Revisit of the Occurrence of the Kuroshio Large Meander South of Japan

2021 ◽  
Author(s):  
Bo Qiu ◽  
Shuiming Chen
Keyword(s):  
Kuroshio Extension ◽  
Surface Wind ◽  
Wind Forcing ◽  
Dynamic State ◽  
Large Meander ◽  
Subtropical Countercurrent ◽  
Eddy Generation ◽  
Anticyclonic Eddies ◽  
The Kuroshio

AbstractA unique characteristic by the Kuroshio off the southern coast of Japan is its bimodal path variations. In contrast to its straight path that follows coastline, the Kuroshio takes a large meander (LM) path when its axis detours southward by as much as 300 km. Since 1950, eight Kuroshio LM events took place and their occurrences appeared random. By synthesizing available in-situ/satellite observations and atmospheric reanalysis product, this study seeks to elucidate processes conducive for the LM occurrence. We find both changes in the inflow Kuroshio transport from the East China Sea and in the downstream Kuroshio Extension dynamic state are not determinant factors. Instead, intense anticyclonic eddies with transport > 20 Sv emanated from the Subtropical Countercurrent (STCC) are found to play critical roles in interacting with Kuroshio path perturbations southeast of Kyushu that generate positive relative vorticities along the coast and lead the nascent path perturbation to form a LM. Occurrence of this intense cyclonic{anticyclonic eddy interaction is favored when surface wind forcing over the STCC is anticyclonic during the positive phasing of Pacific decadal oscillations (PDOs). Such wind forcing strengthens the meridional Ekman flux convergence and enhances eddy generation by the STCC, and seven of the past eight LM events are found to be preceded by 1 ~ 2 years by the persistent anticyclonic wind forcings over the STCC. Rather than a fully random phenomenon, we posit that the LM occurrence is regulated by regional wind forcing with a positive PDO imprint.

On the Reset of the Wind-Forced Decadal Kuroshio Extension Variability in Late 2017

2020 ◽  
Vol 33 (24) ◽  
pp. 10813-10828
Author(s):  
Bo Qiu ◽  
Shuiming Chen ◽  
Niklas Schneider ◽  
Eitarou Oka ◽  
Shusaku Sugimoto
Keyword(s):  
Wind Field ◽  
Kuroshio Extension ◽  
Surface Wind ◽  
Stable State ◽  
Storm Tracks ◽  
Dynamic State ◽  
Large Meander ◽  
Basin Scale ◽  
Kuroshio Large Meander ◽  
The Kuroshio

AbstractDecadal modulations of the Kuroshio Extension (KE) system between a stable and an unstable dynamic state in the western North Pacific have prevailed in the past three decades. This dominance of decadal variations is controlled by the negative feedback loop involving the wind-forced KE variability and its feedback onto the overlying extratropical storm tracks and the basin-scale surface wind field. The wind-forced decadal KE modulations were disrupted in August 2017 due to the development of the Kuroshio large meander south of Japan. By forcing the inflow KE paths northward and by avoiding overriding the shallow Izu Ridge, the Kuroshio large meander was able to compel the KE to change rapidly from the wind-forced, pre-existing, unstable state to a stable state. Following the large meander occurrence in late 2017, the stabilized KE change is found to affect the overlying storm tracks and the basin-scale wind field the same way as those generated by the wind-forced KE change prior to 2017. Given the consistent atmospheric response to both the large-meander-induced and wind-forced KE variability, we expect that the KE dynamic state will resume its decadal modulation after the phase reset relating to the 2017 large meander event.

scholarly journals Long-Term Variations of the Kuroshio Extension Path in Winter: Meridional Movement and Path State Change

2014 ◽  
Vol 27 (15) ◽  
pp. 5929-5940 ◽  
Author(s):  
Yasuharu Seo ◽  
Shusaku Sugimoto ◽  
Kimio Hanawa
Keyword(s):  
Kuroshio Extension ◽  
Thermocline Depth ◽  
Aleutian Low ◽  
Large Meander ◽  
Wind Stress Curl ◽  
Latitudinal Position ◽  
Anticyclonic Eddies ◽  
The Kuroshio ◽  
Main Thermocline

