Studies on Annual and Interannual Variations of Oceanic Thermal Domes

我们研究了太平洋和大西洋海洋热穹窿的年际变化。特别是，哥斯达黎加圆顶、棉兰老圆顶、安哥拉圆顶和几内亚（达喀尔）圆顶使用几个高分辨率的海洋环流模型进行了详细分析。1992年1月，还利用海洋丸号（R/V Kaiyo-maru）巡航对哥斯达黎加圆顶进行了调查。航行期间进行了水文测量（ADCP、XBT、CTD、水样）和气象观测。以下是本研究项目的主要成果。1)利用印度-太平洋模式分析了模式对地表热通量和动量通量的敏感性以及小岛屿的影响。研究发现，这些通量条件对低纬西部边界流的输运有很大影响。此外，即使是一个小岛，如果它位于强大的洋流中，也会严重影响周围的海洋状况。2)印度洋-太平洋模式表明，由于海盆尺度的海洋-大气变率缺乏形成要素，在1981年和1983年等年份无法很好地产生更季节性的哥斯达黎加圆顶。该模型还显示出捕捉几个有趣天气事件的能力。例如，地球卫星测高数据显示，1987年10月在特万特佩克湾产生了一个异常强烈的反气旋，然后向西移动，保持了原有的特征。EPOCS漂移器6858对该涡旋进行了一段时间的跟踪。这一有趣的事件在ECMWF风的强迫下被清楚地解决了，但模拟的涡旋强度（通过旋转速度和动态高度异常估计）是观测到的一半。这主要是由于风太弱，特别是在旋度的压力。3)采用大西洋一般海洋环流模式分析了几内亚球和安哥拉球区域的季节变化。模型结果如下。在6月至10月期间，由于热输运辐散活跃，模型几内亚巨蛋冷却，尽管冷却速率部分被地表加热抵消。降温主要与北纬夏秋季节局地风正旋度的增强有关，局地风正旋度辐合入北移的辐合区。几内亚沿海地区由于沿海下潜开尔文波的传播，每年经历两次升温。安哥拉圆顶模型从3月到9月被冷却。与冷的地下SECC（或SEUC）相关的热输运水平辐散总是倾向于冷却安哥拉圆顶。然而，在南方夏季，地表变暖抵消了上述电流引起的冷却。安哥拉沿海地区每年两次受到来自热带的沿海下行开尔文波向极地传播的影响。下流开尔文波的产生是由于西风分量每半年增强一次

We studied both annual and interannual variations of oceanic thermal domes in the Pacific and the Atlantic. In particular, the Costa Rica Dome, the Mindanao Dome, the Angola Dome and the Guinea (Dakar) Dome are analysed in detail using several high-resolution ocean general circulation models. The Costa Rica Dome was also investigated utilizing the cruise of R/V Kaiyo-maru in January 1992. During the cruise both hydrographic (ADCP,XBT,CTD, water sampling) and meteorological observations were conducted. The following is the main outcome of the present research program. 1) We analyzed the model sensitivity to the surface heat and momentum fluxes and the effects of small islands using the Indo-Pacific model. It is found that the transport of low-latitude western boundary currents is much affected by those flux conditions. Also,even a small island can affect seriously surrounding oceanic conditions if it is located in strong currents. 2) An Indo-Pacific ocean model demonstrates that the sea … More sonal Costa Rica Dome cannot be generated well in some years like 1981 and 1983 because of lack of elements of formation due to basin-scale ocean-atmosphere variabilities. The model also shows an ability to capture several interesting synoptic events. For example, the Geosat altimetry data shows that an unusually strong anticyclone was generated in the Gulf of Tehuantepec in October, 1987 and then moved westward keeping its identity. The eddy was traced for a certain period by the EPOCS drifter 6858. This interesting event is clearly resolved in the model forced by the ECMWF winds but the simulated eddy strength (estimated by rotation speed and dynamic height anomaly) is one half of the observed one. This is mostly due the winds that are too weak, particularly in terms of the curl of the stress. 3) A general ocean circulation model for the Atlantic Ocean is used to analyze the seasonal variations in the Guinea Dome and Angola Dome regions. Model results are the following. The model Guinea Dome is cooled from June trough October due to active divergence of the heat transport, although the cooling rate is partly counteracted by the surface heating. The cooling is mostly related to the intensified positive curl of the local wind which converges into the ITCZ migrating northward during the boreal summer and fall. The coastal Guinea region experiences heating twice a year due to propagation of coastal downwelling Kelvin waves. The model Angola Dome is cooled from March through September. The horizontal divergence of the heat transport associated with the cold subsurface SECC(or SEUC) always tends to cool the Angola Dome. During the austral summer,however,the surface warming cancels the above current- induced cooling. The coastal Angola region is also much affected by the poleward propagation of the coastal downwelling Kelvin waves from the tropics twice a year. The generation of the downwelling Kelvin waves is due to the semiannual intensification of the westerly compone Less