吕宋海峡內潮的季节变化特征及其对背景流的响应研究

基于2008年秋季至2009年夏季共9个月的锚定潜标流速资料,分析了吕宋海峡西南內潮的时空特征.谱分析结果显示,该观测点全日內潮和半日內潮较为显著,尤其体现在顺时针旋转部分.除春季第二模态占优外,全日內潮主在其余三个季节均以第一模态为主,而半日內潮呈现变化的多模态结构.此外,全日內潮的动能具有明显的季节差异,冬季能量最强,夏季紧随其后,而在春、秋两季能量最小.通过分析发现,非相干运动对此季节性特征起主要作用,它反映了內潮与背景场的相互作用.然而,半日內潮却没有显著的季节性差异,而且能量较全日內潮更小,尤其在冬季,只有全日內潮动能的三分之一.同时,半日內潮的不规则变化也是与多变的背景场相关的.半日內潮的非相干部分占到了半日內潮总能量的37%左右,而全日內潮更小一些,只有22.2%.     

Internal solitary waves on the southwest shelf of Dongsha Island observed from mooring ADCP

Internal solitary waves(ISWs) are frequently observed in the area between Dongsha Island(DI) and Taiwan Island. However, there have been few in-situ observations southwest of DI. To improve our knowledge of ISWs in this area, we observed the ISWs over the continental shelf(115.4°E, 20.3°N) from Aug. 29 to Oct. 10, 2011 with temperature sensors and an acoustic Doppler current profiler(ADCP). The observations showed that the a fully developed ISW produced a current whose maximum westward velocity was 0.92 m/s and maximum northward velocity was 0.47 m/s. During the 41-day observation period the ISWs appeared for three periods with about 7-day gaps between each period. During each day, two types of ISWs were observed. The first type of wave arrived regularly diurnally at the same time each day, with a similar pattern to that of the type- a wave identified by Ramp et al.(2004). The second type arrived about 12 h after the first type and was delayed about 1 hour each day; this wave type was related to the type- b wave. Thus, our observations confirmed that both type- a and type- b waves can reach the area southwest of the DI. Moreover, the waves observed by the mooring propagated toward the directions of 270°–315° clockwise from true north, indicating obvious refraction from uneven topography around DI.