Abstract As an indicator of the Kuroshio Extension (KE) path, the KE northern boundary (KENB) was detected based on the position of the strong winter sea surface temperature (SST) gradient between 142° and 155°E, using high spatial resolution satellite-derived SST for the 30 winters (January to March) from 1982 to 2011. The KE path showed meridional movement with a period of 10–15 yr and an amplitude of about 2° latitude. The changes in latitudinal position of the KE path were initiated by a north–south shift of the Aleutian low (AL). Negative wind stress curl anomalies around 35°N in the eastern North Pacific associated with a northward shift of the AL induced a deepening of the main thermocline depth, and then this deepening signal propagated westward, reaching the KE region after about 3 yr, where it caused the KE path to move northward. The path state of the KE (straight path/convoluted path) modulated on a time scale of 8–12 yr, but this was not significantly correlated with the meridional movement of the KE path. The anticyclonic eddies containing warm-salty water that detached northward from the convoluted KE exerted a strong influence on oceanic conditions in the Kuroshio–Oyashio Confluence (KOC) region. The changes in path state of the KE were related to the path of the Kuroshio south of Japan over the long term; a convoluted (straight) KE path was associated with the Kuroshio taking the offshore nonlarge (nearshore nonlarge or typical large) meander path.

scholarly journals A Coupled Decadal Prediction of the Dynamic State of the Kuroshio Extension System

2014 ◽  
Vol 27 (4) ◽  
pp. 1751-1764 ◽  
Author(s):  
Bo Qiu ◽  
Shuiming Chen ◽  
Niklas Schneider ◽  
Bunmei Taguchi
Keyword(s):  
Wind Stress ◽  
Large Scale ◽  
Current System ◽  
Kuroshio Extension ◽  
Surface Wind ◽  
Storm Tracks ◽  
Dynamic State ◽  
Western Boundary ◽  
Wind Stress Curl ◽  
The Kuroshio

Abstract Being the extension of a wind-driven western boundary current, the Kuroshio Extension (KE) has long been recognized as a turbulent current system rich in large-amplitude meanders and energetic pinched-off eddies. An important feature emerging from recent satellite altimeter measurements and eddy-resolving ocean model simulations is that the KE system exhibits well-defined decadal modulations between a stable and an unstable dynamic state. Here the authors show that the decadally modulating KE dynamic state can be effectively defined by the sea surface height (SSH) anomalies in the 31°–36°N, 140°–165°E region. By utilizing the SSH-based KE index from 1977 to 2012, they demonstrate that the time-varying KE dynamic state can be predicted at lead times of up to ~6 yr. This long-term predictability rests on two dynamic processes: 1) the oceanic adjustment is via baroclinic Rossby waves that carry interior wind-forced anomalies westward into the KE region and 2) the low-frequency KE variability influences the extratropical storm tracks and surface wind stress curl field across the North Pacific basin. By shifting poleward (equatorward) the storm tracks and the large-scale wind stress curl pattern during its stable (unstable) dynamic state, the KE variability induces a delayed negative feedback that can enhance the predictable SSH variance on the decadal time scales.

scholarly journals Processes Shaping the Frontal-Scale Time-Mean Surface Wind Convergence Patterns around the Kuroshio Extension in Winter

2020 ◽  
Vol 33 (1) ◽  
pp. 3-25
Author(s):  
Ryusuke Masunaga ◽  
Hisashi Nakamura ◽  
Bunmei Taguchi ◽  
Takafumi Miyasaka
Keyword(s):  
Kuroshio Extension ◽  
Surface Wind ◽  
Convective Precipitation ◽  
Western Boundary ◽  
Boundary Currents ◽  
Sst Front ◽  
Atmospheric Structure ◽  
Mean Convergence ◽  
Daily Scale ◽  
The Kuroshio

AbstractHigh-resolution satellite observations and numerical simulations have revealed that climatological-mean surface wind convergence and precipitation are enhanced locally around the midlatitude warm western boundary currents (WBCs) with divergence slightly to their poleward side. While steep sea surface temperature (SST) fronts along the WBCs have been believed to play an important role in shaping those frontal-scale atmospheric structures, the mechanisms and processes involved are still under debate. The present study explores specific daily scale atmospheric processes that are essential for shaping the frontal-scale atmospheric structure around the Kuroshio Extension (KE) in winter, taking advantage of a new product of global atmospheric reanalysis. Cluster analysis and case studies reveal that a zonally extending narrow band of surface wind convergence frequently emerges along the KE, which is typically observed under the surface northerlies after the passage of a developed synoptic-scale cyclone. Unlike its counterpart around the cyclone center and associated cold front, the surface convergence tends to be in moderate strength and more persistent, contributing dominantly to the distinct time-mean convergence/divergence contrast across the SST front. Accompanying ascent and convective precipitation, the band of convergence is a manifestation of a weak stationary atmospheric front anchored along the SST front or generation of a weak meso-α-scale cyclone. By reinforcing the ascent and convergence, latent heating through convective processes induced by surface convergence plays an important role in shaping the frontal-scale atmospheric structure around the KE.

