Evolution and Structure of the Kuroshio Extension Front in Spring 2019

Satellite data products and high-resolution in situ observations were combined to investigate the evolution and structure of the Kuroshio Extension Front in Spring 2019. The former reveals the variation of the front is influenced by the northward movement of the Kuroshio Extension through transporting warm and saline water to a cold and brackish water region. The latter indicates steep upward slopes of the isopycnals, tilting northward in the frontal zone, as well as several ~300 m thick blobs of North Pacific Intermediate Water between 26.25 and 26.75 kg/m3, where conspicuous thermohaline intrusions occur. Further analysis indicates these thermohaline intrusions prefer to alternate salt fingering and diffusive convection interfaces, and are affected by strong shears.

A case study of Kuroshio Extension Front: evolution, structure, diapycnal mixing and instability

Satellite measurements during April to June in 2019 and direct observations from 28th to 30th May in 2019 about the Kuroshio Extension Front are conducted. The former shows the front experience a process of stable-unstable-stable state caused by the movement of the Kuroshio Extension’s second meander and a pinched-off eddy. The latter indicates the steep upward slopes of the isopycnals tilt northward in the strong frontal zone as well as several over 100 m thick blobs of cold and fresh water in the salinity minimum zone of North Pacific Intermediate Water. Using isopycnal anomaly method and diapycnal spiciness curvature method, characteristic interleaving layers are shown primarily in σθ = 26.3–26.9 kg/m3, which corresponds to large variations of potential spiciness in intermediate layers. Further analysis indicates the development of thermohaline intrusions may be driven by the double diffusive instability and the velocity anomalies. Besides, we find the turbulence mixing attributed to symmetric instability and shear instability is very strong in intermediate layer.

Cloud Response to the Meandering Kuroshio Extension Front

A unique set of observations on board research vessel (R/V) Mirai in April 2010 captured a striking cloud hole over a cold meander of the Kuroshio Extension (KE) east of Japan as corroborated by atmospheric soundings, ceilometer, shipboard radiation data, and satellite cloud images. Distinct differences were also observed between the warm meander farther to the north and warm water south of the KE. The atmosphere is highly unstable over the warm meander, promoting a well-mixed marine atmospheric boundary layer (MABL) and a layer of solid stratocumulus clouds capped by a strong inversion. Over the warm water south of the KE, MABL deepens and is decoupled from the ocean surface. Scattered cumulus clouds develop as captured by rapid variations in ceilometer-derived cloud base. The results show that the meandering KE front affects the entire MABL and the clouds. Such atmospheric response can potentially intensify the baroclinicity in the lower atmosphere.