Long-term tide gauge sea level data from 1969 to 2014 at Davao (7.08°N, 125.63°E) and Malakal (7. 33°N, 134.46°E) are analyzed to examine the decadal frequency modulations embedded in the Mindanao Current (MC) variability. The MC variability inferred from the Davao–Malakal sea level was predominantly biennial in the 1970s. This prevailing period switched to interannual in the 1980s and lengthened to decadal during the last two decades. With the aid of the basin-scale sea level information from satellite altimeter measurements, it is found that the sea level-inferred MC variability represents the coherent changes of the wind-driven tropical gyre in the western North Pacific. An investigation into the long-term wind stress curl data reveals that its prevailing period underwent similar biennial→interannual→decadal transitions in the western tropical Pacific, implying the forced nature of the period-lengthening of the MC variability during the past half-a-century. While the sign of the MC variability is largely determined by the Malakal sea level signals on the interannual and decadal time scales, the Davao sea level change becomes important when the time scale extends to multi-decades.

中文翻译：

---

来自长期潮汐计海平面测量的棉兰老岛海流变化的周期延长

分析了 1969 年至 2014 年达沃 (7.08°N, 125.63°E) 和马拉卡勒 (7. 33°N, 134.46°E) 的长期潮汐计海平面数据，以检查棉兰老洋流中嵌入的年代际频率调制（ MC) 变异性。从达沃 - 马拉卡尔海平面推断的 MC 变异性主要是 1970 年代的两年一次。这一盛行时期在 1980 年代转变为年际，并在过去二十年延长至十年。借助卫星高度计测量的盆地尺度海平面信息，发现海平面推断的 MC 变异性代表了西北太平洋风驱动热带环流的相干变化。对长期风应力旋度数据的调查表明，其盛行期在热带西太平洋经历了类似的两年→年际→年代际转变，暗示了过去半年中MC变率周期延长的强迫性质。世纪。虽然 MC 变化的符号主要由年际和年代际时间尺度上的马拉卡勒海平面信号决定，但当时间尺度扩展到几十年时，达沃海平面变化变得重要。