5:15 PM - 6:30 PM
[ACG29-P07] Interannual and decadal surface velocity variations in the Kuroshio and Kuroshio Extension System
Keywords:air-ocean interaction, western boundary current, interannual–decadal variability, Rossby wave, mesoscale eddy
Interannual and decadal variations of current intensity and current path position are investigated for the entire stream of the Kuroshio and Kuroshio Extension (hereafter, Kuroshio–KE System) in order to clarify how this system is organized with synthesized temporal and spatial features. Our strategy to achieve this purpose is to analyze Hovmöller diagrams of the current intensity and path position, created along an entire stream of this current system using satellite-altimeter derived surface geostrophic velocity data in 1993–2018. The oceanic processes to govern such variations are also examined using satellite-altimetry sea surface height (SSH) data over the North Pacific.
At first, we carried out the study on decadal-scale current variations along the entire stream, and revealed three kinds of coherently organized variations: 1) an out-of-phase current intensity variation between the Kuroshio south of Japan and the KE between 1993–2018; 2) an out-of-phase current intensity variation between the Kuroshio from the east of Taiwan (ETW) to the East China Sea (ECS) and the KE between 2006–2014; and 3) an out-of-phase current path variation between the Kuroshio from the ETW to ECS and the Kuroshio in the Luzon Strait between 1993–2018. These synchronizations were dynamically regulated by the Pacific Decadal Oscillation. The synchronized current intensity variations in 2006–2014, which governed almost the entire current system, were caused by coherent phenomena comprising two kinds of baroclinic Rossby wave propagations along the KE and the subtropical countercurrent, and a regional SSH anomaly advection from the South China Sea (SCS) to the ECS via the Taiwan Strait. However, the synchronized current path variations between 1993–2018 were caused by a long SSH anomaly migration of the Kuroshio from the western North Equatorial Current region to the ECS along with an SSH variation localized in the SCS.
We are now investigating interannual current variations over the Kuroshio-KE System, particularly focusing on those variations in the Kuroshio from the ETW to the ECS, where the interannual variations have strong seasonal dependency probably due to interannual modulations of winter and summer Asian Monsoons. In addition to the above-mentioned decadal features, we will describe the interannual current variations with seasonal dependency over the Kuroshio-KE System in terms of regional syntheses and their underlaying mechanisms.
At first, we carried out the study on decadal-scale current variations along the entire stream, and revealed three kinds of coherently organized variations: 1) an out-of-phase current intensity variation between the Kuroshio south of Japan and the KE between 1993–2018; 2) an out-of-phase current intensity variation between the Kuroshio from the east of Taiwan (ETW) to the East China Sea (ECS) and the KE between 2006–2014; and 3) an out-of-phase current path variation between the Kuroshio from the ETW to ECS and the Kuroshio in the Luzon Strait between 1993–2018. These synchronizations were dynamically regulated by the Pacific Decadal Oscillation. The synchronized current intensity variations in 2006–2014, which governed almost the entire current system, were caused by coherent phenomena comprising two kinds of baroclinic Rossby wave propagations along the KE and the subtropical countercurrent, and a regional SSH anomaly advection from the South China Sea (SCS) to the ECS via the Taiwan Strait. However, the synchronized current path variations between 1993–2018 were caused by a long SSH anomaly migration of the Kuroshio from the western North Equatorial Current region to the ECS along with an SSH variation localized in the SCS.
We are now investigating interannual current variations over the Kuroshio-KE System, particularly focusing on those variations in the Kuroshio from the ETW to the ECS, where the interannual variations have strong seasonal dependency probably due to interannual modulations of winter and summer Asian Monsoons. In addition to the above-mentioned decadal features, we will describe the interannual current variations with seasonal dependency over the Kuroshio-KE System in terms of regional syntheses and their underlaying mechanisms.