.
查看更多>>摘要：Abstract The effects of extratropical sea surface temperature (SST) heterogeneity on various atmospheric phenomena have received much attention recently. In this study, the effects of SST anomalies on heavy precipitation that occurred in northern Kyushu Island, Japan, in August 2021 are investigated with a convection–permitting regional atmospheric model. The mid–August SST anomalies are found to provide the following favorable conditions for the intense precipitation. Mesoscale cyclones and associated moisture fluxes intensified over a warm SST anomaly in the northern East China Sea (ECS). The vertical shear of horizontal winds also intensified over a pair of warm and cool SST anomalies in the eastern ECS. The SST anomaly in the western subtropical North Pacific affected the static stability of the air parcels entering the precipitation area. The air parcels became more unstable even though they passed over the cool SST anomalies south of the precipitation area. This seemingly counterintuitive result can be explained by the stability of the atmospheric boundary layer (ABL) and the height of the air parcels. The less unstable ABL over the cool SST anomaly kept the air parcels at lower altitudes, and thus they tended to be more susceptible to the influence of heat fluxes from the sea surface and, therefore, becoming more unstable. The results of this study thus provide new insight into the role of the complex SST distribution during heavy precipitation events in extratropics, suggesting the need for further studies to deepen our understanding of the atmospheric responses to the extratropical SST.
查看更多>>摘要：Abstract Coupled atmosphere–ocean phenomena known as northeast Pacific marine heatwaves (MHWs) simulated in a climate model with an eddy-permitting ocean model were examined. During the analyzed 270-years of the preindustrial control run, 13 events of MHW (defined here by warm annual-mean SST anomalies with over 1.5 times of the standard deviation) were detected. The simulated MHWs are linked to the decadal-scale climate modes of PDO, inverted NPGO (IV-NPGO), and the central Pacific El Niño (CP-El-Niño): IV-NPGO and then PDO changed the signs from negative to positive a few years before the MHWs at around which PDO took the maxima, when CP-El-Niño occurred. Air–sea interactions between subtropical-tropical and within mid-latitudes suggest playing crucial roles in the evolution of the MHWs.
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