Study of sea surface fluctuations in the Pacific on the basis of satellite altimetry data

卫星高度计可以直接测量海面高度的动力特性，对物理海洋学具有划时代的意义。在本研究中，分析了最近的高度计数据，以研究从盆地尺度到中尺度的宽波长范围内海面波动的特征。结果表明：(1)根据重复观测的前两年(1986-1988年)的Geosat高度计资料，观测到了海面动态地形(SSDT)的时间起伏，其中SSDT是实际海面与大地水准面的偏离，其梯度给出了海面的地转速度。在北太平洋西半部SSDT的涨落场中，有明显的西向位相传播。它们的相速度接近于长斜压Rossby波的理论值，但它们之间存在一些不能用最新理论解释的差异。(2)O…结果表明，在相同资料的基础上，黑潮延伸区充斥着向西传播的明显气旋和反气旋扰动。利用卫星海温资料证实了这些扰动具有斜压特征。结果还表明，黑潮延伸区以南的黑潮逆流强度与黑潮延伸区相关，因此黑潮延伸区的季节周期似乎代表了一个局部次涡旋(水平尺度为1,000-2,000公里)的波动，而不是整个北太平洋副热带涡旋的波动。(3)根据TOPEX/Poseidon高度计的观测资料，分析了日本南部黑潮轴线的波动。根据高度计资料和气候学平均SSDT，得到了近似的绝对SSDT，并根据其水平梯度估算了海面的地转速度。将计算结果与现场海面流速资料得到的黑潮轴线位置的起伏进行了比较。比较表明，近似地转速度的分布能够可靠地描述黑潮轴线的起伏。较少

Satellite altimeters can directly measure the dynamical property of sea surface height, and therefore are epoch-making for physical oceanography. In the present study, recent altimeter data are analyzed to investigate features of sea surface fluctuations for a wide wave-length range from the basin scale to the meso-scale. Followings are the results ;(1) On the basis of Geosat altimeter data from the first two years (1986-88) of the Exact Repeat Mission, temporal fluctuation of the sea surface dynamic topography (SSDT) is detected ; here the SSDT is the departure of the actual sea surface from the geoid and whose gradient gives the geostrophic velocity at the sea surface. There are found clear westward phase propagations in the fluctuation field of the SSDT in the western half of the North Pacific. Their Phase speeds are close to the theorretical value for the long baroclinic Rossby wave, but there are some discrepancies between them which cannnot be explained by the latest theory.(2) O … More n the basis of the same data, it is shown that the Kuroshio Extension region is filled with clear cyclonic and anti-cyclonic disturbances propagating westward. Those disturbances are confirmed to have baroclinic feature, using satellite sea surface temperature data. It is also shown that the intensity of the Kuroshio Countercurrent located south of the Kuroshio Extension fluctuates correlatively with the Kuroshio Extension, and therefore the seasonal cycle of the Kuroshio Extension seems to represent fluctuations of a local sub-gyre (with horizontal scales of 1,000-2,000 km), instead of the whole subtropical gyre of the North Pacific.(3) On the basis of TOPEX/Poseidon altimeter data from the first one year (1992-93) of the mission, fluctuations of the Kuroshio axis south of Japan are analyzed. Approximated absolute SSDT is derived from combination of the altimeter data and the climatological mean SSDT.Geostrophic velocities at the sea surface are estimated from its horizontal gradient. The results are compared with fluctuations of location of the Kuroshio axis derived from in situ surface velocity data. The comparison shows that the distribution of the approximated geostrophic velocity can describe the fluctuation of the Kuroshio axis reliably. Less