Interannual variations of the Hawaiian Lee Countercurrent induced by potential vorticity variability in the subsurface |
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| Authors: | Hideharu Sasaki Shang-Ping Xie Bunmei Taguchi Masami Nonaka Shigeki Hosoda Yukio Masumoto |
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| Institution: | (1) Earth Simulator Center, JAMSTEC, 3173-25 Showa-machi, Kanazawa-ku, Yokohama Kanagawa, 236-0001, Japan;(2) International Pacific Research Center and Department of Meteorology, University of Hawaii at Manoa, 2525 Correa Rd., Honolulu, HI 96822, USA;(3) Research Institute for Global Change, JAMSTEC, 3173-25 Showa-machi, Kanazawa-ku, Yokohama Kanagawa, 236-0001, Japan;(4) Research Institute for Global Change, JAMSTEC, 2-15 Natsushima, Yokosuka Kanagawa, 237-0061, Japan |
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| Abstract: | Interannual variations of the Hawaiian Lee Countercurrent (HLCC) in the 2000s were investigated using satellite and Argo profiling
float observations. The satellite-observed sea surface height shows that the geostrophic eastward current was anomalously
strong to the west away from Hawaii in 2003 and 2005. However, the trade winds and the orographic wind curl dipole in the
lee of Hawaii that drives the climatological mean HLCC were not particularly strong in these years, suggesting that the accelerations
of the HLCC were not caused by the wind stress curl forcing around Hawaii and subsequent Rossby wave propagation. Using Argo
observations, we found negative potential vorticity (PV) anomalies in the subsurface north of the HLCC in these 2 years. The
pycnocline is lifted northward as low PV waters of different densities stack up in the vertical, and the HLCC is then accelerated
via the thermal wind. The intensification and/or southward intrusion of the eastern subtropical mode water and subtropical
mode water seem to have induced negative PV anomalies in 2003 and 2005, respectively. Using high-resolution ocean simulations,
we confirmed the migrations of PV anomalies and their contributions to the HLCC accelerations. Although the HLCC is located
away from the cores of major mode waters, our results suggest that interannual variations of the HLCC are affected by those
of mode waters. |
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