** Progress in Earth and Planetary Science is the official journal of the Japan Geoscience Union, published in collaboration with its society members.
Gallery View of PEPS Articles
Research
Atmospheric and hydrospheric sciences
202409202409
Kuroshio Extension cold-core ring and wind drop-off observed in 2021–2022 winter
Akira Nagano, Minoru Kitamura, Kensuke Watari, Iwao UekiAkira Nagano, Minoru Kitamura, Kensuke Watari, Iwao Ueki
Kuroshio Extension, Cold-core ring, Mixed layer, Turbulent heat flux, Air–sea interaction
Potential temperature (upper left) and salinity (lower left) sections of a Kuroshio Extension cold-core ring observed in January 8—9, 2022．Thick solid lines show the mixed layer depths. Wind speed reduction near the cold-core ring on January 6, 2022 constructed by the second and third rotary empirical orthogonal functions of satellite-observed sea surface wind (right, color shades). Thin solid contours indicate sea surface height.
Energetic cyclonic mesoscale eddies, which are called cold-core rings and are shed southward from the Kuroshio Extension jet and form closed streamlines, affect the atmosphere through the heat exchange across the sea surface. To investigate the effect of rings on the atmosphere, we performed atmosphere and ocean observations across a cold-core ring centered around 34.5° N, 150.0° E using a research vessel from November 2021 to January 2022 and a shallow-water profiling float from November 23 to 28, 2021. As heat is released from the sea surface, no significant spatial contrast in the sea surface and mixed layer temperatures was detected across the ring. Meanwhile, the sea surface wind was occasionally observed to be weak around the ring, possibly through the air–sea interactions. The wind drop-off maintained a turbulent heat flux small around the ring. The wind field associated with the wind drop-off was examined by the rotary empirical orthogonal function analysis of the satellite sea surface wind data. The minimum of the sea surface wind is found to shift northward relative to the ring center and to be more than approximately 5 m s-1 lower than the surrounding region. The shallow-water profiling float deployed around the ring center observed a rapid freshening event in the mixed layer, which can be attributed to the water intrusion from the north of the Kuroshio Extension jet through the interaction with the jet. This suggests that the cold water from the north continually affects the atmosphere without leaving traces in the shipboard sea surface temperature observations.
