南海及西北太平洋卫星高度计资料分析:海洋中尺度涡统计特征

Satellite altimeter data analysis of the South China Sea and the northwest Pacific Ocean:statistical features of oceanic mesoscale eddies

采用AVISO提供的卫星高度计融合数据,对南海及西北太平洋(5°～35°N,105°～150°E)1993～2009年17a间的中尺度涡活动进行统计分析.结果表明南海中尺度涡活动具有明显的年际变化,每年观测到产生的中尺度涡个数平均为21～22个,标准差约为4个,占年平均值的20%;而西北太平洋中尺度涡个数的年际差异不大,平均每年观测到150～151个中尺度涡产生,标准差约为14个,仅占年平均值的9%.中尺度涡的逐月统计结果表明南海和西北太平洋的中尺度涡活动均有明显季节变化,1993～2009年间的各月南海和西北太平洋分别观测到30～31个和213～214个中尺度涡产生,标准差分别约为6个和41个,均占各自月平均值的19%.中尺度涡主要集中分布在南海东北部、越南东部和黑潮流轴附近海域.涡动能、海面高度距平均方根以及涡度均方根的空间分布大致与涡旋个数分布一致,但在西北太平洋的低纬海区和黑潮延伸体区域则不甚吻合.在相同的涡旋判别标准下,西北太平洋低纬海区(5°～15°N)观测到的中尺度涡个数比中高纬海区要少得多.

17 years（ 1993 -2009） of merged gridded satellite altimeter sea level anomaly（MSLA） data obtained from Archiving, Validation and Interpretation of Satellite Oceanographic data（AVISO） are used to analyze the activ ity of mesoscale eddies in the South China Sea（SCS） and the northwest Pacific Ocean（ NPO; 5° -35°N, 105°-150°E）. The results indicate that the eddy activity in the SCS has distinct annual variation. The average number of newly generated mesoscale eddies observed in the SCS is 21 -22 in each year and the standard deviation is around 4, accounting for 20% of the annual mean value. By contrast, in the NPO, the eddy number varies relatively little in different years. Newly generated eddies observed in the NPO average 150 - 151 every year with a standard deviation of about 14, only 9% of its annual mean value. The monthly statistical results suggest that there are remarkable seasonal variations in both the SCS and the NPO. The average number of newly generated mesoscale eddies observed in the SCS and the NPO per month during 1993 -2009 are 30 -31 and 213 -214, relatively, and the standard deviations are approximately 6 and 41, both accounting for 19% of the respective monthly mean value. Eddies are observed more frequently in the northeastern SCS, east off Vietnam and the vicinity of the Kuroshio axis. The spatial patterns of eddy number distribution are about the same with each other for anticyclonic eddies and cyclonic eddies, while there are some discrepancies in terms of the specific amount and positions. The spatial patterns of eddy number distribution are in good agreement with those of the eddy kinetic energy, the root mean square of sea level anomaly and the root mean square of vorticity in the studied area, except for that in the Kuroshio Extension area and in the tropical band of the NPO. The disagreements may be caused by the largeamplitude meanders and baroclinic instabilities for the former area, and that the geostrophic hypothesis is not valid in lowlatitude area for the latter one. Under the premise of the same criteria for eddy identification, mesoscale eddies observed in the tropical area （5 ° 15 °N） of the NPO are quite less than those at higher latitudes, the reason for which may be that the Rossby deformation radius is larger there.