A dual-period response of the Kuroshio Extension SST to Aleutian Low activity in the winter season
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A dual-period response of the Kuroshio Extension SST to Aleutian Low activity in the winter season YU Peilong1, ZHANG Lifeng1*, LIU Hu2, LIU Xing3, ZHU Juan3 1 College of Meteorology and Oceanography, National University of Defense Technology, Nanjing 211101, China 2 No.61741 Troops of PLA, Beijing 100025, China 3 Maritime Environment Project Office, Beijing 100081, China
Received 12 October 2016; accepted 3 February 2017 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2017
Abstract
Based on our previous work, the winter sea surface temperature (SST) in the Kuroshio Extension (KE) region showed significant variability over the past century with periods of ~6 a between 1930 and 1950 and ~10 a between 1980 and 2009. How the activity of the Aleutian Low (AL) induces this dual-period variability over the two different timespans is further investigated here. For the ~6 a periodicity during 1930–1950, negative wind stress curl (WSC) anomalies in the central subtropical Pacific associated with an intensified AL generate positive sea surface height (SSH) anomalies. When these wind-induced SSH anomalies propagate westwards to the east of Taiwan, China two years later, positive velocity anomalies appear around the Kuroshio to the east of Taiwan and then the mean advection via this current of velocity anomalies leads to a strengthened KE jet and thus an increase in the KE SST one year later. For the ~10 a periodicity during 1980–2009, a negative North Pacific Oscillation-like dipole takes 2–3 a to develop into a significant positive North Pacific Oscillation-like dipole, and this process corresponds to the northward shift of the AL. Negative WSC anomalies associated with this AL activity in the central North Pacific are able to induce the positive SSH anomalies. These oceanic signals then propagate westward into the KE region after 2–3 a, favoring a northward shift of the KE jet, thus leading to the warming of the KE SST. The feedbacks of the KE SST anomaly on the AL forcing are both negative for these two periodicities. These results suggest that the dual-period KE SST variability can be generated by the two-way KE-SST-AL coupling. Key words: sea surface temperature, Kuroshio Extension, Aleutian Low activity, dual-period variability Citation: Yu Peilong, Zhang Lifeng, Liu Hu, Liu Xing, Zhu Juan. 2017. A dual-period response of the Kuroshio Extension SST to Aleutian Low activity in the winter season. Acta Oceanologica Sinica, 36(9): 1–9, doi: 10.1007/s13131-017-1104-1
1 Introduction The Kuroshio Extension (KE) carries the eastward flow of the Kuroshio Current into the open basin of the North Pacific. As a result of the cold and dry continental air overriding the warm water transported poleward by the Kuroshio, the KE lies in the region where the largest ocean-to-atmosphere heat loss occurs during mid-latitude winter (Qiu, 2000; Kelly et al., 2010), which acts as the obvious thermal forcing on the atmosphere. Some research works have pointed out that the sea surface temperature (SST) changes in th
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