Co-Occurrence of Marine Extremes Induced by Tropical Storms and an Ocean Eddy in Summer 2016: Anomalous Hydrographic Conditions in the Pacific Shelf Waters off Southeast Hokkaido, Japan

This study proposes an analysis methodology to address how very rare marine extremes can be understood using limited data. In summer 2016, extreme weather and marine events occurred simultaneously around the Pacific shelf off southeastern Hokkaido, Japan. Six successive tropical storms brought extreme precipitation and an anticyclonic mesoscale eddy of subtropical Kuroshio water closely approached the coast, locally causing marine heat waves. We examined how these compound extremes affected oceanographic conditions on the coastal shelf by analyzing data from ship surveys in October 2016 on the Pacific shelf and outputs from a realistic ocean model. Climatologically, warm, high-salinity (33.0–33.7) subtropical water from the Okhotsk Sea (modified Soya Warm Current water) is distributed near the sea surface on the Pacific shelf in October and transported by the along-shelf boundary current. In 2016, however, a vertically well-mixed low-salinity (<33.0) layer associated with the heavy rainfall was observed at 0–50 m depth on the shelf, salinity maxima (≥33.7) associated with Kuroshio water from the mesoscale eddy occurred at 50–150 m depth on the slope, and baroclinic jets formed along the salinity front near the shelfbreak. These observed salinity structures were reproduced by a 1/50° ocean model. Particle-tracking experiments revealed that the low-salinity water originated mainly off eastern Hokkaido, where heavy rainfall events occurred in August, and was modified by mixing with Soya Warm Current water before transport to the Pacific shelf

Subarctic-scale transport of 134Cs to ocean surface off northeastern Japan in 2020

Abstract We studied the spatiotemporal variations in 134Cs, 137Cs, and 228Ra concentrations at the sea surface off southeastern Hokkaido, Japan (off-Doto region) from 2018 to 2022 using low-background γ-spectrometry. The 134Cs concentrations in the off-Doto region, decay-corrected to the date of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, exhibited wide lateral variation each year (e.g., 0.7–1.1 mBq/L in 2020). By studying the 228Ra concentrations and salinity, this variation was explained based on the current mixing patterns. Furthermore, the 134Cs concentrations in the waters highly affected by the Oyashio Current (OYC) gradually increased from 2018 to 2020, and subsequently decreased in 2022. This implies that the water mass maximally contaminated with 134Cs was transported back to the side of the Japanese islands 10 years after the FDNPP accident along with counter-clockwise currents (e.g., the OYC) in the northern North Pacific Ocean. The 134Cs concentrations in the OYC-affected waters in the off-Doto region in 2020 were ~ 1/6 times those in the 134Cs-enriched core of waters off the western American Coast in 2015, which can be ascribed to dilution via spatial dispersion during subarctic current circulation. Overall, we elucidated the ocean-scale subarctic current systems in the northwestern North Pacific Ocean, including water circulation timespans

An Approach for Realization of Low Carbon Society and Revitalization of Mountainous Area by Nano Hydroelectric Generator

A demonstration experiment of pico size hydroelectric power generation was performed in Kamiajimi area, Fukui-city from 2012. In this report, the installation activity of nano size hydroelectric power generation illumination that we did in 2014 will be presented. A nano size hydroelectric generator using a bicycle wheel with a hub dynamo and the LED illumination unit using power LED elements was developed. A workshop to make nano size hydroelectric generators was held with residents of Kamiajimi area. Two sets of nano size hydroelectric power generation illumination were installed respectively in 6 villages in Kamiajimi area. A lamp of 5 linked nano size hydroelectric generation illumination which becomes the symbol of this project was installed in a village, which is used as a gate lamp of the assembly hall. A forum was held to think about energy problems in a mountainous area