Box model analysis of the long-term dissolved oxygen variation in the Japan Sea Proper Water

It has been revealed that the formation of the Japan Sea Proper Water (JSPW) in both intermediate and deep layers has been stagnating since the 1960s, accompanying with a relatively active intermediate water formation. This study demonstrates such a situation using a simple vertical advection-diffusion box model. The box model qualitatively reproduced the interdecadal oscillation superimposed on the decreasing trend in the dissolved oxygen (DO) concentration throughout the JSPW. However, the simulated amplitude of the interdecadal oscillation in the DO concentration in the deep layers is very small compared with the observed one. This implies that the vertical diffusion is not the main cause of the interdecadal oscillation in DO in the deep layer

Flow Intensification Due to the Superposition of Near-Inertial Internal Waves in the Abyssal Yamato and Tsushima Basins of the Japan Sea (East Sea)

[Abstract] / Near-inertial internal waves (NIWs) in the abyssal Yamato and Tsushima Basins of the Japan Sea (East Sea) were investigated using data from a moored acoustic Doppler current profiler (ADCP) and single-point current meters. The NIW events with duration of 3–5 days were observed intermittently in both basins. In particular, an active NIW event occurred below 2,475 m in the Yamato Basin during May 12–16, 2014. This was followed by the upward propagation of a wave packet from 2,475 to 950 m. The near-inertial flows (1.07f) during the event exhibited a vertically coherent phase and intensification with depth by a factor of 1.5 from 2,475 to 2,635 m. The near-inertial flows (1.05f) in the Tsushima Basin also showed a vertically coherent phase and intensification with depth, although the amplitude of the flow exhibited a middepth maximum rather than monotonic intensification. As a possible explanation of the observed flow characteristics, the superposition of downward-propagating NIWs that can be excited by a strong wind event and upward-propagating NIWs that bounced off the seabed was examined. The time series of the Richardson number based on the observed shear showed sporadic unstable conditions during the initial stage of the NIW event during May 2014 in the Yamato Basin. In addition, relatively small values of Richardson number were observed over the range of 2,475–2,635 m during the period of active NIWs. This suggests the promotion of vertical mixing in the deep sea during significant NIW events. / 　 / [Plain Language Summary] / The Japan Sea, a semi-closed marginal sea in East Asia, has its own circulation system driven by the deep water formation. We carried out deep flow observations in the sea 4 times using moored acoustic current meters. The current meters recorded strong flow events accompanying clockwise-rotating cyclic flows of 18–20 h periods. The cyclic flow, called the nearinertial flow, is associated with internal waves that are affected by the Earth rotation. The amplitude of near-inertial flow during the events varied vertically, although the direction of the flow was consistent throughout the observational depths. We tried to explain the observed flow intensification with depth by the superposition of downward-propagating internal wave that can be excited by a strong wind and upward-propagating internal wave that bounced off the seabed. In addition, we suggested that the intensification of near-inertial flow during the events promoted vertical mixing in the deep sea which controls pattern and strength of the deep circulation. / 　 / [Key Points] / • Near-inertial flow events with 3–5 days duration were observed in the abyssal Japan Sea using moored current meters / • Near-inertial flows during the events exhibited a vertically coherent phase and varying amplitude with depth / • Superposition of near-inertial internal waves was suggested as a cause of the deep flow intensification that promotes vertical mixin

Decadal Signal in the Sea Surface Temperatures off the San\u27in Coast in the Southwestern Japan Sea

The decadal-scale variations in the southwestern Japan Sea are investigated on the basis of the offshore sea surface temperature (SST) measured by a ferryboat. The low-pass filtered SST shows alternate warm and cold periods of decadal scale, bounded by a sudden decrease and increase in 1976-1977 and 1983-1984, respectively. These temperature jumps correspond to the regime shifts that occurred in the North Pacific in the mid-1970s and late 1980s, suggesting that the Tsushima current in the Japan Sea is under the influence of the Pacific Decadal Oscillation. Similar warm and cold periods of decadal timescale are seen in the winter-mean SST variations, along with shorter-period fluctuations correlating with the winter monsoon intensity. In contrast, such a decadal variation is not observed in the summer-mean SST. This indicates that the decadal variations (and regime shifts) in the Japan Sea SST field appear clearer in winter, the same as in the North Pacific

Multiple Regression Analysis for the Discharge of Chingjiang in China

An estimation method for the Changjiang discharge from precipitation anomalies is proposed on the basis of multiple regression analysis. The estimated discharge anomaly shows a significant correlation with the observed one (with a multiple correlation coefficient R of +0.45). The root mean square between the estimated and observed discharge anomalies is 5968.6 m3s-1. The partial regression coefficients show a relatively larger contribution to the discharge anomaly from precipitations in the middle region of Changjiang

長江流量の重回帰分析

An estimation method for the Changjiang discharge from precipitation anomalies is proposed on the basis of multiple regression analysis. The estimated discharge anomaly shows a significant correlation with the observed one (with a multiple correlation coefficient R of +0.45). The root mean square between the estimated and observed discharge anomalies is 5968.6 m3s-1. The partial regression coefficients show a relatively larger contribution to the discharge anomaly from precipitations in the middle region of Changjiang

沿岸密度流としての日本海の急潮

Kyucho around the east coast of Noto Peninsula in the Japan Sea consists of the first strong current after passing an atmospheric disturbance and following periodical currents. The first strong current with highest flow speed has been discussed from two points of view: density currents and near-inertial internal waves. In this study, we discuss which phenomena and dominant in a Kyucho occurred in September 2006. The first strong current appeared in the period of rapid temperature increase, while the current speed was reduced when the temperature reached a maximum. Unlike this, for the following periodical currents, temperature and current speed varied in phase, showing a character of progressive waves. Besides, after the first strong current, the offshore water mass north of the peninsula was found in Toyama Bay suggesting a large scale water mass exchange. These facts indicate that the first strong current is a density current in a rotating system; propagation of the offshore warm water which had been piled up to the northern coast of the peninsula by southwesterly winds. On the other hand, following periodical currents are flows accompanied by propagation of coastal trapped waves generated by scattering of near-inertial internal waves at the northern part of the peninsula