scholarly journals Energy Exchange between the Mesoscale Oceanic Eddies and Wind-Forced Near-Inertial Oscillations

2017 ◽  
Vol 47 (3) ◽  
pp. 721-733 ◽  
Author(s):  
Zhao Jing ◽  
Lixin Wu ◽  
Xiaohui Ma
Keyword(s):  
Energy Transfer ◽  
Energy Exchange ◽  
Kuroshio Extension ◽  
Mesoscale Eddies ◽  
Energy Transfer Efficiency ◽  
Layer Model ◽  
Strain Variance ◽  
Anticyclonic Eddies ◽  
The Kuroshio ◽  
Kuroshio Extension Region

AbstractIn this study, the energy exchange between mesoscale eddies and wind-forced near-inertial oscillations (NIOs) is theoretically analyzed using a slab mixed layer model modified by including the geostrophic flow. In the presence of strain, there is a permanent energy transfer from mesoscale eddies to NIOs forced by isotropic wind stress. The energy transfer efficiency, that is, the ratio of the energy transfer rate to the near-inertial wind work, is proportional to , where S2 is the total strain variance, is the effective Coriolis frequency, and ζ is the relative vorticity. The theories derived from the modified slab mixed layer model are verified by the realistic numerical simulation obtained from a coupled regional climate model (CRCM) configured over the North Pacific. Pronounced energy transfer from mesoscale eddies to wind-forced NIOs is localized in the Kuroshio Extension region associated with both strong near-inertial wind work and strain variance. The energy transfer efficiency in anticyclonic eddies is about twice the value in cyclonic eddies in the Kuroshio Extension region because of the influence of ζ on feff, which may contribute to shaping the dominance of cyclonic eddies than anticyclonic eddies in that region.

scholarly journals Interactions between Typhoon Choi-wan (2009) and the Kuroshio Extension System

2013 ◽  
Vol 2013 ◽  
pp. 1-17 ◽  
Author(s):  
Akiyoshi Wada ◽  
Norihisa Usui ◽  
Masaru Kunii
Keyword(s):  
Surface Temperature ◽  
Kuroshio Extension ◽  
Surface Wind ◽  
Specific Humidity ◽  
Central Pressure ◽  
Extension System ◽  
Stationary Front ◽  
Axisymmetric Structure ◽  
The Impact ◽  
The Kuroshio

We investigated interactions between Typhoon Choi-wan (2009) and the Kuroshio Extension system with a coupled atmosphere-wave-ocean model in 14 numerical simulations performed with initial conditions obtained from daily oceanic reanalysis data for the northwestern Pacific Ocean from September 12 to September 25, 2009. Preexisting oceanic conditions affected the simulated central pressure and the inner-core axisymmetric structure of the simulated typhoon differently during the intensification, mature, and decaying phases, but they had little impact on the simulated track. Among the simulations, the simulated central pressure range during the mature phase was ~10 hPa. Simulated central pressure was highly correlated with the axisymmetric mean horizontal specific humidity flux between radii of 50 and 150 km and altitudes of 20 to ~2000 m, suggesting that this flux has potential as a new metric for predicting tropical cyclone intensity. Variations in preexisting oceanic conditions in the Kuroshio Extension region on the simulated atmospheric and oceanic horizontal fields affected the typhoon and a nearby stationary front differently. Around the stationary front, the impact on hourly precipitation was closely related to that on surface wind speed, whereas the impact on surface temperature was greatly affected by that on sea surface temperature through the latent heat flux.

scholarly journals Atmospheric Effects of the Kuroshio Large Meander during 2004–05*

2010 ◽  
Vol 23 (17) ◽  
pp. 4704-4715 ◽  
Author(s):  
Haiming Xu ◽  
Hiroki Tokinaga ◽  
Shang-Ping Xie
Keyword(s):  
Wind Speed ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Atmospheric Effects ◽  
Water Pool ◽  
Large Meander ◽  
Cool Water ◽  
Japanese Coast ◽  
Kuroshio Large Meander ◽  
The Kuroshio

Abstract In the summer of 2004, the Kuroshio took a large meander path south of Japan for the first time since 1991, and this large meander event persisted until the next summer. Satellite observations and numerical model simulations are used to study the effect of this large meander event on the atmosphere. The large meander leaves a cool water pool between the Kuroshio and Japanese coast. Sea surface temperature (SST) in the cool water pool is about 2°–3°C colder than the surroundings during winter and spring, whereas the SST signature substantially weakens in summer. A local reduction of wind speed is found over the cool water pool, and the positive SST–wind speed correlation is indicative of ocean forcing of the atmosphere. Cloud liquid water (CLW) content and precipitation also decrease over the cool SST pool. A regional atmospheric model successfully simulates atmospheric response to the Kuroshio large meander. The model experiments suggest that the reduced surface wind speed and precipitation are due to the large meander-induced SST cooling. Analysis of the surface perturbation momentum budgets shows the importance of the pressure adjustment mechanism in surface wind response to the cold SST anomalies.

scholarly journals Roles of SST Anomalies on the Wintertime Turbulent Heat Fluxes in the Kuroshio–Oyashio Confluence Region: Influences of Warm Eddies Detached from the Kuroshio Extension

2011 ◽  
Vol 24 (24) ◽  
pp. 6551-6561 ◽  
Author(s):  
Shusaku Sugimoto ◽  
Kimio Hanawa
Keyword(s):  
Kuroshio Extension ◽  
Surface Wind ◽  
Surface Air Temperature ◽  
Surface Wind Speed ◽  
Turbulent Heat Flux ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
The North ◽  
Turbulent Heat Fluxes ◽  
The Kuroshio

Abstract Variations of turbulent heat fluxes (sum of sensible and latent heat fluxes) in the North Pacific during 16 winters from December 1992/February 1993 to December 2007/February 2008 are investigated because the months from December to February correspond to the period having peak winter conditions in the atmosphere field. Turbulent heat fluxes are calculated from the bulk formula using daily variables [surface wind speed, surface air specific humidity, surface air temperature, and sea surface temperature (SST)] of the objectively analyzed air–sea flux (OAFlux) dataset and bulk coefficients based on the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) bulk flux algorithm 3.0. The winter turbulent heat fluxes over the Kuroshio–Oyashio Confluence Region (KOCR; 142°–150°E, 35°–40°N) have the largest temporal variances in the North Pacific. The relative contributions among observed variables in SST, surface air temperature, and surface wind speed causing turbulent heat flux variations in the KOCR are assessed quantitatively by performing simple experiments using combinations of two types of variables: raw daily data and daily climatological data. Results show that SST is primarily responsible for the turbulent heat flux variations—a huge amount of heat is released in the state of the positive SST anomaly. Using the datasets of satellite-derived SST and sea surface height with high spatial and temporal resolutions, it is found that the SST anomalies in the KOCR are formed through activities of the anticyclonic (warm) eddies detached northward from the Kuroshio Extension; SSTs take positive (negative) anomalies when more (less) anticyclonic eddies are distributed there, associated with a more convoluted (straight) Kuroshio Extension path.

scholarly journals Marine Heatwave of Sea Surface Temperature of the Oyashio Region in Summer in 2010–2016

2021 ◽  
Vol 7 ◽  
Author(s):  
Toru Miyama ◽  
Shoshiro Minobe ◽  
Hanako Goto
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Kuroshio Extension ◽  
Sea Surface ◽  
Boreal Summer ◽  
Ocean Reanalysis ◽  
Oyashio Region ◽  
Seriola Quinqueradiata ◽  
Anticyclonic Eddies ◽  
The Kuroshio

The sea surface temperature (SST) of the Oyashio region in boreal summer abruptly increased in 2010 and high summertime SST repeated every year until 2016. Observations and an ocean reanalysis show that this marine heatwave occurred not only at the surface but also at deeper depths down to 200 m. Furthermore, salinity in summer also increased in parallel with the temperature. The rises in temperature and salinity indicate the strengthening of the Kuroshio water influence. The sea surface height and velocity show that the southward intrusion of the Oyashio near the coast in summer weakened from 2010 accompanied by an increase in anticyclonic eddies from the Kuroshio Extension. The much more frequent existence of anticyclonic eddies to the east of the first intrusion of the Oyashio in summer is closely associated with the weakening of the first intrusion and the strengthening of the second intrusion. It is suggested that the rise in the water temperature could increase a catch of yellowtail (Seriola quinqueradiata) in northern Japan.

Sign in / Sign up

Export Citation Format

Share Document